15:Qualitative Analysis

Question 1

How to test for carbonates

Answer 1

Add an acid often dilute nitric acid

If CO₃²¯ ions are present there will be effervescence

Question 2

How to test for sulphates

Answer 2

Add aqueous barium nitrate (could be barium chloride)

If SO₄²¯ ions are present, a white precipitate of BaSO₄ will be formed.

Question 3

How to test for Halide

Answer 3

Add silver nitrate

Cl¯ = white precipitate

Br¯ = Cream precipitate

I¯ = Yellow precipitate

Question 4

Why is it important to do the tests in the order 1. Carbonate test 2. Sulphate test 3. Halide test

Answer 4

It is important to do the carbonate test first because BaCO₃ is also insoluble, so a solution containing CO₃²¯ ions would also give a white precipitate with Ba(NO₃)²(aq).

Question 5

How to confirm halide test

Answer 5

AgCl is soluble in dilute aqueous ammonia
AgBr is insoluble in dilute ammonia but dissolves in concentrated aqueous ammonia
AgI is insoluble in aqueous ammonia.

Question 6

Ammonium ion test

Answer 6

Warm a solution of the substance with aqueous sodium hydroxide
If NH₄† ions are present, ammonia gas will be produced. This will turn damp litmus paper blue