Question

Compare the rate at which pH changes when HCl is added to the buffer solution(NH3/NH4Cl) to the rate of change when no buffer or base is present (distilled water).

Answer 1

1)

when buffer is added:

there is an equilibrium

NH3 + H2O <--> NH4+ + OH-

when adding H+ ions, then

OH- + H+ = H2O ,the shift goes to the right, i.e. NH4+ increases

then the overall change is "buffered" due to sotichioimetry

2)

for pure water

when adding H+

then

H2O <--> H+ and OH- Kw = 10^-14

Kw is too low, when adding H+ at very low concetrations will change drastically the H+ concnetration

that is

pH = decreases sinc e H+ increases drastically

the change is notorious, expact pH low as 1-3