A buffer solution contains 0.353 M ammonium bromide and 0.352 M ammonia. If 0.0200 moles of hydrochloric acid are added to 125 mL of this buffer, what is the pH of the resulting solution ? (Assume that the volume change does not change upon adding hydrochloric acid)

9.07

Explanation:

We have to start with the buffer system reaction, so:

When we have the hydrochloric acid (a strong acid) the of the hydrochloric acid () will interact with the base of the buffer system () to produce more acid (), so:

Therefore the concentration of will decrease and the concentration of will increase. The next step then would be the calculation of the moles of the acid and base in the buffer system. So:

If we add 0.02 mol of we can calculate the amount of acid and base that changes in the buffer system.

Now, we can calculate the concentration of each species if we divide by the number of moles:

If we use the hendersson hasselbach equation we can calculate the pH value again:

The final pH value is 9.07

1 a

2 d

3 a

4 c

explanation: