Types of questions:
1. Molar mass calculation
2. Percentage composition
3. mass-mass reaction calculation.
1. Molar mass calculation.
Using the mass (big) numbers off the periodic table the mass of a sunstance can be calculated.
Exampe:
CaCO3
1. Total how many of each atom there are in the formula
Ca = 1
C = 1
O = 3
2. Multiply this amount by the mass number of that atom off the periodic table.
Ca = 1 x 40 = 40
C = 1 x 12 = 12
O = 3 x 16 = 48
3. Add all of these totals together to get the molas mass.
40+ 12+ 48 = 100
2. Percentage composition
This the percentage by mass of an element in a compound.
Once you have calculated the molar mass of a substance you can calculate what percentage each element contributes to the whole mass.
Example; CaCO3
Ca = 1 x 40 = 40
C = 1 x 12 = 12
O = 3 x 16 = 48
Total = 100
% Ca = 40/100 x 100
%Ca = 40%
%C = 12 / 100 x 100
%C = 12%
%O = 48/100 x 100
%O = 48%
3. Mass-Mass calculations
If you know the balanced equation for a reaction and you know either how much reactant is used or how much product is used you can use this information to calculate the mass of other chemicals involved.
Example:
2Mg + O2 --> 2MgO.
Molar mass of 2Mg = 2x24 = 48
Molar mass of O2 = 2x16 = 32
Molar mass of 2MgO = 2(24+16) = 60
The balanced equation tells us that:
2 Mg's react with 1 O2 to make 2 MgO's
OR Using masses:
48g Mg reacts with 32g O2 to make 60g of MgO.
Question:
But what if we only start with 10g of Mg, how much MgO will we make?
What we know:
24g Mg + 32g O2 --> 60g MgO
10g Mg --> ? MgO
10 / 24 X 60
= 25g MgO produced.
Tuesday, September 21, 2010
REVISION -Chemical reactions - Types
Types of chemical reactions.
The only types you need to know for this standard is:
Thermal decomposition
Oxidation - Reduction
Precipitation
Steps:
1. Look for any reaction that has only one reactant. This will be a Thermal decomposition reaction.
2. Any reaction that has two solutions going to a solid and a solution OR a reaction where all of the partners are swappping is a Precipitation reaction.
3. Any remaining reaction will be a Oxidation - Reduction reaction
Example:
Classify the reactions below:
(a) C (s) + O2 (g) → CO2 (g)
(b) Ca(OH)2 (s) → CaO (s) + H2O (g)
(c) Fe (s) + CuSO4 (aq) → FeSO4 (aq) + Cu (s)
(d) CuCl2 (aq) + K2CO3 (aq) → CuCO3 (s) + 2KCl (aq)
Step 1: Thermal decomposition:
(b) Ca(OH)2 (s) → CaO (s) + H2O (g)
Step 2: Precipitation:
(d) CuCl2 (aq) + K2CO3 (aq) → CuCO3 (s) + 2KCl (aq)
Step 3: Oxidation - Reduction
(a) C (s) + O2 (g) → CO2 (g)
(c) Fe (s) + CuSO4 (aq) → FeSO4 (aq) + Cu (s)
The only types you need to know for this standard is:
Thermal decomposition
Oxidation - Reduction
Precipitation
Steps:
1. Look for any reaction that has only one reactant. This will be a Thermal decomposition reaction.
2. Any reaction that has two solutions going to a solid and a solution OR a reaction where all of the partners are swappping is a Precipitation reaction.
3. Any remaining reaction will be a Oxidation - Reduction reaction
Example:
Classify the reactions below:
(a) C (s) + O2 (g) → CO2 (g)
(b) Ca(OH)2 (s) → CaO (s) + H2O (g)
(c) Fe (s) + CuSO4 (aq) → FeSO4 (aq) + Cu (s)
(d) CuCl2 (aq) + K2CO3 (aq) → CuCO3 (s) + 2KCl (aq)
Step 1: Thermal decomposition:
(b) Ca(OH)2 (s) → CaO (s) + H2O (g)
Step 2: Precipitation:
(d) CuCl2 (aq) + K2CO3 (aq) → CuCO3 (s) + 2KCl (aq)
Step 3: Oxidation - Reduction
(a) C (s) + O2 (g) → CO2 (g)
(c) Fe (s) + CuSO4 (aq) → FeSO4 (aq) + Cu (s)
Thursday, August 19, 2010
Chemical equations you may need to know
Complete combustion:
any fuel + O2 --> CO2 + H2O
Balance the C, then H then Os.
Incomplete combustion
any fuel + O2 --> CO + H2O
Reaction of CO2 with limewater:
Ca(OH)2 + CO2 --> CaCO3 + H2O
-------> in excess CO2 if you keep bubbling CO2 through: CaCO3 + CO2 + H2O --> Ca(HCO3)2
Fermentation:
C6H12O6 --> C2H5OH + CO2
Production of CO2 in lab:
CaCO3 + HCl --> CaCl2 + CO2 + H2O
any fuel + O2 --> CO2 + H2O
Balance the C, then H then Os.
Incomplete combustion
any fuel + O2 --> CO + H2O
Reaction of CO2 with limewater:
Ca(OH)2 + CO2 --> CaCO3 + H2O
-------> in excess CO2 if you keep bubbling CO2 through: CaCO3 + CO2 + H2O --> Ca(HCO3)2
Fermentation:
C6H12O6 --> C2H5OH + CO2
Production of CO2 in lab:
CaCO3 + HCl --> CaCl2 + CO2 + H2O
Question 1 Combustion
Ethane and ethanol are organic compounds used as fuel.
Ethane burns with an orange flame and some soot forms.
Ethanol burns with an almost invisible flame with no soot forming.
By considering the products of these reactions, predict and justify which fuel will have the larger impact on people.
Include examples of how people would be affected, and an appropriate balanced equation for each fuel.
Ethane burns with incomplete combustion forming carbon monoxide and water. During this reaction soot is also formed.
The equation for this reaction is:
CH3CH3 + 3.5O2 --> 2CO + 3H2O
This fuel would have a greater impact on people because it produces soot, which leads to pollution and respiratory problems and CO which is a toxic gas because it can bind to the red blood cells better than oxygen preventing oxygen from getting around the body. This leads to asphyxiation.
Ethanol burns with complete combustion forming carbon dioxide and water.
The equation for this reaction is:
C2H5OH + 3O2 --> 2CO2 + 3H2O
This fuel would have a lesser impact on people because the products it produces do not have a direct impact in human health.
The CO2 produced does increase the greenhouse effect, which is the trapping of heat energy from the sun in the Earths atmoshpere causing temperatures to increase. This leads to changes in weather patterns and the melting of the polar ice caps. This leads to water levels increasing which will affect the enviroment in which humans live.
Question 2 Fermentation
Beer is brewed by placing sugar, hops and brewer’s yeast into a fermentation tank. The final product contains alcohol and bubbles of carbon dioxide.
Discuss with reference to the properties of carbon dioxide, how this simple process makes a carbonated (fizzy) drink
• An equation for the fermentation of the sugar is the brewer’s yeast.
• An explanation of the observations regarding the fizziness in terms of the properties of carbon dioxide.
• The tests you could carry out to identify the gas as carbon dioxide and the observation you would make carbon dioxide gas.
Fermentation is the process by which glucose is converted into ethanol and carbon dioxide. This process occurs in a fermentation vat. The brewers yeast is the catalyst for this reaction.
C6H12O6 --> 2C2H5OH + 2CO2
Because the CO2 prduced is a colourless gas which is slightly soluble in water and more dense that air, the carbon dioxide dissolves in the beer. When the cap is removed from the bottle some of the CO2 gas escapes causing the beer to fizz. This is caused by the change in pressure caused when the bottle is opened.
Question 3 Allotropes
Discuss why graphite can be used as an electrode in batteries
It may be useful to include a diagram showing the structure of graphite.
Include in your answer:
• What physical property of graphite allows it to be an electrode?
• A description of the structure of the shape and bonding in graphite.
• What is it about the structure that allows it to be an electrode?
Graphite can conduct electricity because it has free electrons between the graphite layers. This is because its structure consists of layers of C atoms that are each covalently bonded to 3 other C atoms. This leaves on of Carbons valence electrons free to move and carry electrical charge.
Question 4 Polymers
Polythene (polyethene) is a polymer that has many industrial and household uses ranging from buckets to plastic bags
(a) Name the monomer that polythene is produced from?
(b) Draw a short section of the polythene chain showing at least three repeating units.
A) ethene (CH2=CH2)
B) .......CH2-CH2-CH2-CH2.......
Question 5 fractional dist illation
Discuss how crude oil can be separated into its components using fractional distillation.
In your answer, outline what crude oil is and refer to the physical properties of hydrocarbons.
Crude oil is made up of hydrocarbons of differing chain lengths. Because the boiling point of hydrocarbons depends on chain length, the longer the chain the higher the boiling point, these hydrocarbons are able to be separated according to boiling point using a process called fractional distillation.
Question 6 Products of combustion
Discuss how you could conduct an experiment to prove that the products of complete combustion are carbon dioxde and water.
The products of complete combustion are carbon dioxide gas and water. By burning fuel and passing the gases produced through a tube in a beaker of ice water the water vapour produced in the reaction will condense on the side of the tube. This can be confirmed as water by using cobolt chloride paper which turns from pink to blue in the presence of water.
