Electrolysis

Question 1

What is electric current?

Answer 1

The flow of charged particles. Usually refers to electrons, but can also refer to the flow of ions.

Question 2

Why don’t most covalent compounds conduct electricity?

Answer 2

They have no freely moving charged particles to carry the current. They act as insulators.

Question 3

What are some applications of covalent compounds as insulators?

Answer 3

Used in solid, liquid, and gaseous forms as electrical insulators.

Example: Sulfur hexafluoride insulates electrical transformers. Silicone oils and liquid hydrocarbons are used in electrical equipment. Plastic coating on household electrical wiring.

Question 4

Why can’t covalent compounds conduct electricity?

Answer 4

They lack freely moving charged particles.

Question 5

Under what conditions can ionic compounds conduct electricity?

Answer 5

When heated beyond their melting point to become molten. This allows ions to move freely and carry charge.

Question 6

Why can’t ionic compounds conduct electricity in the solid state?

Answer 6

The ions are in fixed positions within the lattice and cannot move.

Question 7

What are cations and anions?

Answer 7

Anions: Negatively charged ions (e.g., Cl-, O2-, SO42-). Cations: Positively charged ions (e.g., K+, Mg2+, H+).

Question 8

What happens during electrolysis?

Answer 8

Electrons move from the anode towards the cathode. Cations migrate towards the cathode (negative electrode). Anions migrate towards the anode (positive electrode).

Question 9

Why are cations attracted to the cathode and anions to the anode during electrolysis?

Answer 9

Because of their opposite charges.

Question 10

What is the main concern in electrochemistry?

Answer 10

The transfer of electrons.

Question 11

How are oxidation and reduction defined in electrochemistry?

Answer 11

Oxidation: Loss of electrons. Reduction: Gain of electrons.

Question 12

What happens when ions come into contact with the electrodes during electrolysis?

Answer 12

Electrons are either lost or gained, forming neutral substances which are discharged as products at the electrodes.

Question 13

What happens at the anode during electrolysis?

Answer 13

Negatively charged ions lose electrons and are oxidized.

Question 14

What happens at the cathode during electrolysis?

Answer 14

Positively charged ions gain electrons and are reduced.

Question 15

What are half equations in electrochemistry?

Answer 15

Equations that describe the movement of electrons at each electrode.

Question 16

What is the half equation at the cathode during the electrolysis of molten lead(II) bromide?

Answer 16

Pb2+ + 2e– ⟶ Pb (Reduction)

Question 17

What is the half equation at the anode during the electrolysis of molten lead(II) bromide?

Answer 17

2Br– – 2e– ⟶ Br2 (Oxidation)

OR 2Br– ⟶ Br2 + 2e–

Question 18

What is the half equation at the cathode during the electrolysis of aqueous sodium chloride?

Answer 18

2H+ + 2e– ⟶ H2 (Reduction)

Question 19

What is the half equation at the anode during the electrolysis of aqueous sodium chloride?

Answer 19

2Cl– – 2e– ⟶ Cl2 (Oxidation)

OR 2Cl– ⟶ Cl2 + 2e–

Question 20

What is the half equation at the cathode during the electrolysis of dilute sulfuric acid?

Answer 20

2H+ + 2e– ⟶ H2 (Reduction)

Question 21

What is the half equation at the anode during the electrolysis of dilute sulfuric acid?

Answer 21

2H2O – 4e– ⟶ O2 + 4H+ (Oxidation)

OR 2H2O ⟶ O2 + 4H+ + 4e–

Question 22

What is the half equation at the cathode during the electrolysis of aqueous copper(II) sulfate?

Answer 22

Cu2+ + 2e– ⟶ Cu (Reduction)

Question 23

What is the half equation at the anode during the electrolysis of aqueous copper(II) sulfate?

Answer 23

2H2O – 4e– ⟶ O2 + 4H+ (Oxidation)

OR 2H2O ⟶ O2 + 4H+ + 4e–

Question 24

What is the aim of the experiment involving electrolysis of aqueous solutions?

Answer 24

To electrolyse aqueous solutions of sodium chloride, sulfuric acid, and copper(II) sulfate. To collect and identify the products at each electrode.

Question 25

How can gaseous products be collected during electrolysis?

Answer 25

By using inverted test tubes above the electrodes to collect the gases.

Question 26

What is the method for performing electrolysis of aqueous solutions?

Answer 26

Add the aqueous solution to a beaker and cover the electrodes with the solution. Invert two small test tubes to collect any gaseous products. Connect the electrodes to a power pack or battery. Turn on the power pack or battery and allow electrolysis to take place. Make observations at each electrode.

Question 27

How can the products at each electrode be identified?

Answer 27

Gases collected in the test tube can be tested and identified.

Question 28

How can you test if the gas produced at the cathode is hydrogen?

Answer 28

If the gas burns with a ‘pop’ when a sample is lit with a lighted splint, the gas is hydrogen.

Question 29

How can you test if the gas produced at the anode is oxygen?

Answer 29

If the gas relights a glowing splint dipped into a sample, the gas is oxygen.

Question 30

How can you test if the gas produced at the anode is chlorine?

Answer 30

If the gas bleaches a piece of litmus paper, chlorine has been produced.

Question 31

How can you test if a metal has been formed at the electrode?

Answer 31

If a solid forms around the electrode, the metal has been produced. The color of the solid can indicate the metal formed.

Question 32

What is oxidation?

Answer 32

• Gain of oxygen. • Loss of electrons.

Question 33

What is reduction?

Answer 33

• Loss of oxygen. • Gain of electrons.

Question 34

What is a redox reaction?

Answer 34

• A reaction where oxidation and reduction happen together.

Question 35

What is an oxidizing agent?

Answer 35

• Causes oxidation. • Accepts electrons (is reduced). • Supplies oxygen.

Question 36

What is a reducing agent?

Answer 36

• Causes reduction. • Donates electrons (is oxidized). • Removes oxygen.

Question 37

Key mnemonic for oxidation/reduction?

Answer 37

• OIL RIG: • Oxidation Is Loss (of electrons). • Reduction Is Gain (of electrons).

Question 38

Example of oxidation (with oxygen)?

Answer 38

• Magnesium gains oxygen → it is oxidized.

Question 39

Example of reduction (with oxygen)?

Answer 39

• Copper(II) oxide loses oxygen → it is reduced.

Question 40

Example of a redox reaction?

Answer 40

• Zinc is oxidized (loses electrons). • Copper is reduced (gains electrons).