Question

Calculate the mass of three moles of ethane.

Answer 1

Hint: In order to solve this question, one must be familiar with the mole concept. Ethane is made up of carbon and hydrogen. Their respective standard atomic weights, when added in their respective proportions (quantities), will provide the mass of one mole of ethane. This will give us the molar mass or molecular weight of ethane.

Complete answer:
The structure of the given compound, ethane is

Ethane is an inflammable alkane, having the chemical formula $C_2{H}_6$ .
Now, as carbon and hydrogen are the respective constituents of ethane, we need to calculate their individual mass in one mole of ethane.
Thus, as the atomic weight of carbon $=12$ and as there are two carbon atoms present in the compound, the amount of carbon in one mole of ethane $=12\times 2=24$ grams.
Similarly, we now compute for hydrogen, whose atomic weight $=1$ , and as there are six hydrogen atoms present in ethane, the amount of hydrogen present in one mole of ethane $=1\times 6=6$ grams.
Therefore, the mass of one mole of ethane (molar mass) $=24+6=30$ grams.
For three moles of ethane, we multiply its molar mass by three (by applying the unitary method), and we get $=30\times 3=90$ grams.
Thus, the mass of three moles of ethane is $90$ grams.

Note:
For solving this question, one must be aware of the concept of atomic weights. The mass of a compound is the sum of standard atomic masses of its constituent atoms in their respective proportions or quantities. The molar mass of a compound, expressed in grams, is the mass of $6.022\times {10}^{23}$ particles of that substance.