Unit 8 – Equilibrium
Section 3 – Acid Base Equilibrium
The Autoionization of Water
1. How does water behave as both an acid and a base?
2. What is the Kw for water at 25 ºC?
3. Calculate the [OH-] for each of the following solutions at 25 ºC;
indicate if the solution is acidic, basic, or neutral.
a. [H+] = 0.0045 M
b. [H+] = 1.5 x 10-9 M
c.
[H+] = 0.00002 M
Strong Acids and Bases (Memorize the strong acids and bases.)
4. If NaOH is added to water, how does the [H+] change? How does the pH change?
5. The average pH of blood is about 7.5. Calculate the [H+], [OH-], and pOH. (Assume temp is 25 ºC.)
6. Determine the pH of each solution. Tell whether the solution is acidic, basic, or neutral.
a. [H+] = 1.0 x 10-10 M pH =
b. [H+] = 2.0 X 10-7 M pH =
c.
[OH-] = 3.0 X 10-2 M pH =
d. [OH-] = 1.0 X 10-7 M pH =
Weak Acids and Bases (Ka and Kb calculations)
7. The pH of a 0.400 M solution of iodic acid, HIO 3, is 0.726 at 25°C. What is the Ka at this temperature?
8. The pH of a 0.150 M solution of hypochlorous acid, HClO, is found to be 4.55 at 25°C. Calculate the Ka for HClO
at this temperature.
9. The compound propylamine, CH3CH2CH2NH2, is a weak base. At equilibrium, a 0.039 M solution of propylamine
has an OH- concentration of 3.74 x 10-3 M. Calculate the pH of this solution and Kb for propylamine.
10. Hydrazoic acid, HN3, is a weak acid. The [H3O+] of a 0.102 M solution of hydrazoic acid is 1.39 x 10-3 M.
Determine the pH of this solution, and calculate Ka at 25°C for HN3.
11. Bromoacetic acid, BrCH2COOH, is a moderately weak acid. A 0.200 M solution of bromoacetic acid has a H3O+
concentration of 0.0192 M. Determine the pH of this solution and the Ka of bromoacetic acid at 25°C.
Acidity of Salt Solutions
12. Predict whether an aqueous solution would be acidic, basic, or neutral.
a. sodium nitrate NaNO3
b. ammonium iodide NH4I
c. sodium bicarbonate NaHCO3
d. ammonium cyanide NH4CN
e. sodium hypochlorite NaOCl
f. potassium acetate KCH3CO2
Acid and Base Character and Structure
13. How does the acid strength of an oxyacid depend on the electronegativity of the central atom?
14. How does the acid strength of an oxyacid depend on the number of nonprotonated oxygen atoms on the
molecule?
15. How does the acid strength depend on the polarity of the H—X bond?
16. Explain the following observations:
a. HNO3 is a stronger acid than HNO2
b. H2S is a stronger acid than H2O
c. H2SO4 is a stronger acid than HSO4d. CCl3COOH is a stronger acid than CH3COOH
Practice AP Question
17. Answer the following questions about acetylsalicylic acid, the active ingredient in aspirin.
a. The amount of acetylsalicylic acid in a single aspirin tablet is 325 mg, yet the tablet has a mass of 2.00 g.
Calculate the mass percent of acetylsalicylic acid in the tablet.
b. The elements contained in acetylsalicylic acid are hydrogen, carbon, and oxygen. The combustion of
3.000 g of the pure compound yields 1.00 g of water and 3.72 L of dry carbon dioxide, measured at 750.
mm Hg and 25° C. Calculate the mass, in g, of each element in the 3.000 g sample.
c.
A student dissolved 1.625 g of pure acetylsalicylic acid in distilled water and titrated the resulting
solution to the equivalence point using 88.43 mL of 0.102 M NaOH(aq). Assuming that acetylsalicylic
acid has only one ionizable hydrogen, calculate the molar mass of the acid.
d. A 2.00 x10-3 mole sample of pure acetylsalicylic acid was dissolved in 15.00 mL of water and then
titrated with 0.100 M NaOH(aq). The equivalence point was reached after 20.00 mL of the NaOH
solution had been added. Using the data from the titration, shown in the table below, determine
i.
the value of the acid dissociation constant, Ka, for acetylsalicylic acid
ii.
the pH of the solution after a total volume of 25.00 mL
of the NaOH solution had been added (assume that
volumes are additive)