Question

The anion nitrate is converted into ammonium ion. The equivalent mass of nitrate ion in the reaction would be:
A.6.20
B.7.75
C.10.5
D.21.0

Answer 1

The equivalent weight of a solution is defined as the molecular weight of the solute divided by the valence of the solute. It is basically used to predict the mass of a substance that reacts with one atom of hydrogen in an acid-base analysis.
Formula used:
Equivalent weight $= \dfrac{{molecular\,weight}}{{valence\,factor}}$

Complete step by step answer:
A nitrate ion is made up of a nitrogen atom and three oxygen atoms. The oxidation number of nitrogen in the nitrate is +5 and has a trigonal planar geometry. Further, the ammonium cation is a positively charged polyatomic ion with the chemical formula $N{H_4}^ +$ .
Now, we have to calculate the equivalent mass of nitrate ions. So basically equivalent mass is defined as the molecular weight of the solution divided by the valence of the solute. Let’s write the reaction and then calculate the equivalent mass. The reaction is as shown:
$N{O_3}^ - \to N{H_4}^ +$
Now, the molecular weight of nitrate ion is 62g
The valence factor of nitrate ion and ammonium ion are +5 and-3 respectively.
Therefore, according to the formula,
Equivalent weight $= \dfrac{{molecular\,weight}}{{valence\,factor}}$
$= \dfrac{{62}}{8}$
=7.75g

Hence, option B is correct.

Note:
The terms ‘nitrite’ and ‘nitrates’ are frequently used interchangeably owing to their similar pronunciations and spellings. It is basically the number of oxygen atoms that bring out the difference in the shape, chemical structure and properties of these compounds. Nitrites are known to have one nitrogen atom along with two oxygen atoms whereas nitrates are known to have one nitrogen atom bonded to three different oxygen atoms.