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

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Hi guys can someone possibly quickly go through ozone depletion content and what exam questions would be asked perhaps tomorrow?
Thanks :wink:
Reply 721
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neza99
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is procedure of reflux and distill likely to come up? e.g. where the equipments go and how you use it??
Reply 722
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I hope the 6 markers go well cos the new mark schemes are so annoyingly specific. it does not have more neutrons, it has three more neutrons like wth
Original post by neza99
is procedure of reflux and distill likely to come up? e.g. where the equipments go and how you use it??


Possibly although I'm not sure they'll ask that directly because based on the specimen paper and practise papers, they ask you how to test for something, describe said experiment and analyse the results not just the method itself.


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always relate to the example, rather than talking about the gist of it - exam technique :smile::smile:
(edited 7 years ago)
Reply 725
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Original post by Firenze26
Possibly although I'm not sure they'll ask that directly because based on the specimen paper and practise papers, they ask you how to test for something, describe said experiment and analyse the results not just the method itself.


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alright cheers! how would you describe the procedure of Making a standard solution? like the main points.
Reply 726
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watch out for units and significant figures - exam technique lol :smile::smile:
Yup, very true! Forgot to put that in!
Reply 728
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Our school told us that 52/70 is an A. 47/70 is a B for chemistry. My chemistry teacher said it could be lower cos it is a new spec:smile:
Original post by neza99
alright cheers! how would you describe the procedure of Making a standard solution? like the main points.


Ok say you start with solid X (just for simplicity):

1. Dissolve known mass of solid X in water (around 50-100cm³).
2. Using a funnel, transfer the solution into a volumetric flask, making sure you use distilled water to clean the funnel so all the solutions goes inside.
3. Make up to the mark with distilled water (via pipette etc.), until it meniscus reaches line.
4. Close the lid, and invert a couple times
5. You know have a standard solution of X

Hope that helped
Original post by 11...
Our school told us that 52/70 is an A. 47/70 is a B for chemistry. My chemistry teacher said it could be lower cos it is a new spec:smile:


I think thats quite close, but higher personally because the first paper was quite fair and if you knew your stuff, it should've been fine. Depending on this paper, for the first paper I'm saying like 56-58 for an A (just about 80&%).
Original post by neza99
alright cheers! how would you describe the procedure of Making a standard solution? like the main points.


Original post by Bahcaci
Ok say you start with solid X (just for simplicity):

1. Dissolve known mass of solid X in water (around 50-100cm³).
2. Using a funnel, transfer the solution into a volumetric flask, making sure you use distilled water to clean the funnel so all the solutions goes inside.
3. Make up to the mark with distilled water (via pipette etc.), until it meniscus reaches line.
4. Close the lid, and invert a couple times
5. You know have a standard solution of X

Hope that helped


Don't forget it's deionised/distilled water when you write it down and three times for each rinses. (Not sure if latter is still the same but in gcse this is what they always say regarding the rinses)

Just to be safe, also add in the words of the final product e.g. "Creating 250cm3 of 0.500 mol/cm^3"
Reply 732
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Original post by Bahcaci
I think thats quite close, but higher personally because the first paper was quite fair and if you knew your stuff, it should've been fine. Depending on this paper, for the first paper I'm saying like 56-58 for an A (just about 80&%).


Yeah true that paper was quite easy, but the fact that this is a new spec and we have to revise everything would make the grade boundaries slightly lower..52/70 is not low low, it is 74% for an A
Original post by JamieHarris1998
Hi guys can someone possibly quickly go through ozone depletion content and what exam questions would be asked perhaps tomorrow?
Thanks :wink:


Chances are you will be asked to write the mechanism (free radical) of ozone depletion & also the name of the steps. And here it is:

Initiation:
Cl2 --> 2Cl•

Propagation:
Cl• + O3 --> ClO• + O2
ClO• + O --> Cl• + O2
(*Small note, notice the Cl• is reformed, so this reaction can go on for a long time, even after we stop use of CFCs)

Termination:
Cl• + Cl• --> Cl2 (main one!)
Cl• + ClO• --> Cl2O
ClO• + ClO• --> Cl2O2
Reply 734
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neza99
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Original post by Bahcaci
Ok say you start with solid X (just for simplicity):

1. Dissolve known mass of solid X in water (around 50-100cm³).
2. Using a funnel, transfer the solution into a volumetric flask, making sure you use distilled water to clean the funnel so all the solutions goes inside.
3. Make up to the mark with distilled water (via pipette etc.), until it meniscus reaches line.
4. Close the lid, and invert a couple times
5. You know have a standard solution of X

Hope that helped

Thank you!
Original post by Firenze26
Don't forget it's deionised/distilled water when you write it down and three times for each rinses. (Not sure if latter is still the same but in gcse this is what they always say regarding the rinses)

Just to be safe, also add in the words of the final product e.g. "Creating 250cm3 of 0.500 mol/cm^3"



Yeah, distilled water is key! You want to be as clear as possible!!
Reply 736
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using the cgp revision guide would be really useful at this point to refresh yourself with all the content cos doing past papers can get a little boring after a while and of course they do not have questions on everything. something that was never asked before may turn up tomorrow who knows, so cgp guides are best for last minute prep
(edited 7 years ago)
Reply 737
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good luck everyone :smile:
Original post by Bahcaci
Chances are you will be asked to write the mechanism (free radical) of ozone depletion & also the name of the steps. And here it is:

Initiation:
Cl2 --> 2Cl•

Propagation:
Cl• + O3 --> ClO• + O2
ClO• + O --> Cl• + O2
(*Small note, notice the Cl• is reformed, so this reaction can go on for a long time, even after we stop use of CFCs)

Termination:
Cl• + Cl• --> Cl2 (main one!)
Cl• + ClO• --> Cl2O
ClO• + ClO• --> Cl2O2


Thank You so Much ! :biggrin:
Good luck to everyone, just don't panic, and you will be fine!

I'm guessing everyone will be on here after the exam anyway 😉

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