Question

Find the molecular mass(in kilogram) of ammonia molecule ${ NH }_{ 3 }$.

Answer 1

Hint: We should know that the molecular mass of one molecule is its mass expressed in unified atomic mass units (1/12 the mass of one atom of the isotope carbon-12. So now you can calculate the mass of the ammonia molecule accordingly.

Complete step by step answer:
> To determine the molecular mass of any compound, all you have to do is add up the molar masses of every atom that makes up the respective compound.
So, herein ammonia (${ NH }_{ 3 }$) we have three hydrogen atoms and one nitrogen atom.
Atomic masses of,
- Hydrogen = 3 x 1.00784 g/mol = 3.02352 g/mol
- Nitrogen = 1 x 14.0067 g/mol = 14.0067 g/mol
Now add them to find the total molecular mass of ${ NH }_{ 3 }$
= 3.02352 + 14.0067
= 17.03022 g/mol
> As we know this is the mass of 1-mole ammonia molecules ($6.022\quad \times \quad 10^{ 23 }$ molecules). So, for one molecule of ammonia, the mass would be
$=\quad \frac { 17.03022 }{ 6.022\quad \times { \quad 10 }^{ 23 } }$
= $2.828\quad \times \quad 10^{ -23 }$
- This answer we have got is in grams. Now to convert this grams into kilograms, we must divide it by 1000. We’ll get $2.828\quad \times \quad 10^{ -26 }$ kg. So, the final answer for the molecular mass of one ammonia molecule will be $2.828\quad \times \quad 10^{ -26 }$ kg.

Note: Molar mass - The molar mass is the mass of a given chemical compound (g) divided by the amount of substance (mol).
- The molar mass of a compound can be calculated by adding the standard atomic masses (in g/mol) of the constituent atoms.
- Molecular mass - The molecular mass is the mass of one molecule of a given chemical compound (g).
- The molecular mass of a compound can be calculated by adding the standard atomic masses (in g/mol) of the constituent atoms and then divide it by avogadro number.