When the gases of the reaction are passed through a test tube containing limewater, the lime water will turn cloudy indicating the presence of carbon dioxide, This is because the carbon dioxide gas reacts with the limewater producing calcium carbonate which is insoluble
Ca(OH)2 + CO2 --> CaCO3 + H2O
limewater insoluble white ppt
Ethane and ethanol are organic compounds used as fuel.
Ethane burns with an orange flame and some soot forms.
Ethanol burns with an almost invisible flame with no soot forming.
By considering the products of these reactions, predict and justify which fuel will have the larger impact on people.
Include examples of how people would be affected, and an appropriate balanced equation for each fuel.
Ethane burns with incomplete combustion forming carbon monoxide and water. During this reaction soot is also formed.
The equation for this reaction is:
CH3CH3 + 3.5O2 --> 2CO + 3H2O
This fuel would have a greater impact on people because it produces soot, which leads to pollution and respiratory problems and CO which is a toxic gas because it can bind to the red blood cells better than oxygen preventing oxygen from getting around the body. This leads to asphyxiation.
Ethanol burns with complete combustion forming carbon dioxide and water.
The equation for this reaction is:
C2H5OH + 3O2 --> 2CO2 + 3H2O
This fuel would have a lesser impact on people because the products it produces do not have a direct impact in human health.
The CO2 produced does increase the greenhouse effect, which is the trapping of heat energy from the sun in the Earths atmoshpere causing temperatures to increase. This leads to changes in weather patterns and the melting of the polar ice caps. This leads to water levels increasing which will affect the enviroment in which humans live.
Question 2 Fermentation
Beer is brewed by placing sugar, hops and brewer’s yeast into a fermentation tank. The final product contains alcohol and bubbles of carbon dioxide.
Discuss with reference to the properties of carbon dioxide, how this simple process makes a carbonated (fizzy) drink
• An equation for the fermentation of the sugar is the brewer’s yeast.
• An explanation of the observations regarding the fizziness in terms of the properties of carbon dioxide.
• The tests you could carry out to identify the gas as carbon dioxide and the observation you would make carbon dioxide gas.
Fermentation is the process by which glucose is converted into ethanol and carbon dioxide. This process occurs in a fermentation vat. The brewers yeast is the catalyst for this reaction.
C6H12O6 --> 2C2H5OH + 2CO2
Because the CO2 prduced is a colourless gas which is slightly soluble in water and more dense that air, the carbon dioxide dissolves in the beer. When the cap is removed from the bottle some of the CO2 gas escapes causing the beer to fizz. This is caused by the change in pressure caused when the bottle is opened.
Question 3 Allotropes
Discuss why graphite can be used as an electrode in batteries
It may be useful to include a diagram showing the structure of graphite.
Include in your answer:
• What physical property of graphite allows it to be an electrode?
• A description of the structure of the shape and bonding in graphite.
• What is it about the structure that allows it to be an electrode?
Graphite can conduct electricity because it has free electrons between the graphite layers. This is because its structure consists of layers of C atoms that are each covalently bonded to 3 other C atoms. This leaves on of Carbons valence electrons free to move and carry electrical charge.
Question 4 Polymers
Polythene (polyethene) is a polymer that has many industrial and household uses ranging from buckets to plastic bags
(a) Name the monomer that polythene is produced from?
(b) Draw a short section of the polythene chain showing at least three repeating units.
A) ethene (CH2=CH2)
B) .......CH2-CH2-CH2-CH2.......
Question 5 fractional dist illation
Discuss how crude oil can be separated into its components using fractional distillation.
In your answer, outline what crude oil is and refer to the physical properties of hydrocarbons.
Crude oil is made up of hydrocarbons of differing chain lengths. Because the boiling point of hydrocarbons depends on chain length, the longer the chain the higher the boiling point, these hydrocarbons are able to be separated according to boiling point using a process called fractional distillation.
Question 6 Products of combustion
Discuss how you could conduct an experiment to prove that the products of complete combustion are carbon dioxde and water.
The products of complete combustion are carbon dioxide gas and water. By burning fuel and passing the gases produced through a tube in a beaker of ice water the water vapour produced in the reaction will condense on the side of the tube. This can be confirmed as water by using cobolt chloride paper which turns from pink to blue in the presence of water.
When the gases of the reaction are passed through a test tube containing limewater, the lime water will turn cloudy indicating the presence of carbon dioxide, This is because the carbon dioxide gas reacts with the limewater producing calcium carbonate which is insoluble
Ca(OH)2 + CO2 --> CaCO3 + H2O
limewater insoluble white ppt
Monday, May 31, 2010
Describing ionic bonding
Describe the bonding found in NaCl
Sodium has a electron arrangement of (2,8,1) and chlorine has an electon arrangement of (2,8,7). When atoms react they either exchange valence electrons to form ionic bonds of they share electrons to form covalent bonds.
When a sodium atom reacts with a chlorine atom the sodium atom transfers it valence electron to the chlorine atom to form Na+ (2,8) and Cl- (2,8,8). By doing this both atoms achieve a full valence shell and so are stable.
The Na+ and Cl- ions are electrostatically attracted to each other and form a very strong ionic bond.
Sodium has a electron arrangement of (2,8,1) and chlorine has an electon arrangement of (2,8,7). When atoms react they either exchange valence electrons to form ionic bonds of they share electrons to form covalent bonds.
When a sodium atom reacts with a chlorine atom the sodium atom transfers it valence electron to the chlorine atom to form Na+ (2,8) and Cl- (2,8,8). By doing this both atoms achieve a full valence shell and so are stable.
The Na+ and Cl- ions are electrostatically attracted to each other and form a very strong ionic bond.
The How To of answering Bonding questions
QUESTION ONE: ELEMENTS OF THE PERIODIC TABLE
(a) (a) Explain the similarities and differences in the chemical reactivity of the elements fluorine and chlorine versus sodium and potassium. Link your answer to the electron configurations of each atom.
Comparing Fluorine and chlorine
Fluorine has an electron arangement of (2,7) and chlorine has an electron arrangement of (2,8,7). Both of these atoms are found in group 17 of the periodic table. This means that the both will react inthe same way, they need to gain one more electron to achieve a stable full valence shell. In doing so they become F- and Cl- ions. The difference between the two atoms is that they have different numbers of protons, neutrons and electrons and because the have different amounts of electron shells they belong to different periods of the periodic table. F is in period 2 and Cl is in Period 3.
Comparing sodium and potassium
Sodium has an electron arangement of (2,8,1) and Potassium has an electron arrangement of (2,8,8,1). Both of these atoms are found in group 1 of the periodic table. This means that the both will react in the same way, they need to lose one electron to achieve a stable full valence shell. In doing so they become Na+ and K+ ions. The difference between the two atoms is that they have different numbers of protons, neutrons and electrons and because the have different amounts of electron shells they belong to different periods of the periodic table. Na is in period 3 and K is in Period 4.
(b) Explain the differences in the chemical reactivity of the elements Fluorine and chlorine compared to sodium and potassium. Link your answer to the electron configuration of each atom.
Both fluorine and chlorine have 7 valence electrons F (2,7) and Cl(2,8,7). These atoms will gain one electron during a chemical reaction to achieve a full valence shell and become stable F- and Cl- ions.
Sodium and potassium both have one valence electron Na (2,8,1) and K(2,8,8,1) and so will lose this electron during a chemical reactions to achieve a full valence shell and become stable Na+ and K+ ions.
QUESTION TWO: COMPOUNDS OF Oxygen
(a) Discuss the melting point of solid lithium oxide, Li2O(s), and gaseous oxygen, O2 (g).
Your answer should include:
• which compound has the higher melting point
• the type of particle found in each compound
• the attractive forces in each compound
• the strength of those forces.
Lithium oxide is an ionic solid made up of lithium ions and oxide ions bonded together in a 3D lattice. These ions are bonded together by an ionic bond that is very strong and hard to break requiring large amounts of energy to break, so lithium chloride will have a higher melting point than oxygen.
Oxygen is a covalent compound that is made up of strong covalent bonds within the molecules, however the molecules are held together by weak intermolecular forces that do not require much energy to break. This means that oxygen has a very low melting point
QUESTION THREE: CONDUCTIVITY
Methane CH3, and lithium chloride, LiCl, are compounds. Discuss which of these substances is more likely to conduct electricity.
Your answer should include:
• What is needed for a substance to conduct electricity
• which compound will conduct electricity
• the type of particle found in each compound
Methane is a simple covalent compound made up of covalently bonded atoms that share electrons. these electrons are not free to move so methane cannot conduct electricity.
LiCl is an ionic substance that is made up of Li+ ions ans Cl- bonded together by a stron electrostatic attraction. These ions are not free to move in the solid LiCl, however they are free to move when LiCl is melted of dissolved in water. This means that LiCl will conduct electricity in these cases are the ions (charged paritcles) are free to move.
(a) (a) Explain the similarities and differences in the chemical reactivity of the elements fluorine and chlorine versus sodium and potassium. Link your answer to the electron configurations of each atom.
Comparing Fluorine and chlorine
Fluorine has an electron arangement of (2,7) and chlorine has an electron arrangement of (2,8,7). Both of these atoms are found in group 17 of the periodic table. This means that the both will react inthe same way, they need to gain one more electron to achieve a stable full valence shell. In doing so they become F- and Cl- ions. The difference between the two atoms is that they have different numbers of protons, neutrons and electrons and because the have different amounts of electron shells they belong to different periods of the periodic table. F is in period 2 and Cl is in Period 3.
