Comments re Chapter 12 Problems:
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12-3 |
An exercise in calculating vapor-pressure lowering for a familiar solution. |
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12-4 |
A T/F problem on the subject of freezing-point depression. Most of the questions (but not (c)) apply to the boiling-point elevation as well. |
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12-13(b) |
An exercise involving the practical osmotic coefficient f, which multiplies the molality and accounts for non-ideality. The coefficient f itself is not so important; what is important is getting n (the number of ions per formula unit) correct for the solute and noticing that the solution is not ideal. |
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12-14 |
A problem in which the extent of dimerization of phenol (as measured by an equilibrium constant Kx) is determined from data about a freezing-point depression. |
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12-15 |
An unusual, but informative, problem involving a freezing-point depression for a solution of two unreactive solutes. Rather than asking for a calculation of DT or molar mass or concentration, Levine asks about the relative amounts of the two solutes. |
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12-18 |
Exercise in calculating osmotic pressure. In part (b) the calculated and observed osmotic pressures are compared to get a value for the activity coefficient of the solvent. |
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12-23 |
Problem involving osmotic pressure and ionic strength. |
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12-28 |
Very short exercise about the Gibbs Phase Rule. |
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12-35 |
Please make the requested plot (a P vs. x diagram for the liquid and vapor
phases of an ideal binary solution) carefully, maybe using a
spreadsheet. (The word carefully means using either a
spreadsheet or graph paper). Draw the
tie line that corresponds to a system that has a total pressure of 40.0 torr |
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12-37 |
A thought problem about two-phase regions and tie lines. |
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12-70 |
A problem that shows that it is possible to get activity coefficients for the liquid components of an azeotrope from the vapor pressures of the pure components and the total pressure. The key is realizing that Xi = Yi for both components of an azeotrope. |
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12-72 |
This question can be answered with a single sentence that requires no calculations or equations. Levine provides a slightly longer answer. |
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12-73 |
Relates the four colligative properties. The hardest part of the problem is the conversion of molality to mole fraction. Remember that for water Kb = 0.513 °/m and that Kf = -1.86 °/m. The needed vapor pressure is given in the problem. |
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12-44 |
Estimate the eutectic temperature and composition of a solution of benzene and cyclohexane by finding the intersection of the two freezing-point depression curves. This is a good problem to do with a spreadsheet. |
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12-49 |
A reasonably simple solid-liquid phase diagram, but partial miscibility (solubility of A in B and B in A) must be considered. Note that neither the temperatures nor the compositions of the eutectics are given so it is necessary to draw lines that look reasonable. |
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12-51 |
Another solid-liquid phase diagram. Several different compounds are present (each one is a line phase) but there are no complications from partial miscibility. |
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12-52 |
Problem that emphasizes that the solubility of a solid in a liquid should depend only on the freezing point and heat of fusion of the solute. For solutes and solvents that are chemically similar (so that the solutions are reasonably ideal) the predicted solubilities are surprisingly accurate. |
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12-66 |
A thought problem that is based on a simple system in which the chemical potential of the solvent differs between two beakers because the solution concentrations are different. Since the liquid solvent is in equilibrium with its vapor, the solvent is constantly vaporizing and condensing. The solvent can therefore migrate from one beaker to the other. |
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