Question

Find number of moles, ions, total number of electrons and total number of protons in $28{\text{gm}}$ of ${{\text{N}}^{{\text{3 - }}}}$ sample.

Answer 1

Hint: To answer this question, you must recall the basic structure of an atom. When an ion is formed, only the number of electrons change, the number of protons and neutrons remains the same.
Formula used : ${\text{moles = }}\dfrac{{{\text{mass}}}}{{{\text{molar mass}}}}$

Complete step by step answer:
${{\text{N}}^{{\text{3 - }}}}$ is an ion of the nitrogen atom. We know that ion formation does not have any effect on the mass of the atom. The mass of the atom is considered equal to the mass of the nucleus as the mass of electrons is negligible in comparison to the mass of protons.
So, the molar mass of ${{\text{N}}^{{\text{3 - }}}}$$ = 14{\text{g}}$.
The number of moles of a substance is equal to the ratio of the given mass of substance and its molar mass.
Number of moles of ${{\text{N}}^{{\text{3 - }}}}$$ = \dfrac{{28}}{{14}} = 2{\text{mols}}$
We know that one mole of any substance contains $6.023 \times {10^{23}}$ particles (atoms, ions, molecules).
So the number of ions in two moles of ${{\text{N}}^{{\text{3 - }}}}$ is given as,
${\text{N}} = 2 \times {{\text{N}}_{\text{A}}} = 2 \times \left( {6.023 \times {{10}^3}} \right)$
Where, ${{\text{N}}_{\text{A}}}$ is Avogadro’s number
Therefore, number of ions of ${{\text{N}}^{{\text{3 - }}}}$ in the given sample ${\text{ = N}} = 12.046 \times {10^{23}}$
We know that a nitrogen atom has atomic number 7. This means that in its atomic state it has 7 electrons and 7 protons.
In ${{\text{N}}^{{\text{3 - }}}}$ ion, there is a negative charge of magnitude three on the ion, which suggests that it has 3 extra electrons.
So the number of electrons in one ion is $7 + 3 = 10$
Thus, the number of electrons in 2 moles of the sample is
$ = 10 \times 2 \times {{\text{N}}_{\text{A}}} = 10 \times 2 \times 6.023 \times {10^{23}}$
$ = 12.046 \times {10^{24}}$
Similarly, the number of protons in one ion is $7$.
Thus, the number of protons in 2 moles of the sample is
$ = 7 \times 2 \times {{\text{N}}_{\text{A}}} = 7 \times 10 \times 6.023 \times {10^{23}}$
$ = 42.161 \times {10^{24}}$.

Note:
An Atom of each element contains a fixed number of protons. Rather, we can say that the number of protons determines the atom we are considering. We are familiar with the fact that the number of protons in an atom is called the atomic number of the atom. Unlike the number of protons, the number of neutrons for a certain element can vary. Atoms of the same element that differ only in the number of neutrons in their nucleus are called isotopes. Together, the number of protons and the number of neutrons determine the atomic mass of the element.