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
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