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 an unknown concentration of Ba²⁺. When 50 mL of a 1 M solution of Na₂SO₄ is added, BaSO₄ just begins to precipitate. The final volume is 500 mL. The solubility product of BaSO₄ is 1 $$\times$$ 10^–10. What is the original concentration of Ba²⁺?

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 :