AP Chemistry 8.4: Acid-Base Mixtures

Practice AP Chemistry questions on predicting whether mixed acid-base solutions are acidic, basic, neutral, or buffered using species and proton-transfer equations.

Exam points

Explain how acid-base equilibria depend on proton transfer and conjugate pairs in solution.
Apply pH, pOH and equilibrium relationships to calculate concentrations and predict acid-base behavior.

[Maximum number: 1]

Methanoic acid, HCOOH, ionizes according to the equation above.

In aqueous solution, the compound $\mathrm{H}_{2} \mathrm{NNH}_{2}$ reacts according to the equation above. A 50.0 mL sample of $0.25 M \mathrm{H}_{2} \mathrm{NNH}_{2}(a q)$ is combined with a 50.0 mL sample of 0.25 M HCOOH(a q).

Is the resulting solution acidic, basic, or neutral? Justify your answer.

When a catalyst is added to a solution of HCOOH(a q), the reaction represented by the following equation occurs.

\mathrm{HCOOH}(a q) \rightarrow \mathrm{H}_{2}(g)+\mathrm{CO}_{2}(g)

For the correct answer and a valid justification: 1 point Acidic. The $\mathrm{K}_{a}$ of $\mathrm{H}_{2} \mathrm{NNH}_{3}{ }^{+}$ is greater than the $\mathrm{K}_{b}$ of $\mathrm{HCOO}^{-}$ , so the production of $\mathrm{H}_{3} \mathrm{O}^{+}$ (aq) occurs to a greater extent than the production of OH (aq). Total for part (d) 2 points

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8.4.A—Explain the relationship among the concentrations of major species in a mixture of weak and strong acids and… question 1