Page 77 - [B._MURPHY,_C._MURPHY,_B._HATHAWAY]_A_working_meth

Equilibrium II 61

1. K;,; Kh problems/ Aqueous Solution 4. Polyprotic
4 b
Common ion effect Equilibrium Questions acids - K;,(l),

+
5. Solubility product type questions - K,,
--
I-

Figure 5.3 Summary of numerical problem solving in aqueous solution type
equilibrium questions

The final two sections of this chapter contain a short multiple-choice
test, and three longer, more challenging questions. The only way of
becoming skilled at equilibrium type questions is to work through a
series of standard problems, applying the working method.

MULTIPLE-CHOICE TEST
1. The acid HA has an acid dissociation constant, Ka. The equili-
brium constant for the reaction, A- + H30+ + HA + H20, is:
(a) KalKw (b) 1/Ka (c) Ka (d) KwlKa
2. A sample of sea water was analysed in the laboratory to have a
pH = 8.32. What is the concentration of OH- ion in the sample
(in M)?
(a) 4.8 x (b) 5.68 (c) 2.1 x (d) -5.68
3. What is the molar solubility of MgF2, in 0.25 M NaF solution,
given that Ksp of MgF2 = 8 x M?
(a) 2.6 x (b) 5.1 x (c) 2 x (d) 1.3 x
4. pKa of HOCl = 7.46. What is the pH of a 0.35 M HOCl
solution?
(a) 3.96 (b) 0.46 (c) 0.87 (d) 7.46
5. The reaction 2Na(,] * Na2(,) has an equilibrium constant of
at 298 K. If 0.2 mol of Na(,) are introduced into a 1 dm3
volume at that temperature, the equilibrium pressure of Na(,) (in
bars) is (R = 0.08314 dm3 bar K-' mol-' ):
(a) 5.0 (b) 0.3 (c) 0.03 (d) 1.8