correction to solution to #23 in practice exam

[robert zellmer]

There was a typo in the solution to #23 of the practice exam. However,
this typo wasn't part of the question itself but and added bit of info.
After the solution to the question there's a part which was suppose to
discuss what conc of Ag+ would remain just as PbI would start to ppt.
Instead it had Pb^2+.  It's been corrected.

Old:

If asked what conc. of Pb^2+ remains maximum separation when the PbI2 
just starts
to ppt. you would take the conc. of the I− at which the PbI2 would start 
to ppt. and
substitute it into the Ksp for AgI to determine the [Ag+] at this point.

New:

If asked what conc. of Ag^+ remains maximum separation when the PbI2 
just starts
to ppt. you would take the conc. of the I− at which the PbI2 would start 
to ppt. and
substitute it into the Ksp for AgI to determine the [Ag+] at this point.

Dr. Zellmer