C3 Chemicals in Our Lives – Risks & Benefits Lesson 9: Electrolysis of Brine

Objectives MUST remember that useful products are produced by the electrolysis of brine SHOULD explain how electrolysis produces new materials COULD examine the environmental consequences of the electrolysis of brine

Key Words You need to be able to define the following: ◦ Electrolysis ◦ Membrane cell ◦ Electrodes ◦ Anode ◦ Cathode

Textbook Answers 1)Chlorine – PVC, water treatment; sodium hydroxide – soaps and detergents, papermaking, aluminium extraction; hydrogen – fuel, margarine. 2)36% 3)sodium chloride + water (+ energy)  chlorine + hydrogen + sodium hydroxide 4)10 ÷100 × 5 million = tonnes 5)Water 6)Pollutants from burning fossil fuels – carbon dioxide, carbon monoxide, particulates, nitrogen oxides, sulfur dioxide. 7)200 g × 6 million = 1200 million g = 1200 tonnes.

Worksheet Answers Activity 1 (Low demand) Hydrogen – fuel; chlorine – water treatment and making PVC; sodium hydroxide – making oven cleaners. Activity 2 (Standard demand) 1) Salt, water 2) Electricity/energy 3) Anode – chlorine; cathode – hydrogen 4) Separates the two halves of the cell keeping the gases apart. 5) Can be reused; more salt can be added to it. 6) 11.3 million tonnes Activity 3 (High demand) 1)The letter should acknowledge the dangers of mercury but state that losses have been reduced and that the process will be changed to a membrane cell, which uses no mercury. The letter may also point out the usefulness of the products. 2) Students should discover that mercury is concentrated in the food chain, particularly by fish; and mention the effects it has on the nervous system. They may refer particularly to the Minamata disaster.

Practical Answers 1)a) Chlorine; b) Hydrogen; c) Sodium hydroxide. 2)Has been electrolysed; conducted electricity and decomposed.

Practical Answers