Question

72. Polyethylene is a hydrocarbon polymer used to produce food-storage bags and many other flexible plastie items. A combustion analysis of a 0.00125-g sample of polyethylene yields 0.00394 g of CO, and 0.00161 g of H.O. What is the empirical formula of polyethylene?

Answer 1

Hydrocarbon on combustion gives carbon dioxide and water.

C_{​​​​​​X}​​​​​H_​Y +. (x+ y/2)O_{​​​​​​2.}   $\rightarrow$. xCO₂ +. yH_​​2O

44 g of carbon dioxide has 12 g of carbon

1 g of carbon dioxide has 12/44 g of carbon

0.00394 g of carbon dioxide has 12 * 0.00394 / 44 g

= 0.0010745 g of carbon

18 g of water contains 2 g of hydrogen

1 g of water contains 2/18 g of hydrogen

0.00161 g of water contains 2 * 0.00161 / 18 g of hydrogen

= 0.000178 g of hydrogen

% of carbon in sample = 0.0010745 / 0.00125 * 100 = 85.9%

% of hydrogen in sample = 0.000178 / 0.00125 * 100 = 14.2%

Number of moles = given mass / atomic mass

x = 1 and y = 2

Element 1 % c 185.9 Atomic I 12 no-of Simple males 85.9= 12 14.2 214. 2114.221.98 17.157 na 215 4 14 2 1

Empirical formula = C_{​​​​​​1}​​​​​H_​2