An aqueous solution of acetic acid solution [CH3CO2H(aq)] has a pH of 3.25. Which of these substances raises the pH of the solution upon addition?

Question

BlackTom AI · Accepted Answer

To determine which substance raises the pH of an acidic solution, we need to consider how each additive affects acidity and the overall proton balance in solution.
Option 1: HCO2H (formic acid) is a weak acid. Adding more of a weak acid to an acidic solution tends to increase the concentration of H+, unless it also shifts equilibrium in a way that reduces H+, but for a standalone addition, it would typically not raise pH and may even lower it depending on buffering, so this choice is unlikely to raise pH.
Option 2: CH3CO2Na (sodium acetate) is a salt containing the conjugate base of acetic acid (CH3CO2–). When dissolved, it hydrolyzes to form acetate ions that can accept protons (acting as a weak base) and water, producing OH– in the process. In an acetic acid solution, adding acetate shifts the equilibrium toward consumption of H+ to form acetic acid, thereby increasing pH. This is the classic buffer and base-augmenting behavior.
Option 3: HCl (hydrochloric acid) is a strong acid. Adding a strong acid to an already acidic solution will increase the concentration of H+, thus lowering the pH, not raising it.
Option 4: NaCl (sodium chloride) is a neutral salt from a strong acid and a strong base. In pure water it has negligible effect on pH; in an acidic solution, it does not provide a conjugate base or acid that would neutralize H+ significantly, so its effect on pH would be minimal or neutral rather than raising it.
Overall, the only additive that can raise the pH of an acidic acetic acid solution by supplying conjugate base that consumes protons is CH3CO2Na, due to its basic acetate ion component capable of buffering and reducing free H+.

Chem 1C General Chemis... Self Assessment Quiz 16

An aqueous solution of acetic acid solution [CH3CO2H(aq)] has a pH of 3.25. Which of these substances raises the pH of the solution upon addition?

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