Question

1.6g of a hydrocarbon on complete combustion gave 4.4g of CO2 and 3.6g of H2O. Show that this data proves law of conservation of mass.

Answer 1

moles of carbon present in 4.4 g of carbon dioxide = 1.2 / 12 = 0.1
 moles of hydrogen present in 3.6 g of water = 0.4 / 2 = 0.2
 therefore molar ratio of carbon : hydrogen in products = molar ratio of carbon and hydrogen in the hydrocarbon = 1: 2 
 therefore the hydrocarbon is an alkene 
if the simplest alken is assumed ie ethene than the reaction of ethene with oxygen can be represented as
2 C2H6 +   7O2 ----> 4CO2 + 6 H20 
 hence amount of oxygen rqd to react with 1.6 g of ethene in the given reaction is equal to( 7 x 32 / 60) x 1.6 = 5.97 
 therefore total mass of reactant = 1.6 + 5.97 =7.57 
 the total mass of products = 4.4 + 3.6 = 8 since mass of product is almost equal to mass of reactant hence law of conservation of mass is proved .

Answer 2

1mole=given w.t/molar mass

given co2 w.t=4.4g (1.2+3.2=4.4)

no of moles of carbon in co2=1.2/12=0.1

and, given H2O w.t=3.6 (0.2+1.6=1.8)

no of moles of hydrogen in H2O=0.2/2=0.1

data proves law of conservation of mass

hope it's help ful