Comparing sodium and potassium
Sodium has an electron arangement of (2,8,1) and Potassium has an electron arrangement of (2,8,8,1). Both of these atoms are found in group 1 of the periodic table. This means that the both will react in the same way, they need to lose one electron to achieve a stable full valence shell. In doing so they become Na+ and K+ ions. The difference between the two atoms is that they have different numbers of protons, neutrons and electrons and because the have different amounts of electron shells they belong to different periods of the periodic table. Na is in period 3 and K is in Period 4.
(b) Explain the differences in the chemical reactivity of the elements Fluorine and chlorine compared to sodium and potassium. Link your answer to the electron configuration of each atom.
Both fluorine and chlorine have 7 valence electrons F (2,7) and Cl(2,8,7). These atoms will gain one electron during a chemical reaction to achieve a full valence shell and become stable F- and Cl- ions.
Sodium and potassium both have one valence electron Na (2,8,1) and K(2,8,8,1) and so will lose this electron during a chemical reactions to achieve a full valence shell and become stable Na+ and K+ ions.
QUESTION TWO: COMPOUNDS OF Oxygen
(a) Discuss the melting point of solid lithium oxide, Li2O(s), and gaseous oxygen, O2 (g).
Your answer should include:
• which compound has the higher melting point
• the type of particle found in each compound
• the attractive forces in each compound
• the strength of those forces.
Lithium oxide is an ionic solid made up of lithium ions and oxide ions bonded together in a 3D lattice. These ions are bonded together by an ionic bond that is very strong and hard to break requiring large amounts of energy to break, so lithium chloride will have a higher melting point than oxygen.
Oxygen is a covalent compound that is made up of strong covalent bonds within the molecules, however the molecules are held together by weak intermolecular forces that do not require much energy to break. This means that oxygen has a very low melting point
QUESTION THREE: CONDUCTIVITY
Methane CH3, and lithium chloride, LiCl, are compounds. Discuss which of these substances is more likely to conduct electricity.
Your answer should include:
• What is needed for a substance to conduct electricity
• which compound will conduct electricity
• the type of particle found in each compound
Methane is a simple covalent compound made up of covalently bonded atoms that share electrons. these electrons are not free to move so methane cannot conduct electricity.
LiCl is an ionic substance that is made up of Li+ ions ans Cl- bonded together by a stron electrostatic attraction. These ions are not free to move in the solid LiCl, however they are free to move when LiCl is melted of dissolved in water. This means that LiCl will conduct electricity in these cases are the ions (charged paritcles) are free to move.
Wednesday, May 26, 2010
Types of Bonding
Ionic bonding.:
- Between a metal and a non-metal atom,
- Electrons are transferred
- Metals lose electrons to form positive (cations).
- Non-metals gain electrons to form negative (anions)
- Ions bond together in an ionic bond to form a giant ionic lattice.
Covalent bonding:
- Between nonmetal atoms
- Electrons are shared
- Atoms bond together to form simple covalent molecules.
- Between a metal and a non-metal atom,
- Electrons are transferred
- Metals lose electrons to form positive (cations).
- Non-metals gain electrons to form negative (anions)
- Ions bond together in an ionic bond to form a giant ionic lattice.
Covalent bonding:
- Between nonmetal atoms
- Electrons are shared
- Atoms bond together to form simple covalent molecules.
Tuesday, May 11, 2010
Chemical reactions questions and answers.
Questions 1
For this reaction:
• Describe the observations that you would make
• Write the net ionic equation for the reaction.
• Explain what happens to each ion present in the solutions used in this reaction.
If chose silver chloride precipitate
Describe the observations that you would make.
Two colourless solutions (silver nitrate and sodium chloride) are mixed together forming a white precipitate ( silver chloride).
Write the net ionic equation for the reaction.
AgNO3 (aq) + NaCl(aq) --> AgCl (s) + NaNO3 (aq)
or
Ag+(aq) + Cl-(aq) --> AgCl (s)
Explain what happens to each ion present in the solutions used in this reaction.
This is a precipitation reaction. Silver ions will react with chloride ions to form insoluble silver chloride
The other ions in the reaction, sodium and nitrate do not react with each other, so stay in solution. They are not written in the ionic equation; they are spectator ions.
If chose aluminium carbonate precipitate
Describe the observations that you would make.
Two colourless solutions ( aluminum nitrate and sodium carbonate) are mixed together forming a white precipitate ( aluminum carbonate)
Write the net ionic equation for the reaction.
2Al(NO3)3 (aq) + 3Na2CO3 (aq) -->Al2(CO3)3 (s) + 6NaNO3(aq)
or
2Al3+(aq) + 3CO32-(aq) --> Al2(CO3)3 (s)
Explain what happens to each ion present in the solutions used in this reaction.
This is a precipitation reaction. Aluminium ions will react with carbonate ions to form insoluble aluminium carbonate.
The other ions in the reaction, sodium and nitrate, NO3–, do not react with each other, so stay in solution. They are not written in the ionic equation; they are spectator ions.
Question 2
When Copper carbonate is heated it undergoes thermal decomposition.
Discuss the chemical reaction occurring including the following:
• Describe what observations would be made and explain them using a balanced equation for the reaction taking place.
• Describe the test you could carry out to identify the gas produced in the chemical reaction. Include observations made in your answer and a balanced equation for the reaction taking place.
When solid green copper carbonate is heated in a test tube using a Bunsen burner flame it turns from green to black as it is forming black copper oxide
The equation for the reaction taking place is
Copper carbonate --> copper oxide + carbon dioxide gas
CuCO3(s) --> CuO (s) + CO2(g)
The gas produced during thermal decomposition is carbon dioxide gas
To test for this gas the gas from the reaction can be bubbled through lime water which would turn from clear to cloudy indicating carbon dioxide gas has been produced.
CO2 + Ca(OH)2 --> CaCO3 + H2O
( A splint going out is unacceptable as is not conclusive)
Question 3
When an iron nail is placed in a beaker of copper sulfate a redox reaction occurs.
Discuss the chemistry of this reaction.
In your answer:
• state what you would observe as this reaction proceeds
• explain why this is an oxidation-reduction reaction
• identify the reduction and oxidation processes
• include all appropriate equations in your discussion.
The grey nail will be covered in a reddish –brown solid which is copper and the blue colour (due to Cu2+ ions) of the solution will start to fade.
This is a redox reaction because the Fe loses electrons to form Fe2+ and the Cu2+ ions gain these electrons to form Cu. The electrons are therefore transferred from one substance to another.
The Fe is oxidised: Fe --> Fe2+ + 2e
The Cu2+ ions are reduced Cu2+ + 2e --> Cu
Overall equation: Cu2+ + Fe --> Cu + Fe2+
For this reaction:
• Describe the observations that you would make
• Write the net ionic equation for the reaction.
• Explain what happens to each ion present in the solutions used in this reaction.
If chose silver chloride precipitate
Describe the observations that you would make.
Two colourless solutions (silver nitrate and sodium chloride) are mixed together forming a white precipitate ( silver chloride).
Write the net ionic equation for the reaction.
AgNO3 (aq) + NaCl(aq) --> AgCl (s) + NaNO3 (aq)
or
Ag+(aq) + Cl-(aq) --> AgCl (s)
Explain what happens to each ion present in the solutions used in this reaction.
This is a precipitation reaction. Silver ions will react with chloride ions to form insoluble silver chloride
The other ions in the reaction, sodium and nitrate do not react with each other, so stay in solution. They are not written in the ionic equation; they are spectator ions.
If chose aluminium carbonate precipitate
Describe the observations that you would make.
Two colourless solutions ( aluminum nitrate and sodium carbonate) are mixed together forming a white precipitate ( aluminum carbonate)
Write the net ionic equation for the reaction.
2Al(NO3)3 (aq) + 3Na2CO3 (aq) -->Al2(CO3)3 (s) + 6NaNO3(aq)
or
2Al3+(aq) + 3CO32-(aq) --> Al2(CO3)3 (s)
Explain what happens to each ion present in the solutions used in this reaction.
This is a precipitation reaction. Aluminium ions will react with carbonate ions to form insoluble aluminium carbonate.
The other ions in the reaction, sodium and nitrate, NO3–, do not react with each other, so stay in solution. They are not written in the ionic equation; they are spectator ions.
Question 2
When Copper carbonate is heated it undergoes thermal decomposition.
Discuss the chemical reaction occurring including the following:
• Describe what observations would be made and explain them using a balanced equation for the reaction taking place.
• Describe the test you could carry out to identify the gas produced in the chemical reaction. Include observations made in your answer and a balanced equation for the reaction taking place.
When solid green copper carbonate is heated in a test tube using a Bunsen burner flame it turns from green to black as it is forming black copper oxide
The equation for the reaction taking place is
Copper carbonate --> copper oxide + carbon dioxide gas
CuCO3(s) --> CuO (s) + CO2(g)
The gas produced during thermal decomposition is carbon dioxide gas
To test for this gas the gas from the reaction can be bubbled through lime water which would turn from clear to cloudy indicating carbon dioxide gas has been produced.
CO2 + Ca(OH)2 --> CaCO3 + H2O
( A splint going out is unacceptable as is not conclusive)
Question 3
When an iron nail is placed in a beaker of copper sulfate a redox reaction occurs.
Discuss the chemistry of this reaction.
In your answer:
• state what you would observe as this reaction proceeds
• explain why this is an oxidation-reduction reaction
• identify the reduction and oxidation processes
• include all appropriate equations in your discussion.
The grey nail will be covered in a reddish –brown solid which is copper and the blue colour (due to Cu2+ ions) of the solution will start to fade.
