Summary AQA Chemistry- Amount of Substances Notes

Amount of Substance

Relative Atomic Mass→ average mass of one atom relative to 1/12th of the mass of
one atom of C-12
Empirical Formula→ simplest integer ratio of atoms in each element in a compound
Molecular Formua→ actual number of atoms of each element in a compound

How many moles of X atoms are present in p moles of XnYm?⇒ n * p= number of moles

Empirical and Molecular Formula⇒
1. Divide each mass (or % mass) by the atomic mass of the element
2. For each of the answers from (1) divide by the smallest one of those
3. Turn the ratio into whole numbers which give the empirical formula
4. Find the Mr of the empirical formula
5. Divide the Mr of the molecular formula by the empirical to find the multiple
6. Multiply the empirical formula by your whole number answer in (5)

Water of Crystalisation⇒
Find x from M·xH2O:
(1) Mass of beaker (g) b

(2) Mass of hydrated salt in w+s+b
beaker (g)

(3) Mass of anhydrous salt s+b
after heating in beaker (g)

Mass of hydrated salt= (2) - (1) (w+s+b) - b=w+s
Mass of water lost= (2) - (3) (w+s+b) - (s+b)=w
Mass of anhydrous salt= (3) - (1) (s+b) - b=s
1. Find the moles of M (anhydrous salt)
2. Moles of M·xH2O=moles of M
3. Find Mr of M·xH2O by dividing the mass of the hydrated salt by its moles
4. Solve for x

Dilution⇒ Original concentration * (original volume/total volume)

Ideal Gas Equation⇒
P(Pa) * V(m3) = n * R(8.31J/K/mol) * T(K) → must state