Required practical 4: Ion tests

Question 1

Method to test for group 2 ions using the flame test:

Answer 1

1. Dip the nichrome wire in concentrated hydrochloric acid.
2. Dip into the sample.
3. Place the loop into blue bunsen burner and observe colour.

Question 2

What are the positive test for the group 2 ions in the flame test?

Answer 2

Dark red - Calcium Ca 2+
Red - Strontium Sr 2+
Green - Barium Ba 2+

Question 3

How to test for ammonium compounds and hydroxides using litmus paper?

Answer 3

Add sodium hydroxide and if ammonium compound is present ammonia gas will be present. Place damp red litmus above the test tube and it should turn blue as ammonia gas dissolves in the water.
Hydroxides are alkaline so turn red litmus paper blue but further tests are needed as every alkali does that.

Question 4

What is a test for carbonates?

Answer 4

Add hydrochloric acid and if carbonate is present carbon dioxide gas is produced. Bubble through limewater and if it turns cloudy CO2 is present.

Question 5

What is a test for sulphates?

Answer 5

Add hydrochloric acid to remove any carbonates which can give false positive. Then add barium chloride and if sulphates are present white precipitate should form which is barium sulphate which is insoluble.

Question 6

What order should you test to avoid false positives?

Answer 6

1. Test for carbonates
2. Test for sulphates
3. Test for halides