I got the first one and it is correct:
AgI-------------->Ag + I
I 9.6E-9 0
C -s +s +s
E -s 9.6E-9+s +s w/9.6E-9+s approx. = to 9.6E-9
8.3E-17 = (9.6E-9)(s)
I did the second one (b) exactly the same way and the program is saying off by order of magnitude, I got 4.7E-25
This is how I sat it up
Al(OH)3----------------->Al3+ + OH-
C +s 3.8E-9+s
E -s s approx. 3.8E-9
What am I doing wrong?
Solution This solution is FREE courtesy of BrainMass!
Well, first thing I noticed was that your Ksp doesn't match what I looked up in a general chemistry text. I believe the Ksp of Al(OH)3 should be 1.8E-33, not 1.8E-25.
The next thing thing you need to consider is the actual solubility product expression.
For example, in the first one, the expression is:
Ksp = [Ag+][I-]
as you know.
However, for the second one it is:
Ksp = [Al3+][OH-]^3
Ksp = [Al3+][OH-]
Why? Because the equation is this:
If you consider the correct Ksp expression, you should be fine.
Hopefully, that gets you back on track!