How to Solve Acid-base Titration Related Problems ─ Part 1

An acid–base reaction can be used to determine pH via titration.


pH is a logarithmic scale used to specify the acidity or basicity of aqueous solutions.

Acidic solutions (with higher concentrations of hydrogen (H+) cations) are measured to have lower pH values than basic or alkaline solutions. The neutral pH is 7. A 𝑝𝐻 meter may be used for a precise and accurate measurement of the 𝑝𝐻 of a solution.

Titrations are quantitative neutralization reactions between acids and bases.

The equivalence point, or stoichiometric point, of a chemical reaction is the point at which chemically equivalent quantities of reactants have been mixed. The endpoint refers to the point at which the indicator changes color in a colorimetric titration. The endpoint is related to the equivalence point, but these two are not necessarily the same.

Four combinations of strong and weak (monoprotic) acid and (monohydroxy) base are possible.

Polyprotic acid titrations have more than one equivalence or stoichiometric points.

A buffer solution is a solution where the pH does not change significantly on dilution or if an acid or a base is added at constant temperature.

Question:


Concentration (M)

pH

Acid 1

Acid 2

Acid 3

Acid 4

0.0010

3.87

3.00

3.17

3.94

0.0050

3.52

2.30

2.82

3.59

0.010

3.37

2.00

2.67

3.44

End point pH for

0.0010 M solution

5.79

7.00

7.93

8.84

Based on the table above, answer the following:

  1. Which one is the strongest acid?
  2. Will a mixture of 50.0 mL of 0.010 M acid 2 produce an effective buffer solution with 25.0 mL of 0.010 M NaOH?
  3. Which acid is most likely polyprotic if each acid is titrated with NaOH to the endpoint?

Solution:



Click/tap to enlarge the image

NOTE: A strong acid is completely ionized and the molar concentration is equal to the [H+].

* assuming it’s a weak acid

Thrilling or terrifying titrations❓ Let Chemaficionado know in the comments below or at mychemistryhomework@gmail.com❗

References:

(1)    Equivalence point. Wikipedia. https://en.wikipedia.org/wiki/Equivalence_point.
(2)    Wikipedia Contributors. Buffer solution. Wikipedia. https://en.wikipedia.org/wiki/Buffer_solution.
(3)    Wikipedia Contributors. pH. Wikipedia. https://en.wikipedia.org/wiki/PH.

‌(4)    Jespersen, N. D.; Barron's Educational Series, Inc. Barron’s AP Chemistry; Barron’s Educational Series: Hauppauge, N.Y., 2012.

‌(5)    Brown, C.; Ford, M. Higher Level Chemistry, 2nd ed.; Pearson Education: Harlow, Essex, 2014.

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