Question

On complete combustion, 0.246 g of an organic compound gave 0.198g of carbon dioxide and 0.1014g of water. Determine the percentage composition of carbon and hydrogen in the compound.

Answer 1

Hint :Combustion, also known as burning, is a high-temperature exothermic redox chemical reaction that takes place between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, to produce oxidized, often gaseous products in a mixture known as smoke. Because a flame is only visible when substances undergoing combustion vapourize, combustion does not always result in fire, but when it does, a flame is a characteristic indicator of the reaction.

Complete Step By Step Answer:
Combustion is frequently a complex series of elementary radical reactions. Endothermic pyrolysis converts solid fuels like wood and coal into gaseous fuels, whose combustion provides the heat needed to produce more of them. Combustion is frequently hot enough to produce incandescent light in the form of glowing or a flame.
A simple example is the reaction of hydrogen and oxygen into water vapor, which is commonly used to fuel rocket engines. This reaction produces $ 242\text{ }kJ/mol $ of heat and thus decreases the enthalpy (at constant temperature and pressure):
 $ 2{{H}_{2}}\left( g \right)\text{ }+~{{O}_{2}}\left( g \right)\text{ }\to \text{ }2{{H}_{2}}O\left( g \right) $
In the above example,
Weight of $ C{{O}_{2}} $ = $ 0.198 $ gm
Weight of $ {{H}_{2}}O $ = $ 0.1014 $ gm
Weight of compound = $ 0.246 $ g
 $ % $ of $ carbon $ = $ \dfrac{12}{44}\times \dfrac{waightofC{{O}_{2}}}{total wt.of compound}\times 100 $
 $ =\dfrac{12}{44}\times \dfrac{0.198}{0.246}\times 100 $
 $ =0.2727\times 80.4887 $
 $ =21.94% $
 $ % $ $ of $ $ Hydrogen $ = $ \dfrac{2}{18}\times \dfrac{weight of{{H}_{2}}O}{total wt.of compound}\times 100 $
 $ =\dfrac{2}{18}\times \dfrac{0.1014}{0.246}\times 100 $
 $ =4.579% $
Thus,
 $ % $ $ of $ $ carbon $ $ =21.94% $
 $ % $ $ of $ $ Hydrogen $ $ =4.579% $ .

Note :
The combustion of an organic fuel in air is always exothermic because the double bond in $ {{O}_{2}} $ is much weaker than other double bonds or pairs of single bonds, resulting in the formation of stronger bonds in the combustion products $ C{{O}_{2}} $ and $ {{H}_{2}}O $ .