Reference no: EM132418381

These four problems refer to the same reaction.

(i) A 100.0 ml aqueous buffer solution at 25  °C contains a mixture of 0.100 M CH₃COOH (acetic acid) and 0.100 M NaCH₃CO₂ (sodium acetate). The pKa of acetic acid is 4.75. What is the pH of this buffer solution? In doing this calculation, you can assume that the hydronium ion concentration is small relative to the acid and base concentrations, but you must validate this assumption after carrying out the calculation.

CH₃COOH(aq) + H₂O ? H₃O⁺ + CH₃CO₂^-

(ii) What is the pH change after the addition of 2.00 ml of 1.00 M NaOH (aq) to the buffer solution? In carrying out this calculation you should assume that the reaction between the strong base and the weak acid is stoichiometric. In other words, assume that the following reaction goes to completion:

CH₃COOH (aq) + OH^-(aq) ? CH₃CO₂^-(aq) + H₂O(l)

Using this assumption, you will need to calculate new "initial" concentrations of the acid and base to use in the pH calculation.

(iii) Compare the pH change that you calculated above to the pH change that would result from adding an equal amount of NaOH to 100.0 ml of water. Will this buffer be good in resisting pH change?

(iv) An aqueous buffer solution at 25  °C consists of 0.080 M chlorous acid (HClO₂) together with 0.040 M sodium chlorite (NaClO₂, the salt of the conjugate base of chlorous acid). The Ka of chlorous acid is 1.0 x 10^-2. Calculate the pH of the solution by assuming that the hydronium ion concentration is small relative to the concentrations of the acid and conjugate base. Is this approximation valid. If not, why does it fail this time, while it succeeded in #7 above? If the approximation is invalid, find an expression for the Ka without making this approximation.