- Principles of Chemistry II: Honors
Spring 2014, Unique 51880
Homework, Week 10
Homework week 10 (Solubility and complex formation)
In some cases, there are “hints” at the bottom of the problem set. In these cases the word Hint is shown after the question. Try struggling with the question for a while before jumping to the hint which, by the way, is often not a “big hint”.
a) What is
the molar solubility of BaSO4(s) in water?
Ksp = 4.3x10-11 (ignore hydrolysis
of SO4 to form HSO4-.)
Ni(OH)2(s) is minimally soluble in water.
(Ksp = 6x10-16)
To what pH would you have to buffer the solution in order
to bring [Ni2+] to 1.00x10-3 M?
6.0 g of NaCl is added slowly to a 1.0 L solution
containing both 1x10-3 M Ag+ and Pb2+.
(For AgCl Ksp = 1.8x10-10; for PbCl2
Ksp = 1.7x10-5)
a) It seems
peculiar that the solubility of PbF2 increases if HNO3
is added to the solution, but the addition of this acid to PbCl2
has little effect. Why
might that be? Hint
One form of a chemical heating pad consists of a solution of supersaturated sodium acetate
(CH3CO2Na). When a
“physical shock” (a small clicker disk) is given the solution it
proceeds to equilibrium, precipitates sodium acetate and generates
Copper tetraamine (AKA tetraaminecopper(II)) is a
water-soluble complex formed between copper and the ammonia
It has step-wise formation constants of 1x104,
2x103, 5x102 and 9x101 for K1
to K4, respectively.
K1 K2 K3 K4 = 9x1011.
“Austin's alkaline soil can help get the lead out of
homegrown veggies” is the title of an Austin American Statesman
article back in 2009 (http://testmygarden.com/austin-tx-soil-testing_5_1322066470.pdf)
Scale (CaCO3(s)) precipitates from water,
forms on pipes and can severely restrict (or stop!) the flow of
water. It is a
particular problem in hot water pipes, hot water heaters, boilers
and the like both in your home and in industry.
>0, =0 or <0 for the reaction Ca2+(aq)
+ CO32-(aq) à
= = = = = Spoiler alert: Don’t look at hints below until you tried the above on your own = = = = = =
Hints for selected problems:
Consider using the exact treatment remembering that you
cannot write a charge balance expression because you are in a
buffer. Is there
anything unique about the solution composition because pH ~ pKa2?
a system at equilibrium, all equilibrium constants must be
Be sure to see the final concentrations are not more than
you started with!
Think LeChatlier and the impact (or lack of impact) by
LeChatlier to consider which species dominates, i.e., there is a
lot of NH3 present relative to the Cu2+,
yes? Are the Ks for
the formation of the complexes large or small?
7 You have to visualize the “soil” as a solution of a given pH with Pb(OH)2(s) sitting at the bottom of the beaker. This is not a bad visualization since the plants feed from the water in the soil; and now we simply have to assume that that water and its solutes are in equilibrium with the soil composition.