How to Calculate Moles and Mass in a Copper Sulphate Pentahydrate Sample?

[Sace Ver]

Homework Statement

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. Homework Equations

n=N/Na
m=nM

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?

 

[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.

 

[Sace Ver]

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.

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)?

 

[epenguin]

Yes