8.3

Question 1

How do we test for carbonates?

Answer 1

Add a dilute acid to a mystery sample
If carbonates are present then carbon dioxide will be released.
To test for carbon dioxide using limewater turns cloudy- just bubble the gas through a test tube of limewater.
Carbonate + acid —> carbon dioxide + water
CaCO3 (g) + HCl (aq) —-> CO2 (g) + H20 (l)
CO3 2- (g) + 2H+ (aq) —-> CO2 (g) + H20 (l)

Question 2

How do we test for sulphates?

Answer 2

Most suplphates are soluble in water but barium sulphate is insoluble.
To test for a sulphate ion (SO4 2-) add dilute HCl, followed by barium chloride/nitrate solution (BaCl2)- white precipitate is barium sulfate
Ba 2+ + SO4 2- —-> BaSO4 (s)

Question 3

What is the test for ammonia compounds?

Answer 3

NH3 is alkaline so we can check for it using damp litmus paper
If ammonia is present it would turn red to blue
We can test if a substance contains ammonium (NH4) ions. Add aqueous sodium hydroxide to unknown substance in test tube and warm mixture.
If ammonia is given off that means there are ammonia ions in your mystery substances
NH4+ + OH- —-> NH3 (g) + H20 (l)