Assessed HWK question (AGAIN)

A student heated 4.38g of hydrated zinc sulfate and got 2.46g of anhydrous zinc sulfate
Use this data to calculate the value of the integer x in ZnSO4.xH20

--can someone go through this step by step and explain it please im stupid--

Reply 1

RoseMango

So essentially you need to work out how many moles of zinc sulfate you have in comparison to the number of moles of water.
First you should work out the number of moles of zinc sulfate using the equation moles=mass/mr.
The mass of zinc sulfate is 2.46g and the mr is
65.4+32.1+(4x16)=161.5
So the number of moles is 2.64/161.5=0.01523
Then work out the mass of H2O by taking the mass of the anhydrous ZnSO4 from the original mass of the hydrated ZnSO4
4.38-2.46=1.92g
Do the same as before to work out the number of moles of water present
Mr of H2O=(2x1.0)+16.0=18.0
Mass/mr=1.92/18.0=0.10667
Finally divide the number of moles of water by the number of moles of ZnSO4 to get the value of x
0.10667/0.01523=7.00
I find it easiest to lay this kind of question out in a table that shows the mass, mr and number of moles of each thing. :smile: