A mixture of 100 m mol of Ca(OH)₂ and 2 g of sodium sulphate was dissolved in water and the volume was made up to 100 mL. The mass of calcium sulphate formed and the concentration of OH^– in resulting solution, respectively, are : (Molar mass of Ca (OH)₂, Na₂SO₄ and CaSO₄ are 74, 143 and 136 g mol^–1 , respectively; K_sp of Ca(OH)₂ is 5.5 × 10^–6 )

The pH of rain water, is approximately :

20 mL of 0.1 M H₂SO₄ solution is added to 30 mL of of 0.2 M NH₄OH solution. The pH of the resultant mixture is : [pk_b of NH₄OH = 4.7].

An aqueous solution contains 0.10 M H₂S and 0.20 M HCl. If the equilibrium constants for the formation of HS^– from H₂S is 1.0 $$\times$$ 10^–7 and that of S^2- from HS^– ions is 1.2 $$\times$$ 10^–13 then the concentration of S^2- ions in aqueous solution is :