FC15

Question 1

What do you need to add to test for Anions?

Answer 1

To test for Halides (Cl-, Br-, I-) add aqueous silver nitrate

If Cl- is present a white precipitate of AgCl forms that is soluble in both dilute and conc NH3

If Br- is present a cream precipitate of AgBr forms that is insoluble in dilute but soluble in conc NH3

If I- is present a yellow precipitate of AgI forms that’s insoluble in both dilute and conc NH3

Question 2

What do you do for the Teat for sulphate (SO4 2-)

Answer 2

Add aqueous barium ions
e.g Ba(NO3)2 or BaCl2

If SO4 2- is present a white precipitate of BaSO4 forms

Question 3

To test for Carbonate

Answer 3

Add dilute inorganic acid
e.g (nitric acid)

If CO3 2- is present, fizzing occurs due to CO2 being formed

Question 4

What do you do for the test for ammonium cations?

Answer 4

Add aqueous sodium hydroxide and then warm the mixture.

If a vapour that turns damp red litmus indicate paper blue then this is due to ammonia gas being formed from the ammonium ions in solution

Question 5

Order of tests

Answer 5

1) Add dilute nitric acid to remove any carbonate ions that will give false positives

2) Add AgNO4 to test for halide

3) Add Ba(NO3)2 to test for sulphate

4) add Sodium hydroxide and then warm mixture to test for ammonium ions