F.3 Chemistry

X is a metal. Given that it can react with cold water to form a colourless gas. It means it is potassium, sodium or calcium. When it reacts with copper(II) sulphate solution, there is a formation of a colourless gas and a reddish brown solid.
Question is: Why is a colorless gas formed when X is added to copper(II) sulphate solution? (Explain with an equation)

The colourless gas is properbly water vapour.
The X is far away from copper in the reactivity series. So the enthalpy change is large and release a lot of energy, therefore boils the water in the solution.
2 K + CUSO4 → K2SO4 + Cu + Energy

Copper(II) sulphate solution is an aqueous solution containing water.
When metal X(K, Na or Ca) reacts with water, it will give out a colourless gas(hydrogen gas).
2X(when X = K/Na) + 2H2O --> 2XOH + H2
X(when X = Ca) + 2H2O --> Ca(OH)2 + H2