【Daily Question】Theoretical Foundation 2020.07.26
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Multiple-choice question: In an acetic acid solution, adding an appropriate amount of solid NaAc will result in ( ). A. The pH value of the solution increases. B. The pH value of the solution decreases. C. The dissociation constant of acetic acid increases. D. The dissociation constant of acetic acid decreases. Answer: A. Hint: Extra rewards will be given to those who can explain the solution process; the answer can be found in the response
Choose A； Sodium acetate is a salt of a strong base and a weak acid; it exhibits basic properties in solution, so the pH value of the entire solution increases ； The dissociation constant of acetic acid is simply a constant that does not change upon the addition of sodium acetate.
First, write the ionization equation: NaAC = Na+ + Ac-. Then, the hydrolysis equation is Ac- + H2O ⇌ HAc + OH-. After adding sodium acetate, the concentration of acetate ions increases significantly, which promotes hydrolysis. Although more acetic acid ions are hydrolyzed, this cannot offset the increase; in other words, the increase is much greater than that caused by hydrolysis, so the concentration of acetic acid ions continues to rise, and thus the amount of acetic acid also increases. Sodium ions also increase.