Question

If $0.2$ mol of sodium chloride is required, how many grams of sodium chloride should be taken?

Answer 1

Hint: The larger unit which is used for comparing the amounts of different substances is called mole. One mole is defined as the number of particles (atoms, molecules, ions, electrons, etc.) which are equal to the number of atoms present in 12 g of C-12 isotope.
The number of moles of a substance is also related to the mass of the substance.

Complete step by step answer:
Given that number of moles of sodium chloride is $0.2$ mol.
We need to find out the mass of sodium chloride taken in grams.
We know that the mass of a substance is related to its number of moles according to the following relation:
${\text{n = }}\dfrac{{\text{w}}}{{\text{M}}}$
Here, ‘n’ represents the number of moles of the substance, ‘w’ represents the weight or the mass of the substance in grams and ‘M’ represents the molar mass of the substance.
This relation can also be rearranged and expressed as follows:
${\text{w}} = {\text{n}} \times {\text{M}}$
We can use the above relation to find out the mass of sodium chloride in grams from the given number of moles.
Now, according to the given question, ‘n’ is equal to $0.2$ mol.
The molar mass of sodium chloride can be calculated by adding the atomic masses of all the atoms present in it. Since sodium chloride is made up of two constituent atoms, one sodium atom and one chlorine atom, so, the molar mass of sodium chloride ‘M’ is obtained by the sum of the atomic mass of sodium which is 23 and the atomic mass of chlorine which is $35.5$ .
Hence, the molar mass of sodium chloride:
$
  {\text{M = 23 + 35}}{\text{.5}} \\
   \Rightarrow {\text{M = }}58.5 \\
 $
Substitute the values of ‘n’ and ‘M’ in the relation. Thus, mass of sodium chloride in grams is:
$
  {\text{w}} = 0.2 \times 58.5 \\
   \Rightarrow {\text{w}} = 11.7{\text{g}} \\
 $

Note:
According to the mole concept, the quantity of matter containing $6.02 \times {10^{23}}$ number of particles represents one mole of that species. This number is called the Avogadro’s number. It is denoted by the symbol ${{\text{N}}_{\text{A}}}$ .
The mole concept or Avogadro’s number ${{\text{N}}_{\text{A}}}$ can be used in evaluating the mass of one molecule of the substance from its gram molecular mass M.
Thus, mass of one molecule of the substance $ = \dfrac{{\text{M}}}{{{{\text{N}}_{\text{A}}}}}$