This is a redox reaction because the Fe loses electrons to form Fe2+ and the Cu2+ ions gain these electrons to form Cu. The electrons are therefore transferred from one substance to another.
The Fe is oxidised: Fe --> Fe2+ + 2e
The Cu2+ ions are reduced Cu2+ + 2e --> Cu
Overall equation: Cu2+ + Fe --> Cu + Fe2+
Monday, May 3, 2010
Determining formula
2006 QUESTION FIVE: CALCULATING MOLAR MASSES
Calculate the molar masses of the following compounds.
Refer to the Resource Booklet provided. Show your working.
(a) CaCO3
Ca = 1 x 40 = 40
C = 1 x 12 = 12
O = 3 x 16 = 48
Molar mass = 100 g/mol
(b) Al2O3
Al = 2 x 26.9 = 53.8
O = 3 x 16 = 48
Molar mass = 101.8 g/mol
(c) (NH4)2SO4
N= 2 x 14 = 28
H = 8 x 1 = 8
S = 1 x 32 = 32
O = 4 x 16 = 64
Molar mass = 132 g /mol
2007 QUESTION FOUR: MOLAR MASSES
Calculate the relative molar masses of the following compounds. Use the relative atomic masses provided in the periodic table in the Resource Booklet.
(a) ZnO
Zn = 1 x 65.4 = 65.4
O = 1 x 16 = 16
Molar mass = 81.4 g/mol
(b) CuSO4
Cu = 1 x 63.5 = 63.5
S = 1 x 32 = 32
O = 4 x 16 = 64
Molar mass = 159.5 g/mol
(c) Pb(NO3)2
Pb = 1 x 207.2 = 207.2
N = 2 x 14 = 28
O = 6 x 16 = 96
molar mass = 331.2 g/mol
2006 QUESTION SIX: CALCULATING MASS
Ammonia, NH3 , can be prepared by heating ammonium chloride, NH4Cl, with calcium hydroxide, Ca(OH)2 .
2NH4Cl + Ca(OH)2 → CaCl2 + 2NH3 + 2H2O
Calculate the mass of calcium hydroxide required to react with 2.14 grams of ammonium chloride.
107g --------> 74
2NH4Cl + Ca(OH)2 → CaCl2 + 2NH3 + 2H2O
2.14g --------> ?
2.14/107 x 74 = 1.48g
2007 QUESTION FIVE: CALCULATING MASS
(a) Calculate the mass of zinc hydroxide that must be heated to produce 1.00 gram of water. Use the equation below. Show all of your working clearly.
Zn(OH)2(s) --> ZnO(s) + H2O(g)
99.4 --------> 18
Zn(OH)2 --> H2O
? ------------> 1.00
1.00 / 18 x 99.4 = 5.52g
(b) Calculate the mass of sodium hydrogen carbonate, NaHCO3, required to form 5.40 grams of carbon dioxide, CO2, when heated. Show all of your working clearly.
2NaHCO3(s) --> Na2CO3(s) + H2O(g) + CO2(g)
168 ------------> 44
2NaHCO3 ----> CO2
? ---------------> 5.40
Calculate the molar masses of the following compounds.
Refer to the Resource Booklet provided. Show your working.
(a) CaCO3
Ca = 1 x 40 = 40
C = 1 x 12 = 12
O = 3 x 16 = 48
Molar mass = 100 g/mol
(b) Al2O3
Al = 2 x 26.9 = 53.8
O = 3 x 16 = 48
Molar mass = 101.8 g/mol
(c) (NH4)2SO4
N= 2 x 14 = 28
H = 8 x 1 = 8
S = 1 x 32 = 32
O = 4 x 16 = 64
Molar mass = 132 g /mol
2007 QUESTION FOUR: MOLAR MASSES
Calculate the relative molar masses of the following compounds. Use the relative atomic masses provided in the periodic table in the Resource Booklet.
(a) ZnO
Zn = 1 x 65.4 = 65.4
O = 1 x 16 = 16
Molar mass = 81.4 g/mol
(b) CuSO4
Cu = 1 x 63.5 = 63.5
S = 1 x 32 = 32
O = 4 x 16 = 64
Molar mass = 159.5 g/mol
(c) Pb(NO3)2
Pb = 1 x 207.2 = 207.2
N = 2 x 14 = 28
O = 6 x 16 = 96
molar mass = 331.2 g/mol
2006 QUESTION SIX: CALCULATING MASS
Ammonia, NH3 , can be prepared by heating ammonium chloride, NH4Cl, with calcium hydroxide, Ca(OH)2 .
2NH4Cl + Ca(OH)2 → CaCl2 + 2NH3 + 2H2O
Calculate the mass of calcium hydroxide required to react with 2.14 grams of ammonium chloride.
107g --------> 74
2NH4Cl + Ca(OH)2 → CaCl2 + 2NH3 + 2H2O
2.14g --------> ?
2.14/107 x 74 = 1.48g
2007 QUESTION FIVE: CALCULATING MASS
(a) Calculate the mass of zinc hydroxide that must be heated to produce 1.00 gram of water. Use the equation below. Show all of your working clearly.
Zn(OH)2(s) --> ZnO(s) + H2O(g)
99.4 --------> 18
Zn(OH)2 --> H2O
? ------------> 1.00
1.00 / 18 x 99.4 = 5.52g
(b) Calculate the mass of sodium hydrogen carbonate, NaHCO3, required to form 5.40 grams of carbon dioxide, CO2, when heated. Show all of your working clearly.
2NaHCO3(s) --> Na2CO3(s) + H2O(g) + CO2(g)
168 ------------> 44
2NaHCO3 ----> CO2
? ---------------> 5.40
5.40 / 44 x 168 = 20.62g
2006 QUESTION SEVEN: DETERMINING A FORMULA
Determine the formula of the compound made when 3.55 g of chlorine combines with 5.60 g of oxygen.
The molar mass of the compound is 183.0.
Refer to the Resource Booklet provided. Show your working.
Chlorine----------> oxygen
3.55g/35.5 --------> 5.60 / 16
0.1 mol/ 0.1--------------> 0.35 mol / 0.1
1 --------------------------> 3.5
2 ---------------------------> 7
Emperical formula: Cl2O7
empirical formula mass = molar mass so molecular formula = empirical formula
2007 QUESTION SEVEN: MOLECULAR FORMULA
A compound was analysed and found to contain:
• 20.2% phosphorus
• 10.4% oxygen and
• 69.4% chlorine.
It has a relative molar mass of 153.5.
Determine the molecular formula of this substance. Show all of your working clearly.
phosphorus _________ oxygen __________chlorine
20.2 / 31 ____________ 10.4 / 16 _________ 69.4 / 35.5
0.65 mol/0.65 ________0.65mol/0.65 _____1.95 mol/0.65
1 __________________ 1 ______________ 3
Emperical formula = POCl3
Emperical mass = 153.5, Molar mass = 153.5
Chemical Reactions
2006 QUESTION FOUR: OBSERVING REACTIONS
A group of students carried out an investigation into the thermal decomposition of the following solid carbonates: sodium carbonate, calcium carbonate, and copper carbonate.
(a) Describe the appearance of each carbonate before it was heated.
(i)
Sodium carbonate - A white solid
(ii)
Calcium carbonate - A white solid
(iii)
Copper carbonate -A green solid
(b) Describe the observations the students would have made when heating each of the carbonates.
(i)
Sodium carbonate - A white solid of sodium oxide
(ii)
Calcium carbonate -A white solid of calcium oxide
(iii)
Copper carbonate - A black solid of copper oxide
(c) Write a balanced equation for the thermal decomposition of copper carbonate.
Copper carbonate --> copper oxide + carbon dioxide gas
CuCO3 --> CuO + CO2
Some grey powdered magnesium was added to a green solution of iron (II) sulfate in a beaker, and mixed well. The green colour of the solution faded and the grey powder disappeared. A new dark grey solid formed on the bottom of the beaker.
(d) (i) State what type of reaction this is.
REDOX reaction
(ii) Discuss what happened in this reaction. Your answer should link the reactants and products involved in the reaction to the observations made.
The green Fe2+ ions in the iron sulfate is displaced by the grey magnesium metal forming a colourless solution of magnesium sulfate and Iron metal. This explains why the green iron(II) sulfate fades as the magnesiun sulfate formed is colourless.
The dark grey solid froming at the bottom of the beaker is the Iron metal that is forming in the reaction
Include an appropriate balanced equation in your answer. Spectator ions may be omitted.
FeSO4 + Mg --> MgSO4 + Fe
2007 QUESTION THREE: OBSERVING CHEMICAL REACTIONS
A small amount of zinc hydroxide is heated in a test tube over a Bunsen burner. The following reaction occurs.
heat
Zn(OH)2 (s) --> ZnO(s) + H2O(g)
(a) State what type of reaction is occurring.
Thermal decomposition
(b) Fully describe the observations that would be expected if this reaction was carried out in a school laboratory. Remember to link your observations to the substances involved.
The zinc hydroxide would react to form zinc oxide, both of which are white, however the reaction produces water which would be seen as condensation on the side of the tube.
2007 QUESTION SIX: CHEMICAL REACTIONS
Part A
A colourless solution of barium nitrate is added to a pale green solution of iron(II) sulfate in a beaker. A reaction occurs.
(a) Describe the observations that would be expected for this reaction.
Upon addition of the two solutions a white precipitate of barium sulfate would form.
(b) State what type of reaction is occurring.
Precipitation reaction
(c) Discuss the chemistry of this reaction. Your discussion should refer to the observations you made in part (a). Include a balanced equation in your answer. Spectator ions may be omitted.
