Chemistry Paper 1 #3

Question 1

What is the purpose of electrolysis?

Answer 1

Electrolysis is used to decompose ionic compounds into their constituent elements by passing an electric current.

Question 2

What are the products at the anode and cathode in the electrolysis of aqueous sodium chloride?

Answer 2

At the anode, chlorine gas is produced, and at the cathode, hydrogen gas is produced as sodium remains in solution.

Question 3

What factors determine the discharge of ions in the electrolysis of an aqueous solution?

Answer 3

The discharge depends on the reactivity of ions: less reactive cations and specific anions (like halides) are discharged preferentially.

Question 4

What is the significance of the reactivity series in metal extraction?

Answer 4

The reactivity series predicts the method of extraction: metals above carbon require electrolysis, while those below can be reduced by carbon.

Question 5

Name two metals that do not react with dilute acids.

Answer 5

Copper and silver do not react with dilute acids because they are less reactive than hydrogen.

Question 6

What is a redox reaction?

Answer 6

A redox reaction is one where oxidation and reduction occur simultaneously; one substance gains electrons while another loses electrons.

Question 7

Identify the oxidizing and reducing agents in the reaction: Zn + CuSO₄ → ZnSO₄ + Cu

Answer 7

Zn is the reducing agent (it loses electrons), and Cu²⁺ is the oxidizing agent (it gains electrons).

Question 8

What is a neutralisation reaction and give an example.

Answer 8

A neutralisation reaction is when an acid reacts with a base to form water and a salt. Example: HCl + NaOH -> NaCl + H₂O.

Question 9

Define pH and explain what a pH of 7 represents.

Answer 9

pH is a measure of hydrogen ion concentration. A pH of 7 represents a neutral solution where [H⁺] equals [OH⁻].

Question 10

What distinguishes a strong acid from a weak acid?

Answer 10

A strong acid fully dissociates in water, while a weak acid only partially dissociates, producing fewer hydrogen ions in solution.

Question 11

What is the difference between exothermic and endothermic reactions?

Answer 11

Exothermic reactions release energy to the surroundings (temperature rises), while endothermic reactions absorb energy (temperature falls).

Question 12

Give an example of an exothermic reaction and an endothermic reaction.

Answer 12

Exothermic: Combustion of methane. Endothermic: Dissolving ammonium nitrate in water.

Question 13

How do you calculate the energy change of a reaction using bond energies?

Answer 13

Energy change = Sum of bond energies of bonds broken - Sum of bond energies of bonds made.

Question 14

What does a negative energy change in bond energy calculations indicate?

Answer 14

A negative energy change indicates an exothermic reaction, where more energy is released in bond-making than consumed in bond-breaking.

Question 15

How does an electrochemical cell produce electricity?

Answer 15

It produces electricity by a redox reaction between two metals with different reactivities in an electrolyte, generating electron flow.

Question 16

Describe the function of the anode and cathode in a Daniell cell.

Answer 16

In a Daniell cell, the anode is where oxidation occurs (zinc loses electrons), and the cathode is where reduction occurs (copper gains electrons).

Question 17

What is a hydrogen fuel cell, and what are its products?

Answer 17

A hydrogen fuel cell converts hydrogen and oxygen into electricity, producing water and releasing heat as by-products.

Question 18

List two advantages and two disadvantages of hydrogen fuel cells.

Answer 18

Advantages: No harmful emissions, high efficiency. Disadvantages: Difficult storage of hydrogen, high production costs.

Question 19

What is activation energy?

Answer 19

Activation energy is the minimum energy required to initiate a chemical reaction by breaking bonds in the reactants.

Question 20

How does the reactivity of metals relate to their position in the reactivity series?

Answer 20

Metals higher in the reactivity series are more reactive and readily lose electrons to form positive ions.

Question 21

What is a displacement reaction?

Answer 21

A displacement reaction is when a more reactive metal displaces a less reactive metal from its compound.

Question 22

Define spectator ion and give an example in a reaction.

Answer 22

A spectator ion is an ion that does not participate in the reaction. Example: SO₄²⁻ in the reaction between Zn and CuSO₄.

Question 23

What is bond enthalpy?

Answer 23

Bond enthalpy is the energy needed to break one mole of a bond in a gaseous molecule, measured in kJ/mol.