chemistry:ionic equilibrium

[devkothari]

Q1.) calculate pH of a mixture containing 50ml of 0.1(M) NaOH and 50ml of 0.1(M) CH3COOH

Q2.) 50% neutralization of a solution of formic acid(Ka=2 * 10^ -4) with NaOH would result in a solution having a hydrogen ion concentration of ____.

Q3.) what is the pH of solution which have NH3 concentration 0.1M and (NH4)2SO4 concentration 0.05M .given that Kb of NH3=10^ -5

[sahus]

Answer 1. concentration of salt = (50 mL * 0.1 M) /(50 mL + 50 mL) = .05 M
               pH = 7 + 1/2 pK_a + 1/2 log c                                     
                    = 7 + 1/2 * 4.7 + 1/2 log(.05)
                    = 7 + 2.4 + -0.65
                    = 8.75

Answer 2. use the formula
               pH = pK_a + log([salt]/[Acid])
                    = -log(2 * 10^ -4) + log(1)               since now concentration of salt and acid is same
       =>   [H] = 2 * 10^ -4

Answer 3. use the formula
               pOH = pK_b +  log([salt]/[Acid])
                      = 5 + log(.05/0.1)
                      = 4.7
              =>pH = 14 - pOH = 14 - 4.7 = 9.30