C2h - Chemicals from the sea: the chemistry of sodium chloride

Question 1

How is salt mined(in Cheshire)(2)

Answer 1

mining from the ground as rock salt

solution mining by pumping in water and extracting saturated salt solution

Question 2

Explain how mining for salt can lead to subsidence(3)

Answer 2

when there is insufficient salt left underground after mine

weight of the ground above mine causes ground to sink downwards

leads to cracked buildings and holes appearing in the ground

Question 3

What are the products of electrolysis of brine (3)

Answer 3

chlorine made at anode

hydrogen made at cathode

sodium hydroxide also made, which stays dissolved

Question 4

Why it is important to use inert electrodes in the electrolysis of sodium chloride solution

Answer 4

stops the electrodes from reacting with the reactive products from the electrolysis of brine and to make sure the electrodes do not dissolve

Question 5

How does the electrolysis of sodium chloride solution (brine) produce sodium hydroxide, hydrogen and chlorine? (4)

Answer 5

NaCl (aq) contains a mixture of diff ions: Na+and Cl- from sodium chloride; H+ and OH- from water

at anode, Cl- ions lose electrons and are oxidised to chlorine gas: 2Cl- - 2e- –> Cl2

at cathode, H+ ions gain electrons and are reduced to hydrogen gas: 2H+ + 2e- –> H2

remaining Na+ and OH-ions are not discharged and make sodium hydroxide

Question 6

Why does the electrolysis of sodium chloride involve both reduction and oxidation? (2)

Answer 6

chloride ions lose electrons at anode and are oxidised to chlorine gas

hydrogen ions gain electrons at cathode and are reduced to hydrogen gas

Question 7

How can you test for chlorine

Answer 7

It bleaches moist litmus paper

Question 8

How is household bleach made(word and balanced symbol equation)

Answer 8

sodium hydroxide + chlorine –> sodium chloride + water + sodium chlorate (bleach)

2NaOH + Cl2 → NaCl + H2O + NaClO

Question 9

Explain the economic importance of the chlor-alkali industry(2)

Answer 9

Chlorine and sodium hydroxide are important raw materials
-they are involved in making about half the chemicals we use on a daily basis e.g. solvents, plastics, paints, soaps, medicines and food additives

Question 10

What are the uses of chlorine(4)

Answer 10

to sterilise water

solvents

household bleach

plastics (PVC)

Question 11

What are the uses of sodium hydroxide(2)

Answer 11

soap

household bleach