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SOLUTIONSMANUAL TO ACCOMPANY ATKINS' PHYSICAL CHEMISTRY 155
Likewise, xNa2SO4 ⋅ 10 H2O = 0.040 and xH2O = 0.74; this point is plotted in the
ternary phase diagram shown in Fig 5.28.
�e line with varying amounts of water but the same relative amounts of the
two salts (in this case, equal by mass), passes through this point and the vertex
corresponding to xH2O = 1.�is line intersects the NaCl axis at a mole fraction
corresponding to a 50:50 mixture (by mass) of the two salts
xNaCl =
(50 g)/(58.44 gmol−1)
(50 g)/(58.44 gmol−1) + (50 g)/(322.20 gmol−1)
= 0.85
�e line is shown on the diagram.
0.0
0.2
0.4
0.6
0.8
1.0
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
NaCl
Na2SO4H2O
xNaClxH2O
xNa2SO4 ⋅ 10 H2O
Figure 5.28
E5E.3(b) �e composition by mass needs to be converted to mole fractions, which re-
quires the molar masses: MCHCl3 = 119.37 gmol
−1, MH2O = 18.016 gmol−1,
andMCH3COOH = 60.052 gmol−1.�e mole fraction of CHCl3 is
xCHCl3 =
mCHCl3/MCHCl3
mCHCl3/MCHCl3 +mCH3COOH/MCH3COOH +mH2O/MH2O
= (8.8 g)/(119.37 gmol−1)
(8.8 g)/(119.37 gmol−1) + (3.7 g)/(60.052 gmol−1) + (55.0 g)/(18.016 gmol−1)
= 0.023
Likewise, xCH3COOH = 0.019 and xH2O = 0.958. �is point in marked with
the open circle on the phase diagram shown in Fig. 5.29; it falls clearly in the
one-phase region.
(i) When water is added to the mixture the composition moves the distance
to the lower-le� corner. �e system remains in the one-phase region
throughout.