A buffer solution has 0.625 M HCN and 0.575 M CN-. If 0.030 moles of NaOH is added to 400. mL of the buffer solution, what is the pH after the addition? The pKa of hydrocyanic acid is 9.31.

Question

Cristopher Kaiser

Chemistry

4 February, 23:50

A buffer solution has 0.625 M HCN and 0.575 M CN-. If 0.030 moles of NaOH is added to 400. mL of the buffer solution, what is the pH after the addition? The pKa of hydrocyanic acid is 9.31.

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Answers (1)

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Cecelia Roy · Answer 1

pH = 9.393

Explanation:

Give that 400mL buffer 1L = 1000mL 0.625 mol of HCN solution = 0.250 mol HCN

Therefore,

400mL buffer solution 1L = 1000mL 0.575 mol CN^ - solution = 0.230 mol of CN^-

Pka HCN = 9.31

Therefore, to get ph:

pH = 9.32 + log (0.230 mol + 0.030 mol) / (0.250 mol - 0.030 mol)

pH = 9.32 + 0.0726

pH = 9.393