Barium nitrate + iron (II) sulfate --> barium sulfate + iron (ii) nitrate
Ba2+ + SO42- --> BaSO4 - ionic equatiion
The colourless solution of barium nitrate is added to the pale green solution of iron (II) sulfate. These two solutions contain ions in solution. The reaction results in the formation of a white barium sulfate precipitate where the barium ions and sulfate ions bond together to form the white solid.
The iron (II) ions and nitrate ions remain in solution.
Part B
A strip of magnesium ribbon is heated over a Bunsen burner. It burns with a bright white light and forms a white ash.
Discuss the chemistry of this reaction in terms of oxidation and reduction. Write the appropriate half equations and overall balanced equation in your answer.
(Mg --> Mg2+ + 2e-) 2 Oxidation
O2 + 4e- --> 2O2- Reduction
2Mg + O2 --> 2Mg2+ + 2O2-
The silver magnesium metal is oxidised to magnesium ions as is loses electrons. In this reaction it is acting as the reductant.
The colourless oxygen gas is reduced to oxide ions as it gains electrons. In this reaction it is acting as the oxidant.
A group of students carried out an investigation into the thermal decomposition of the following solid carbonates: sodium carbonate, calcium carbonate, and copper carbonate.
(a) Describe the appearance of each carbonate before it was heated.
(i)
Sodium carbonate - A white solid
(ii)
Calcium carbonate - A white solid
(iii)
Copper carbonate -A green solid
(b) Describe the observations the students would have made when heating each of the carbonates.
(i)
Sodium carbonate - A white solid of sodium oxide
(ii)
Calcium carbonate -A white solid of calcium oxide
(iii)
Copper carbonate - A black solid of copper oxide
(c) Write a balanced equation for the thermal decomposition of copper carbonate.
Copper carbonate --> copper oxide + carbon dioxide gas
CuCO3 --> CuO + CO2
Some grey powdered magnesium was added to a green solution of iron (II) sulfate in a beaker, and mixed well. The green colour of the solution faded and the grey powder disappeared. A new dark grey solid formed on the bottom of the beaker.
(d) (i) State what type of reaction this is.
REDOX reaction
(ii) Discuss what happened in this reaction. Your answer should link the reactants and products involved in the reaction to the observations made.
The green Fe2+ ions in the iron sulfate is displaced by the grey magnesium metal forming a colourless solution of magnesium sulfate and Iron metal. This explains why the green iron(II) sulfate fades as the magnesiun sulfate formed is colourless.
The dark grey solid froming at the bottom of the beaker is the Iron metal that is forming in the reaction
Include an appropriate balanced equation in your answer. Spectator ions may be omitted.
FeSO4 + Mg --> MgSO4 + Fe
2007 QUESTION THREE: OBSERVING CHEMICAL REACTIONS
A small amount of zinc hydroxide is heated in a test tube over a Bunsen burner. The following reaction occurs.
heat
Zn(OH)2 (s) --> ZnO(s) + H2O(g)
(a) State what type of reaction is occurring.
Thermal decomposition
(b) Fully describe the observations that would be expected if this reaction was carried out in a school laboratory. Remember to link your observations to the substances involved.
The zinc hydroxide would react to form zinc oxide, both of which are white, however the reaction produces water which would be seen as condensation on the side of the tube.
2007 QUESTION SIX: CHEMICAL REACTIONS
Part A
A colourless solution of barium nitrate is added to a pale green solution of iron(II) sulfate in a beaker. A reaction occurs.
(a) Describe the observations that would be expected for this reaction.
Upon addition of the two solutions a white precipitate of barium sulfate would form.
(b) State what type of reaction is occurring.
Precipitation reaction
(c) Discuss the chemistry of this reaction. Your discussion should refer to the observations you made in part (a). Include a balanced equation in your answer. Spectator ions may be omitted.
Barium nitrate + iron (II) sulfate --> barium sulfate + iron (ii) nitrate
Ba2+ + SO42- --> BaSO4 - ionic equatiion
The colourless solution of barium nitrate is added to the pale green solution of iron (II) sulfate. These two solutions contain ions in solution. The reaction results in the formation of a white barium sulfate precipitate where the barium ions and sulfate ions bond together to form the white solid.
The iron (II) ions and nitrate ions remain in solution.
Part B
A strip of magnesium ribbon is heated over a Bunsen burner. It burns with a bright white light and forms a white ash.
Discuss the chemistry of this reaction in terms of oxidation and reduction. Write the appropriate half equations and overall balanced equation in your answer.
(Mg --> Mg2+ + 2e-) 2 Oxidation
O2 + 4e- --> 2O2- Reduction
2Mg + O2 --> 2Mg2+ + 2O2-
The silver magnesium metal is oxidised to magnesium ions as is loses electrons. In this reaction it is acting as the reductant.
The colourless oxygen gas is reduced to oxide ions as it gains electrons. In this reaction it is acting as the oxidant.
Equations
2006 QUESTION THREE: WORD EQUATIONS
Complete the following word equations.
(a) barium chloride + magnesium sulfate → barium sulfate + magnesium chloride
(b) sodium hydrogen carbonate → sodium carbonate + carbon dioxde gas + water
(c) iron + copper sulfate → iron sulfate + copper
2007 QUESTION TWO: EQUATIONS
(a) Complete the following word equations.
(i) magnesium + oxygen ---> magnesium oxide
(ii) calcium carbonate --> calcium oxide + carbon dioxide gas
(iii) lead nitrate + potassium chloride ---> lead chloride + potassium nitrate
(b) Complete and balance the following equations.
(i) I–(aq) + Cl2(aq) --> I2(aq) + 2Cl- (aq)
(ii) Zn(s) + 2AgNO3(aq) --> Zn (NO3)2 (aq) + Ag(s)
Hints
How do you know what kind of reaction it is?
If there is only one reactant then it is a thermal decomposition reaction.
If there are two reactants, both having two parts to their names, then it is a precipitation reaction.
If there are two reactants, one is a metal and the other a chemical with two parts to its name then it is a redox reaction and depending on the reactivity of the metals (refer to data book) the two metals will swap places during the reaction. (see (ii) above)
Complete the following word equations.
(a) barium chloride + magnesium sulfate → barium sulfate + magnesium chloride
(b) sodium hydrogen carbonate → sodium carbonate + carbon dioxde gas + water
(c) iron + copper sulfate → iron sulfate + copper
2007 QUESTION TWO: EQUATIONS
(a) Complete the following word equations.
(i) magnesium + oxygen ---> magnesium oxide
(ii) calcium carbonate --> calcium oxide + carbon dioxide gas
(iii) lead nitrate + potassium chloride ---> lead chloride + potassium nitrate
(b) Complete and balance the following equations.
(i) I–(aq) + Cl2(aq) --> I2(aq) + 2Cl- (aq)
(ii) Zn(s) + 2AgNO3(aq) --> Zn (NO3)2 (aq) + Ag(s)
Hints
How do you know what kind of reaction it is?
If there is only one reactant then it is a thermal decomposition reaction.
If there are two reactants, both having two parts to their names, then it is a precipitation reaction.
If there are two reactants, one is a metal and the other a chemical with two parts to its name then it is a redox reaction and depending on the reactivity of the metals (refer to data book) the two metals will swap places during the reaction. (see (ii) above)
Chemical reactions - precipitation reactions
2006 QUESTION ONE: TYPES OF REACTION
Classify each of the reactions in the table below by writing the letter from the key list in the space provided.
Key list: oxidation-reduction – O
precipitation – P
thermal decomposition – T
Type of reaction
(Choose from O, P or T)
(a)
CaCl2(aq) + K2CO3(aq) → 2KCl(aq) + CaCO3(s)
Precipitation
(b)
Pb(OH)2(s) → PbO(s) + H2O(l)
Thermal decomposition
(c)
AgNO3(aq) + NaCl(aq) → NaNO3(aq) + AgCl(s)
Precipitation
(d)
Cl2(aq) + 2I–(aq) → 2Cl–(aq) + I2(aq)
Redox
(e)
CO(g) + PbO(s) → Pb(s) + CO2(g)
Redox
2006 QUESTION TWO: PRECIPITATION
The following solutions are mixed in the pairs shown. Use the solubility rules in your Resource Booklet to identify the precipitate (if any) that is formed for each pair.
(a) Write the name of the precipitate or, if none is formed, write no precipitate.
(i)
Sodium chloride and copper nitrate --> sodium nitrate and copper chloride
no precipitate
(ii)
Lead nitrate and potassium chloride --> lead chloride + potassium nitrate
HINTS:
here the spectator ions are potassium ions and nitrate ions, these ions stay in solution and the lead and chloride ions bond to form a solid of lead chloride.
lead chloride precipitate
(iii)
Potassium hydroxide and magnesium sulfate ---> magnesium hydroxide + potassium sulfate
magnesium hydroxide precipitate
(b) Write a balanced equation for the formation of ONE precipitate identified in Question Two (a) above. Spectator ions may be omitted from ionic equations.
Pb2+ + 2Cl- ---> PbCl2
Mg2+ + 2OH- --> Mg(OH)2
2007 QUESTION ONE: PRECIPITATION
The following pairs of solutions are mixed. Use the solubility rules in your Resource Booklet to identify if a precipitate is formed.
(a) Write the name of the precipitate. If none is formed, write no precipitate.
