[madscientist]

If anyone can help me at all with this question i would be much appreciative, its driving me nuts!!

The question states:

Only 1.06g of Ca(NO3)2 will dissolve per litre of sollution that is buffered to a pH of 13.00.
What is the value of Ksp for Ca(OH)2 ? The molar mass of Ca(NO3)2 is 164.1g/mol.

a.) 1.8x10^-10
b.) 4.2x10^-7
c.) 1.1x10^-6
d.) 4.2x10^-5
e.) 6.5x10^-5

my working so far:

I took this Ksp from my text book but have found different values in other texts?

Ksp=5.5x10^-5

solubility =Ksp/[OH-] ²

pOH=14-13
      =1

[OH-]=10^-1
        =0.1

[Ca2+]= 5.5x10^-5 / 0.1
          = 5.5x10^-4

none of the choices we are given matches this answer?
please help.

madscientist

[AWK]

You should calculate Ksp - it can slightly different from this in tables.
1 Calculate molar concentration of Ca2+ in solution (1.06/164.1)
2. You calculated OH- properly
3. Put both numbers into expression for Ksp (6.4x10^5)

[madscientist]

Thankyou,
I cant beleive how easy that question is afterall.

cheers,

madscientist