in the lab you heat 2.058g of unknown. this unknown gives off condesation and after heating you notice that ur

Question

sample now weighs extremely less: 1.208g. with the white residue you hav left you decide to perform a molar mass experimentation giving u 105.99g/mol.
a.) using the original mass and the molar mass of ur anhydrous salt, determine the moles of salt you are working with?
b.)using the mass of water lost and the molar mass of water determine the moles of water you are working with?
c.)divide b by c. this whole number of moles of water in your molecular formula.
d.)if your anhydrous salt is sodium carbonate write the formula for this hydrate.

when i tries this i got it wrong!
this is what i got!
a.) 218.1 mol of salt
b.) 90.09 mol water
c.) 2.421
d.) Na2CO3

Answer 1

You are working out the moles the wrong way round. Divide the mass by the Mr, and not vice versa.

Eg 1.208/105.99 = 0.0114 moles of anhydrous salt.

(2.058 - 1.208)/18 = 0.0472

But somewhere your other figures are wrong. I've got a non-whole-number value for the water of crystallisation, and I was expecting it to be 1 or 10.

You may have copied down the question slightly wrong.