【Daily Question】Theoretical Foundation 2020.07.21
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Multiple-choice question: When equal volumes of HCl solution with pH=2 and NaOH solution with pH=13 are mixed together, what is the pH of the resulting solution? A. 7.00 B. 12.65 C. 3.00 D. 11.00 Answer: B Hint: Extra rewards will be given to those who can explain the solution process; the answer can be found in the response
PH is the negative logarithm of the hydrogen ion concentration. When the solutions are mixed, their volume doubles; therefore, the concentration of HCl is 0.005 M, while the concentration of NaOH is 0.05 M. Upon mixing, an acid-base reaction occurs, and the excess concentration of NaOH in the solution is c = (0.1 – 0.01)/2 = 0.045 mol.L-1. Thus, pH = 12.65