3.1.4 qualitative analysis

Question 1

Test for carbonate

Answer 1

Add dilute acid and observe effervescence

Bubble gas through limewater.

CO2 - will turn limewater cloudy

2HCl + Na2CO3 > 2NaCl + H2O + CO2

Question 2

Test for sulfate

Answer 2

Acidified BaCl2 used as reagent

Will form white precipitate

Ba2+ + SO4^2- > BaSO4 (s)

Question 3

Testing for halide ions

Answer 3

Test solution is made acidic with nitric acid

Add Silver nitrate - AgNO3

Chlorine - white
Bromine - cream
Iodine - pale yellow

Nitric acid reacts with any carbonates to prevent formation of precipitate Ag2CO3

Question 4

If halide colour too similar

Answer 4

AgCl dissolves in dilute ammonia

AgBr dissolves in concentrated ammonia

AgI doesnt react - too insoluble

Question 5

Sequence of tests

Answer 5

Carbonate, sulfate then halide

Prevents false results as both BaCO3 and Ag2SO4 are insoluble

Question 6

Testing for positive ions (cations)

Answer 6

Test for NH4+

Reaction with warm NaOH, forming NH3 gas

Turns red litmus paper blue