Page 146 - Modern physical chemistry

Problems 137

6.2 Hydrogen, bromine, and hydrogen bromide are mixed. How many components does the
system possess ( a) before and (b) after equilibrium is set up? (c) Salt AlCl 3 is added to water.
How many components are there?
6.3 The freezing point of solutions of tin in lead was found to vruy with the percentage of tin
as shown in table 6.A.

TABLE 6.A
wtO!6 0 10 20 30 40 50 60 70 80 90 100

t,OC 326 295 276 262 240 220 190 185 200 216 232

Plot the data and graphically estimate the composition and temperature at the eutectic point.
6.4 Calculate the melting point of acetic acid at 10.0 atm if at 1.00 atm the melting point is 16.610
C, the heat of fuSion, 180.8 J g'!, and the specific volumes of liquid and solid phases are
0.9315 and 0.7720 cm 3 go!, respectively.
6.5 The vapor pressure of benzene was found to vruy with temperature as shown in table 6.B.

TABLE 6.B
P. torr 1.00 10.0 40.0 100 400 760
t,OC -36.7 -11.6 7.6 26.1 60.6 80.1

Plot the data so that a straight line would be obtained if L were constant and from this curve
get the vapor pressure at 40 0 C.
0
6.6 From the data in problem 6.5, determine the heat of vaporization of benzene at 40 C.
6.7 At 90 0 C, the vapor pressure of toluene is 400 torr while that of a-xylene is 150 torr. Esti-
mate the composition of the liquid mixture that boils at 90 0 C with a pressure of 300 torr.
What is the composition of the vapor coming off?
6.8 Adding 10.0 g AgN0 3 to 490 g H 20 yields a solution of density 1.0154 g cm-s. What are the
( a) mole fraction, (b) molality, and (c) molarity of silver nitrate in this solution?
0
6.9 Solutions of benzene (B) in acetic acid (A) yielded the partial pressures at 50 as shown in
table 6.C.

TABLE 6.C

X B 0.0069 0.1563 0.3396 0.4166 0.6304 0.7027
PA> torr 54.7 50.7 40.2 36.3 28.7 24.8
P B , torr 3.5 75.3 135.1 153.2 195.6 211.2

X B 0.8286 0.8862 0.9165 0.9561 0.9840
P A , torr 18.4 14.2 11.51 7.25 3.63
P B , torr 231.8 244.8 249.6 257.2 262.9

Plot PIX. against Xi and extrapolate to Xi = 1 and to Xi = 0 to obtain the constants Pia and ki
of equations (6.63) and (6.64) for both A and B. Then calculate the activity of benzene in
the solutions on both the Raoult's law and the Henry's law basis.
6.10 What is the activity of CCl 4 in a solution made by adding 20.0 g CCl 4 to 30.0 g CBr4?
6.11 When some ethyl benzoate was dissolved in benzene at 80 0 C, the vapor pressure was lowered
from 753.6 to 745.9 torr. (a) What was the mole fraction of ethyl benzoate in the solution?
(b) How much ethyl benzoate would have to be added to 100 g benzene to prepare such a
solution?