Test your skills on the following problems.

**Problem:** How many molecules of hexane are contained in 55.0 mL of hexane? The density of hexane is 0.6548 g/mL and the molar mass is 86.17 g/mol.

**Problem:** How many SO_{3} ions are contained in 120.0 mg of Na_{2}SO_{3}? The molar mass of Na_{2}SO_{3} is 126.05 g/mol.

**Problem:** What mass of phosphorus pentafluoride, PF_{5}, has the same number of fluorine atoms as 50.0 g of oxygen difluoride, OF_{2}?

**Problem:** How many moles of oxygen atoms are required to combine with 3.05 moles of Pb to create lead (IV) phosphate?