Thermodynamics and Chemistry

CHAPTER 10 ELECTROLYTE SOLUTIONS

PROBLEMS 301

Problems

An underlined problem number or problem-part letter indicates that the numerical answer appears

in AppendixI.

10.1 The mean ionic activity coefficient of NaCl in a 0.100 molal aqueous solution at298:15K

has been evaluated with measurements of equilibrium cell potentials,^4 with the result ln (^) D
0:2505. Use this value in Eq.10.6.9, together with the values of osmotic coefficients in Table
10.1, to evaluate (^) at each of the molalities shown in the table; then plot (^) as a function of
mB.
Table 10.1 Osmotic coefficients of aqueous NaCl at
298:15Ka
mB=mol kg^1 m mB=mol kg^1 m
0.1 0.9325 2.0 0.9866
0.2 0.9239 3.0 1.0485
0.3 0.9212 4.0 1.1177
0.5 0.9222 5.0 1.1916
1.0 0.9373 6.0 1.2688
1.5 0.9598
aRef. [ 31 ].
10.2 Rard and Miller^5 used published measurements of the freezing points of dilute aqueous so-
lutions of Na 2 SO 4 to calculate the osmotic coefficients of these solutions at298:15K. Use
their values listed in Table10.2to evaluate the mean ionic activity coefficient of Na 2 SO 4 at
298:15K and a molality ofmBD0:15mol kg^1. For the parameterain the Debye–Huckel ̈
equation (Eq.10.4.7), use the valueaD3:0 10 ^10 m.
Table 10.2 Osmotic coefficients of aqueous Na 2 SO 4
at298:15K
mB=mol kg^1 m mB=mol kg^1 m
0.0126 0.8893 0.0637 0.8111
0.0181 0.8716 0.0730 0.8036
0.0228 0.8607 0.0905 0.7927
0.0272 0.8529 0.0996 0.7887
0.0374 0.8356 0.1188 0.7780
0.0435 0.8294 0.1237 0.7760
0.0542 0.8178 0.1605 0.7616
0.0594 0.8141
(^4) Ref. [ 145 ], Table 9.3. (^5) Ref. [ 141 ].