OCR Chemistry A 2016 unofficial mark scheme 27/05/16

This guy is a teacher and will do the whole paper and post the mark scheme https://twitter.com/ChemistryALevel

Not sure about some of these...

Not sure about some of these...

You cannot use Br2 because you will make a dihaloalkane and you cannot make an alcohol from dihaloalkane. You had to use HBr to make haloalkane and then NaOH to make alcohol.

You cannot use Br2 because you will make a dihaloalkane and you cannot make an alcohol from dihaloalkane. You had to use HBr to make haloalkane and then NaOH to make alcohol.

Thanks for the marks scheme really appreciate can I just ask if possible could you update with what the question was if possible, obviously multiple choice may not be possible but for the others could you say what the question was

Oh **** it's ammonium sulfide!!!! not sulphate.

That was a b***chy question haha managed to suss it out tho

which ones in that are wrong?

*No of atoms in 5.00g coin: 3.98 x 10^22 (3sf) *

For this one, I got 3.97 x 10^22 for using the RAM calculated in the part before?? Did you have to use the periodic table one or the calculated one?

Here's my attempt at an unofficial mark scheme, it is for the OCR Chemistry A, new spec, breadth in chemistry paper, really can only put the maths questions down, but if there are written ones I can remember I will put them down. This is only really for comparison of numbers, and general ideas

Multiple choice:
BCDACCBDCBCBBCBDDBBD [20] (if anyone happened to store their multiple choice answers on their calculator, please post them below to compare)

Similarities and differences of isotopes: Same number of protons and electrons, different number of neutrons [2]
Relative atomic mass: 63.62 [2]
No of atoms in 5.00g coin: 3.98 x 10^22 (3sf) [2]
Equation with nickel (II) oxide and nitric acid: NiO + 2HNO3 --> Ni(NO3)2 + H2O [1]
Dot and cross: [2]
Empirical formula with water of crystallisation: CrCl3 • 6H2O [3]
Percentage error of water removed mass: 1.72% [2]
Ways to reduce percentage uncertainty: use a larger mass of crystals to get larger mass of water removed, reducing % error [1]
To make sure mass of water removed is correct: reweigh and reheat, repeat until constant mass is achieved [1]
Volume of H2SO4 required to neutralise NaOH: 24.8cm^3 [3]
Oxidation: Al oxidised from 0 to +3 and H reduced from +1 to 0 [2]
Electron configuration of bromide ion: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 [1]
Displacement question: Cl2(g) + 2Br-(aq) = 2Cl- (aq) + Br2 (aq) [1] chlorine is more reactive than bromine [1]
Adding chlorine to water: benefit, kills bacteria, risk, chlorine is toxic [1]
Reagent for halide precipitate: AgNO3 (aq) [1]
Halogen precipitate colours: chloride, white; bromide, cream; iodide, yellow [1]
Enthalpy change of reaction: -58.5 kJmol^-1 [4]
Ionic equation: Pb2+(aq) + 2I-(aq) = PbI2 (s) [1]
Concentration of KI required: 3.3 moldm^-3 [2]
Equilibrium question: The equilibrium position will shift to the right, as the forward reaction is exothermic, in an attempt to reduce the effect of the temperature decrease. The equilibrium position will also shift to the right as there are fewer gas molecules in the products of the forward reaction, in an attempt to reduce the effect of the pressure increase. This may vary to the actual conditions as low temperature reduces rate of reaction, and it's expensive to have a high pressure. [5]
Concentration in equilibrium question: 0.876 moldm^-3 [4]
Homologous series: alkenes, general formula: CnH2n [1]
Alkene to alkane: H2, nickel catalyst, 150 degrees C [1]
Alcohol --> H2SO4 + heat --> alkene (this question was to draw the alcohol I think) [1]
Empirical formula: C2H5O [1]
Last question: step 1 reagent, Cl2/Br2/I2, step 2 reagent, NaOH [3]

Any incorrect (although I don't think there are) please tell and I'll correct

Also, post about how you found the exam, as this will give a good indication of grade boundaries

Last step 2 reagent would probably allow KOH and probably LiOH as well
Potentially water but not sure on that