2 g) Tests for ions and gases

Question 1

2. 37 describe tests for the cations:

i) Li+, Na+,K+,Ca2+ using flame tests

Answer 1

Lithium: red
Sodium: orange (so strong will mask other colours)
Potassium: lilac
Calcium: brick red

Question 2

ii) NH4+, using sodium hydroxide solution and identifying the ammonia evolved

Answer 2

(NH4)2 SO4 + NaOH ==> NH3 + Na2SO4 + H2O

Ammonium sulphate + sodium hydroxide gives ammonia gas, sodium sulphate and water. Ammonia is a pungent smelling gas which turns red litmus paper blue

Question 3

iii) Cu2+,Fe2+ and Fe3+, using sodium hydroxide solution

Answer 3

• Copper(ii) sulphate + sodium hydroxide > blue precipitate
• Iron(ii) sulphate + sodium hydroxide > green precipitate
• Iron(iii) sulphate + sodium hydroxide > brown precipitate

Question 4

2. 38 describe tests for the anions:

i) CI-, Br- and I-, using dilute nitric acid and silver nitrate solution

Answer 4

• Chloride ions + nitric acid + silver nitrate ==> white precipitate (silver chloride)
• Bromide ions + nitric acid + silver nitrate ==> cream precipitate (silver bromide)
• Iodide ions + nitric acid + silver nitrate ==> yellow precipitate (silver iodide)

Question 5

ii) SO 4 2- , using dilute hydrochloric acid and barium chloride solution

Answer 5

SO4(2-) + HCl + Ba(2+) ==> white precipitate (barium sulphate)

Question 6

iii) CO 3 2- , using dilute hydrochloric acid and identifying the carbon dioxide evolved

Answer 6

Carbonate + acid ==> salt + water + carbon dioxide

Carbon dioxide produced will turn lime water cloudy

Question 7

2. 39-

i) hydrogen

Answer 7

Make popping sound when hydrogen is burned.

Question 8

ii) oxygen

Answer 8

Relights a glowing splint.

Question 9

iii) carbon dioxide

Answer 9

Make lime water cloudy

Question 10

iv) ammonia

Answer 10

Have a pungent smell

Turns red litmus paper blue

Question 11

v) chlorine

Answer 11

Turns damp litmus paper white.