Question

Calculate following in $5.6g$ of $nitrogen$
A. Number of moles
B. Number of molecules of ${N_2}$
C. Number of atoms of $nitrogen$

Answer 1

To find the above all solutions, one must be familiar with the concept of moles. The above quantity is the provided or given mass of the element$nitrogen$. Simply putting that value in the number of moles formula, we will be able to find the solution.

Complete answer:
One mole is the amount of a substance that contains as many particles or entities as there are atoms in exactly $12g$ of the $^{12}C$ isotopes. It is similar to the quantities as we denote one dozen or a gross for $12$ or $144$ items. The S.I. unit is $mole$ and the symbol for mole is $mol$. The mole of a substance always contains the same number of entities, no matter what the substance may be. This is represented by which is equal to $6.022 \times {10^{23}}atoms/mol$
Also the molar mass is the mass of one mole of a substance in $grams$. The molar mass in $grams$ is numerically equal to atomic or molecular formula mass in $u$
The number of moles is given by the formula-
$No.{\text{ }}of{\text{ }}moles = \dfrac{{Given{\text{ mass}}}}{{Molar{\text{ mass}}}}$
Now that we are familiar with these concepts we will solve the given question.
A. To find the number of moles of $nitrogen$ atom we will use the same formula-
$No.{\text{ }}of{\text{ }}moles = \dfrac{{Given{\text{ mass}}}}{{Molar{\text{ mass}}}}$
Molar mass of ${N_2}$= $2 \times 14 = 28g/mol$
No. of moles= $\dfrac{{5.6}}{{28}} = 0.2mol$
B. Number of molecules of ${N_2}$
$= 6.022 \times {10^{23}} \times no.{\text{ of moles of }}{N_2}$
$= 6.022 \times {10^{23}} \times 0.2$
$= 1.2 \times {10^{23}}$
C. Number of atoms of ${N_2}$
(There are two $nitrogen$ atoms in ${N_2}$)
$= 2 \times {\text{no}}{\text{. of }}{{\text{N}}_2}{\text{ molecules}}$
$= 2 \times 1.2 \times {10^{23}} = 2.4 \times {10^{23}}$

Note:
Atoms and molecules are extremely small in size and their numbers in even a small amount of any substance is really very large. To handle such large numbers, a unit of similar magnitude is required. Therefore the mole concept was introduced.