Test for ions

Question 1

Test for halide ions

Answer 1

React with acidified silver nitrate solution. Forms coloured precipitate

Ag+(aq) + X-(aq) —> AgX(s)

Question 2

Precipitate colours for halide test

Answer 2

AgCl - white
AgBr - Cream
AgI - yellow
AgF - soluble so no precipitate

Question 3

How can ammonia solution distinguish between sliver nitrate precipitates

Answer 3

Add ammonia
AgCl - Soluble
AgBr - Soluble in excess
AgI - Insoluble

Question 4

Why must silver nitrate be acidified when used to test halide ions

Answer 4

Prevents formation of silver carbonate
Forms from atmospheric CO2 dissolving in solution

Question 5

Test for ammonium ions

Answer 5

Warm with NaOH solution. Produces basic gas NH3
Test with damp red litmus, turns blue
NH4+(aq) + OH-(aq) —> NH3(g) + H2O(l)

Question 6

Test for carbonate ions

Answer 6

Add acid
Bubble gas produced in limewater
White precipitate formed from CO2, limewater turns cloudy

2H+(aq) + CO3^2-(aq) —> H2O(l) + CO2(g)

Question 7

Test for hydroxide ions

Answer 7

Add Mg2+ solution
Forms white precipitate of Mg(OH)2

Mg2+(aq) + 2OH-(aq) —> Mg(OH)2(s)

Question 8

Test for sulfate ions

Answer 8

Add acidified barium chloride solution. White pot of BaSO4 formed

Ba2+(aq) + SO4^2-(aq) —> BaSO4(s)

Question 9

Why must barium chloride be acidified when testing for sulfate ions

Answer 9

Prevent formation of white ppt of baCO3
Formed when atmospheric CO2 dissolves in solution

Question 10

Why do acidified barium chloride or acidified silver nitrate react with carbonate ions

Answer 10

Both solutions contain acid that reacts with the carbonate ions o produce CO2 gas

2H+(aq) + CO3^2-(aq) —> H2O(l) + CO2(g)

Question 11

Give 2 sources of aqueous sulfate ions

Answer 11

Solutions of group 1 sulfate salts (Na2SO4 in solution produces SO4^2- (aq) ions)

Sulfuric acid (H2SO4 contains some SO4^2- ions)

Question 12

What is the first step to test any unknown inorganic solid

Answer 12

Dissolve in water