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# Problems

Author: John Hutchinson

 Problem 1 Strong acids have a higher percent ionization than do weak acids. Why don't we use percent ionization as a measure of acid strength, rather than Ka? Problem 2 Using the data in table 4 for nitrous acid, plot [H3O+] versus c0, the initial concentration of the acid, and versus [HNO2] the equilibrium concentration of the acid. On a second graph, plot [H3O+]2 versus c0, the initial concentration of the acid, and versus [HNO2] the equilibrium concentration of the acid. Which of these results gives a straight line? Using the equilibrium constant expression, explain your answer. Problem 3 Using Le Châtelier's principle, explain why the concentration of [OH-] is much lower in acidic solution than it is in neutral solution. Problem 4 We considered mixing a strong base with a weak acid, but we did not consider mixing a strong acid with a weak acid. Consider mixing 0.1M HNO3 and 0.1M HNO2. Predict the pH of the solution and the percent ionization of the nitrous acid. Rationalize your prediction using Le Châtelier's principle. Problem 5 Imagine taking a 0.5M solution of nitrous acid and slowing adding water to it. Looking at table 3, we see that, as the concentration of nitrous acid decreases, the percent ionization increases. By contrast, [H3O+] decreases. Rationalize these results using Le Châtelier's principle. Problem 6 We observed that mixing a strong acid and a strong base, in equal amounts and concentrations, produces a neutral solution, and that mixing a strong base with a weak acid, in equal amounts and concentrations, produces a basic solution. Imagine mixing a weak acid and a weak base, in equal amounts and concentrations. Predict whether the resulting solution will be acidic, basic, or neutral, and explain your prediction. Problem 7 Using the electronegativity arguments presented above, explain why, in general, compounds like M-O-H are bases rather than acids, when M is a metal atom. Predict the relationship between the properties of the metal atom M and the strength of the base MOH. Problem 8 Ionization of sulfuric acid H2SO4 produces HSO4-, which is also an acid. However, HSO4- is a much weaker acid than H2SO4. Using the conclusions from above, explain why HSO4- is a much weaker acid. Problem 9 Predict and explain the relative acid strengths of H2S and HCl. Predict and explain the relative acid strengths of H3PO4 and H3AsO4. Problem 10 Using arguments from above, predict and explain the relative acidity of phenol and methanol.

Last Update: 2011-04-07