Chapter 8.3 – Electrolysis

Book Name	: Madhyamik Physical Science And Environment
Subject	: Physical Science
Class	: 10 (Madhyamik)
Publisher	: Oriental Book Company Pvt. Ltd
Chapter Name	: Physical and Chemical Properties of Matter

In-text Questions

Question 8.3.1

Give an example where electricity causes a chemical change. 

Answer

Electrolysis of water

Question 8.3.2

What are electrolytes? Give example. 

Answer

Electrolytes are substances that conduct electricity in their aqueous or molten state by the movement of ions. Examples of electrolytes include sodium chloride (NaCl) and hydrochloric acid (HCl).

Question 8.3.3

What are metallic conductors? Give example. 

Answer

Metallic conductors are substances that conduct electricity through the movement of electrons. Examples of metallic conductors include copper, silver, and aluminium.

Question 8.3.4

Give example of a strong electrolyte. 

Answer

Strong electrolytes are substances that ionize completely in their aqueous state. Examples of strong electrolytes include hydrochloric acid (HCl) and sodium hydroxide (NaOH).

Question 8.3.5

What are ions? Give examples. 

Answer

Ions are electrically charged atoms or molecules that result from the loss or gain of one or more electrons. Examples of ions include sodium ion (Na⁺), chloride ion (Cl^–), and hydrogen ion (H⁺).

Question 8.3.6

What are non-conductors and insulators?

Answer

Non-conductors and insulators are materials that do not allow the flow of electric current. Insulators, a subset of non-conductors, have extremely high electrical resistance and include materials like rubber, plastic, glass, ceramic, and wood. They are used to prevent electrical conduction and ensure safety in various applications.

Question 8.3.7

How electricity is conducted in an electrolytic solution? 

Answer

Electricity is conducted in an electrolytic solution by the movement of ions towards the oppositely charged electrode under the influence of an electric field.

Question 8.3.8

Why the electrolytic solution remain electrically neutral before and after electrolysis?

Answer

The electrolytic solution remains electrically neutral before and after electrolysis because the number of positively charged ions is equal to the number of negatively charged ions in the solution.

Question 8.3.9

What is cation?

Answer

A cation is a positively charged ion that is formed by the loss of one or more electrons by an atom.

Question 8.3.10

What types of reactions take place during the electrolysis of an electrolyte? 

Answer

During the electrolysis of an electrolyte, oxidation reactions take place at the anode, and reduction reactions take place at the cathode.

Question 8.3.11

Define cathode and anode. 

Answer

1. Cathode (Negative Charge): The cathode is the electrode with a negative charge, where reduction or electron gain occurs.
2. Anode (Positive Charge): The anode is the electrode with a positive charge, where oxidation or electron loss occurs.

Question 8.3.12

Why AC cannot be used in electrolysis? 

Answer

AC cannot be used in electrolysis because it changes its direction of flow continuously, which causes the ions to move back and forth between the electrodes, leading to the formation of undesirable by-products.

Question 8.3.13

Why during the electrolysis of water, it is acidified?

Answer 

Water is acidified during electrolysis to increase the concentration of H⁺ ions in the solution, which enhances the conduction of electricity.

Question 8.3.14

Why during electrolysis of CuSO₄ solution using Cu-electrode the weight anode decreases?

Answer

The weight of the anode decreases during the electrolysis of CuSO₄ solution using Cu electrodes because it undergoes oxidation and dissolves into the solution as Cu²⁺ ions.

Question 8.3.15

Mention some use of electrolysis.

Answer

Some of the uses of electrolysis include electroplating, extraction of metals, electrolytic refining, and electrochemical machining.

Question 8.3.16

What is the melting point of alumina?

Answer

The melting point of alumina is high, which is 2050°C or 2323 K.

Question 8.3.17

Write the composition of the electrolyte used for the extraction of alumina.

Answer

The electrolyte used for the extraction of alumina is a mixture of 60% cryolite (AIF₃, 3NaF), 20% alumina (Al₂O₃), and 20% fluorspar (CaF₂).

Question 8.3.18

What is gilding?

