SCH 4U Acid-Base Equilibrium

Student Name

Total 30

CLEARLY MARK THE LETTER OF THE BEST ANSWER.

1. Which of the following 0.10 mol/L aqueous solutions gives the lowest pH?

a) CH3COOH (pKa = 4.75) d) H3PO4 (pKa1 = 2.12)

b) HIO3 (pKa = 0.77) e) HF (pKa = 3.45)

c) Since all are acids, the pH is the same for all solutions.

2. What is the pH of 0.010 mol/L HCN(aq) (Ka = 4.9 10-10)?

a) 5.65 c) 4.65 e) 9.31 b) 2.00 d) 6.69

3. When 500 mL of 0.120 mol/L KOH (aq) is mixed with 500 mL of 0.0480 mol/L Ba(OH)2 (aq),

the pH of the resulting solution is

a) 13.03 c) 14.00 e) 13.23 b) 12.92 d) 13.33

4. Which of the following is a strong acid?

a) HF b) H3PO4 c) HCl d) H2CO3

5. For the following reaction, which of the following is a conjugate acid-base pair?

HC2O4-1 (aq) + H2O (l) H3O+1 (aq) + C2O4

2- (aq)

a) HC2O4-1 and H2O c) H2O and C2O4

2-

b) HC2O4-1 and H3O+1 d) HC2O4

-1 and C2O42-

6. In the following reaction, which is a Brønsted-Lowry base?

HC2O4-1 (aq) + H2O (l) H3O+1 (aq) + C2O4

2- (aq)

a) HC2O4-1 b) H2O c) H3O+1 d) None of these

7. When KNO2 is dissolved in water, which of the following is the principal acid-base equilibrium?

a) K(H2O)6+(aq) K(H2O)5OH(aq) + H+(aq)

b) HNO2(aq) H+ (aq) + NO2- (aq)

c) NO2- (aq) + H2O(l) HNO2(aq) + OH- (aq)

d) NO2- (aq) + H2O(l) HNO3(aq) + H+ (aq)

8. A Brønsted-Lowry base is defined as a substance that

a) acts as a proton donor.b) increases [H+] when placed in water.c) acts as a proton acceptor.d) decreases [H+] when placed in water.

9. For the following reaction, which of the following is a conjugate acid-base pair?

H2PO4- (aq) + NH3 (aq) HPO4

2- (aq) + NH4+ (aq)

a) H2PO4- and NH3

b) HPO42- and NH4

+

c) H2PO4- and HPO4

2-

d) None of the above

10. Which of the following reactions corresponds to hydrolysis of NH4+ in water

solution?

a. NH4+ (aq) + OH– (aq) NH3(aq) + H2O(l)

b. NH4+ (aq) + H2O(l) NH3(aq) + H3O+(aq)

c. NH4+ (aq) + H2O(l) NH5

2+(aq) + OH–(aq)d NH4

+ (aq) NH2+(aq) + H2(g)

11. What is the conjugate base of HCO3-1?

a) OH-1 c) H2CO3 e) CO32–

b) HCO3+ d) H3CO3

+

12. What is the pH of an aqueous solution at 25.0oC in which [OH-] is 0.00250 mol/L.

a) +2.60 c) –2.60 e) +11.4 b) –11.4 d) –2.25

13. The magnitude of Kw indicates that __________.

a) water autoionizes very slowlyb) water autoionizes very quicklyc) water autoionizes only to a very small extentd) the autoionization of water is exothermice) water autoionizes completely

14. Which of the following solutes, when dissolved in water to 1.0 mol/L, gives the solution with the highest pH?

a) HNO2 c) NaNO2 e) HCl b) NaCl d) NH4Cl

15. The pH of a 0.0025 mol/L aqueous solution of calcium hydroxide, Ca(OH)2, is:

a) 11.70 c) 12.40 e) 11.10 b) 12.00 d) 2.30

16. The pH of 0.20 mol/L CH3NH2 (aq) is 11.93. What is the value of Kb for CH3NH2?

a) 8.5 × 10-3 c) 1.4 × 10-5 e) 7.2 × 10-5 b) 1.7 × 10-3 d) 3.8 × 10-4

17. The pH of 1.0 mol/L HCO2H(aq) is 1.88. What is the percent ionization of HCO2H?

a) 1.3% c) 1.8% e) 13% b) 50% d) 94%

18. Which of the following is the strongest acid?

a) HClO2 (pKa = 2.00) c) HF (pKa = 3.46) e) HNO2 (pKa = 3.34)b) HCN (pKa = 9.32) d) CH3COOH (pKa = 4.75)