Solutions that are mixed
Name of the Precipitate, OR No Precipitate
(i)
Silver nitrate + calcium chloride --> silver chloride + calcium nitrate
silver chloride precipitate
(ii)
Potassium sulfate + iron(II) nitrate --> potassium nitrate + iron sulfate
no precipitate
(iii)
Calcium nitrate + sodium sulfate --> calcium sulfate + sodium nitrate
calcium sulfate precipitate
(b) Write a balanced equation for the formation of ONE precipitate identified in Question One (a) above. Spectator ions may be omitted from ionic equations.
Ag+ + Cl- --> AgCl
Classify each of the reactions in the table below by writing the letter from the key list in the space provided.
Key list: oxidation-reduction – O
precipitation – P
thermal decomposition – T
Type of reaction
(Choose from O, P or T)
(a)
CaCl2(aq) + K2CO3(aq) → 2KCl(aq) + CaCO3(s)
Precipitation
(b)
Pb(OH)2(s) → PbO(s) + H2O(l)
Thermal decomposition
(c)
AgNO3(aq) + NaCl(aq) → NaNO3(aq) + AgCl(s)
Precipitation
(d)
Cl2(aq) + 2I–(aq) → 2Cl–(aq) + I2(aq)
Redox
(e)
CO(g) + PbO(s) → Pb(s) + CO2(g)
Redox
2006 QUESTION TWO: PRECIPITATION
The following solutions are mixed in the pairs shown. Use the solubility rules in your Resource Booklet to identify the precipitate (if any) that is formed for each pair.
(a) Write the name of the precipitate or, if none is formed, write no precipitate.
(i)
Sodium chloride and copper nitrate --> sodium nitrate and copper chloride
no precipitate
(ii)
Lead nitrate and potassium chloride --> lead chloride + potassium nitrate
HINTS:
here the spectator ions are potassium ions and nitrate ions, these ions stay in solution and the lead and chloride ions bond to form a solid of lead chloride.
lead chloride precipitate
(iii)
Potassium hydroxide and magnesium sulfate ---> magnesium hydroxide + potassium sulfate
magnesium hydroxide precipitate
(b) Write a balanced equation for the formation of ONE precipitate identified in Question Two (a) above. Spectator ions may be omitted from ionic equations.
Pb2+ + 2Cl- ---> PbCl2
Mg2+ + 2OH- --> Mg(OH)2
When a precipitate
2007 QUESTION ONE: PRECIPITATION
The following pairs of solutions are mixed. Use the solubility rules in your Resource Booklet to identify if a precipitate is formed.
(a) Write the name of the precipitate. If none is formed, write no precipitate.
Solutions that are mixed
Name of the Precipitate, OR No Precipitate
(i)
Silver nitrate + calcium chloride --> silver chloride + calcium nitrate
silver chloride precipitate
(ii)
Potassium sulfate + iron(II) nitrate --> potassium nitrate + iron sulfate
no precipitate
(iii)
Calcium nitrate + sodium sulfate --> calcium sulfate + sodium nitrate
calcium sulfate precipitate
(b) Write a balanced equation for the formation of ONE precipitate identified in Question One (a) above. Spectator ions may be omitted from ionic equations.
Ag+ + Cl- --> AgCl
Friday, March 19, 2010
Thursday, March 18, 2010
Metals and acids end of unit test answers
CHEM 1.4 End of Unit Test – Model Answers
Question 1
Iron is one of the most important industrial metals due to its use in the manufacture of steel. Iron will readily react in the atmosphere to produce reddish-brown rust. For this rust to form the presence of both oxygen and water is required. The rusting process can be sped up by the presence of either salt or acid.
Below is an experiment designed to test which method is best for preventing rust on a steel (iron) nail.
Discuss why the nail wrapped in copper foil would have more rust than the nail wrapped in magnesium ribbon.
Include in your answer:
• Any observations for each of the above reactions
• An explanation for the observation in each test tube
• All relevant balanced equations for each of the above experiments
• Suggestions for how the above idea could be used commercially (hint: you must discuss the uses of iron and link these to the above experiment)
Observation Test tube with just nail in (A) – rusty.
Middle test tube (B) – no rust on nail.
Test tube with nail wrapped in copper (C) – rusty.
Explanation (A) Iron in steel reacts in the presence of oxygen, water and carbon dioxide to form iron(III) oxide.
(B) Magnesium is more reactive than iron, so will react with oxygen first. This is magnesium acting as a sacrificial metal
(C) Copper is a less reactive metal than iron. It will not react with the oxygen or water, so iron reacts first, faster than copper.
Balanced equations (A) 4 Fe + 3 O2 --> 2 Fe2O3
(B) 2 Mg + O2 -->2 MgO
(C) No equation for copper (4 Fe + 3 O2--> 2 Fe2O3)
Commercial use Sacrificial protection used in boats. A piece of more reactive metal is attached to the steel hull of a ship and so the more reactive metal will react first, protecting the iron in the steel.
Question 2
A student carried out an experiment with sulfuric acid (H2SO4) and calcium carbonate (CaCO3), as detailed below:
In test tube A she mixed 1 mL of sulfuric acid with a 2 gram lump of calcium carbonate.
In test tube B she mixed 1 mL of sulfuric acid with 2 grams of powdered calcium carbonate.
The sulfuric acid in both experiments was the same concentration.
Discuss, in terms of particles, how changing the surface area of the calcium carbonate affected the rate of reaction.
Include in your answer:
• A comparison of the observations you would make during these reactions
• An explanation of your observations
• A balanced equation for the chemical reaction taking place.
Comparison of observations - In both test tubes heat was produced, bubbles of gas and CaCO3 would disappear. The reaction in test tube A would be slower than the same reaction in test tube B.
Explanation of observations – Test tube B contained powdered CaCO3 which has a higher surface area than the lump of CaCO3. This means that more calcium carbonate particles are immediately available to react with the acid particles so there will be more collisions per unit time and so the rate of reaction will be faster.
Balanced equation – CaCO3 + H2SO4 --> CaSO4 + CO2 + H2O
Question 3
Discuss the similarities and differences between the reactions of magnesium and aluminium in oxygen and in hydrochloric acid.
Include in your answer:
• Any observations made during these reactions
• An explanation of why these similarities and differences occur
• All relevant balanced equations
Observations of reaction with oxygen – Mg burns with a bright white light. A white/grey powder is formed. Al reacts immediately with oxygen to form a white oxide layer.
Observations of reaction with HCl – Mg reacts with HCl to produce a gas and the magnesium will disappear. Al does not react with HCl.
Explanation of differences – Mg is more reactive than Al so reacts with oxygen more quickly.
Al does not react with HCl due to the impenetrable oxide layer on the surface, so the metal itself does not come into contact with the acid.
Explanation of similarities – Mg is more reactive than Al but both react with oxygen.
Balanced equations – 2 Mg + O2 --> 2 MgO
4Al + 3 O2 --> 2 Al2O3
Mg + 2 HCl --> MgCl2 + H2
No reaction for Al and HCl
Question 4
Calcium carbonate is commonly known as limestone, and is often used in fertilizers to reduce the acidity of soil.
Discuss why limestone can be used to reduce the acidity of soil.
Include in you answer:
• The property of limestone that allows it to reduce acidity.
• Any relevant equations.
• A definition of a neutralisation reaction
Property of limestone that allows it to reduce acidity – limestone is basic. It will react with any acid particles in the soil, neutralising them and so reducing the acidity of the soil. The salt and water produced are neutral so the pH of the soil will increase (acidity will decrease).
Any relevant equations acid + metal carbonate --> metal salt + carbon dioxide + water
e.g. CaCO3 + 2 HCl --> CaCl2 + CO2 + H2O
Or... CaCO3 + 2 H+_--> Ca2+ + CO2 + H2O
A definition of a neutralisation reaction – the number of H+ ions and OH- ions will be equal so pH = 7
Question 5
Cork rockets can be made using a plastic bottle and a cork. The cork is fitted into the neck of the bottle. Propulsion is generated by reacting baking soda (sodium bicarbonate) with acid. The carbon dioxide produced in the reaction builds up pressure inside the bottle causing the cork to fire out of the neck of the bottle when a particular pressure is reached.
For a particular class experiment with the cork rocket, the time that elapsed between mixing the chemicals in the bottle and the cork firing out was measured.
A student in the class suggested that they had to wait too long.
Another student suggested that it would be possible to reduce the time elapsed between the loading and the firing of the rocket. The teacher agreed.
Discuss ALL possible factors that you could change in the experiment, in chemical terms, to decrease this time. Include in your answer:
• clear reference to the particles involved
• link the steps you take to their effect on the reaction.
Increase surface area of baking soda. Particles – more sodium bicarbonate particles immediately available to react, so more collisions per unit time.
Effect on reaction – rate of reaction will increase and so the time taken to fire the cork will decrease.
Increase concentration of acid. Particles – more acid particles per unit volume, so more collisions per unit time between acid particles and sodium bicarbonate particles.
Effect on reaction – rate of reaction will increase and so the time taken to fire the cork will decrease.
Increase temperature. Particles – all particles will have more kinetic energy and so be moving faster, which means that there will be more collision per unit time.
Effect on reaction – rate of reaction will increase and so the time taken to fire the cork will decrease.
Question 1
Iron is one of the most important industrial metals due to its use in the manufacture of steel. Iron will readily react in the atmosphere to produce reddish-brown rust. For this rust to form the presence of both oxygen and water is required. The rusting process can be sped up by the presence of either salt or acid.
Below is an experiment designed to test which method is best for preventing rust on a steel (iron) nail.
Discuss why the nail wrapped in copper foil would have more rust than the nail wrapped in magnesium ribbon.
