[rannekk]

Greetings!
I could use some help with this question:
3.40g of CaSO4 (M=136g mol-1) is formed when 4.30g of hydrated calcium sulfate is heated to constant mass. How many moles of water of crystallisation are combined with each mole of calcium sulfate?

A: 1
B: 2
C: 3
D: 4

.. I have been baffled with this question, not knowing where I am supposed to start.

Cheers

[Borek]

How many moles of CaSO₄ was left? How much water was lost? How many moles of water were lost?

[rannekk]

0.500mol water lost 0.0250mol CaSO₄ is left... umm from 0.0315mol of reactant... let me have a think..

[rannekk]

yes hahaaa its B.. 2 moles!. Cheers mate! Prob the easiest question ever, now that one looks at it  Thanks again! 

[Borek]

from 0.0315mol of reactant...

Wrong here!

[rannekk]

True... slip of mind.
its
CaSO₄ + H₂O  ->  CaSO₄
0.0250mol    0.500mol    0.0250mol
      1        :       2      :       1