Comments re Chapter 10 Problems:

10-1

A T/F exercise. Part (d) is true.  Convention I activity coefficients are based on an ideal solution (both components follow Raoult’s Law) while Convention II activity coefficients are based on an ideally dilute solution (the solvent obeys Raoult’s Law but the solute obeys Henry’s Law).  In part (e) remember that a real (or actual) solution with mole fraction = 1 is not the same as a standard state with mole fraction = 1.  The solvent always behaves ideally as XA approaches 1, but a solid solute only behaves ideally (ie, follows Henry’s Law) as XB approaches 0.

10-6

A shorter T/F exercise.  This one is just about definitions.

10-7

An exercise in calculating activities, activity coefficients, change in chemical potential, and DmixG for a solution (alcohol/chloroform) that is somewhat nonideal.

10-12

An exercise in calculating the activity and activity coefficients for the water in two sucrose solutions. Note that g for the solvent water is very close to 1 in part (b) even though the solution concentration is quite high. The solvent may act nearly ideally even if the solute does not.

10-21
(not assigned recently)

A problem related to 10-12, but this problem focuses on the solute (sucrose) rather than on the solvent (H2O). Note that the concentration of the solution in 10-13 is a little lower than the concentration of the solution in 10-11, so the activity coefficient for the H2O would be very close to 1.

 

 

10-68

A rough calculation to find out the (very approximate) average distance between ions in a 1 M solution.

10-69

Thought exercise relating mixing quantities (DmixH, etc.) to intermolecular interactions.

10-8

Calculate activities and activity coefficients for the solvent and solute in a solution of two liquids using both conventions.  In part (b) the Henry’s Law constant for the solute must be determined.  This can be done in a simple way by using the first two points or by extrapolating a tangent to the PB vs. XB curve, but the result will be in error by almost a factor of two.  A better way to determine the Henry’s Law constant is to plot PB/XB vs. XB and extrapolate that curve to XB = 0.  The simplest way to do this is to use a spreadsheet.  In part (c) it is necessary to decide which activity to use for component B.  The Convention I activity should be used because it is the two pure liquids that are mixed.

 

 

10-24

An exercise in identifying the ions in some simple salts (review of General Chemistry).

10-35

An exercise in calculating the ionic strength for a solution of several electrolytes containing ions of different charges (1+/1-; 2+/1-; 2+/2-). This is an important problem because of the role of the ionic strength in the activity coefficients of ions.

10-37
(a, b only)

Exercise in using the Davies equation to estimate activity coefficients for ions. Omit part (c)  In part (b) remember that the charges in the Davies equation are for the ions of CaCl2 rather than for any of the other ions present.

 

 

10-49

Demonstration that DrxnGo for reactions involving ions can be calculated from the data available in standard tables. What is needed is DfGo for each of the ions. The standard states for the ions are 1 m solutions that have the properties that the solutions would have at infinite dilution (m = 0). The values of DfGo and DfGo for one ion may be arbitrarily taken as zero because the ionic charge must always sum to zero in any macroscopic system;  the ion chosen in H+(aq) because it is the most common ion.   For part (a) calculate Ko to convince yourself that DrxnGo is correct.

10-73
(omit e)
(not always assigned)

Another of Levine's T/F puzzles.  Omit part (e) because the needed equation will not covered in class and does not need to be learned.

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