Problem 16.97:
Use Le Châtelier's principle to predict whether the solubility of BaF2 will increase, decrease, or remain the same on addition of each of the following substances:
For reference, here is the reaction:
| (a) | HCl | Increase. Adding H+ ion would decrease fluoride ion concetration and, thus, drive the reaction to the right. |
| (b) | KF | Decrease. Adding fluoride would send the reaction to the left. |
| (c) | NaNO3 | No effect here. Neither the sodium nor the nitrate ion has anything to do with this equilibrium. |
| (d) | Ba(NO3)2 | Adding barium ion would shift the reaction to the left and decrease the solubility. |
Problem 16.99:
Calculate
the molar solubility of SeF2
in:
| (a) | 0.010M Sr(NO3)2 | 
(Note that we use the fact that
x
is small to simplify the above calculation. This is not always warranted
and you should check you result to be sure that the approximation was really
applicable. Usually, iterative solutions in systems such as these
are unnecessary but, on occasion you should be on the lookout for them.
Luckily, unless Ksp
is abnormally large, such events are rare.)
|
| (b) | 0.010M NaF | This is relatively simple.
However, note that you need to keep track of what the molar solubility
is!
This one went fairly easily. Note that, after writing the correct expression for the equilibrium constant, we were able to drop 2x and get a much easier problem to solve. |
Problem 16.101:
Which
of the following compounds are more soluble in acidic solution than in
pure water? Write a balanced net ionic equation for each dissolution
reaction.
| (a) | MnS | More soluble.
We show two forms of some of these. The top form in each case is the form as it would be done in McMurry/Fay. The second is a more convenient way used by most chemists. In the attached tables, there is
a special one for metal sulfides. Read the footnotes of that table
to be sure that you know why such a special table had to be constructed.
Incidentally, sulfides of many kinds tend to be quite strange!
|
| (b) | Fe(OH)3 | More soluble.
|
| (c) | AgCl | No change.
|
| (d) | BaCO3 | More soluble.
We could also react this further to give carbonic acid (which would probably evolve as carbon dioxide. However, we shall stop this one here.)
|
Problem 16.105:
Write
a balanced net ionic equation for each of the following dissolution reactions
and use the appropriate Ksp
and Kf
values in Appendix C to calculate the equilibrium constant for each.
| (a) | Zn(OH)2
in aqueous NaOH to form Zn(OH)42-:
Here we just write the reactions
and do the calculations without commment. You should feel quite comfortable
with combining equilibria now.
|
| (b) | Cu(OH)2
in aqueous NH3 to
form Cu(NH3)42+:
|
| (c) | AgBr in aqueous NH3
to form Ag(NH3)2+:
|
Problem 16.106:
Calculate
the molar solubility of AgI in:
| (a) | Pure water
This part is just the same as many
simple problems we have already done!
|
| (b) | 0.10M NaCN; Kf
for Ag(CN)2-
is 3.0 x 1020.
Fairly complicated but still straight
forward! The exercise should have been good for you!
|
Problem 16.107:
Calculate the molar solubility of Cr(OH)3 in 0.50M NaOH; Kf for Cr(OH)4- is 8 x 1029.
This is another extensive calculation. However, this time, we are saved by the fact that the total, combined, equilibrium constant is really quite simple!
Here are the need tables as promised!
