Eq point of a buffer solution help?

100. mL of 0.200 M HCl is titrated with 0.250 M NaOH

A. What is the pH of the solution after 50.0 mL of base has been added?

I got pH of 1.3

B. But then it asks what the pH of the solution at the equivalence point is?

1 Answer

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  • 8 years ago

    This isn't a buffer problem, because NaOH and HCl do not make a buffer. This is a simple acid/base neutralization reaction.

    Moles HCl = 0.1 L x 0. 2 mol/L = 0.02 moles

    Moles NaOH after 50 mls added = (0.05 L)(0.25 mol/L) = 0.0125 moles

    Moles HCl not neutralized = 0.02 - 0.0125 = 0.0075 moles HCl left over

    Total volume = 100 mls HCl + 50 mls NaOH = 150 mls = 0.15 L

    [HCl] = 0.0075 mole/0.15 L = 0.05 M

    pH = -log 0.05 = 1.3. So you go that much correct.

    The pH at the equivalence point is when moles HCl = moles NaOH. Since you have a strong acid and a strong base, the pH at equivalence will be 7.

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