Chapter 8 - Chemical Composition

We have looked at compounds and completed dimensional analysis problems using quantities within the full compound.

What if you were asked about part of the compound?

For instance, how many moles of chlorine are there in 47.61g of MgCl₂?

To answer, first use the molar mass of MgCl₂ to convert to moles of magnesium chloride

But next, you will need to consider that there are 2 moles of Cl in one moles of MgCl₂

Calculate the total mass of water --> 18.02g/mol

Now calculate the total mass of hydrogen in the compound --> 2.02g/mol

Divide part by whole, 2.02/18.02

Then finish by multiplying by 100!

You've now calculated the part of water that is hydrogen only.

The rest, of coursem, is oxygen. So the %H +%O = 100%

This is only true in this case because the compound is only made up of hydrogen and oxygen.