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C4: Quiz 11 – Answers

1)

a) H⁺ and OH^- (or positive hydrogen ions and negative hydroxide ions)

b) H⁺, OH^-, Na⁺, Cl^- (or positive hydrogen ions, negative hydroxide ions, positive sodium ions and negative chloride ions)

c)

i) Negative electrode

ii) A solid layer of the metal will appear around the cathode

iii) Hydrogen gas will be produced at the cathode

d)

i) Positive electrode

ii) Gas molecules of the halogen will form at the anode

iii) Oxygen gas and water (liquid) will form at the anode

 

2)

a)

i) Hydrogen

ii) 2 H⁺ + 2 e^- –> H₂

iii) Hold a lit splint above where the hydrogen is potentially produced; if hydrogen is present, we will hear a squeaky pop

b)

i) Chlorine (Cl₂)

ii) 2 Cl^- –> Cl₂ + 2 e^-

iii) Chlorine bleaches damp blue litmus paper turning it white (the paper may turn red for a while)

 

3)

a) Cu²⁺, SO₄^2-, H⁺, OH^-

b)

i) A layer of copper will form around the cathode because copper is less reactive than hydrogen

ii) Cu²⁺ + 2 e^- –> Cu

c)

i) Oxygen and water

ii) 4 OH^- –> O₂ + 2 H₂O + 4 e^-

iii) We hold a glowing splint above where the oxygen is potentially produced; if oxygen is present, the glowing splint will reignite/ relight

 

4)

a)

i) A layer of copper will form around the cathode because copper is less reactive than hydrogen

ii) Cu²⁺ + 2 e^- –> Cu

b)

i) Chlorine gas is produced

ii) 2 Cl^- –> Cl₂ + 2 e^-

 

5)

a)

i) Hydrogen gas is produced as sodium is more reactive than hydrogen

ii) 2 H⁺ + 2 e^- –> H₂

b)

i) Oxygen and water are produced. This is because there are no halide ions present

ii) 4 OH^- –> O₂ + 2 H₂O + 4 e^-

 

6)

a)

i) Bromine gas is produced as halide ions are present

ii) 2 Br^- –> Br₂ + 2 e^-

b)

i) Hydrogen gas is produced as potassium is more reactive than hydrogen

ii) 2 H⁺ + 2 e^- –> H₂

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Questions
Click here for a PDF of the diagrams in this quiz. 
​

1)

a) When the electrolyte for electrolysis is an aqueous solution, what additional ions do we get from the water in the aqueous solution?

b) Give the 4 ions that are present in an aqueous sodium chloride electrolyte. Sodium chloride is NaCl. You can either give the names or the charges.

c)

i) Is the cathode the positive or negative electrode?

ii) If the metal in the electrolyte is less reactive than hydrogen, what will happen at the cathode?

iii) If the metal in the electrolyte is more reactive than hydrogen, what will happen at the cathode?

d)

i) Is the anode the positive or negative electrode?

ii) If halide ions are present in the electrolyte, what will happen at the anode?

iii) If no halide ions are present in the electrolyte, what will happen at the anode?

 

 

2) Aqueous sodium chloride can be electrolysed by using the apparatus below. Sodium chloride is NaCl.

a) A gas is produced at the cathode.

i) What gas is produced at the cathode?

ii) Write the half equation for the production of this gas.

iii) What is the test for this gas?

b) A gas is produced at the anode.

i) What gas is produced at the anode?

ii) Write the half equation for the production of this gas.

iii) What is the test for this gas?

 

 

3) Aqueous copper sulfate (CuSO₄) can be electrolysed by using the apparatus below.

a) Write the symbols for the 4 ions present in the electrolyte (2 of the ions come from copper sulfate and the other 2 come from the water).

b)

i) What will the student observe at the cathode? Explain why the student will observe this.

ii) Write the half equation for the cathode.

c) A gas and another product are produced at the anode.

i) What are the names of these two products produced at the anode?

ii) Write the half equation at the anode.

iii) What is the test for the gas produced at the anode?

 

 

4) An aqueous copper chloride solution can be electrolysed by using the apparatus below. Copper chloride is CuCl₂.

a)

i) What happens at the cathode? Explain why.

ii) Write the half equation for what happens at the cathode.

b)

i) What happens at the anode?

ii) Write the half equation for what happens at the anode.

 

 

5) Aqueous sodium sulfate can be electrolysed by using the apparatus below. Sodium sulfate is Na₂SO₄.

a)

i) What happens at the cathode? Explain why.

ii) Write the half equation for what happens at the cathode.

b)

i) What happens at the anode? Explain why.

ii) Write the half equation for what happens at the anode.

 

 

6) Aqueous potassium bromide can be electrolysed by using the apparatus below. Potassium bromide is KBr.

a)

i) What happen at the anode? Explain why.

ii) Write the half equation for what happens at the anode.

b)

i) What happens at the cathode? Explain why.

ii) Write the half equation for what happens at the cathode.

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