Question

Cembrene a is a naturally occurring hydrocarbon, extracted from coral. Combustion of 0.0341 g of cembrene a yields 0.1101 g co2 and 0.0360 g h2o. What is the empirical formula of cembrene a?

Answer 1

let the hydrocarbon is CxHy

the combustion equation will be:

CxHy  + (x + y/4)O2  ---> xCO2(g)  + y/2H2O

So here

12x grams of carbon will give 44x grams of carbondioxide (molar mass of CO2 is 44)

y grams of hydrogen will give 9y grams of water

Or if 44g of carbondioxide is formed the mass of carbon = 12g

if 1 g of CO2 is formed the mass of carbon = 12/ 44

if 0.1101 g of CO2 is formed the mass of carbon = 0.1101 X 12 / 44 =0.03 grams

Moles of Carbon = mass / atomic mass = 0.0025 moles

if 9g of water is present the mass of hydrogen = 1 gram

if 1g of water is formed the mass of hydrogen = 1 / 9

If 0.0360g of water is formed the mass of hydrogen  = 0.0360 / 9= 0.004

Moles of Hydrogen = 0.004 /4 = 0.004

let us divide the moles of each C and H by lowest 0.0025 moles

moles of C = 1

Moles of H = 0.004/ 0.0025 = 1.6

Let us multiply both with 5

Moles of C : Moles of H = 5 : 8

so empirical formula = C5H8