Questions 32-34 refer to the following. 5 H2O2(aq) + 2 MnO4 −(aq) + 6 H+(aq) → 2 Mn2+(aq) + 8 H2O(l) — Acids and Bases Chemistry Question

STEPS:

1. Identify the role of $\text{H}^+$ in the chemical equation: Locate the hydrogen ions in the balanced chemical equation:
$$5\text{ H}_2\text{O}_2(aq) + 2\text{ MnO}_4^-(aq) + \mathbf{6\text{ H}^+(aq)} \rightarrow 2\text{ Mn}^{2+}(aq) + 8\text{ H}_2\text{O}(l) + 5\text{ O}_2(g)$$
Because $\text{H}^+$ is on the reactant side of the equation, these ions must be consumed as the titration proceeds.
2. Relate consumption to ion concentration: As the reaction proceeds forward, $\text{H}^+$ ions are continuously used up to produce water. Consequently, the concentration of hydrogen ions ($[\text{H}^+]$) in the Erlenmeyer flask steadily decreases.
3. Understand the relationship between acidity and pH: Acidity is determined by the concentration of free hydrogen ions; a lower concentration of $[\text{H}^+]$ means the solution is less acidic. Mathematically, pH is defined as:
$$\text{pH} = -\log[\text{H}^+]$$
Because of the negative sign in the logarithmic definition, a decrease in the concentration of $[\text{H}^+]$ causes the pH to increase.
4. Formulate the final conclusion: As $\text{H}^+$ ions are consumed, the solution becomes less acidic and the pH increases. This corresponds to Option C.

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WHY_OTHERS_WRONG:

• A is incorrect: Although $\text{Mn}^{2+}$ ions are produced, highly diluted transition metal cations with a $+2$ charge under strongly acidic conditions do not significantly contribute to or maintain the overall acidity of the solution. The pH is governed by the concentration of free strong acid hydronium ions, which are being consumed.
• B is incorrect: While water is indeed produced as a product, the small volume of water generated by the reaction is far too minor to act as a significant diluent, and dilution of an acidic solution can only pull the pH closer to neutral ($7.0$), never making it basic.
• D is incorrect: This option correctly identifies that the consumption of $\text{H}^+$ ions makes the solution less acidic, but it makes a mathematical error by stating that the pH decreases. A less acidic solution with a lower $[\text{H}^+]$ concentration must have a higher pH.