Question

$10$ g of a hydrocarbon exactly requires $40$ g of oxygen for complete combustion. The products formed are $C{O}_2$ and water. When $C{O}_2$ gas formed is absorbed completely in lime water, the mass of the solution increases by $27.5$ g. What is the mass of water formed in the combustion reaction?

• A. $22.5$ g
• B. $27.5$ g
• C. $50$ g
• D. $10$ g

Answer 1

The correct option is A $22.5$ g

Reaction occurs as follows :-

Hydrocarbon + Oxygen $\to$ $C{O}_2$ + Water
As when $C{O}_2$ is absorbed in lime water, the mass of solution increases by $27.5$ g.
$\therefore$ Increase in mass of solution is due to $C{O}_2$
$\therefore$ Mass of $C{O}_2$ = $27.5$ g
Also it is given in question that,
mass of Hydrocarbon = $10$ g
mass of Oxygen = $40$ g
According to law of conservation of mass, in a chemical reaction,
$Massofreactant=Massofproduct$
$\therefore$ Mass of Hydrocarbon + Mass of Oxygen = Mass of $C{O}_2$ + Mass of $H_{2}O$
$\therefore$ $10$ g + $40$ g = $27.5$ g + Mass of $H_{2}O$
$\therefore$ Mass of $H_{2}O$ = $22.5$ g