Question

$3000\;cc$ of oxygen was burnt with $600\;cc$ of ethane $({C_2}{H_6})$. Calculate the volume of unused oxygen.
A) $300\;cc$
B) $600\;cc$
C) $900\;cc$
D) $1200\;cc$

Answer 1

As we know that whenever a compound burns in the presence of oxygen it results into the formation of carbon dioxide and water and the stoichiometric coefficients can be used to determine the moles, amount of substances as well as the volumes of the given substances and the products formed.

Complete answer:
As we already know that when ethane burns in the presence of oxygen it results in the formation of carbon dioxide and water molecules. We can show this with the help of a chemical reaction as:
$2{C_2}{H_6} + 7{O_2} \to 4C{O_2} + 6{H_2}O$
From the above equation we can say that two moles of ethane reacts with seven moles of oxygen to give four moles of carbon dioxide and six moles of water. Also we can say that two moles of ethane requires seven moles of oxygen to burn.
In terms of volume we can say that two volumes of ethane requires seven volumes of oxygen, so $600\;cc$ of ethane would require $= \dfrac{7}{2} \times 600 = 2100\;cc$.
And we are given the condition that $3000\;cc$ of oxygen is burnt in the reaction. And we just calculated that only $2100\;cc$ of oxygen is required to burn the given volume of ethane. So we can now easily calculate the unused amount of oxygen simply by subtracting both the values and we will get:
${O_2}\;unused = 3000 - 2100 = 900\;cc$
Therefore, from the above equation we can say that the correct answer is (C).

Note: At STP, ethane is generally a colourless and odourless gas and it is the second most abundant gases used in households. It is also used in the production of ethylene chemicals which is used in the manufacturing of plastics, detergents and automotive antifreeze etc.