WAEC Chemistry 2015 Theory — Question 48

Model answer

I. Boiling temporary hard water removes the (temporary) hardness, since it decomposes the dissolved calcium/magnesium hydrogen carbonate into insoluble carbonate, which precipitates out: Ca(HCO₃)₂ →(Δ) CaCO₃(s) + H₂O(l) + CO₂(g). II. Adding sodium trioxocarbonate (IV) (washing soda) to permanent hard water removes the permanent hardness by precipitating out the calcium/magnesium ions as insoluble carbonates.