M3 ,, Qualitative Analysis

Question 1

Testing for Negative ions (anions) methods?

Answer 1

Testing for Presence of a carbonate
Testing for presence of a sulfate
Testing for halide ions with silver nitrate.

Question 2

Testing for Presence of a carbonate?

Answer 2

Add any dilute acid and observe effervescence.
Bubble gas through limewater to test for CO2 – will turn limewater cloudy
Fizzing due to CO2 would be observed if carbonate was present

2HCl + Na CO —> 2NaCl + H O + CO 23 22

Question 3

Testing for presence of a sulfate?

Answer 3

Acidified BaCl2 solution is used as a reagent to test for sulfate ions.
If barium chloride is added to a solution that contains sulfate ions a white precipitate forms.

The acid is needed to react with carbonate impurities that are often found in salts which would form a white barium carbonate precipitate and so give a false result.

Sulfuric acid cannot be used to acidify the mixture because it contains sulfate ions which would form a precipitate.

Ba2+ (aq) + SO42-(aq) —> BaSO4 (s).

Question 4

Testing for positive ions (cations)?

Answer 4

Test for ammonium ion NH4+, by the reaction with warm NaOH(aq), forming NH3 gas

Ammonia gas can be identified by its pungent smell or by turning red litmus paper blue.