Include in your answer:
• Any observations for each of the above reactions
• An explanation for the observation in each test tube
• All relevant balanced equations for each of the above experiments
• Suggestions for how the above idea could be used commercially (hint: you must discuss the uses of iron and link these to the above experiment)
Observation Test tube with just nail in (A) – rusty.
Middle test tube (B) – no rust on nail.
Test tube with nail wrapped in copper (C) – rusty.
Explanation (A) Iron in steel reacts in the presence of oxygen, water and carbon dioxide to form iron(III) oxide.
(B) Magnesium is more reactive than iron, so will react with oxygen first. This is magnesium acting as a sacrificial metal
(C) Copper is a less reactive metal than iron. It will not react with the oxygen or water, so iron reacts first, faster than copper.
Balanced equations (A) 4 Fe + 3 O2 --> 2 Fe2O3
(B) 2 Mg + O2 -->2 MgO
(C) No equation for copper (4 Fe + 3 O2--> 2 Fe2O3)
Commercial use Sacrificial protection used in boats. A piece of more reactive metal is attached to the steel hull of a ship and so the more reactive metal will react first, protecting the iron in the steel.
Question 2
A student carried out an experiment with sulfuric acid (H2SO4) and calcium carbonate (CaCO3), as detailed below:
In test tube A she mixed 1 mL of sulfuric acid with a 2 gram lump of calcium carbonate.
In test tube B she mixed 1 mL of sulfuric acid with 2 grams of powdered calcium carbonate.
The sulfuric acid in both experiments was the same concentration.
Discuss, in terms of particles, how changing the surface area of the calcium carbonate affected the rate of reaction.
Include in your answer:
• A comparison of the observations you would make during these reactions
• An explanation of your observations
• A balanced equation for the chemical reaction taking place.
Comparison of observations - In both test tubes heat was produced, bubbles of gas and CaCO3 would disappear. The reaction in test tube A would be slower than the same reaction in test tube B.
Explanation of observations – Test tube B contained powdered CaCO3 which has a higher surface area than the lump of CaCO3. This means that more calcium carbonate particles are immediately available to react with the acid particles so there will be more collisions per unit time and so the rate of reaction will be faster.
Balanced equation – CaCO3 + H2SO4 --> CaSO4 + CO2 + H2O
Question 3
Discuss the similarities and differences between the reactions of magnesium and aluminium in oxygen and in hydrochloric acid.
Include in your answer:
• Any observations made during these reactions
• An explanation of why these similarities and differences occur
• All relevant balanced equations
Observations of reaction with oxygen – Mg burns with a bright white light. A white/grey powder is formed. Al reacts immediately with oxygen to form a white oxide layer.
Observations of reaction with HCl – Mg reacts with HCl to produce a gas and the magnesium will disappear. Al does not react with HCl.
Explanation of differences – Mg is more reactive than Al so reacts with oxygen more quickly.
Al does not react with HCl due to the impenetrable oxide layer on the surface, so the metal itself does not come into contact with the acid.
Explanation of similarities – Mg is more reactive than Al but both react with oxygen.
Balanced equations – 2 Mg + O2 --> 2 MgO
4Al + 3 O2 --> 2 Al2O3
Mg + 2 HCl --> MgCl2 + H2
No reaction for Al and HCl
Question 4
Calcium carbonate is commonly known as limestone, and is often used in fertilizers to reduce the acidity of soil.
Discuss why limestone can be used to reduce the acidity of soil.
Include in you answer:
• The property of limestone that allows it to reduce acidity.
• Any relevant equations.
• A definition of a neutralisation reaction
Property of limestone that allows it to reduce acidity – limestone is basic. It will react with any acid particles in the soil, neutralising them and so reducing the acidity of the soil. The salt and water produced are neutral so the pH of the soil will increase (acidity will decrease).
Any relevant equations acid + metal carbonate --> metal salt + carbon dioxide + water
e.g. CaCO3 + 2 HCl --> CaCl2 + CO2 + H2O
Or... CaCO3 + 2 H+_--> Ca2+ + CO2 + H2O
A definition of a neutralisation reaction – the number of H+ ions and OH- ions will be equal so pH = 7
Question 5
Cork rockets can be made using a plastic bottle and a cork. The cork is fitted into the neck of the bottle. Propulsion is generated by reacting baking soda (sodium bicarbonate) with acid. The carbon dioxide produced in the reaction builds up pressure inside the bottle causing the cork to fire out of the neck of the bottle when a particular pressure is reached.
For a particular class experiment with the cork rocket, the time that elapsed between mixing the chemicals in the bottle and the cork firing out was measured.
A student in the class suggested that they had to wait too long.
Another student suggested that it would be possible to reduce the time elapsed between the loading and the firing of the rocket. The teacher agreed.
Discuss ALL possible factors that you could change in the experiment, in chemical terms, to decrease this time. Include in your answer:
• clear reference to the particles involved
• link the steps you take to their effect on the reaction.
Increase surface area of baking soda. Particles – more sodium bicarbonate particles immediately available to react, so more collisions per unit time.
Effect on reaction – rate of reaction will increase and so the time taken to fire the cork will decrease.
Increase concentration of acid. Particles – more acid particles per unit volume, so more collisions per unit time between acid particles and sodium bicarbonate particles.
Effect on reaction – rate of reaction will increase and so the time taken to fire the cork will decrease.
Increase temperature. Particles – all particles will have more kinetic energy and so be moving faster, which means that there will be more collision per unit time.
Effect on reaction – rate of reaction will increase and so the time taken to fire the cork will decrease.
Thursday, March 11, 2010
Metals and acids questions
Question 1
The students created a chemical volcano using the baking soda and vinegar.
Discuss what is happening in this reaction. Use the information in the table in (a) to help you.
Include in your answer
• the type of reaction that has occurred
• observations that would be made
• the products of the reaction
• an appropriate balanced equation.
ANSWER:
Type of reaction:
The reaction is a neutralisation reaction because the acid is being turned into a new substance that is neither acid of base..that has a pH =7
Observations:
Fizzing would be observed as CO2 gas is produced and the sodium hydrogen carbonate would disappear
Word equation: (must be all in words – no formulae)
Sodium hydrogen carbonate (or sodium bicarbonate) + ethanoic / acetic acid-->sodium ethanoate / acetate + water + carbon dioxide.
Balanced equation: NaHCO3 + CH3COOH -->CH3COONa + H2O + CO2
(NaCH3COO also accepted.)
Question 2
(a) A student put some water in a beaker, added a few drops of litmus solution, and then added a small piece of calcium metal. Calcium reacts vigorously in water.
(i) Describe TWO observations that would be made when calcium is added to the water in the beaker and explain why they occur.
ANSWER:
Fizzing / bubbling / effervescence
• Explanation: hydrogen / H2 / gas is produced
OR
Litmus / water / solution turns blue or blue-purple / purple-blue
• Explanation: an alkali Ca(OH)2 forms
OR
White solid forms or solution goes cloudy
• Explanation: calcium hydroxide is not very soluble it forms suspension.
OR
Calcium / metal disappears.
• Explanation: has formed a compound in solution / forms a solution / has reacted with the water / forms product that dissolves / disperses in the water
OR
The beaker contents get warmer
• Explanation: exothermic reaction / reaction releases heat energy
OR
Ca pieces sink, float up, sink (and cycle repeats)
Explanation: light H2 gas forms on Ca & helps it floats up etc (but not floats / fizzes around surface)
(ii) Write a balanced equation for the reaction of calcium in water.
ANSWER
Ca + 2H2O --> Ca(OH)2 + H2
b)
THREE metals labelled X, Y and Z need to be identified based on some characteristic physical and chemical properties.The possible metals are:
Identify metals X, Y and Z and justify your answer using the reactions described in the table opposite. Include the products of any reactions in your answer.
Question 3
Magnesium ribbon reacts with dilute hydrochloric acid in a conical flask, which is connected to an inverted measuring cylinder in a trough of water. The volume of gas produced is measured over a few minutes, and the results are used to sketch a graph.
(a) Explain why, in terms of particles involved, the line on the graph levels off over time.
ANSWER
• The reaction has stopped and no more gas is produced.
• The reactants are being converted into products. This means there are fewer particles available to collide as the reaction progresses.
• The rate of the reaction will decrease and eventually the reaction will stop.
• Incorrect chemistry referring to changes in energy or speed of particles or “gas levelling off” or changes to activation energy negated some answers.
(b) Discuss the effect on the rate of reaction when repeating this experiment using the same mass of magnesium powder with the dilute hydrochloric acid.
ANSWER
• The reaction rate will increase.
• There are more reactant particles immediately available to react because the surface area of the powder is greater than that of the ribbon. There is greater exposure of the magnesium particles so more can collide at any one time.
• This means there will be more (effective) collisions per second / more frequent collisions between the Mg / powder and the acid, leading to an increase in the rate of the reaction.
The students created a chemical volcano using the baking soda and vinegar.
Discuss what is happening in this reaction. Use the information in the table in (a) to help you.
Include in your answer
• the type of reaction that has occurred
• observations that would be made
• the products of the reaction
• an appropriate balanced equation.
ANSWER:
Type of reaction:
The reaction is a neutralisation reaction because the acid is being turned into a new substance that is neither acid of base..that has a pH =7
Observations:
Fizzing would be observed as CO2 gas is produced and the sodium hydrogen carbonate would disappear
Word equation: (must be all in words – no formulae)
Sodium hydrogen carbonate (or sodium bicarbonate) + ethanoic / acetic acid-->sodium ethanoate / acetate + water + carbon dioxide.
