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-
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-
