CCEA AS Chemistry Exam Thread

Original post by Mr.bob

Why what did everyone write( please say rate of reaction, please say rate of reaction) :biggrin:

I wrote rate of reaction but the answer above seems more likely

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Reply 41

sarahs1

I said because the reaction was endothermic?? Its most likely wrong...

Reply 42

Sharpshooter

I said it doesn't react at room temperature and needs to be heated therefore to initiate the reaction. (you'd be surprised how simple a lot of the answers are in the mark schemes)

What about the one after with regards to "how do you know the reaction has stopped with the hydrochloric acid", I just said no more fizzing?

I'm assuming I got 0 marks worst case scenario for those two, but if I get any of them it would be a bonus.

What about the Bromine question guys?

- Why use a fume cupboard? To prevent inhalation of harmful fumes (a guess).
- Why do you need to add the bromine slowly? To prevent the 2-methylbut-2-ene from dehydrating.

Millie-3

Was anyone else thrown by the fact that they asked us for observations instead of deductions? Because I didn't learn that properly. I kind of learnt it in relation to the observations.

The problem is you see because of the new format we have no idea generally what the scope of stuff they can ask for as we can only go by the one past paper.

I made this mistake with the A23 this year when we did the Iodine-Thiosulfate titration in the actual practical, arrogantly assuming they were going to follow it on in the theory, but instead the theory question was about Potassium Manganate titration (there's 3 titrations to learn at A2). I only revised the redox reactions for the Iodine-Thiosulfate titration and you NEED the redox reactions in order work out the final equation you're working with (in terms of mole ratios from burette to conical flask). I didn't know the redox equations for the Potassium Manganate titration so I couldn't do a lot of the question (I'll be repeating in next year for certain).

So for the AS3 I damn well made sure not only did I revise the acid-base titration (which we did in the practical) but both the degree of hydration and back titration, which obviously paid off. You just don't know and we haven't got a lot to go on to be fair.

As Q5 proved not only do you need to know the observations and deductions, but the method of preparation. Thankfully I looked over those too.

(edited 8 years ago)

Reply 43

Millie-3

Original post by Sharpshooter

You sound like youre all set :smile:

totally not jealous at all :s

Reply 44

CERC

hey!!
have youse started AS unit 2 revision??? if so, how much have you done!!!

Im so scared, I really want a A but I don't know!! the exams can be soo tricky sometimes!!

Reply 45

Original post by CERC

hey!!
have youse started AS unit 2 revision??? if so, how much have you done!!!

Im so scared, I really want a A but I don't know!! the exams can be soo tricky sometimes!!

I haven't even started unit 1 revision yet, haha! But I know what you mean, probably my most difficult exam apart from history.

Reply 46

CERC

Oh god!!! get revising lol!!!

which do you think is hardest? unit 1 or unit 2 chemistry???

sometimes unit 2 can be a breeze but unit 1 is so twisted. like they questions seem easy and then the mark schemes have these really weird answers that you would never even think of!!!

and also, for ionisation energies, sometimes they want the shielding effect increases and the radius increases. and then sometimes they want the electron is further from the nucleus and the effective nuclear charge decreases!!!

does anyone know which answers to use???

Reply 47

Original post by CERC

I know my situation sounds horrid, but I have biology and history exams on the same week as chemistry, haha! Find history a lot harder, but for me unit 1 is a breeze. Unit 2 organics causes me issues mainly haha!

For those type of trend questions, I write it all down. As long as it's correct, I'd just list it. Normally it's shielding, nuclear charge and how full the outer shell is, along those lines anyway haha!

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Reply 48

CERC

Original post by Sonyaa46

I have technology, English , biology and chemistry all in the space of 4 days!!! how do you think I feel!!! im freaking out for English. its just so varied but chemistry could go either way. and technology is so tricky as well!!!
how much revision for unit 2 have you done!!! I haven't looked at halogenoalkanes or alcohols yet!!! :colondollar:

Reply 49

Can someone please help with this question, I hope you can see the attachment.

In this question I can see that the answer is B because the Cl2 molecule has an mr of 71, but why should it not be present?

mass spec.png20.3KB

Reply 50

Original post by kirsty98

Remember the Cl2 molecule is 71 because of the two 35.5 atoms. But you can't actually have an atom with 35.5 mass number, it's only an average of the isotopes. They give you values of 35 and 37. Think of all the different total mass numbers possible with those two values. 71 isn't possible.

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Reply 51

Could someone explain haha?

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1433863246300.jpg24.7KB

Reply 52

Original post by Sonyaa46

Could someone explain haha?

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A polar molecule will be attracted to the rod. CCl3 is the only polar molecule.

Reply 53

Original post by Sonyaa46

Could someone explain haha?

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because the rod is positive your looking for the most negative compound because opposites attract. its easier to understand if you draw all thecompunds out with their charges. CCL4 looks like the most negative but the delta negatives cancel, so the ChCL3 is the most negative because the H+ prevents the cl- from cancelling. i hope this makes sense

Reply 54

Yeah, I didn't even think to look at polarity- thank you!

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Reply 55

can someone tell me how you would work this out? (Number 6)

Reply 56

Millie-3

Original post by kirsty98

can someone tell me how you would work this out? (Number 6)

I think it should remain 30g since mass can neither be created nor destroyed, and all of the water is converted to gas as H2 or O2. Is it B?

Reply 57

Original post by Millie-3

I think it should remain 30g since mass can neither be created nor destroyed, and all of the water is converted to gas as H2 or O2. Is it B?

Yes and thank you

Reply 58