i) electrolysis

Question 1

1.48 understand that an electric current is a flow of electrons or ions

Answer 1

Electric current is the flow of electrons.

Question 2

1.49 understand why covalent compounds do not conduct electricity

Answer 2

In covalent compounds there are no free electrons to move. That’s why they don’t conduct electricity.

Question 3

1.50 understand why ionic compounds conduct electricity only when molten or in solution

Answer 3

Ionic compounds normally don’t have free moving electrons. But when they are molten or dissolved in solution they form ions, which allow them to conduct electricity.

Question 4

1.51 describe experiments to distinguish between electrolytes and non- electrolytes

Answer 4

An electrolyte is a substance that conducts electricity.

Experiment:

Take a led bulb and attach the wire at the end of the substance. Now supply electricity from the other end. If the led bulb glows, that substance is an electrolyte if it doesn’t it is not an electrolyte.

Question 5

1.52 understand that electrolysis involves the formation of new substances when ionic compounds conduct electricity

Answer 5

Electrolysis is the process of using electricity to break down or decompose a compound. The compound is usually dissolved in water or molten.

Question 6

1.53 describe experiments to investigate electrolysis, using inert electrodes, of molten salts such as lead(II) bromide and predict the products

Answer 6

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Lead bromide is heated until it becomes molten. Then it forms two ions: Pb2+ & Br-.

Electricity is provided. In the anode bubble of bromine gas is formed. Bromine ion loosed one electron and became bromine gas.

Br- ==> Br2 + e-

In the cathode lead received electrons and formed lead metal.

Pb 2+ + 2e - ==> Pb

Question 7

1.55 write ionic half-equations representing the reactions at the electrodes during electrolysis

Answer 7

Example- electrolysis of dillute sulphuric acid

At the anode:

OH- ions and SO42- ions are attracted to the anode. OH- ions give up electrons more readily than SO 42- ions. Consequently, OH- ions are preferentially discharged to give oxygen gas.

4OH - (aq) ==> 2H 2 O (l) + O 2 (g) + 4e -

The SO42 ions remain in solution.

At the cathode:

H+ ions and Cu2+ ions are attracted to the cathode. Copper is lower than hydrogen in the reactivity series. Cu2+ ions accept electrons more readily than H+ ions. As a result, Cu2+ ions are preferentially discharged as copper metal (atoms).

Cu 2+ (aq) + 2e - ==> Cu (s)

The H+ ions remain in solution.