Electrolysis Quiz

What kind of substances can form electrolytes?

• Ionic

• Covalent

• Metallic

Answer explanation

Ionic substances can form electrolytes.

Most covalent substances cannot conduct electricity in any state.

Metals are not used as electrolytes in electrolysis because they cannot be split into elements.

What is the positive electrode in electrolysis called?

• Cathode

• Anode

• Positrode

Answer explanation

The positive electrode is called the anode.

The cathode is the negative electrode.

The positrode is not a real word.

Which of the following is a true statement about the electrolysis of sodium chloride solution?

• Hydrogen forms at the positive electrode

• Sodium forms at the negative electrode

• Chlorine forms at the positive electrode

Answer explanation

During the electrolysis of sodium chloride, chlorine forms at the positive electrode.

Hydrogen is produced at the negative electrode.

Sodium is not produced as it is higher up the reactivity series than hydrogen.

What is formed at each electrode during the electrolysis of dilute sulfuric acid?

• Hydrogen at the positive electrode and oxygen at the negative electrode

• Hydrogen at the negative electrode and oxygen at the positive electrode

• Hydrogen at the negative electrode and sulfur dioxide at the positive electrode

Answer explanation

During the electrolysis of sulfuric acid hydrogen is formed at the negative electrode and oxygen is formed at the positive electrode.

Sulfate ions are not oxidised during the electrolysis of solutions.

Which of these describe a property of the gas formed during the electrolysis of copper sulfate solution using inert electrodes?

• The gas relights a glowing splint

• The gas pops when lit

• The gas turns limewater milky

Answer explanation

The gas formed during the electrolysis of copper sulfate solution will relight a glowing splint because it is oxygen.

Hydrogen pops when lit.

Carbon dioxide turns limewater milky.

What can happen to the carbon electrodes during the electrolysis of copper sulfate solution?

• The negative electrode loses mass

• The negative electrode gains mass

• The positive electrode gains mass

Answer explanation

During the electrolysis of copper sulfate solution the negative electrode will gain mass.

The negative electrode gains mass because that is where the copper ions are reduced to form copper metal.

Which of the following is a true statement about the purification of copper by electrolysis?

• The positive electrode is impure copper

• The positive electrode is pure copper

• The negative electrode is impure copper

Answer explanation

During electrolysis, the impure positive electrode dissolves to form ions.

At the negative electrode, ions are attracted and then reduced to form copper metal.

Which of these changes occurs during electrolysis?

• Negative ions lose electrons at the negative electrode and are oxidised

• Negative ions lose electrons at the positive electrode and are oxidised

• Negative ions gain electrons at the negative electrode and are oxidised

Answer explanation

Negative ions are attracted to the positive electrode, where they lose electrons.

Oxidation is loss of electrons. Negative ions will not be attracted to the negative electrode.

Which of these statements about reduction is correct?

• Reduction involves the loss of electrons

• Reduction involves the gain of electrons

• Reduction involves a reaction in which oxygen atoms are gained by another atom

Answer explanation

Reduction is the gain of electrons (OIL RIG).

Oxidation is the loss of electrons.

Reduction can sometimes involve a compound losing oxygen in a reaction.

Which of these is a correct half equation for the oxidation of copper metal?

• Cu → Cu²⁺ + e^-

• Cu²⁺ + 2e^- → Cu

• Cu → Cu²⁺ + 2e^-

Answer explanation

Cu → Cu²⁺ + 2e^- shows a balanced half equation in which copper atoms lose electrons and are therefore oxidised (OIL RIG).

Cu → Cu²⁺ + e^- is a half equation which is not balanced.

Cu²⁺ + 2e^- → Cu is a half equation which shows reduction.