mole concept and stoichiometry

Mole concept, stoichiometry, reacting masses – few terms you will find in the specification of different GCSE chemistry specifications like Cambridge, EdExcel, Oxford AQA. Questions ask in the form of mcq, and with experimental questions.

Let us address this in multiple ways. The first question is are you good in algebra, then mole concept would be more easier for you compared to the one who is not good in mathematics.

Let us try to break down the concept of mole concept, mainly how it is structured and how to study this concept.

To start with this, take a periodic table with you. Look at the atomic number of each element, you will find two numbers on each atom, simply the smaller one is the atomic number, for examples: take Sodium, Na – 11 is its atomic number and 23 is its atomic mass.

Now, the atomic mass of any element is equal to 1 mol of that element. That means 23g Na = 1 mol , 16g Oxygen = 1 mol of oxygen atom, like for all elements in periodic table.

Now, each of this element contains Avogadro number of atom, ie 6.022x 10^23 atoms. So we can say 1 mol of Na has 6.022x 10^23 Na atoms or 1 mol of Potassium (K) has 6.022x 10^23 K atoms.

Now mole concept for molecules or compounds.

Simply, compounds are having more than one atom. Examples include oxygen molecule (O2), nitrogen molecule (N2), water molecule (H2O), sulfuric acid (H2SO4) etc…

Now; we need to know how to calculate molecular mass, simply it is the total mass of all elements present in a compound.

Example ; O2 = 16+16 = 32g, H2O = (2x1g) + 16 g = 18g, H2SO4 = (2x1g) + (32g) + (4x16g) = 98g

So, 32g O2 = 1 mol O2

18 g H2O = 1 mol H2O

98 g H2SO4 = 1 mol H2SO4

They all have Avogadro number of molecules.

ie 32g O2 = 1 mol O2 = 6.022x 10^23 oxygen molecules

18 g H2O = 1 mol H2O =6.022x 10^23 water molecules

98 g H2SO4 = 1 mol H2SO4 = 6.022x 10^23 H2SO4 molecules.

If you want to calculate the number atoms in them, multiply number of molecules by atomicity ( in water it is 3, in sulfuric acid atomicity = 7).

Room Temperature and pressure (rtp)

At rtp, the volume of any 1 mol gas = 24 dm3 or 24000 cm3

if it is 2 mol of gas = 48 dm3 or 48000 cm3.

if it is 0.5 mol then 12 dm3 or 12000 cm3.

That is for this post. All the best for your exams.

mole concept and stoichiometry

Now mole concept for molecules or compounds.

Room Temperature and pressure (rtp)

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