[lttoler]

I had a chemistry test yesterday and one of the questions stated:

Calculate the number of water moles in 10.0 grams of CoCl2.6H2O.


The answer I got after working out the problem was 0.0420 grams, but it was marked incorrect.  Can someone show me how this is not correct?

The test was multiple choice and the choices were:
A.  0.0420 grams
B.  0.252 grams
C.  0.462 grams
D.  0.504 grams
E.  2.120 grams

Thanks in advance!

[Dan]

1. Show your working (Forum Rules)

2. Are you trying to calculate moles of water or grams of water?

I had a chemistry test yesterday and one of the questions stated:

Calculate the number of water moles in 10.0 grams of CoCl2.6H2O.

The test was multiple choice and the choices were:
A.  0.0420 grams
B.  0.252 grams
C.  0.462 grams
D.  0.504 grams
E.  2.120 grams

[lttoler]

Well it isn't stated in the question but since the only choices are in grams, it would have to be grams.

What I did was found the percentage of H20 and determined that 4.5 grams of the substance was H20.  Then I divided 4.5 by the molar mass of 6H20 (4.5/108) to get my answer.

[Dan]

I also have 4.54 g H₂O.

You are trying to find the moles of H₂O, not of "6H₂O". How many moles of H₂) are there in 4.54 g of H₂O?

By the way, there is a typo in the answers, the units should be mol, not g.