Question

Prior to their phaseout in the 1980s, chemicals containing lead were commonly added to gasoline as anti-knocking agents. A 6.495 g sample of one such additive containing only lead, carbon, and hydrogen was burned in an oxygen rich environment. The products of the combustion were 7.069 g of CO2(g) and 3.617 g of H2O(g). Insert subscripts below to appropriately display the empirical formula of the gasoline additive: CHPb

Answer 1

step 1 : calculate moles of C and H in CO2 and H2O

moles of CO2 = 7.069/44.01 = 0.1606 mols

C = 0.1606 mols

moles of H2O = 3.617/18.02 = 0.2007 mols

H = 2 x 0.2007 = 0.4014 mols

step 2 : find mass of Pb in the sample

grams of C = 0.1606 mols x 12.01 g/mol = 1.93 g

grams of H = 0.4014 mols x 1.008 g/mol = 0.405 g

grams of Pb = total sample weight - (C + H) = 6.495 - (1.93 + 0.405) = 4.16 g

step 3 : find moles of each and divide by smallest factor

moles of C = 0.1606 mols

moles of H = 0.4014 mols

moles of Pb = 4.16/207.2 = 0.0201 mols

Dividing by smallest factor,

C = 0.1606/0.0201 = 8

H = 0.4014/0.0201 = 20

Pb = 0.0201/0.0201 = 1

So the empirical formula becomes : C8H20Pb