Qualitative Analysis

Question 1

What are the three tests that can be run to test for anions?

Answer 1

Carbonate test,
Sulfate test,
Halide test.

Question 2

How is the carbonate test conducted?

Answer 2

1) Add dilute nitric acid to the solution or solid being tested.
2) If bubbles form, the unknown compound can be a carbonate.
3) Prove the gas is CO2 by performing a lime water test with the gas.

Question 3

How is the sulfate test conducted?

Answer 3

1) Add a solution containing Ba2+ ions to the solution being tested.
2) If a white precipitate forms, BaSO4, a sulfate is may be present.

Question 4

How is the halide test conducted?

Answer 4

1) Add a solution of Ag+ ions, in the form of AgNO3, to the solution being tested.
2) If a precipitate is formed, a halide is most likely present.

Question 5

What order should the tests be conducted?

Answer 5

First ten carbonate test, then the sulfate test and finally the halide test.

Question 6

Why should the carbonate test be conducted first?

Answer 6

The sulfate and halide tests get inaccurate results as they can both react with a carbonate as well as their intended anion.

Question 7

Why should the halide test be conducted last?

Answer 7

The Ag+ ions will react with both carbonates and sulfates to form a precipitate, so it is best to follow the other tests first to ensure there is not carbonate or sulfate, but only a halide.

Question 8

What is the test for an ammonium cation?

Answer 8

1) Aqueous sodium hydroxide, NaOH, is added to a solution of an ammonium ion.
2) Ammonia gas is produced, but as ammonia is very soluble it is unlikely to form bubbles.
3) As the mixture is warmed the gas is releases, if it is ammonia, then a damp pH indicator paper should turn it blue.