Chemicals from Salt

Common and Chemical Names

Name of substance

Chemical composition

Rock salt Mineral containing mainly sodium chloride mixed with a red clay.

Salt Sodium chloride, NaClBrine Aqueous solution of

sodium chloride.Caustic soda Sodium hydroxide,

NaOH

Solid Salt1. Used as a preservative for foods2. Used to treat and preserve animal

skins.3. Added to foods for flavouring.4. Used to treat ice on roads in the

winter.5. The raw material for the manufacture

of many other important chemicals.

Extraction of Rock SaltIn countries like Britain there are large underground deposits of rock salt.The rock salt is mined as a solid and brought to the surface as a powdered rock.

Extraction of brineThe rock salt can be dissolved when water is pumped down onto the solid mineral. A solution containing dissolved salt is pumped back to the surface.

Electrolysis of the Brine1. The brine is purified.2. The solution is passed into an

electrolytic cell containing a diaphragm.

3. A continuous process converts the brine(sodium chloride) into three useful products.

AnswersIn the diaphragm process the gaseous products are separated from each other. ExplainThe hydrogen and chlorine react together and can form an explosive mixture.

AnswersThe anode product is separated fro mthe solution drawn off at S and Q. ExplainThe chlorine reacts with the sodium hydroxide to form a mixture of products.

The Ions that are Discharged

In the initial solution there are ions from both the water and the sodium chloride.

NaCl(aq) → Na+ (aq) + Cl- (aq)

H2O(l) → H+ (aq) + OH- (aq)

Ion Discharged at the Anode

Only one ion is discharged from the anode. There are two negative ions in the solution, Cl- and OH-. The ion from the element lowest in the Reactivity Series is the one discharged.

2Cl- (aq) - 2e- → Cl2(g)

Ion Discharged at the Cathode

Only one ion is discharged from the cathode. There are two positive ions in the solution, Na+ and H+. The ion from the element lowest in the Reactivity Series is the one discharged.

2H+ (aq) + 2e- → H2(g)

Ions Left in SolutionThe sodium ion and hydroxide ion are not discharged. This leaves a solution of sodium hydroxide.

Products from Electrolysis

1. Sodium hydroxide.2. Hydrogen.3. Chlorine.

AnswersIn what state are the chlorine and hydrogen transported fro mthe electrolysis plant?Hygrogen – GasChlorine – Liquid

AnswersChlorine is used in the manufacture of chlorinated solvents (30 %), monomers for plastics (25 %) and bleaching agents (15 %).(i)Name TWO chlorinated solvents and state ONE use for the solvents.

Uses of Chlorine

Uses of Sodium Hydroxide

Uses of Hydrogen