Calculate the relative molecular weight of NH3.

To calculate the relative molecular mass, you need to add the atomic mass of all elements of the substance:

NH3 – 1 N atom + 3 H atoms

1 N atom weighs 14 g / mol (gram per mol)

1 H atom weighs 1 g / mol

If an element has an index, that is, there is more than one atom, then the number of atoms is multiplied by the element’s atomic mass. In this case, there are three hydrogen atoms:

Mr (NH3) = 14 + 3 * 1 = 17 g / mol

Answer: Mr (NH3) = 17 g / mol