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OCR Chemistry A - AS in Depth - 2015 (new spec) UNOFFICIAL MARK SCHEME watch
- 11-06-2016 18:24
(Original post by alkaline.)
- 11-06-2016 18:28
yo we don't have one yet.
this is what I remember pls feel free to correct and also add missed questions.
the colour scheme is to try and separate whole questions.
draw the apparatus you'd use:
I put a clamp stand with a syringe on the left, and a clamp stand holding a test tube with metal and water in with the bung connected to the syringe.
the unknown metal: calcium
percentage yield: 67.4%
explain oxidation of magnesium in terms of electrons (1 mark)
oxidation of magnesium is loss of two electrons.
electron configuration of a magnesium atom
1s2 2s2 2p6 3s2
Magnesium vs Silicon
Magnesium = giant metallic, metallically bonded = electrostatic attraction between negatively charged delocalised sea of electrons and positively charged Mg ions.
Silicon = giant molecular, covalently bonded (electrostatic attraction between shared pairs of electron and the nuclei of bonding atoms), forming a lattice.
the difference in melting point - p4 and cl2 - on the graph chlorine was lower
I put: they are both covalently bonded, butchlorine is a smaller molecule, and so has weaker london forces therefore less energy is required to break the intermolecular forces therefore lower melting point.
second ionisation energy for strontium inc state symbols
Sr+ (g) --> Sr2+ (g) + e-
a question to do with explaining ionisation energy trend down group 2 but I can't remember btwn which elements
nuclear charge increases down the group however this is outweighed by increase in shielding and also increase in atomic radius, therefore there is less nuclear attraction (between nucleus and outer electrons) so outer electrons are more easily lost/less energy is required to remove them therefore lower first ionisation energy.
mass of strontium carbonate = 1.845g
rates question: why was there loss in mass or something?
(2 mol of) gas formed = products escaped.
describe and explain the trend in the graph up to 200s.
Steep negative gradient, mass rapidly decreases as time goes on = decreasing rate of reaction, reactants are being used up.
explain why enthalpy change of formation for NO was exothermic in terms of bonds
I put because more bonds made than were broken and making bonds releases energy whereas bond breaking uses up energy.
enthalpy profile diagram: endothermic
bottom left = reactants = N2 + 0.5 O2
top right = products = n20
pv=nrt question: (in standard form) 4.46*10^6 Pa
show NO catalyses the break down of ozone:NO• + O3 -> NO2• + O2NO2• + O -> NO• + O2
mechanism for the reaction of compound A an alkene with a hydrogen halide (HBr)
show the mechanism, the two different products, explain which of two would form more of.
unsymmetrical alkene CH3HC=CCH3CH3 , basically the second possible product just had the H and Br on the resulting haloalkane switched around, more of the tertiary halogenoalkane would be formed because it's more stable.
why can't compound A (alkene) exhibit E/Z isomerism?
because it doesn't have 2 different groups on each carbon of the double bond.
Z isomer for the alkene:
structural isomers: 2 methyl 2 butan-2-ol and 3 methyl butan-2-ol
why is it a secondary alcohol?
because the OH is attached to the carbon that is attached to 2 alkyl groups
write equation for butan-2-ol oxidising
I drew out: butan-2-ol + [O] - butanone + h20
bond angle around the oxygen in the butan-2-ol (3 marks)
reason: 2 bonding pairs and 2 lone pairs around the central atom, electron pairs repel to maximum separation = non-linear shape.Spoiler:why is this apparatus not suitable for oxidising a secondary alcohol?ShowI personally think: 4 electron regions = tetrahedral = 109.5, but then 2 lone pair so 109.5 - ( 2 x 2.5) = 104.5 is also an acceptable part of the answer.
i didn’t know this but I put: because nowhere to separately collect the products, reflux apparatus would be better.
aluminium sulfide and water forming aluminium nitrate and hydrogen sulfide
Al2S3 + 6H2O -> 2Al(OH)3 + 3 H2S
last question (mass spectrum/ infrared red) conspiracy as it currently stands = methylpropanoic acid
(Original post by Citric_Xenon)
- 11-06-2016 18:35
why did you get 1.845g of strontium carbonate. Didn't you have to find the number of moles of nitric acid, which was 0.025 moles then times it by 2 then you find the Mr of SrCo3 which is 147.6 gmol-1 then moles x Mr. I got 7.38g. Can you tell me where I went wrong if i made a mistake in the calculation?
But you probably wont lose that many marks for doing that one thing wrong
(Original post by Citric_Xenon)
- 11-06-2016 18:59
why did you get 1.845g of strontium carbonate. Didn't you have to find the number of moles of nitric acid, which was 0.025 moles then times it by 2 then you find the Mr of SrCo3 which is 147.6 gmol-1 then moles x Mr. I got 7.38g. Can you tell me where I went wrong if i made a mistake in the calculation?Last edited by multieman; 11-06-2016 at 18:59. Reason: .
- 12-06-2016 07:20
I didn't even read that it said anything about a secondary carbocation on the last question .-. So I put the m/z 43 was caused by CH3CH2CH2+ fragment... and so got butanoic acid.
- 12-06-2016 10:57
Damn I hydrated the pent 2 end instead 2 methylbut2ene. That's another two marks down the drain. Goodbye A grade
(Original post by Awsomedude)
- 12-06-2016 14:51
the pv=nrt, that was 4,460,000 but I put 4460
I got pent-2-ene for another
I don't know this but got 1.845
another question I got 0.48
percentage yield was 67% something, but I got 21.9 % how many marks could I get?
and the last one I got butanoic acid, but people are debating that it could be 2-methylpropanoic acid
- 12-06-2016 14:53
calcium metal 40.1
gas syringe for the apparatus
- 13-06-2016 20:06
I have done AQA chemistry AS this year but my family is moving so I'm going to have to change schools and the exam board in the only school nearby is OCR, have you guys found the content to be really hard? any advice as to how to revise for OCR?
- 14-06-2016 14:25
Is this the 2015 or 2016 paper?
- Thread Starter
- 17-06-2016 15:07
someone tag in a mod to change the title
- 25-06-2016 16:51
2015 never had a depth paper. this year is the new spec 2016. this is probs a typo. chill
- 25-06-2016 16:52
CHEMISTRY is the BEST compared to biology lol
- 25-06-2016 16:53
- 30-06-2016 17:54
Is this the OCR Chemistry A Specimen (In Depth) Paper?
I am sitting it tomorrow, and loads of my friends have warned me about questions that aren't listed above...