Question

Calculate the number of atoms present in each of the following:
a) $0.5moles$ of atoms of nitrogen
b) $0.2mol$ of molecules of nitrogen
c) $3.2g$ of sulphur

Answer 1

Hint: Number of atoms that is present in one mole of element is the Avogadro’s number. Avogadro’s number $ = 6.023 \times {10^{23}}mo{l^{ - 1}}$ . It is denoted by the symbol ${N_A}$ .

Complete step by step answer:
Avogadro’s number is defined as the elementary particles such as molecules, atoms or compounds present in one mole of a substance.
Avogadro’s number ${N_A} = 6.023 \times {10^{23}}mo{l^{ - 1}}$ .
Number of atoms is given as follows:
Number of atoms \[ = {N_A} \times \] number of moles or
Number of atoms \[ = 6.023 \times {10^{23}} \times \] number of moles.
Given data:
Number of moles of atoms of nitrogen $ = 0.5mol$
Number of atoms of nitrogen $ = {N_A} \times $ number of moles of nitrogen
Number of atoms of nitrogen $ = 6.023 \times {10^{23}} \times 0.5$
Number of atoms of nitrogen $ = 3.01 \times {10^{23}}$ atoms.
Therefore, $0.5$ moles of atoms of nitrogen consists of $ = 3.01 \times {10^{23}}$ atoms.
Number of atoms of nitrogen $ = 0.2mol$
Number of atoms of nitrogen $ = {N_A} \times $ number of moles of nitrogen
Number of atoms of nitrogen $ = 6.023 \times {10^{23}} \times 0.2$
Number of atoms of nitrogen $ = 1.205 \times {10^{23}}$ atoms.
Therefore, $0.2$ moles of atoms of nitrogen consists of $ = 1.205 \times {10^{23}}$ atoms.
Atomic mass of sulphur $ = 32$
This means $32g$ of sulphur consists of $6.023 \times {10^{23}}$ atoms
Therefore, $3.2g$ of sulphur will contain$ = ?$atoms of sulphur
Number of atoms of sulphur $ = \dfrac{{3.2 \times 6.023 \times {{10}^{23}}}}{{32}}$
Number of atoms of sulphur $ = \dfrac{{19.273 \times {{10}^{23}}}}{{32}}$
Number of atoms of sulphur $ = 0.6023 \times {10^{23}}$
Therefore, $3.2g $ of sulphur contains $0.6023 \times {10^{23}}$ atoms of sulphur.

So, the correct answer is Option A.

Note: A mole is a measure of the quantity of atoms, molecules, protons, electrons and so on.
A mol is defined as the amount of substance that contains particles as much as they are present in $12g$ of carbon atoms.
Avogadro’s number is that the one mole of a substance is equal to the molecular weight of the substance. Avogadro’s number is a dimensionless quantity.