In: Chemistry
You would like to make a buffer that has a pH of 7.00. Starting with 100.0 mL solution of 0.10 M NaH2PO4 and 0.10 M Na2HPO4, how much 0.1 M NaOH would you need to add to bring the pH of the buffer up to 7.00?
pH = 7.00
pKa = 7.21
millimoles of NaH2PO4 = 100 x 0.1 = 10
H2PO4- + NaOH -----------> HPO42-
10 0.1V 0
10 - 0.1V 0 0.1V
pH = pKa + log [salt / acid]
7.00 = 7.21 + log [0.1 V / 10 - 0.1 V]
[0.1 V / 10 - 0.1 V] = 0.6166
0.1 V = 6.166 - 0.06166 V
V = 38.14
volume of NaOH = 38.14 mL