A Level OCR A Chemistry Paper 3

A Level OCR
A-
Chemistry
Paper 3

Amount of substance equations answermass = mr x moles

mol = vol x conc

vol(gas) = mol x 24 (dm)

PV=nRT
(pressure, Pa, volume, m3, moles, -, 8.314, temp, k)

, Empirical formula answerThe simplest whole number ratio of atoms of each element in
a compound

Molecular formula answerThe number and type of atoms of each element in a molecule

Celsius to Kelvin answerK=C+273

% yield and atom economy answer% yield = (actual/ theoretical) x 100

atom economy = (desired products/all reactants) x 100

Oxidising agent answerit itself is reduced, causes another species to be oxidised

Reducing agent answerit itself is oxidised, causes another species to be reduced

Oxidation answerLoss of electrons, increased oxidation number

Reduction answerGain in electrons, decreased oxidation number

Balancing half equations answerBalance all atoms apart from oxygen and hydrogen
Add H2O to balance oxygen
Add H+ to balance hydrogen
Add e- to balance charges

Potassium manganate and iron ions [or (COOH)2] titrations answerPotassium
manganate reduced (burette)
Iron solution + excess dilute H2SO4 (provides H+ ions)
added to conical flask (colourless)
doesnt need indicator (self indicating)
end point = permanent pink colour

Fe2+ --> Fe3+ + e-
MnO4- + 8H+ + 5e- --> Mn2+ + 4H2O

MnO4- + 8H+ + 5Fe2+ --> Mn2+ + 4H2O + 4Fe3+

Iodine and sodium thiosulfate titrations answerNa2S2O3 oxidised (burette)
oxidisng agent + excess KI produces iodine in conical flask (yellow-brown)
titration --> pale straw colour
add starch indicator (end point= blue-black --> colourless)

I2 + 2e- --> 2I-
2S2O3 2- --> S4O6 2- + 2e-

2S2O3 2- + I2 --> S4O6 2- + 2I-