CHEMISTRY 31

Spring, 2015 - Dixon

Homework Set 2

Note: this will be updated with Additional Problem 2.2 later

Chapter                                       Problems                                             Date to finish

Set 2.1                                                                                                          Mar. 10

Ch. 6                                              15-17, 19, 23, 25, 33, 36, 43, 48

Ch. 7                                              1, 3, 4a,b

An industrial solution contains 1.0 x 10-2 M CrO42- and 2.0 x 10-3 M Cl-.  It is desired to separate the two ions so that at least 99% of the CrO42- is recovered and Cl- is present at less than 0.1% by mole of the recovered CrO42-.  By using the Ksp values for Ag2CrO4 and AgCl in Appendix F, determine if this is possible by adding Ag+ to selectively precipitate out one ion. To solve this problem, determine: a) which ion is removed first as Ag+ is added, b) the concentration of the first ion to precipitate in the solution when the second ion starts to precipitate, and c) whether this will meet the criteria desired.  If it does not meet the criteria, indicate to what extent the separation could be used (e.g. isolation of less than 99% or with more than 0.1% Cl present).

Set 2.2                                                                                                          April 1

Ch. 7                                              9, 12, 19, 21, 23, 27, 28a, b

Ch. 8                                              3

Ch. 17                                            1, 3, 4

Text Solutions

By using the constants in Appendix F, H, Iand J, determine the equilibrium concentration of Mg2+ and F- in a saturated MgF2 solution (e.g. from dissolving solid in water).
a) Do this first by assuming the only reaction that matters is the dissolution of MgF2 (ignoring any reactions of products of its dissolution and ignoring activity).
b) Using your initial results in a), calculate the ionic strength and recalculate the equilibrium concentration of Mg2+ and F-after accounting for the ionic strength.  Do not consider any other reaction. You only need to do one iteration.

c)  List three more reactions (besides simple dissolution) that may need to be considered if determining the concentration of Mg2+ using the systematic method.

Set 2.3                                                                                                          April 8

Ch. 17                                             11, 16

Ch. 22                                             7a, 17, 19, 22, 28a-f, 30, 38