Question

What is the mass in grams of \[5.90{\text{ }}mol\]\[{C_8}{H_{18}}\]?

Answer 1

Hint: You must recall the concept of molar mass which refers to the ratio of mass of a sample of that particular compound and the amount of substance in that particular sample (in moles). The molar mass is actually a bulk characteristic of a substance rather than molecular. The molar mass is generally represented as \[gmo{l^{ - 1}}\].

Complete step by step answer:
In this question, we are given the number of moles of octane \[{C_8}{H_{18}}\]i.e. \[5.90{\text{ }}mol\]. And the mass of \[5.90{\text{ }}mol\]\[{C_8}{H_{18}}\] can be found out if we know the mass of one mole of \[{C_8}{H_{18}}\]. The molar mass of any compound can be found out by adding the relative atomic masses of each element present in that particular compound. The number of atoms in a compound can be determined from their chemical formula.
Now, let us calculate the molar mass of the given compound i.e. octane having a chemical formula of \[{C_8}{H_{18}}\]. We already know the atomic mass of carbon and hydrogen which is mentioned below:
$
  C = 12.0107u \\
  H = 1.0078u \\
$
From the chemical formula, it is clear that the given compound octane comprises of eight atoms of carbon and eighteen atoms of hydrogen and thus molar mass of this compound can be easily calculated by adding the mass of eight carbon atoms and eighteen hydrogen atoms as shown below:
$Molar{\text{ }}mass{\text{ }}of {\text{ }}{{\text{C}}_8}{H_{18}} = (8 \times C) + (18 \times H) = (8 \times 12.0107) + (18 \times 1.0078) = 114.226gmo{l^{ - 1}}$
Now, mass in grams of \[5.90{\text{ }}mol\] \[{C_8}{H_{18}}\] can be calculated as:
$5.90mol \times 114.226\dfrac{g}{{mol}} = 673.9334g$
Hence, 673.9334 is the mass in grams of \[5.90{\text{ }}mol\] \[{C_8}{H_{18}}\].

Note: Molar mass plays a significant role in chemistry especially during setting up an experiment. During testing principles which involve specific amounts or quantities of a substance, molar mass is used to figure out the exact quantity to be weighed of that particular substance. Basically molar mass is used to determine the stoichiometry in the chemical reactions as well as equations.