A buffer is a mixture of a conjugate acid-base pair. In other words, it is a sol

Question

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, CH3COO?. Because ions cannot simply be added to a solution, the conjugate base is added in a salt form (e.g., 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]

Explanation / Answer

A)let the concentration of acetic acid be x and that of acetate be 0.1-x

so,

pH=pKa+log(salt/acid)

or 5=4.76+log((0.1-x)/x)

or x=0.036 M

so [acetic acid]=0.036 M

[acetate]=0.1-0.036

=0.064 M

now when the acid is added,

pH=4.76+log((110*0.64-5*0.32)/(110*0.64+5*0.32))

=4.74

pH change=4.74-5

=-0.26

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