Question

10. What is the pH of a solution which contains 0.05 moles benzoic acid and 0.075 moles sodium benzoate dissolved to make 0.5000 L of solution? (Ignore Activities)

Answer 1

10. - Total volume of the solution, - 0.5 L No. of moles of benzoic acid - = 0.05 mol . Molarity of benzoic acid = 0.05 mol 0.5 L = 0.1 mol/l = 0.1 M Again. No. of moles of sodium benzoate = 0.075 moles i Molarity of sodium benzoate 0.075 moles 0.5 L = 0.15 mol/l = 0.15 M pka of benzoic acid pka= 4.19 Now this is a solution of weak acid (benzoic acid) and itz salt (sodium benzoate).

So, it acts as a buffer solution. Now, pH of the buffer solution can be given by the following equation pH = pka & log [salt] Tacia a pH = 4.19 + log 0.15 0.1 - 4.19 + 0.176 i pH ? 4.37 of the solution = (4.37) Ane