Problem Solving Strategy: Remember that 1 mole of any compound contains 6.022 x 10²³ molecules.

Thus

6.022 x 10²³ molecules = 1 mole of compound

Solution:

6.022 x 10²³ molecules = 1 mole of formaldehyde

1 molecule = $\frac{1}{6.022 \times 10^{23}}$ moles of formaldehyde

3.011 x 10²³ molecules = $\frac{1}{6.022 \times 10^{23}} \times 3.011 \times 10^{23}$ moles of formaldehyde

3.011 x 10²³ molecules = 0.05 moles of formaldehyde