Question

a) A solution contains 0.500 M ammonium iodide and 0.413 M ammonia.  
The pH of this solution is .

b) A buffer solution contains 0.280 M KHCO₃ and 0.469 M K₂CO₃. If 0.0252 moles of perchloric acid are added to 150 mL of this buffer, what is the pH of the resulting solution ? (Assume that the volume change does not change upon adding perchloric acid)

pH =

c) A buffer solution contains 0.327 M hypochlorous acid and 0.441 M sodium hypochlorite.  If 0.0242 moles of nitric acid are added to 150. mL of this buffer, what is the pH of the resulting solution ?  (Assume that the volume change does not change upon adding nitric acid)
pH =

Answer 1

a) Using,

pH = pKa + log(base/acid)

feeding the given values,

pH = 9.25 + log(0.413/0.500)

      = 9.17

b) after adding perchloric acid = 0.0252 mol

[KHCO3] = 0.280 M x 0.150 L + 0.0252 = 0.0672 mol

[K2CO3] = 0.469 M x 0.150 L - 0.0252 = 0.04515 mol

pH = 10.33 + log(0.04515/0.0672)

     = 10.16

c) after adding nitric acid = 0.0242 mol

[hypochlorous acid] = 0.327 M x 0.150 ml + 0.0242 mol = 0.07325 mol

[sodium hypochlorite] = 0.441 M x 0.150 L - 0.0242 mol = 0.04195 mol

pH = 7.53 + log(0.04195/0.07325)

     = 7.29