Question

A 5.00 gram sample of an oxide of lead PbxOy contains 4.33 g of lead. Determine simplest formula for the compund

Answer 1

Answer: The empirical formula is $PbO_2$

Explanation:

Mass of Pb =  4.33 g

Mass of O = (5.00-4.33) g = 0.67 g

Step 1 : convert given masses into moles

Moles of Pb =$\frac{\text{ given mass of Pb}}{\text{ molar mass of Pb}}= \frac{4.33g}{207g/mole}=0.021moles$

Moles of O =$\frac{\text{ given mass of O}}{\text{ molar mass of O}}= \frac{0.67g}{16g/mole}=0.042moles$

Step 2 : For the mole ratio, divide each value of moles by the smallest number of moles calculated.

For Pb = $\frac{0.021}{0.021}=1$

For O = $\frac{0.042}{0.021}=2$

The ratio of Pb O=  1: 2

Hence the empirical formula is $PbO_2$