I. Multiple Choice (60 points) Select the best response for each of the following and record on the Scantron. Do not erase; erasures may result in a misgrading of your response.
1. A sample of sea water is known to contain the following ions: Ca2+, Na+, K+, NO3-, Cl-, CO32-, and SO42-. What prediction can be made about the sample?
a. the sample contains a precipitate
b. the solution has a (nearly) neutral pH
c. the sample is a blue color
d. the solution is definitely acidic
e. the solution is definitely basic
2. Consider a solution of bicarbonate ion, HCO3-(aq). Added to the solution is a lower molar concentration of OH-. Which of the following occurs as a result?
a. the pH decreases
b. the molar concentration of H3O+ increases
c. the molar concentration of HCO3- increases
d. the molar concentration of HCO3- decreases and the molar concentration of CO32- increases
e. the solution consists of a mixture of HCO3- and OH-, but at lower concentrations
3. The pH at the stoichiometric (equivalence) point of a hydrocyanic acid/sodium hydroxide titration is
a. =7, because only spectator ions are present in the system
b. >7, because sodium hydroxide is used in the titration
c. >7, because HCN is a very weak acid
d. >7, because cyanide ions are present in the system
e. <7, because of the excess hydrocyanic acid present in the system
4. The solubility for all of the following slightly soluble salts is increased with the addition of acid except:
a. AgCl(s)
b. CaCO3(s)
c. Fe(OH)3(s)
d. BaF2(s)
e. Ca3(PO4)2(s)
5. Consider the weak acid equilibrium: HF(aq) + H2O(l) « H3O+(aq) + F-(aq)
Which of the following will result in an increase of the pH of the solution?
a. addition of HCl(aq)
b. addition of H2O
c. precipitation of F-(aq)
d. addition of NaF(aq)
e. addition of NaCl(aq)
6. Which of the following mixtures does not result in the formation of a buffer system?
a. a 1:1 mole ratio of CH3COOH and CH3CO2-
b. a 2:1 mole ratio of CH3COOH and NaOH
c. a 1:1 mole ratio of NH4Cl and NH3
d. a 1:1 mole ratio of CH3COOH and NaOH
e. all of the above produce a buffer solution
7. One of the following acids (along with its conjugate base) is not suitable for preparing a buffer solution with a pH of 4.50. Which one?
a. p-chlorobenzoic acid, Ka = 1.1 x 10-4
b. formic acid, Ka = 1.8 x 10-4
c. benzoic acid, Ka = 6.3 x 10-5
d. hydrofluoric acid, Ka = 3.5 x 10-4
e. acetic acid, Ka = 1.8 x 10-5
8. Which of the following aqueous solutions is predicted to be neutral (i.e., pH = 7)?
a. a 1:1 mole ratio of FeCl3 and NaCl
b. a 1:1 mole ratio of HCl and NaOH
c. a 1:1 mole ratio of H2SO4 and KOH
d. a 1:1 mole ratio of NH4Cl and NH3
e. a 1:1 mole ratio of K3PO4 and HCl
9. Which of the following solutions has a pH nearest to 7.00 at 25°C?
a. 0.010 M Ba(OH)2
b. 0.010 M KOH
c. 0.010 M HClO
d. 0.010 M HCl
e. 0.010 M H2SO4
10. Equal moles of nitrous acid, HNO2, Ka = 4.6 x 10-4, and sodium nitrite, NaNO2, are mixed to form 500 mL of solution. What is the pH of the solution?
a. 7
b. 10.66
c. 4.6
d. 3.34
e. need exact number of moles of each reagent
11. Equal moles of nitric acid, HNO3, and sodium nitrate, NaNO3, are mixed to form 500 mL of solution. What is the pH of the solution?
a. 7
b. 10.66
c. 4.6
d. 3.34
e. need exact number of moles of each reagent
12. In a sample of pure water, the one statement that is always true at all conditions of temperature and pressure is
a. [OH-] = 1.0 x 10-7 mol/L
b. [H3O+] = 1.0 x 10-7 mol/L
c. [H3O+] = [OH-]
d. pH = 7.0
e. all of the above are always true
13. pH
a. is an abbreviation for a new anti-histamine called "phog Horn"
b. the abbreviation for the new action figure hero, "punk Hunk"
c. refers to the film clips shown during the intermission of a new film, "porno Highlights"
d. is code for Washington insiders, meaning "poor Hillary"
e. is –log [H3O+]
II. Completion. (16 points) Complete the following table.
Predict whether the pH of the
following salt solutions will be equal to, greater than, or less
than 7 at 25°C.
If the pH is >7 or <7, write an equation justifying
your decision.
| Salt(aq) | pH =7, >7, <7 |
Equation to Justify pH |
| KCN | >7 |
CN- + H2O « HCN + OH- |
| Ba(NO3)2 | =7 |
No equation |
| K3PO4 | >7 |
PO43- + H2O « HPO42- + OH- |
| FeCl3 | <7 |
Fe(H2O)3+ + H2O « H3O+ + FeOH2+ |
III. Exercises. (90 points) All work must be shown clearly and legibly in order to receive credit. Answers, without a logical presentation, will receive only 10% credit.
1. (40 points) The buffer solution of hydrojavelinic acid, HJa, and potassium javelinate, KJa, is very versatile for the research performed at this university and South Texas. Ka of HJa is 1.0 x 10-5
a. (15 pts) What is the pH of a solution that is 0.800 M HJa and 0.400 M KJa?
pH = 4.70
b. (15 pts) A 0.120 mole amount of HCl(aq) is inadvertently added to 400 mL of the solution in part a. What is the resulting pH and DpH of the solution? Assume no volume change.
pH = 3.96; DpH = 0.74
c. (10 pts) What must be the [Ja-]/[HJa] in the preparation of a buffer solution with a pH of 4.66?
[Ja-]/[HJa] = 0.46 / 1.00
2. (20 points) A 10.0 mL sample of 0.800 M HJa, hydrojavelinic acid is titrated with 0.500 M LiOH. Ka of HJa is 1.0 x 10-5
a. (5 pts) What volume of titrant, 0.500 M LiOH, is necessary to reach the stoichiometric (equivalence) point in the titration?
16.0 mL
b. (15 pts) What is the expected pH after the addition of 10.0 mL of 0.500 M LiOH?
pH = 5.22
3. (15 points) A 50.0 mL volume of 1.20 M HCl is mixed with 75.0 mL of 0.600 M KOH. What is the pH of the resulting solution?
pH = 0.92
4. (15 points) Sodium carbonate, Na2CO3, is used in laundry detergent formulations. If 15.9 g Na2CO3 (molar mass = 106.0 g/mol) is dissolved in 1.50 L of solution, what is the resulting pH of the solution? Ka2 of H2CO3 is 5.6 x 10-11.
pH = 11.63