Sodium chloride (salt)

Question 1

how can sodium chloride be obtained?

Answer 1

from the sea or from salt deposits

Question 2

what does the electrolysis of concentrated sodium

chloride give?

Answer 2

chlorine and hydrogen

Question 3

what is the chemical test for chlorine?

Answer 3

it bleaches moist litmus paper

Question 4

what is sodium chloride used as?

Answer 4

• as a preservative

* as a flavouring

Question 5

where is sodium chloride important?

Answer 5

it is an important raw material in the chemical industry, including use as a source of chlorine and sodium hydroxide

Question 6

what are household bleach, PVC and solvents are

made from?

Answer 6

substances derived from salt.

Question 7

what is chlorine used for?

Answer 7

to sterilise water and to make solvents, household bleach and plastics

Question 8

what is hydrogen used in?

Answer 8

the manufacture of margarine

Question 9

what is sodium hydroxide used to make?

Answer 9

soap

Question 10

Explain how mining for salt can lead to subsidence

Answer 10

taking salt out leaves a hole underground, rock can collapse into hole, buildings collapse

Question 11

Recall the products of the electrolysis of concentrated

sodium chloride solution (brine)

Answer 11

• hydrogen made at the cathode
• chlorine made at the anode
• sodium hydroxide is also made

Question 12

Explain how the electrolysis of sodium chloride
solution (brine) produces sodium hydroxide, hydrogen
and chlorine:

Answer 12

• NaCl(aq) contains Na+, OH−, Cl−, H+
• cathode 2H+ + 2e− → H2
• anode 2Cl− – 2e− → Cl2
• ions not discharged make sodium hydroxide.

Question 13

Explain the economic importance of the chlor-alkali

industry

Answer 13

industry based on the electrolysis of brine, very important and worth billions of pounds a year

Question 14

Describe how sodium hydroxide and chlorine are

used to make household bleach.

Answer 14

by reacting sodium hydroxide and chlorine together

Question 15

Explain why it is important to use inert electrodes in

the electrolysis of sodium chloride solution

Answer 15

so that they don’t react with hydrogen, chlorine or sodium hydroxide

Question 16

Describe how salt can also be mined as rock salt and

by solution mining in Cheshire

Answer 16

solution mining in Cheshire (water pumped down pipe, salt dissolves, salt water pumped up second pipe)

Question 17

Explain why the electrolysis of sodium chloride

involves both reduction and oxidation

Answer 17

reduction at cathode 2H+ + 2e− → H2

oxidation at anode 2Cl− – 2e− → Cl2