Homework Help: Copper Sulphate Pentahydrate

1. Nov 20, 2015

Sace Ver

1. The problem statement, all variables and given/known data
A sample contains 2.5x1020 formula units of CuSO4•5H2O...
a) calculate the number of moles present in this sample
b) calculate the mass of this sample

N=2.5x1020
M=249.69g/mol

2. Relevant equations

n=N/Na
m=nM

3. The attempt at a solution

a)
n=N/Na
n=2.5x1020/6.02x1023
n=0.000415mol

b)
m=nM
m=(0.000415mol)(249.69g/mol)
m=0.10369g

Am I correct?

2. Nov 20, 2015

epenguin

Yes but that looks correct. I have got through a lifetime without ever hearing the term 'formula units'. Unnecessary IMO and I expect you will forget it, like those formulae you used. All it means is 'number of molecules' right? Which would see you through. I expect this pedantry is because CuSO4.5H2O isn't strictly a molecule but, oof, it's just like one for this purpose.

3. Nov 20, 2015

Sace Ver

There was another part to this question and it asked how many moles of this substance are in this sample? Would that not just be the same as the answer to a)?

4. Nov 21, 2015

Yes