Question

To understand how buffers use reserves of conjugate acid and conjugate base to counteract the effects of acid or base addition on pH.

A buffer is a mixture of a conjugate acid-base pair. In other words, it is a solution that contains a weak acid and its conjugate base, or a weak base and its conjugate acid. For example, an acetic acid buffer consists of acetic acid, CH3COOH, and its conjugate base, the acetate ion CH3COO−. Because ions cannot simply be added to a solution, the conjugate base is added in a salt form (e.g., sodium acetate NaCH3COO).

Buffers work because the conjugate acid-base pair work together to neutralize the addition of H+ or OH− ions. Thus, for example, if H+ ions are added to the acetate buffer described above, they will be largely removed from solution by the reaction of H+ with the conjugate base:

H++CH3COO−→CH3COOH

Similarly, any added OH− ions will be neutralized by a reaction with the conjugate acid:

OH−+CH3COOH→CH3COO−+H2O

This buffer system is described by the Henderson-Hasselbalch equation

pH=pKa+log[conjugate base][conjugate acid]    

Question: A beaker with 165 mL of an acetic acid buffer with a pH of 5.000 is sitting on a benchtop. The total molarity of acid and conjugate base in this buffer is 0.100 M. A student adds 6.10 mL of a 0.360 M HCl solution to the beaker. How much will the pH change? The pKa of acetic acid is 4.740.

Express your answer numerically to two decimal places. Use a minus ( − ) sign if the pH has decreased.

Answer 1

The numerical has been solved using Henderson equation. Upto 2 decimal place has been taken in the answer, described in the image uploaded.