Question

Which of the following gives OH
ions on dissociation in water?
(a) Calcium carbonate
(b) Iron sulphide
(c) Calcium oxide
(d) All of these​

Answer 1

Explanation:

b iron sulphide gives oH ions when we dissociate in water

Answer 2

None of the following gives OH  ions on dissociation in water.

Explanation:

Reaction of calcium carbonate with water:

• Calcium carbonate doesn’t react with pure water. It reacts with carbonic acid which is water with dissolved carbon dioxide to produce soluble calcium bicarbonate.
• $CaCO_{3} + CO_{2} + H_{2}O \rightarrow Ca(HCO_{3})_{2}$
• But theoretically, calcium carbonate can react with water to produce calcium hydroxide and carbon dioxide.
• $CaCO_{3} + H_{2}O \rightarrow Ca(OH)_{2} + CO_{2}$

Reaction of iron sulphide with water:

• $3Fe + 4H_{2}O \rightarrow Fe_{3} O_{4} + 4H_{2}O$

Reaction of calcium oxide with water:

• Calcium oxide reacts vigorously with water to produce calcium hydroxide (slaked lime) and a large amount of heat is evolved.
• $CaO + H_{2} O \rightarrow Ca(OH)_{2}$