Topic 1 : Formulae, Equations and Amount of Substance (EDEXCEL AS 2018)

In chemistry the amount of substance is always measured in moles

A mole is the amount of substance containing the Avogadro constant number of atoms,molecules or groups of ions


Avogadro constant




1.1
know the terms ‘atom', 'element', 'ion', 'molecule', 'compound', 'empirical formula' and 'molecular formula’

Molar mass (M)

Molar mass is the mass of 1 mole of substance. Its unit is g mol-1 (also written as g/mol and read as gram per mole).


The molar mass of any substance can be found by adding the relative atomic mass of all the constituent atoms of the formula.


Example to find the molar mass of glucose C6H12O6


First find the relative atomic masses of each element

C=12, H=1 and O =16


Then multiply this value by the number each element is repeated

So Carbon repeated 6 times, its mass = 12X6 = 72

And hydrogen is repeated 12 times its mass = 1X12 =12

Oxygen is repeated 6 times its mass = 16X6 = 96

If you add all, the molar mass of the glucose compound is 72+12+96 = 180 

Next Main point
Empirical and molecular formula
See also
calculations from percentage composition

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