Question

Find the number of moles of $MgS{O}_4.7H_{2}O$ in a pure sample that contains 0.0022 moles of oxygen atoms.

• A. 2 moles
• B. 0.2 moles
• C. 0.002 moles
• D. 0.2 millimoles

Answer 1

The correct option is D 0.2 millimoles

11 O-atoms are present in one formula unit of $MgS{O}_4.7H_{2}O$.

So, 11 moles of O-atoms are present in 1 mole of $MgS{O}_4.7H_{2}O$.

The number of moles of $MgS{O}_4.7H_{2}O$ that would have 0.0022 moles of O-atoms are
$=\frac{0.0022}{11}$
$=$ 0.0002
$=$ 0.2 millimoles