17. Acid and Base Equilibrium

What is the pH of a 0.750 M solution of NaCN (K_a of HCN is 4.9 × 10^-10)?

What is the pH of a 0.320 M solution of Ca(NO₂)₂ (ka of HNO₂ is 4.5 × 10^-4)?

Determine the pH of a solution made by dissolving 6.1 g of sodium cyanide, NaCN, in enough water to make a 500.0 mL of solution. (MW of NaCN = 49.01 g/mol). The K_a value of HCN is 4.9 × 10⁻¹⁰.

An unknown weak base has an initial concentration of 0.750 M with a pH of 8.03. Calculate its equilibrium base constant. 

How can the pH of a solution be calculated if the pOH is known?