【Daily Question】Theoretical Foundation 2020.07.23
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Multiple-choice question: When a 0.1 molL-1 HAc solution is diluted by half, which of the following statements is correct? ( ) A. The degree of dissociation of HAc increases ； B. The concentration of relevant ions in the solution increases ； C. The dissociation constant of HAc increases ； D. The pH value of the solution decreases. Answer: A. Hint: Extra rewards will be given to those who can explain the solution process; the answer can be seen in the response
A. Correct. Explanation: A. Diluting acetic acid promotes its ionization. Therefore, A is correct ； B. When acetic acid is diluted, its ionization is promoted; as a result, the amount of acetate ions and hydrogen ions increases while the amount of acetic acid molecules decreases. However, the increase in the amount of acetate ions and hydrogen ions is less than the increase in the volume of the solution. Therefore, the concentrations of acetate ions, hydrogen ions, and acetic acid molecules all decrease, whereas the concentration of hydroxide ions increases. Hence, B is incorrect ； C. The ionization equilibrium constant of acetic acid depends only on temperature; when the temperature remains constant, the ionization equilibrium constant of acetic acid also remains constant, hence C is incorrect ； D. Diluting acetic acid with water promotes its ionization; as a result, the amount of hydrogen ions increases while the amount of acetic acid molecules decreases. Therefore, D is incorrect ； Therefore, the answer is A