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When 0.025 moles of HCl are added to 325 mL of a buffer solution containing 0.620 M HF and 0.710 M F−, what will be the pH of the solution? (pKa of hydrofluoric acid is 3.16)

User LivaX
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When 0.025 moles of HCl are added to 325 mL of a buffer solution. The pH of the buffer solution after adding 0.025 moles of HCl will be 13.85.

What is the pH of the buffer solution?

Initial concentrations of HF and F- in the buffer solution:

[H+] = [HF] = 0.620 M

[OH-] = [F-] = 0.710 M

Change in concentration of HF and F- after adding HCl:

[H+] = [HCl]

[H+] = 0.025 moles / 0.325 L (325 mL = 0.325 L)

= 0.077 M

New concentration of HF is:

[HF] = 0.620 M - 0.077 M

= 0.543 M

The concentration of F- remains the same.

pOH of the solution:

pOH = -log [OH-]

= -log (0.710)

≈ 0.150

pH of the solution:

pH + pOH = 14

pH = 14 - pOH

≈ 14 - 0.150

≈ 13.85

Therefore the pH of the buffer solution after adding 0.025 moles of HCl will be 13.85.

User Bayard Randel
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