18.4 CHAPTER 18. REACTIONS IN AQUEOUS SOLUTION
Test for a sulphate
Add a small amount of barium chloride solution to a solution of the test salt. If a white
precipitate forms, the salt is either a sulphate or a carbonate.
SO^24 −(aq)+Ba2+(aq)+Cl−(aq)→BaSO 4 (s)+Cl−(aq) (BaSO 4 is a white precipitate)
CO^23 −(aq)+Ba2+(aq)+Cl−(aq)→BaCO 3 (s)+Cl−(aq) (BaCO 3 is a white precipitate)
If the precipitate is treated with nitric acid, it is possible to distinguish whether the salt is a
sulphate or a carbonate (as in the test for a chloride).
BaSO 4 (s)+HNO 3 (ℓ)→(no reaction; precipitate is unchanged)
BaCO 3 (s)+2HNO 3 (ℓ)→Ba2+(aq)+2NO− 3 (aq)+H 2 O(ℓ)+CO 2 (g) (precipitate disappears)
Test for a carbonate
If a sample of the dry salt is treated with a small amount of acid, the production of carbon
dioxide is a positive test for a carbonate.
2 HCl+K 2 CO 3 (aq)→CO 2 (g)+ 2KCl (aq)+H 2 OℓIf the gas is passed through limewater (an aqueous solution of calcium hydroxide) and the
solution becomes milky, the gas is carbon dioxide.
Ca2+(aq)+2OH−(aq)+CO 2 (g)→CaCO 3 (s)+H 2 O(ℓ)(It is the insoluble CaCO 3 precipitate
that makes the limewater go milky)
Exercise 18 - 2
1. Silver nitrate (AgNO 3 ) reacts with potassium chloride (KCl) and a white
precipitate is formed.
a. Write a balanced equation for the reaction that takes place. Include
the state symbols.
b. What is the name of the insoluble salt that forms?
c. Which of the salts in this reaction are soluble?
2. Barium chloride reacts with sulphuric acid to produce barium sulphate
and hydrochloric acid.
a. Write a balanced equation for the reaction that takes place. Include
the state symbols.
b. Does a precipitate form during the reaction?
c. Describe a test that could be used to test for the presence of barium
sulphate in the products.324 Chemistry: Chemical change