Quantitative Chemistry

Question 1

Relative Molecular Mass (RMM) or formula mass

Answer 1

The RMM is found by adding the relative atomic masses of all the atoms in the molecule.

e.g.
A water molecule has 2 H atoms and 1 O atom.
The relative atomic masses can be found in the periodic table.
e.g. H= 1.0079, H=1 and O=15.9994 O=16

RMM of H20 = (2x1) + 16
= 18

Question 2

Mole

Answer 2

A unit called the mole is used to convey the actual number of particles present.

Question 3

Molar Mass

Answer 3

The mass of one mole (molar mass) of a substance is always equal to the formula mass of a substance in grams.

Question 4

Molar Mass, example

Answer 4

Water, H2O, has an RMM or formula mass of 18.

This means that 1 mole of water will weigh 18 grams.

Hence the molar mass of H2O is18 grams per mole.

In a glass of water containing180 g, there is 10 moles of water

(since 18 x 10 = 180)