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# Water of crystallisation calculation help! Watch

1. Okay so I've just done a quantitative assessment on water of crystallisation.

I had had to work out the metal 'X' in the formula XCl2 • 2H2O

what I'm stuck on:

determine the the amount in mol of anhydrous salt (XCl2)

mass of of anhydrous salt = 1.68g

so the equation is

n(XCl2) = 1.68g / x + (35.5 + 35.5)

how the bloody hell do I rearrange this to work out the Mr/ moles?

Ps Im terrible at maths so the answer could be really simple lol
2. (Original post by Georgiam247)
Okay so I've just done a quantitative assessment on water of crystallisation.

I had had to work out the metal 'X' in the formula XCl2 • 2H2O

what I'm stuck on:

determine the the amount in mol of anhydrous salt (XCl2)

mass of of anhydrous salt = 1.68g

so the equation is

n(XCl2) = 1.68g / x + (35.5 + 35.5)

how the bloody hell do I rearrange this to work out the Mr/ moles?

Ps Im terrible at maths so the answer could be really simple lol
You need the mass of water lost ...
3. (Original post by charco)
You need the mass of water lost ...
To workout that particular thing? I thought it was n = M/m
4. (Original post by Georgiam247)
To workout that particular thing? I thought it was n = M/m
You thought wrong ...
5. (Original post by charco)
You thought wrong ...
Well can you please tell me how I forgot the water loss but can you give me a hypothetical example? Say the hydrate was 2.525g, and the anhydrous was 1.68g
6. (Original post by Georgiam247)
Well can you please tell me how I forgot the water loss but can you give me a hypothetical example? Say the hydrate was 2.525g, and the anhydrous was 1.68g
Oh my God. It's just the same as the moles of water lost isn't it.
7. (Original post by Georgiam247)
Oh my God. It's just the same as the moles of water lost isn't it.
mass of water lost ===> moles of water lost

use the given formula to get moles of anhydrous salt from moles of water

moles of anhydrous salt and mass ====> relative mass and hence X
8. (Original post by charco)
mass of water lost ===> moles of water lost

use the given formula to get moles of anhydrous salt from moles of water

moles of anhydrous salt and mass ====> relative mass and hence X

Woo thank you
9. PLEASE HELP!Just wondering if anyone would be able to help ASAP? I found the number of moles for h2o to be 0.04694 by doing 0.845 divided by 18 and divided that by 2 to find XCl2 equals 0.02347mol. I then divided that by 1.68 (mass of anhydrous salt) and found the Mr of it to be 71.57gmol.
I thought that I'd do 71.51 - 71 (Mr of Cl2) to find X but that can't be correct?

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