The Student Room Group

Chemistry a level question!

would really appreciate any help with this question. found it really tricky.

3.22g of a hydrated salt with the formula X2SO4.10H2O was heated until no further lossin mass occured; the mass of the residue was 1.42g. calculate the relative atomic mass of X and and hence identify X.
Original post by Niklas000
would really appreciate any help with this question. found it really tricky.

3.22g of a hydrated salt with the formula X2SO4.10H2O was heated until no further lossin mass occured; the mass of the residue was 1.42g. calculate the relative atomic mass of X and and hence identify X.


What have you tried ?
Reply 2
thanks for the reply
Basically i have know idea.
i have tried a few things. i worked out the difference in mass before and after heating which is 1.8g. knowing that this must obviously be 1.8g of H2O so i worked out what was lost in moles (0.1 moles of H2O). i have tried working out what moles of X2SO4.10H2O was but that isnt possible because we are not sure what the mr of X is.
Original post by Niklas000
thanks for the reply
Basically i have know idea.
i have tried a few things. i worked out the difference in mass before and after heating which is 1.8g. knowing that this must obviously be 1.8g of H2O so i worked out what was lost in moles (0.1 moles of H2O). i have tried working out what moles of X2SO4.10H2O was but that isnt possible because we are not sure what the mr of X is.


You are on the right lines.

Calculate the moles of water.

Then you know that the formula is X2SO4.10H2O

What is the ratio in terms of moles of water to the X2SO4 ?

What is left behind after the water is driven off?

Can you see where to go now?
Reply 4
Original post by charco
You are on the right lines.

Calculate the moles of water.

Then you know that the formula is X2SO4.10H2O

What is the ratio in terms of moles of water to the X2SO4 ?

What is left behind after the water is driven off?

Can you see where to go now?


still struggling with this question. so the moles of water lost must be 0.1.
by ratio do you mean 1:10?. we then have 1.42g of X2SO4 left after the water is driven off. does this mean we have 0.01 moles of X2SO4?
Original post by Niklas000
still struggling with this question. so the moles of water lost must be 0.1.
by ratio do you mean 1:10?. we then have 1.42g of X2SO4 left after the water is driven off. does this mean we have 0.01 moles of X2SO4?


Correct :smile:

Quick Reply