Please help with part B & C ± pH Changes in Buffers Part A What is the pH of a b

Question

Please help with part B & C

± pH Changes in Buffers

Part A

What is the pH of a buffer prepared by adding 0.809 mol of the weak acid HA to 0.609 mol of NaA in 2.00 L of solution? The dissociation constant Ka of HA is 5.66×107.

Express the pH numerically to three decimal places.

pH = 6.124

Part B

What is the pH after 0.150 mol of HCl is added to the buffer from Part A? Assume no volume change on the addition of the acid.

Express the pH numerically to three decimal places.

pH = ???

Part C

What is the pH after 0.195 mol of NaOH is added to the buffer from Part A? Assume no volume change on the addition of the base.

Express the pH numerically to three decimal places.

pH = ???

Explanation / Answer

pKa = 6.25

part B)

on addition of acid

pH = pKa + log [NaA - C / HA + C]

pH = 6.247 + log (0.609 - 0.150 / 0.809 + 0.150)

pH = 5.927

part C)

on addition of acid

pH = pKa + log [NaA + C / HA - C]

pH = 6.247 + log (0.609 + 0.195 / 0.809 - 0.150)

pH = 6.333

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