Question

Ammonium sulfate, $\,{\left( {{\mathbf{N}}{{\mathbf{H}}_4}} \right)_2}{\mathbf{S}}{{\mathbf{O}}_4}\,$ and ammonium nitrate $\,{\mathbf{N}}{{\mathbf{H}}_4}{\mathbf{N}}{{\mathbf{O}}_3},\,$ are used as fertilizers. These salts have different percentages by mass of nitrogen. They have the same effect as each other on the pH of neutral soil. Which row is correct?

Higher percentage of nitrogen by mass	Effect on pH of soil
A	ammonium nitrate	decrease
B	ammonium nitrate	increase
C	ammonium sulfate	decrease
D	ammonium sulfate	increase

A.A
B.B
C.C
D.D

Answer 1

Hint:In order to get the answer to this question, we have to first understand the molecular mass of each compound so that we can calculate which one has the highest percentage of nitrogen by mass. After that we have to analyse the effect on $\,pH\,$.
-Molecular mass of ammonium sulfate $\, = 132g\,$
-Molecular mass of ammonium nitrate $\, = 80g\,$
Complete answer:
First, let us calculate the compound with highest percentage of nitrogen by mass;
-Ammonium sulfate: $\,{(N{H_4})_2}S{O_4}\,$
-Molecular mass is $\,132g\,$. Here as two nitrogen atoms are present, $\,28g\,$of nitrogen is present in $\,132g\,$of ammonium sulfate.
-Ammonium nitrate: $\,N{H_4}N{O_3}\,$
-Molecular mass is $\,80g\,$. Here also we can see that two nitrogen atoms are present, hence $\,28g\,$
of nitrogen is present in $\,80g\,$of ammonium nitrate.
-From this we understand that highest percentage of nitrogen by mass is present in ammonium nitrate as in $\,80g\,$of it we have $\,28g\,$of nitrogen and this is higher when compared to ammonium sulfate whose mass is higher than ammonium nitrate.
-Ammonium nitrite contains both a weak acid and a weak base, so because the ammonium ion's $\,{K_a}\,$ is stronger than the nitrite ion's $\,{K_b}\,$, the measure indicates that the solution is much more acidic. Hence, it reduces the pH of the soil.
So, for this question, option B is the correct answer.

Note:
It is important to note that, ammonium nitrate is not actually an acid rather it is a salt, but since it is a salt with a weak base as ammonium hydroxide and a strong nitric acid, the solution is acidic. As the nitrogen content in ammonium nitrate is higher it helps in the growth of plants ten times more than other fertilizers.