A 300 mL volume of 0.4 M phosphate buffer contains a total of
0.04 moles of phosphate species:
(a) Calculate the moles of
H2PO4- and
HPO42- in the buffer solution if the pH
is 7.4.
(b) Calculate the moles of
H2PO4- and
HPO42- in the buffer solution if the pH
is 6.4.
(c) If you need to adjust the pH
of the buffer from 7.4 to 6.4, should you use HCl or NaOH and how
many moles of it do you expect to need? Show your reasoning and
calculations.
(d) To adjust the pH from 7.4 to 6.4 (which is sometimes
referred to as titrating) there are two concentrations of your
strong acid, HCl (or base, NaOH) available in the lab, 2.0 M or 5.0
M. Calculate the volume required for each of these concentrations.
Show your calculations.
(e) Which concentration would be more appropriate to use. Use
calculations to explain.