Question

1) A buffer is prepares in which ratio [HCO3-]/[CO3^2-] is 4.0:

a) what is the pH of this buffer (ka HCO3- = 4.7×10^-11)?

b) what is the pH of the buffer if 0.0100 moles of HCL are added?

c) what is the pH of the buffer if 0.0200 moles of NaOH are added

Answer 1

Using ph = pka + log salt/acid = -log(ka) + log[[co_3^2-3/[hco_3 ^2 -3] = -log(4.7 times 10^-11) + log(1/4) = 10.527 + log(0.25) = 9.7256 since the conc of total acid.

b) and c) can't be solved as the initial conc of acid or salt must be provided ...or else we won't be able to exactly say how much of acid got converted to base ....

suppose we have 100 moloes of acid and 100 moles of salt and it so forms a buffer solution ..then when we add 1 mol of acid to see the change of pH of buffer ...then the conc of new salt/acid ratio willbe ...

[99/101] which earlier was [100/100]

and suppose we add 2 oles of base to it ...the new ratio will be ...[100/98]