Question

A sample of ammonium phosphate, ${(N{H_4})_3}P{O_4}$ , contains $6moles$ of hydrogen atoms. The number of moles of oxygen atoms in the sample is:
A. $1$
B. $2$
C. $4$
D. $6$

Answer 1

Hint: Ammonium phosphate is an ammonium salt of orthophosphoric acid. It is a highly unstable compound with the formula ${(N{H_4})_3}P{O_4}$ . The ratio of the number of moles of any substance is equal to the number of atoms present in the compound.

Complete step by step answer:
Ammonium phosphate has a chemical formula of ${(N{H_4})_3}P{O_4}$ . This signifies that one molecule of ammonium phosphate has three atoms of nitrogen, twelve atoms of hydrogen, one atom of phosphorus and four atoms of oxygen. The number of moles of a substance is directly proportional to the number of atoms of the substance. In other words, if one molecule has a number of a particular type of atom in it then the molecule will have $(x \times n)$ number of that atom in it.
Thus, one molecule of ammonium phosphate contains:
Number of hydrogen atoms = $H = 12$
Number of oxygen atoms = $O = 4$
The ratio of the number of hydrogen and oxygen atoms is a constant in the compound.
One mole of ammonium phosphate contains:
Moles of hydrogen atoms = ${({n_H})_1} = 12$
Moles of oxygen atoms = ${({n_O})_1} = 4$
Hence, the ratio of moles of hydrogen and oxygen atoms is also a constant in the compound.
Let the moles of oxygen be ${n_O}$ and the number of moles of hydrogen be ${n_H}$ .
$\dfrac{{{{({n_H})}_1}}}{{{{({n_O})}_1}}} = \dfrac{{{{({n_H})}_2}}}{{{{({n_O})}_2}}}$
In the question, it is given that ${({n_H})_2}$ = 6 $moles$ . ${({n_O})_2}$ is the number of moles oxygen when the number of moles of hydrogen is $6moles$ .
Substituting the values in the above equation, we have:
$ \Rightarrow \dfrac{{12}}{4} = \dfrac{6}{{{{({n_O})}_2}}}$
Hence, ${({n_O})_2} = 2$ .

Thus, the correct option is B .

Note:
Ammonium phosphate is a colorless and crystalline solid. It is a solid which has the odor of ammonia and is soluble in water to a high extent. Because of its instability, it is elusive and of no commercial value.