please help with following questions regarding G chem

[tlcmqn]

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hi, first time posing, just a few General Chem questions

For which one of the following mixtures is the ideal gas law most likely to produce an accurate prediction of volume at STP?
Answer: HCl and CH4
Why?? How do you approach this?

Silver hydroxide, AgOH, is a slightly soluble ionic compound whose Ksp=1.5 X (10^-8) at 20 degree Celcius. What is the minimum pH at which AgOH will precipitate from a solution, 0.010 M in Ag+ ?
Answer: 8+log(1.5)
Why? my answer was 6-log(1.5)

A voltaic cell is constructed by connecting a nickel electrode in a Ni 2+ (aq) solution to a tin electrode in a Sn 2+ (aq) solution. Given that the standard reduction potentials for Ni 2+ and Sn 2+ are -0.28V and -0.14V respectively, what is the cell EMF?
Answer: +0.14V
Why?? what's there to know about the set up of voltaic cell?

The concentratin of Pb 2+ is 1.15X(10^-3) M in a saurated solution of PbF2. Calculate the Ksp of PbF2.
Answer: 6X(10^-9) I got 1.325 X (10^-9)

please go over these problems and help me out!

 

[karrotcake]

For the last one, i followed the bb and did this:

PbF2(s) <-> Pb+2(aq) + 2F-(aq)

Pb2+ = x
F- = 2x

Ksp = [Pb2+][F-]^2 = x(2x)^2 = 4x^3 = 4(1.15e-3)^3 = 6.08e-9

 

[karrotcake]

since i'm doing one prob, might as well do another hehe.

I think the EMF question is like this:

look at the E's given. Sn2+ (-0.14V) will be reduced, meaning Ni will be oxidized so flip the E to positive.

Use EMF = Eox + Ered = 0.28 + -0.14 = +0.14V

 

[karrotcake]

6-log(1.5) = pOH

you're looking for pH so subtract that from 14 and you'll get 8+log(1.5) = pH