Question

Calculate the pH of a 1 L solution that contains 1.0 M HCl and 1.5 M CH₃COOK. The K_a for CH₃COOH is 1.8 x 10^-5.

9.56                             b) 4.74                         c) 4.44                       

d) 0.30                         e) 7.45

Answer 1

1 litre of 1.0M HCl = 1 mole of HCl

1 litre of 1.5 M CH3COOK = 1.5 mole of CH3COOK

HCl + CH3COOK ............> CH3COOH + KCl

so here 1 mole of HCl neutralise 1 mole of CH3COOK

remaining is 0.5 mole CH3COOK

and 1mole of CH3COOH forms

Concentration of CH3COOK = no.of moles remaining /vol.in lt = 0.5/1 = 0.5 M

Concentration of CH3COOH = no.of moles formed /vol.in lt = 1/1 = 1M

now

Ph = Pka + log{[salt]/[acid]}

Ph = - log(1.8*10^-5) + log(0.5/1)

Ph = 4.74 -0.30

Ph = 4.44

so the option C is correct