## Chemistry: The Molecular Science (5th Edition)

There are $5.37 \times 10^{23} atoms$ of oxygen in 20g of Epsom salt.
As we calculated in the last exercise, there are 0.081 moles of Epsom salt in 20g. The chemical formula for Epsom salt is $MgSO_4 ∙7H_2O$,; therefore, we have 4 + 7 = 11 moles of oxygen for each mole of this compound. $0.081 moles (Epsom$ $Salt) \times \frac{11 moles (O)}{1 mole (Epsom-Salt )} = 0.891 moles (O)$ $0.891 moles \times \frac{6.022 \times 10^{23} atoms}{1 mol} = 5.37 \times 10^{23} atoms$