19. The solution at the equivalence point in a titration of 0.10 mol/L NH3(aq) with 0.10 mol/L HCl(aq) is best described as:

a) a solution of pH = 7.00 d) a 0.10 mol/L solution of NH4Clb) a 0.050 mol/L solution of NH4Cl e) a 1:1 buffer solutionc) a solution containing equal concentrations of NH3 and NH4Cl

20. If one were to prepare a buffer solution using pyridine (C5H5N, Kb = 1.8 × 10-9 ) and pyridinium chloride (C5H5NHCl), its pH would be in the approximate range:

a) 7.7 to 9.7 c) 4.3 to 6.3 e) 2.9 to 4.9 b) 9.3 to 11.3 d) 11.1 to 13.1

21. If the pH of a solution of a salt is 5.0, the salt must be one which could be formed from the neutralization of

a) a strong acid and a strong base. c) a weak acid and a strong base.b) a strong acid and a weak base. d) HCl and NaOH.

22. Which indicator (identified by a letter) could be used to titrate aqueous NH3 (Kb = 1.8 x 10-5) with HCl solution of equal concentration?

Indicator Colour Range Color-Change pHa) Pink-yellow 1.2 - 2.8b) Blue-yellow 5.2 – 6.2c) Yellow-purple 6.5 - 7.8d) Colorless-red 8.3 - 9.9e) none of these

23. The following titration curve is the kind of curve expected for the titration of a ____ acid with a ____ base.

a) strong, strong b) weak, strong c) strong, weak d) weak, weak e) none of these

24. What is the hydronium ion concentration in a solution which has [OH-1] = 1.0 x 10- 2 mol/L?

a) 1.0 x 10-12 mol/L c) 1.0 x 10-2 mol/L e) 1.0 x 10-16 mol/Lb) 12 mol/L d) 1.0 x 10-7 mol/L

25. Identify the INCORRECT statement:

a) As the pH increases the hydroxide ion concentration decreases. b) As the pH increases the hydronium ion concentration decreases. c) As the pH increases the Kw of water remains the same. d) As the pH increases the product [H3O+][OH-] remains constant. e) As the pH increases the solution becomes less acidic and more alkaline.

26. Calculate the pH of a 0.136 mol/L solution of aqueous sodium fluoride, NaF. (HF has a Ka value of 3.5 × 10-4)

a) 2.16 c) 5.71 e) 8.30 b) 8.73 d) 11.84

27. Which of the following can behave as a Brønsted-Lowry acid or as a Brønsted-Lowry base in aqueous solution?

a) HSO3-1 b) NH3 c) HI d) H3PO4

28. What is the hydroxide ion concentration and pH for the hydrochloric acid solution that has a hydronium ion concentration of 1.50 x 10-4 mol/L?

a) 6.67 x 10-10 mol/L, 4.82 c) 6.67 x 10-10 mol/L, 9.18 b) 6.67 10-11 mol/L, 3.82 d) 6.67 10-11 mol/L, 10.18

29. If the auto-dissociation constant of water, Kw, at 40°C is 2.92 × 10-14 then what is [H+] for a neutral solution in water at 40 °C?

a) 1.00 x 10-7 mol/L c) 1.00 x 10-14 mol/Lb) 2.92 x 10-14 mol/L d) 1.71 x 10-7 mol/L

30. What is the pH of 0.10 mol/L sodium acetate (NaAc) solution? The Ka of acetic acid (HAc) is 1.8 x 10-5.

a) 1.0 c) 0.10 e) 7.0b) 8.9 d) 5.1