Answer

Gilding is the process of coating a surface with a thin layer of gold to improve its appearance or increase its value. It is commonly used in jewellery-making and decorative arts.

Question 8.3.19

What is the electrolyte used for Ag plating?

Answer

The electrolyte used for electroplating an article with silver is Sodium argentocyanide solution Na [Ag(CN)₂ ]

Question 8.3.20

What is anode mud?

Answer

Anode mud is a black, sticky residue that forms at the anode during the electrolytic refining of copper. It contains various impurities such as lead, zinc, and silver.

Question 8.3.21

What are the cathode, anode and electrolyte used in the refining of copper?

Answer

The cathode, anode, and electrolyte used in the refining of copper are:

• Cathode: pure copper sheet
• Anode: impure copper
• Electrolyte: a solution of copper sulfate (CuSO₄) and sulfuric acid (H₂SO₄)

Question 8.3.22

What are the cathode and anode used in gold plating?

Answer

The cathode used in gold plating is usually made of pure gold, while the anode is made of a metal that does not react with the electrolyte, such as platinum. The electrolyte used for gold plating is typically a solution of gold cyanide (AuCN) and potassium cyanide (KCN).

Multiple Choice Questions (MCQ)

Question 1

Which one of the following is a non-electrolyte?

1. NaCl
2. HCI
3. Urea
4. H₂SO₄

Answer

(c) Urea

Explanation:

Urea is a non-electrolyte because it does not dissociate into ions when dissolved in water.

Question 2

Which one is a strong electrolyte?

1. NaOH
2. NH₄OH
3. CH₃COOH
4. glucose

Answer

(a) NaOH

Explanation:

NaOH is a strong electrolyte.

Question 3

In electrolytic solution electricity is conducted by

1. electrons
2. atoms
3. ions
4. molecules

Answer

(c) ions

Explanation:

In an electrolytic solution, electricity is conducted by ions that are free to move and carry the electrical charge. These ions are produced by the dissociation of the electrolyte in the solution.

Question 4

Electrolysis of CuSO₄, solution using Cu electrodes, the products at electrodes are –

1. Cu^– at anode
2. Cu²⁺ at anode
3. H₂ at cathode
4. O₂ at anode

Answer

(c) H₂ at cathode

Explanation:

The products at the cathode are Cu metal and H2 gas, while the products at the anode are Cu²⁺ ions and O₂ gas.

Question 5

The reaction takes place during electrolysis at electrodes are

1. Oxidation at cathode 
2. reduction at anode 
3. reduction at cathode
4. no chemical reaction

Answer

(b) reduction at anode

Explanation:

During electrolysis, oxidation occurs at the anode and reduction occurs at the cathode. At the anode, the negatively charged ions lose electrons and are oxidized to form neutral atoms or molecules, which may combine to form a gas or remain in solution.

Very Short Answer Type Questions (VSA)

Question

1. Electrolysis of molten NaCl produces ____ and ____  at the cathode and anode respectively. 
2. With the increase in the temperature of the electrolytic solution, its conductivity will ____
3. An example of a strong electrolyte is ____.
4. It is the ____ which is responsible for the conduction of electricity in the electrolytic solution. 
5. In electroplating with gold, the anode used is ____.

Indicate whether the following statements are true or false

1. In electronic conductors, the current is conducted by electrons. 
2. Electrolysis of acidified water produce 2 parts of O₂ and 1 part of H₂ by volume. 
3. lons are charged atoms or group of atoms. 
4. During electrolysis of aqueous CuSO₄ solution using cu-electrodes, the weight of Cu-anode increases. 
5. During electrolysis chemical reaction takes place at the anode is reduction.

Answer

1. True
2. False; Electrolysis of acidified water produces 2 parts of H₂ and 1 part of O₂ by volume.
3. True
4. False; The weight of the Cu-cathode increases
5. False; Oxidation occurs at the anode.

Match the Column-1 with Column-2

Answer the following questions

Question 1

Which current is used for electrolysis?

Answer

Direct current (DC) is used for electrolysis.

Question 2

In metallic conductors which is responsible for the conduction of electricity.

Answer 

Electrons are responsible for the conduction of electricity in metallic conductors.

