A 50.0-mL sample of a 0.100 M solution of a weak acid HA has an equilibrium pH of 4.00. After 1.0 × 10^-3mol of a substance X is added to the solution, it is observed that the pH of the solution increases. What might be true about substance X? I. X might be a strong base that partially neutralized some weak acid.
II) X might be a strong acid that made the solution more acidic.
III) X might be a soluble ionic compound containing the anion A^-.

Question

Quizplus · Accepted Answer

Since the addition of substance X increased the pH, it must have decreased the concentration of H+ ions in the solution. One possible way for substance X to do this is by reacting with some of the weak acid HA to form its conjugate base A- and some other compound. This reaction would consume H+ ions, leading to an increase in pH. This scenario is consistent with choice I, which suggests that X might be a strong base that partially neutralized some weak acid. It is also possible that substance X could have reacted with water to produce OH- ions, which would then react with H+ ions from the weak acid to form water molecules. This reaction would also consume H+ ions and lead to an increase in pH. This scenario is consistent with choice III, which suggests that X might be a soluble ionic compound containing the anion A^-. Examples of such compounds could include hydroxides of alkali or alkaline earth metals. Choice II is incorrect because the addition of a strong acid would make the solution more acidic, not less acidic.

A 500-ML Sample of a 0