I assume you have solved for the pKa. Here is what you do for the NaOH addition. The addition of HCl is handled the same way. I like to work in millimoles instead of M but you may use your choice.
mmols HPO4^- = (mg/molar mass) = approx 10 but you need a more accurate answer. I will estimate ALLhe following calculations.
mmols H2PO4^- = approx 12
Add NaOH, mmols = approx 5
.......H2PO4^- + OH^- ==> HPO4^2- + H2O
I......12........0.........10
add..............5..............
C......-5.......-5...........5
E......7.........0..........15
Substitute the E line into the HH equation together with your valu for pKa and solve for the new pH of the solution. The HCl addition works the same way but use the base form; i.e
.........HPO4^2- + H^+ ==> H2PO4^-
A 1X Phosphate Buffered Saline solution was prepared by adding 1.44g of Na2HPO4 and 1.44g of H2PO4- to 800mL of water. Additional components were dissolved in the solution: 8g of NaCl, 0.2g of KCl and 0.24g KH2PO4. The resulting buffer solution had a pH of 7.2.
a. Calculate the pKa of the buffer.
b. Calculate the pH of the buffer solution after 5.0 mL of 1.0M NaOH.
c. Calculate the pH of the buffer solution after the addition of 5.0 mL 1.0M HCl.
I'm not sure how to incorporate these additional components into my calculations. I got the molarities for everything, but that is as far as I've gotten.
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