17. Acid and Base Equilibrium

State whether each of the following statements is true or false. Justify your answer in each case. (a) Sulfuric acid is a monoprotic acid.

Which of the following pictures represents a solution of a weak diprotic acid, H2A? (Water molecules have been omitted for clarity.) Which pictures represent an impossible situation? Explain.

(a)

(b)

(c)

(d)

Calculate the pH of each of the following solutions (Ka and Kb values are given in Appendix D): (b) 0.100 M hydrogen chromate ion 1HCrO4-2

Rainwater is acidic because CO21g2 dissolves in the water, creating carbonic acid, H2CO3. If the rainwater is too acidic, it will react with limestone and seashells (which are principally made of calcium carbonate, CaCO3). Calculate the concentrations of carbonic acid, bicarbonate ion 1HCO3-2 and carbonate ion 1CO32 - 2 that are in a raindrop that has a pH of 5.60, assuming that the sum of all three species in the raindrop is 1.0 * 10-5 M.

The pH of a particular raindrop is 5.6. (b) What experiments could you do to test the hypothesis that the rain also contains sulfur-containing species that contribute to its pH? Assume you have a large sample of rain to test.

Write balanced net ionic equations and the corresponding equilibrium equations for the stepwise dissociation of the diprotic acid H2SeO4.

Calculate the pH and the concentrations of all species present (H2CO3, HCO3-, CO32-, H3O+ , and OH-) in 0.010 M H2CO3 1Ka1 = 4.3 * 10-7; Ka2 = 5.6 * 10-112.

Calculate the concentrations of H3O+ and SO4 2- in a solution prepared by mixing equal volumes of 0.2 M HCl and 0.6 M H2SO41Ka2 for H2SO4 is 1.2 * 10-22.

Write chemical equations and corresponding equilibrium expressions for each of the two ionization steps of carbonic acid.

Calculate the [H3O+] and pH of each polyprotic acid solution. b. 0.350 M H2C2O4

The following observations are made about a diprotic acid H2A: (i) A 0.10 M solution of H2A has pH = 3.30. (ii) A 0.10 M solution of the salt NaHA is acidic. Which of the following could be the value of pKa2 for H2A: (i) 3.22, (ii) 5.30, (iii) 7.47, or (iv) 9.82?

Calculate the concentration of all species in a 0.155 M solution of H2CO3.

Atmospheric CO2 levels have risen by nearly 20% over the past 40 years from 320 ppm to 400 ppm. (a) Given that the average pH of clean, unpolluted rain today is 5.4, determine the pH of unpolluted rain 40 years ago. Assume that carbonic acid 1H2CO32 formed by the reaction of CO2 and water is the only factor influencing pH. CO21g2 + H2O1l2 Δ H2CO31aq2