Problem: Calculate the pH at the halfway point and at the equivalence point for each of the following titrations.a. 100.0 mL of 0.10 M HC7H5O2 (Ka = 6.4 x 10-5) titrated by 0.10 M NaOH

FREE Expert Solution

a. at half equivalence point

  • At half equivalence point for weak species + strong species, the moles of each species are equal
  • Therefore, pH is equal to the pKa 

pH = pKa = -log(Ka)

pH = - log (6.4x10-5) = 4.19


b. at equivalence point

  • The pH will be determined by the c.base (C7H5O2-) produced by the reaction.
  • If both species (weak and strong) have the same concentration, the concentration of the conjugate species is half of the concentration:

0.1 M → 0.05 M

Calculating the pH:

(1) Setup an ICE chart:

(2) Setup Kb expression

Kb=productsreactants=[OH-][HC7H5O2][C7H5O2-]


Solving for x = [OH-]


Kb = KwKa=1x10-146.4x10-5=1.56x10-10Kb=1.56x10-10=[OH-][HC7H5O2][C7H5O2-]1.56x10-10=[x][x][0.05 - x], ignore -x:[C7H5O2-]Kb>5001.56x10-10(0.05)=x2x = 1.56x10-10(0.05)


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Problem Details

Calculate the pH at the halfway point and at the equivalence point for each of the following titrations.

a. 100.0 mL of 0.10 M HC7H5O2 (Ka = 6.4 x 10-5) titrated by 0.10 M NaOH

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What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the Equivalence Point concept. If you need more Equivalence Point practice, you can also practice Equivalence Point practice problems.

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Based on our data, we think this problem is relevant for Professor Campbell's class at Tufts University.

What textbook is this problem found in?

Our data indicates that this problem or a close variation was asked in Chemistry: An Atoms First Approach - Zumdahl Atoms 1st 2nd Edition. You can also practice Chemistry: An Atoms First Approach - Zumdahl Atoms 1st 2nd Edition practice problems.