O level Chemistry Practice Questions
1. Choose from the following substances to answer the questions below.
Copper(II) sulfate solution, potassium chloride solution, potassium dichromate(VI) solution, potassium iodide solution, magnesium sulfate solution, aqueous ammonia, zinc sulfate solution
Each substance can be used once, more than once, or not at all.
Name a substance which,
(a) reacts with chlorine in a displacement reaction,
(b) can be used to test for sulfur dioxide,
(c) can oxidize hydrogen peroxide,
(d) gives a white precipitate with aqueous sodium hydroxide which dissolves in excess sodium hydroxide to form a colourless solution,
(e) is blue in colour,
(f) gives a white precipitate with aqueous silver nitrate.
Answers:
(a) potassium iodide solution
(b) potassium dichromate(VI) solution
(c) potassium dichromate(VI) solution
(d) zinc sulfate solution
(e) copper(II) sulfate solution
(f) potassium chloride solution
2. Ethanol is a liquid fuel. Ethanol can be manufactured either from glucose, or from ethene.
(a) Describe the manufacture of ethanol from glucose. Include the balanced equation in your answer.
Clue: Refer to textbook on the chapter of ethanol
(b) Draw the displayed formula for ethene.
Clue : Draw out CH2=CH2
(c) Name the substance that reacts with ethene to make ethanol.
Answer: phosphoric acid, 300oC, 65 atm
(d) Give the conditions needed for this reaction.
(e) Ethene can also be polymerized to form poly(ethene). Draw the formula of the polymer.
Answer : [-CH2-CH2-]n
3. Magnesium oxide and sodium chloride are ionic lattice solids.
(a) Explain why these two solids do not conduct electricity.
Answer : Both are giant ionic solids. They contain fixed ions which are not mobile to conduct electricity.
(b) Explain why magnesium oxide has a very high melting point.
Answer : MgO is a giant ionic solid. It consists of oppositely charged ions with strong ionic bonds. A lot of energy is required to overcome the ionic bonds. Hence, it has a high melting point.
(c) Suggest a use of magnesium oxide.
Answer: As a refractory.
(d) Draw the dot and cross diagram of magnesium oxide.
Clue : Mg2+ O2-
4. Lithium is in Group I of the Periodic Table.
Lithium reacts with oxygen to form an ionic compound Y.
(a) Write a balanced equation for the above reaction.
Answer: 2Li + (1/2)O2 Li2O
(b) Y is dissolved in water to form an alkaline solution Z.
Write a balanced equation for the reaction in (b).
Answer: 2LiO + H2O --> 2LiOH
(c) Write down the formula of the salt when Z reacts with dilute nitric acid.
Answer : LiNO3
(d) Suggest what is observed when Z is added to a solution of copper(II) sulfate.
Answer : LiOH is similar to NaOH. A blue precipitate is observed.
Copper(II) sulfate solution, potassium chloride solution, potassium dichromate(VI) solution, potassium iodide solution, magnesium sulfate solution, aqueous ammonia, zinc sulfate solution
Each substance can be used once, more than once, or not at all.
Name a substance which,
(a) reacts with chlorine in a displacement reaction,
(b) can be used to test for sulfur dioxide,
(c) can oxidize hydrogen peroxide,
(d) gives a white precipitate with aqueous sodium hydroxide which dissolves in excess sodium hydroxide to form a colourless solution,
(e) is blue in colour,
(f) gives a white precipitate with aqueous silver nitrate.
Answers:
(a) potassium iodide solution
(b) potassium dichromate(VI) solution
(c) potassium dichromate(VI) solution
(d) zinc sulfate solution
(e) copper(II) sulfate solution
(f) potassium chloride solution
2. Ethanol is a liquid fuel. Ethanol can be manufactured either from glucose, or from ethene.
(a) Describe the manufacture of ethanol from glucose. Include the balanced equation in your answer.
Clue: Refer to textbook on the chapter of ethanol
(b) Draw the displayed formula for ethene.
Clue : Draw out CH2=CH2
(c) Name the substance that reacts with ethene to make ethanol.
Answer: phosphoric acid, 300oC, 65 atm
(d) Give the conditions needed for this reaction.
(e) Ethene can also be polymerized to form poly(ethene). Draw the formula of the polymer.
Answer : [-CH2-CH2-]n
3. Magnesium oxide and sodium chloride are ionic lattice solids.
(a) Explain why these two solids do not conduct electricity.
Answer : Both are giant ionic solids. They contain fixed ions which are not mobile to conduct electricity.
(b) Explain why magnesium oxide has a very high melting point.
Answer : MgO is a giant ionic solid. It consists of oppositely charged ions with strong ionic bonds. A lot of energy is required to overcome the ionic bonds. Hence, it has a high melting point.
(c) Suggest a use of magnesium oxide.
Answer: As a refractory.
(d) Draw the dot and cross diagram of magnesium oxide.
Clue : Mg2+ O2-
4. Lithium is in Group I of the Periodic Table.
Lithium reacts with oxygen to form an ionic compound Y.
(a) Write a balanced equation for the above reaction.
Answer: 2Li + (1/2)O2 Li2O
(b) Y is dissolved in water to form an alkaline solution Z.
Write a balanced equation for the reaction in (b).
Answer: 2LiO + H2O --> 2LiOH
(c) Write down the formula of the salt when Z reacts with dilute nitric acid.
Answer : LiNO3
(d) Suggest what is observed when Z is added to a solution of copper(II) sulfate.
Answer : LiOH is similar to NaOH. A blue precipitate is observed.
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