Question

What is the molar quantity of a $20.0g$ mass of citric acid, whose formula mass is ${C_6}{H_8}{O_7}$ ?

Answer 1

Citric acid belongs to the functional group of carboxylic acid as it contains three carboxylic acids along with one hydroxyl group. But due to the presence of three acid groups it was classified under carboxylic acid. The molar quantity is nothing but the number of moles that can be calculated from the given mass and molar mass of carboxylic acid.
$n = \dfrac{w}{M}$
$n$ is molar quantity or number of moles
$w$ is mass of citric acid given
$M$ is a molar mass of citric acid.

Complete answer:
Given that citric acid has a molecular formula of ${C_6}{H_8}{O_7}$ containing six carbon atoms, eight hydrogen atoms, and seven oxygen atoms.
Carbon is an element with atomic number $6$ and has molar mass of $12gmo{l^{ - 1}}$
Hydrogen is an element with atomic number $1$ and has molar mass of $1gmo{l^{ - 1}}$
Oxygen is an element with atomic number $8$ and has molar mass of $16gmo{l^{ - 1}}$
From the molecular formula of citric acid, the molar mass will be $6\left( {12} \right) + 8\left( 1 \right) + 7\left( {16} \right) = 192gmo{l^{ - 1}}$
Thus, the molar mass of citric acid is $192gmo{l^{ - 1}}$
Given that the mass of citric acid is $20g$
The number of moles will be obtained by dividing the given amount of mass with the molar mass of citric acid.
$n = \dfrac{{20}}{{192}} = 0.1mol$
The molar quantity of a $20.0g$ mass of citric acid, whose formula mass is ${C_6}{H_8}{O_7}$ is $0.1mol$

Note:
Citric acid is a carboxylic acid that can be obtained naturally from citrous fruits like oranges. It has many applications in medicine. It can also be used as an artificial flavouring agent. Citric acid is commonly used as a food preservative.