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.
Monday, May 31, 2010
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
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