Question

$10ml$ of a gaseous hydrocarbon is exploded with $100ml$ of oxygen. The residual gas on cooling is found to measure $95ml$ of which $20ml$ is absorbed by causative soda and the remainder by alkaline pyrogallol. The formula of the hydrocarbon is:
a.) $C{H_4}$
b.) ${C_2}{H_6}$
c.) ${C_2}{H_4}$
d.) ${C_2}{H_2}$

Answer 1

Hint: To solve this problem firstly we should learn about purification of organic compounds and qualitative and quantitative Analysis and percent composition and gather all the information regarding it. By using the concept behind it, we can use the given knowledge to approach our answer easily.

Complete step by step solution: When an organic compound is extracted from a natural source or synthesized in the laboratory, it is essential to purify it. So, various methods are used for the purification of organic compounds based on the nature of the compound and the impurity present in it.
The common techniques used for purification are Sublimation, Crystallization, Distillation, Chromatography.
Qualitative Analysis: Fundamentally it is to measure something by its quality. In qualitative analysis, we are exploring how we describe something. We can’t use numbers or numerical expressions to describe those things.
Quantitative Analysis: Fundamentally it is the opposite to measure by quantity. In quantitative analysis, we are exploring facts, measure, numbers and percentage. In this analysis we work with numbers, statistics, formulas and data.
Percent composition: In percent composition of a component in a compound is the percent of the total mass of the compound that is due to that component.

${C_x}{H_y} + \left( {x + \frac{y}{4}} \right){O_2} \to xC{O_2} + \frac{y}{2}{H_2}O$
$1ml\left( {x + \frac{y}{4}} \right)ml\,xml\frac{y}{2}ml$
$10ml\,10\left( {x + \frac{y}{4}} \right)ml\,10xml$
Volume absorbed by$KOH$ = Volume of $C{O_2}$
Volume of $C{O_2} = 20$
$x = 2ml = 2mol$
Volume absorbed by alkaline pyrogallol$ = $ Volume of ${O_2}$
$ = 95 - 20 = 75ml$
Excess of ${O_2} = 75ml$
Total ${O_2} = 100ml$
Volume of ${O_2}$ reacted$ = 100 - 75 = 25ml$
$10\left( {x + \frac{y}{4}} \right) = 25ml$
$y = 2$
Formula of hydrocarbon is${C_2}{H_2}$

Hence, the correct answer is option D. ${C_2}{H_2}$

Note: The percentage composition of a compound is defined as the ratio of amount of each element to the total amount of individual element present in the compound multiplied by $100$. Here the quantity is measured in grams. It expresses its composition in terms of all the elements present, thus helping in chemical Analysis.