Effect of Added Base Ć Na He Poy (NaHPO4. 7. 37 Calculate the pH of a...

Question

Question

Answer 1

Answer #1

Solution:

Part A)

pH of the phosphate buffer is calculated as,.

pH = pka + log [Na2HPO4] / [NaH2PO4]

pH = 7.21 + log (0.450 L x 0.35 M) / (0.250 L x 0.45 M)

pH = 7.21 + log (0.1575 / 0.1125)

pH = 7.21 + log 1.4 = 7.21 + 0.15 = 7.36

Part B):

15 mL and 0.10 M NaOH = 0.015 L x 0.10 M = 0.0015 mol

Thus, on addition of 0.0015 mol of NaOH increases the concentration of Na2HPO4 and decreases the concentration of NaH2PO4.

Thus, [Na2HPO4] = 0.1575 + 0.0015 = 0.1590 mol

[NaH2PO4] = 0.1125 - 0.0015 = 0.111

Thus, new pH,

pH = 7.21 + log 0.1590 / 0.111

pH = 7.21 + log 1.432 = 7.21 + 0.16 = 7.37

Answer 2

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