Question

What is the formula mass of ammonia ?

Answer 1

Hint: The formula mass of any compound is calculated by taking into consideration the masses of the individual atoms involved in the formation of the particular compound. Each atom contributes a mass equal to its gram atomic mass.

Complete answer:
Ammonia is the trihydride of nitrogen that is a polar inorganic solvent and a strong organic base as it contains a lone pair of electrons. The formula of ammonia is \[N{H_3}\] which gives us the information that there are three hydrogen atoms and one nitrogen atom in the formula of ammonia.
The formula mass can be calculated by taking the sum of all the gram atomic masses of nitrogen and hydrogen atoms multiplied by the number of atoms that are there in the formula.
The following formula can be used to calculate the mass:
\[{\text{formula mass}} = 1 \times ({\text{mass of nitrogen)}} + 3 \times ({\text{mass of hydrogen)}}\]
The mass of one mole of nitrogen is \[14gmo{l^{ - 1}}\] and that of one mole of hydrogen is \[1gmo{l^{ - 1}}\] .
Putting in the values of masses of nitrogen and hydrogen in the formula of formula mass we get,
\[{\text{formula mass}} = 1 \times (14gmo{l^{ - 1}}{\text{)}} + 3 \times (1gmo{l^{ - 1}}{\text{) = 17}}gmo{l^{ - 1}}\]
\[ \Rightarrow \] Hence, the formula mass of ammonia comes out to be equal to \[{\text{17}}gmo{l^{ - 1}}\]

Note:
The formula mass of any compound is not the same as the molecular mass or the molar mass even though it has the same units. The molecular mass deals with the total mass of atoms present in one molecule and the formula mass deals with the net mass associated with the formula. Certain ionic compounds like sodium chloride have a simple formula but their molecules and clusters are complex and in those cases formula mass is used.