Chemistry Extension 1

Mole Calculations

• n = amount of substance or mols
• Remember 1 mol is equal to 6 x 1023 particles
• Two formulae you should remember are n = m/M and n = cV

Percentage Yield

• Percentage yield = actual yield/theoretical yield x 100
• As many reactions involve alternative reactions.

Empirical and Molecular Formulae

• Divide m by M
• Divide all by the smallest n
• Determine ratio
• If working out the molecular formula then calculate M(empirical formula)
• Then divide by M(molecular) and multiply the formula by the simplest ratio

Titration Calculations

• Calculate the mols of the known
• Calculate the mols of the unknown from the equation
• Calculate the concentration of the unknown

Titration Technique

• Clean all gear with distilled water
• Rinse the burette and the pipette with the solutions going in them
• Check there are no stray drops on the burette or pipette
• Don't add too much indicator
• Go slowly!!!

Standard Solutions

• These are solutions which you make up that you know the exact concentration

Mixing Solutions

• c1V1 = c2V2
• Don't forget to add up all the volume

Oxidation-Reduction Chemistry

• Electrons are transferred from one species to another
• One species loses electrons (is oxidised)
• One species gains electrons (is reduced)

Oxidation Numbers

• All elements are 0
• O is always -2 unless in H2O2 where it is -1
• H is always +1 unless in metal hydrides where it is -1
• Ions carry their normal charge
• Atoms in a polyatomic ion add together to equal the charge on the ion

Two Step Redox Calculations

• These follow the same pattern 
• But the unknown and known varies as you use both equations