# Finding X in hydrated compounds

Hey guys

Here is how to find X in a compound such as CuSO4.xH2O.

Hope it helps

P.s this is for unit 1/2 AS AQA Chemistry
:)

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## Exam question:

Q) A sample of hydrated copper sulphate (CuSO4.xH2O) was weighed heated, cooled and then reweighed again. 1.738g of the hydrated copper sulphate gave a residue of 1.112g of copper sulphate (CuSO4). Calculate the value of x.

First step: n(CuSO4) = Mass / Mr = 1.112/ 159.6 = 0.00679mol

Second step: n(H2O) = Mass / Mr = The mass of water will be the mass of copper sulphate minus the mass of residue left, 1.738 - 1.112 = 0.626g

So n(H2O) = Mass /Mr = 0.626 / 18 = 0.0348mol

Third step: 0.0348 / 0.00697 = 5 So x = 5

Each step explained:
Step 1: Calculate the number of moles of copper sulphate present in the experiment.
Step 2: Calculate the number of moles of water present. You first have to work out the amount in grams (even though liquids are measured in ml) of water because you are not provided that information in the question.
Step 3: Work out x by dividing the amount of moles in water with the compound.

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