Question

If there are 4.214x10^22 Molecules of Water in a sample of MgSO4 7H2O epsom salt, what is the mass (in grams) of that sample of epsom salts?

Answer 1

1) Convert molecules of water into moles of water.

`\text{molesofH}_2O=4.214\cdot10^(22)moleculesofH_2O\cdot(1molofH_2O)/(6.022\cdot10^(23)moleculesofH_2O)=0.0700molofH_2O`

2) Use the moles of water in step 1 to find out the number of moles of Epsom salt

`\text{molesofEpsomsalt}=0.0700molofH_2O\cdot\frac{1\text{molofEpsom salt}}{7molesofH_2O}=0.01\text{molof Epsom salt.}`

3) Find the molecular mass of one mol of Epsom salt.

Mg: 24.30 g/mol

S: 32.065 g/mol

O: 15.999 g/mol

H: 1.008 g/mol

The molecular mass of Epsom salt (MgSO4 * 7H2O) is

(24.30*1)+(32.065*1)+(15.999*4)+(1.008*14) +(15.999*7) =826.3571 g/mol

4) Convert moles of Epsom salt into grams of Epsom salt.

`\text{gramsofEpsomsalt}=0.01\text{molofEpsomsalt}\cdot\frac{826.3571\text{ g of Epsom salt}}{1\text{molofEpsom salt}}=8.263\text{ g of Epsom salt.}`