Balanced equation: NaHCO3 + CH3COOH -->CH3COONa + H2O + CO2
(NaCH3COO also accepted.)
Question 2
(a) A student put some water in a beaker, added a few drops of litmus solution, and then added a small piece of calcium metal. Calcium reacts vigorously in water.
(i) Describe TWO observations that would be made when calcium is added to the water in the beaker and explain why they occur.
ANSWER:
Fizzing / bubbling / effervescence
• Explanation: hydrogen / H2 / gas is produced
OR
Litmus / water / solution turns blue or blue-purple / purple-blue
• Explanation: an alkali Ca(OH)2 forms
OR
White solid forms or solution goes cloudy
• Explanation: calcium hydroxide is not very soluble it forms suspension.
OR
Calcium / metal disappears.
• Explanation: has formed a compound in solution / forms a solution / has reacted with the water / forms product that dissolves / disperses in the water
OR
The beaker contents get warmer
• Explanation: exothermic reaction / reaction releases heat energy
OR
Ca pieces sink, float up, sink (and cycle repeats)
Explanation: light H2 gas forms on Ca & helps it floats up etc (but not floats / fizzes around surface)
(ii) Write a balanced equation for the reaction of calcium in water.
ANSWER
Ca + 2H2O --> Ca(OH)2 + H2
b)
THREE metals labelled X, Y and Z need to be identified based on some characteristic physical and chemical properties.The possible metals are:
iron, magnesium, sodium, copper, zinc
Identify metals X, Y and Z and justify your answer using the reactions described in the table opposite. Include the products of any reactions in your answer.
ANSWER
X is sodium because it is shiny grey and the reactions with oxygen, water and acid are all very strong / vigorous. Sodium is the only metal in the list that has such vigorous reactions. It is high in the activity series. Sodium reacting with oxygen in air would produce sodium oxide. Sodium reacting with water would produce sodium hydroxide and hydrogen gas. Sodium reacting with acid would produce sodium sulfate and hydrogen gas.
Y is copper because it is pink-brown in colour and has no reaction with oxygen, water or acid, reflecting the position of copper on the activity series. Copper is a very unreactive metal.
Z is magnesium because it is shiny grey and it burns with a characteristic / distinctive bright (white) light in oxygen to form magnesium oxide. It has a relatively high position in the activity series but is not as reactive as metal X/Na. Magnesium reacting with water would produce magnesium hydroxide and hydrogen gas. Magnesium reacting with acid would produce magnesium sulfate and hydrogen gas.
(Equations can be used to identify products. They do not have to be balanced. However, if formulae are used they should be correctly written.)
(Equations can be used to identify products. They do not have to be balanced. However, if formulae are used they should be correctly written.)
Question 3
Magnesium ribbon reacts with dilute hydrochloric acid in a conical flask, which is connected to an inverted measuring cylinder in a trough of water. The volume of gas produced is measured over a few minutes, and the results are used to sketch a graph.
(a) Explain why, in terms of particles involved, the line on the graph levels off over time.
ANSWER
• The reaction has stopped and no more gas is produced.
• The reactants are being converted into products. This means there are fewer particles available to collide as the reaction progresses.
• The rate of the reaction will decrease and eventually the reaction will stop.
• Incorrect chemistry referring to changes in energy or speed of particles or “gas levelling off” or changes to activation energy negated some answers.
(b) Discuss the effect on the rate of reaction when repeating this experiment using the same mass of magnesium powder with the dilute hydrochloric acid.
ANSWER
• The reaction rate will increase.
• There are more reactant particles immediately available to react because the surface area of the powder is greater than that of the ribbon. There is greater exposure of the magnesium particles so more can collide at any one time.
• This means there will be more (effective) collisions per second / more frequent collisions between the Mg / powder and the acid, leading to an increase in the rate of the reaction.
Saturday, March 6, 2010
Friday, February 26, 2010
Thursday, February 25, 2010
Reactions of metals and metal compounds with acids
1. Metals react with acid to form metal salts and hydrogen gas.
The general equation is:
Metal + acid --> metal salt + hydrogen gas.
example: Magnesium + sulfuric acid --> Magnesium sulfate + hydrogen gas
2. Metal hydroxides and metal oxides react with acids to from metal salts and water.
The general equation is:
Metal hydroxide + acid --> metal salt + water
or metal oxide
example: Lithium hydroxide + nitric acid --> lithium nitrate + water
Sodium oxide + hydrochloric acid --> sodium chloride + water
3. Metal carbonates react with acids to form metal salts and water and carbon dioxide gas.
The gerenal equation is:
Metal carbonate + acid --> metal salt + water + carbon dioxide gas.
example: Lead carbonate + sulfuric acid -->lead sulfate + water + carbon dioxide gas.
The general equation is:
Metal + acid --> metal salt + hydrogen gas.
example: Magnesium + sulfuric acid --> Magnesium sulfate + hydrogen gas
2. Metal hydroxides and metal oxides react with acids to from metal salts and water.
The general equation is:
Metal hydroxide + acid --> metal salt + water
or metal oxide
example: Lithium hydroxide + nitric acid --> lithium nitrate + water
Sodium oxide + hydrochloric acid --> sodium chloride + water
3. Metal carbonates react with acids to form metal salts and water and carbon dioxide gas.
The gerenal equation is:
Metal carbonate + acid --> metal salt + water + carbon dioxide gas.
example: Lead carbonate + sulfuric acid -->lead sulfate + water + carbon dioxide gas.
Tuesday, February 16, 2010
Reactions of Metals with oxygen and water
Metals react with oxygen depending on how reactive they are.
This is termed as either burning, oxidation, corrosion or rusting.
The term rusting is for the reaction of iron with oxygen only.
General equation:
Metal + oxygen --> metal oxide
Iron + Oxygen --> iron oxide (rust)
Metals react with water again depending on how reactive they are.
Highly reactive metals react to form metal hydroxides.
General equation:
Metal + water --> metal hydroxide + Hydrogen gas
Sodium + water --> sodium hydroxide + hydrogen gas
Less slows reactive metals will react slowly with HOT water to form metal oxides.
General equation:
Metal + steam --> metal oxide + hydrogen gas
Copper + steam --> copper oxide + hydrogen gas
This is termed as either burning, oxidation, corrosion or rusting.
The term rusting is for the reaction of iron with oxygen only.
General equation:
Metal + oxygen --> metal oxide
Iron + Oxygen --> iron oxide (rust)
Metals react with water again depending on how reactive they are.
Highly reactive metals react to form metal hydroxides.
General equation:
Metal + water --> metal hydroxide + Hydrogen gas
Sodium + water --> sodium hydroxide + hydrogen gas
Less slows reactive metals will react slowly with HOT water to form metal oxides.
General equation:
Metal + steam --> metal oxide + hydrogen gas
Copper + steam --> copper oxide + hydrogen gas
Saturday, February 13, 2010
Neutralisation reactions
Naming salts:
Common acids reacted during neutralisation reaction are:
hydrochloric acid: -HCl salt name: ____________ chloride
Nitric acid: -HNO3 salt name: ____________ nitrate
Sulfuric acid: -H2SO4 salt name: ____________ sulfate
General equations:
Common acids reacted during neutralisation reaction are:
hydrochloric acid: -HCl salt name: ____________ chloride
Nitric acid: -HNO3 salt name: ____________ nitrate
Sulfuric acid: -H2SO4 salt name: ____________ sulfate
General equations:
metal + acid --> water + salt
calcium + hydrochloric acid --> water + calcium chloride
metal oxide + acid --> water + salt
magnesium oxide + sulfuric acid --> water + magnesium sulfate
metal hydroxide + acid --> water + salt
sodium hydroxide + nitric acid --> water + sodium nitrate
metal carbonate + acid --> water + salt + carbon dioxide gas
calcium carbonate + sulfuric acid --> water + calcium sulfate + carbon dioxide gas
Writing chemical formula
This is done by using the the table of ions.
Take the charge of the ions and drop and swap the numbers.
copper hydroxide: = Cu2+ OH 1-
= Cu1 OH2
= Cu(OH)2
When do I use brackets??
Brackets are used when a number bigger than 1 is placed behind an ion that has two capital letters in its formula. eg OH-.
copper hydroxide = Cu(OH)2 not CuOH2
calcium nitrate = Ca(NO3)2 not CaNO32.
Aluminium sulfate = Al2(SO4)3
Take the charge of the ions and drop and swap the numbers.
copper hydroxide: = Cu2+ OH 1-
= Cu1 OH2
= Cu(OH)2
When do I use brackets??
Brackets are used when a number bigger than 1 is placed behind an ion that has two capital letters in its formula. eg OH-.
copper hydroxide = Cu(OH)2 not CuOH2
calcium nitrate = Ca(NO3)2 not CaNO32.
Aluminium sulfate = Al2(SO4)3
Rules for writing chemical equations
When writing chemical equations you MUST follow the following rules.
- Write a word equation for the reaction.
- Convert the words into symbols using the table of ions.
- Balance the equation by making a telly of the number of each atom in both sides of the equation.
- Place large numbers in front of any formula you require more of.
- Do NOT add and small numbers within a formula when balancing.
Acids and alkalis
Indicators and the pH scale
Litmus Vs Universal indicators.
Litmus only shows whether a substance is an acid or alkali.
Universal indicator also shows whether a substance is an acid or alkali, but also shows the strength of the acid or alkali and gives an indication of the substances pH.
Welcome to year 11 chemistry
This blog is set up as a place where we can put important hints and facts that will hopefully help you when you come to study for exams.
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