The buffer solution target has a pH value smaller than that of pKw (i.e., pH < 7.) The solution is therefore acidic. It contains significantly more protons than hydroxide ions
. The equilibrium equation shall thus contain protons rather than a combination of water and hydroxide ions as the reacting species.
Assuming that of the 0.307
sodium hydroxide solution was added to the acetic acid. Based on previous reasoning,
is sufficiently small that acetic acid was in excess, and no hydroxide ion has yet been produced in the solution. The solution would thus contain
moles of acetic acid and
moles of acetate ions.
Let denotes an acetic acid molecule and
denotes an acetate ion. The RICE table below resembles the hydrolysis equilibrium going on within the buffer solution.
The buffer shall have a pH of 4.250, meaning that it shall have an equilibrium proton concentration of . There were no proton in the buffer solution before the hydrolysis of acetic acid. Therefore the table shall have an increase of
in proton concentration in the third row. Atoms conserve. Thus the concentration increase of protons by
would correspond to a decrease in acetic acid concentration and an increase in acetate ion concentration by the same amount. That is:
By definition:
The question states that
such that
Thus it takes of sodium hydroxide to produce this buffer solution.