Question 3

What are ions? 

Answer

Ions are electrically charged particles formed by the gain or loss of electrons from an atom.

Question 4

Between ions and atoms which are more stable. 

Answer

Ions are more stable than atoms because they have a complete valence shell configuration.

Question 5

Give one example of each strong and weak electrolyte. 

Answer

NaCl is an example of a strong electrolyte, while acetic acid (CH3COOH) is an example of a weak electrolyte.

Question 6

What type of reactions takes place during electrolysis?

Answer

Reduction and oxidation (redox) reactions take place during electrolysis. At the anode, oxidation takes place, and at the cathode, reduction takes place.

Short Answer Type Questions

Long Answer (LA) type Questions

Question 1

What are electrolytes and non-electrolytes? Give examples. 

Answer

Electrolytes are substances that can conduct electricity when dissolved in water or molten form. Examples of electrolytes are NaCl, HCl, and CuSO₄.

Non-electrolytes are substances that cannot conduct electricity. Examples of non-electrolytes are sugar and urea.

Question 2

What are the characteristics of electrolytic and electronic conductors? 

Answer

Question 3

Define voltmeter and electrodes. 

Answer

A voltmeter is an instrument used to measure the potential difference between two points in a circuit. It is usually connected in parallel with the component or portion of the circuit whose voltage needs to be measured.

Electrodes are conductive materials used to make electrical contact with a non-metallic part of a circuit, typically an electrolyte.

Question 4

What are cathodes and anodes?

Answer

Cathode: The cathode is the electrode in an electrochemical cell or circuit that is connected to the negative terminal of a power source. It is the electrode where reduction takes place during electrolysis or where oxidation takes place during galvanic cell reactions.

Anode: The anode is the electrode in an electrochemical cell or circuit that is connected to the positive terminal of a power source. It is the electrode where oxidation takes place during electrolysis or where reduction takes place during galvanic cell reactions.

Question 5

Describe in short the electrolysis of water. 

Answer

The electrolysis of water is the process of breaking down water molecules into their constituent elements, hydrogen and oxygen, using an electric current. Water is a covalent compound, meaning it does not readily conduct electricity. Therefore, a small amount of acid or alkali is added to the water to increase its conductivity. Two electrodes, usually made of inert metals such as platinum or graphite, are inserted into the water and connected to a DC power source.

When the electric current is applied, hydrogen ions (H⁺) are attracted to the negatively charged electrode (cathode) and are reduced to form hydrogen gas (H₂). At the same time, oxygen ions (O^2-) are attracted to the positively charged electrode (anode) and are oxidized to form oxygen gas (O₂).

Question 6

Describe the principle of electrolysis of an aqueous solution of CuSO₄ using Cu-electrodes. 

Answer

The aqueous solution of CuSO₄ acidified with dilute H₂SO₄ is used as an electrolyte. This electrolytic solution contains H⁺, Cu²⁺ cations and SO₄^2- and OH^– anions.

H₂O ⇔ H⁺ + OH^–;

CuSO₄ ⇔ Cu²⁺+ SO₄^2-

Between the cations H⁺ and Cu²⁺, the Cu²⁺ ion has a greater tendency to be reduced. So Cu²⁺ ion in solution takes two electrons from the cathode and is reduced to copper and is adhered on the surface of the Cu cathode. Thus the weight of the Cu-cathode increases. Copper anode (is not inert) gives up two electrons and is oxidised to Cu²⁺ ion and remains in solution, the weight of Cu – anode decreases. The concentration of the electrolytic solution CuSO, remains constant.

Cathode reaction: Cu²⁺ + 2e → Cu (reduction)

Anode reaction: Cu-2e → Cu²⁺ (oxidation)

Question 7

Mention the composition of electrolyte and electrode reactions of extraction of aluminium.

Answer

Composition of electrolytes: Mixture of 60% cryolite (AIF₃, 3NaF), 20% alumina (Al₂O₃), and 20% fluorospar (CaF₂).

Cathode reaction:

2Al³⁺ + 6e → 2Al (Reduction)

Anode reaction:

30^2- – 6e → (3/2)O₂ (oxidation)

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