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OCR Chemistry A Exam Thread (Breadth - May 27 2016 and Depth - June 10 2016)

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Original post by kiwifruit99
Is shapes of molecules likely to come up?


I think so.
Reply 861
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Cherx
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Original post by 4nonymous
yes, free radical substitution is homolytic
electophilic addition and nucleophillic substitution are heterolytic


How comes the nucleophilic substitution is heterolytic? Doesn't the chlorine atom take both electrons. Oh wait lol. I got my definition mixed up looool. Homolytic fission take one electron.
Heterolytic is where one atom takes both of the electrons in an uneven split so ions form
Homolytic is the even split so both atoms end up with an unpaired electron and thus are radicals

Original post by Cherx
How comes the nucleophilic substitution is heterolytic? Doesn't the chlorine atom take both electrons.
anyone got list of possible practical questions?
Original post by Cherx
How comes the nucleophilic substitution is heterolytic? Doesn't the chlorine atom take both electrons. Oh wait lol. I got my definition mixed up looool. Homolytic fission take one electron.


Yes, homolytic forms free radicals so thats why its used for free radical substitution. Heterolytic is when one of the atoms receives both electrons.
lol you almost confused me for a sec too.
Reply 865
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Cherx
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Original post by JamieHarris1998
Heterolytic is where one atom takes both of the electrons in an uneven split so ions form
Homolytic is the even split so both atoms end up with an unpaired electron and thus are radicals


Last minute stress loool. Forgetting everything. Really don't want titrations to come up. If you go over the meniscus line the concentration of the known solution decreases doesn't it?
We had a few titration calculations to do in the last paper so maybe other maths questions will come up instead
Original post by asinghj
Combustion and bond enthalpies is reactants - products
Formation is the odd one out so products - reactants


So if they give us a table of formation values to work out combustion, would you do products- reactants?! Or the other way around?
Reply 868
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Cherx
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Original post by JamieHarris1998
We had a few titration calculations to do in the last paper so maybe other maths questions will come up instead


Ah I was thinking they might ask about the practical aspect of it. Can't really think of some other practical's they could ask.
Original post by Jitesh
Ah, I see now - so it is to do with the molar quantities

Why does it show adding the sum of the stoichiometric number of entity B?

Edit: nevermind misread it

Thanks a bunch! Not seen a question like that before lol


Hey, I done this question and got the same answer as you and I don't really understand the Wikipedia article. Could you explain it please?
Reply 870
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amysed
1
what definitions do we need to know?
Maybe asking about how to set up oxidation/distilliation of alcohols or the practical we did about testing for ions because we only mentioned the colours of precipitates last exam. But titrations aren't too bad to setup, the process if ok but just tricky to remember the small steps and the equipment

Original post by Cherx
Ah I was thinking they might ask about the practical aspect of it. Can't really think of some other practical's they could ask.
Original post by Cherx
Ah I was thinking they might ask about the practical aspect of it. Can't really think of some other practical's they could ask.


There are others they could ask such as:
oxidation of alcohols
calorimetry
Tests for ammonia, sulfates, halides etc
Original post by amysed
what definitions do we need to know?

Who knows. Could be any of them but the most probable are relative atomic mass, isotopes and isomers.
Do we need to know about the history of the periodic table for this exam?
Reply 875
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Cherx
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Original post by JamieHarris1998
Maybe asking about how to set up oxidation/distilliation of alcohols or the practical we did about testing for ions because we only mentioned the colours of precipitates last exam. But titrations aren't too bad to setup, the process if ok but just tricky to remember the small steps and the equipment


Original post by 4nonymous
There are others they could ask such as:
oxidation of alcohols
calorimetry
Tests for ammonia, sulfates, halides etc


Oh gosh I have so many to go over know. Actually Ik the ammonium ion test. How does the sulfate one work?

Calorimetry? Isnt that bio?

O2 of alchols is not too bad... I think. When you say set up though? As in the equipment? So anti bumbing granules (idk why I can remember this), condenser, heat bath?

Yeah I'm gonna count on the fact they don't give titration as we did have a 3 marker on it in the last paper.
Original post by Cherx
Oh gosh I have so many to go over know. Actually Ik the ammonium ion test. How does the sulfate one work?

Calorimetry? Isnt that bio?

O2 of alchols is not too bad... I think. When you say set up though? As in the equipment? So anti bumbing granules (idk why I can remember this), condenser, heat bath?

Yeah I'm gonna count on the fact they don't give titration as we did have a 3 marker on it in the last paper.


The sulfate one is when you add barium chloride solution and you get barium sulfate which is a white precipitate.

Calorimetry is the experiment with the polystyrene cup and spirit burner.

As for alcohols I think you need to know the setting up equipment for distillation and reflux which I still need to go over.
Original post by Cherx
Oh gosh I have so many to go over know. Actually Ik the ammonium ion test. How does the sulfate one work?

Calorimetry? Isnt that bio?

O2 of alchols is not too bad... I think. When you say set up though? As in the equipment? So anti bumbing granules (idk why I can remember this), condenser, heat bath?

Yeah I'm gonna count on the fact they don't give titration as we did have a 3 marker on it in the last paper.


Test for sulfates is adding dilute HCl then BaCl and if a white precipitate forms a sulfate is present.
I can't remember the calorimetry test
Oxidation might ask about why we reflux (prevents the loss of volatile liquids by preventing the evapourated liquids from escaping by condensing them back).
Also about why we left the top open, which was to prevent explosions from pressure created by heating gas which would be danagerous if sealed by a stopper when condensing
Original post by Normy18
Do we need to know about the history of the periodic table for this exam?


Don't think so.
Reply 879
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Cherx
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Original post by 4nonymous
The sulfate one is when you add barium chloride solution and you get barium sulfate which is a white precipitate.

Calorimetry is the experiment with the polystyrene cup and spirit burner.

As for alcohols I think you need to know the setting up equipment for distillation and reflux which I still need to go over.


Oh gosh not that.. Hoping they don't ask of calorimetry I mean they did have quite a hefty calculation question on it.

Ah ok. I need to go over it too. Lmao I'm going over so many stuff rn. The only green chemistry we have is the polymer stuff isn't it? So waste polymers you could make into other new polymer, sort and recycle, organic feedstock.

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