WJEC AS Chemistry CH1 May 22nd 2015

Welcome to this year's WJEC CH1 thread! Pretty much the same as the PH1 thread I just made: how is preparation going? Any questions about content/exam?

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Reply 1

isaact

In every CH1 paper I've been through, there's always a question on Ionisation Energies and I just can not get my head around it :////// :2in1:

Reply 2

PrimeLime

Original post by isaact

In every CH1 paper I've been through, there's always a question on Ionisation Energies and I just can not get my head around it :////// :2in1:

That's my favourite type of question! (Although, I have to admit I only like the 'physics' topics in chemistry; I don't like chemistry itself.) It's really logical and straightforward:
- you need to know your definition of ionisation energy
- you need to be aware of the effects of shielding, atomic radius, more shells, proximity of outer electron to nucleus and nuclear charge
- you need to be aware and MAKE IT CLEAR IN THE EXAM that shielding, etc. OUTWEIGHS the effect of an increased/decreased nuclear charge
- you need to realise that nuclear charge increases across a period/down a group and every time you go down the group there will be one more shell
- lastly, the tricky one:
You get a decrease in ionisation energy from the group 5 N to the group 6 O. Why, since nuclear charge increases and everything else stays the same, so shouldn't the ionisation energy increase? Well, this is the A grade question. You need to say that the 'next electron' in O (the electron that N doesn't have) pairs up with an electron in one of the p orbitals, since by this time there is exactly one electron in EACH of the THREE p orbitals, so there is repulsion between these two electrons and so on.

Those are basically the bare bones of CH1 ionisation energies (you may have all of this in your notes anyway XD), any other questions feel free to ask! :biggrin:

Reply 3

ZeroShun

I am doing this exam too and the mark schemes seem quite tight to me. What do you think?

Reply 4

PrimeLime

Original post by ZeroShun

I am doing this exam too and the mark schemes seem quite tight to me. What do you think?

They are, and that's a big reason why I don't like A Level Chemistry. You just never know exactly which points the examiner wants for that specific paper, even if you know and understand all the content inside-out and back-to-front. So all us high-mark-hopefuls have to spew out everything that we know about the topic just to ensure full marks! :angry:

I end up using double the space than the lines provided and sometimes I end up having to write ON the next question! :colondollar:

Good thing I'm dropping it next year and I don't need any higher UMS than 80... :redface:

Reply 5

ZeroShun

Original post by PrimeLime

I end up using double the space than the lines provided and sometimes I end up having to write ON the next question! :colondollar:

Good thing I'm dropping it next year and I don't need any higher UMS than 80... :redface:

Ha! Don't you use any extra paper in the exam? And I have to take it next year as I want to do medicine... :s-smilie:

Reply 6

PrimeLime

Original post by ZeroShun

Ha! Don't you use any extra paper in the exam? And I have to take it next year as I want to do medicine... :s-smilie:

Well good luck!! I've heard it's very very difficult to get an A* in A2 Chemistry if that's what your aiming for, so that's a lot of work for you but I'm sure you'll do fine.
Extra paper is too much of a hassle XD.

Reply 7

ZeroShun

Thanks! Well if its so difficult I'll try to get one in maths or biology instead!

Reply 8

Faisalshamallakh

CH1 is easy, you either know it or you don't though. Hopefully a couple of "Find the empirical formula given the percentage composition" comes up, easiest marks ever. A bit of Equilibria and we should be good! Have a feeling some challenging Emission Spectrum questions may come up. But nothing that nobody can handle!

Reply 9

PrimeLime

Original post by Faisalshamallakh

I tend to lose lots of marks for silly mistakes. This only happens in CH1, and it happens every time, no matter how hard I try...
I guess chemistry hates me back XD. I find CH1 very easy apart from the stupid mistakes. How's CH2 for you? I'm yet to start past papers (or even finish learning my notes :frown:

Reply 10

Faisalshamallakh

Original post by PrimeLime

I don't tend to make 'mistakes' as much in Chemistry. But I'll sometimes answer larger questions and lose a mark or two simply because I couldn't be bothered to write down everything I know related to the question because of time loss. But then again in the real thing I'll do my best to fill in as much info as I can.

People think CH2 is hard. It is true. However the only hard thing about it is Topic 7. But if you learn all of your 13 reactions and the mechanisms etc. CH2 will be a breeze. It is basically a memory test and very little mathematics involved. If you don't memorise your stuff. You will struggle to hit 40% imo.

Tbh if you learn your CH2 off by heart, you could easily be hitting 90%+ UMS

I haven't started past paper revision either, will start tomorrow.

Reply 11

PrimeLime

Original post by Faisalshamallakh

About CH2, I agree, but I really don't know my mechanisms or reactions or anything really from organic chemistry onwards (I know the stuff roughly enough to get 80% maybe in a paper). I'm currently trying to learn my mechanisms and it's going ok but there are still far too many reaction questions that I just don't know the answers too and I struggle to find in my notes. Would it be ok if you could post the reactions and precipitates and tests (that sort of thing) in brief? It would really help a lot.
And I have to put it out there, I hate those massive back-to-back 6-marks-each practical questions in the papers. Just... so... annoying...

Reply 12

Faisalshamallakh

Yeah sure, I made flash cards to memorise my reactions & conditions...

1) Reagents & conditions to convert a halogenoalkane into an alkene: Concentrated NaOH in hot Ethanol, heat under reflux

2) Reagents & conditions to convert a halogenoalkane into an alcohol: AQUEOUS NaOH and Heat [below 110 degrees C]

3) Reagents & conditions to convert an alkene into alcohol: 300 degrees C, 70 atm, and Phosphoric Acid as a catalyst (H3PO4)

4) Test to distinguish between alkene & alkane: Adding bromine water; in presence of an Alkene the solution will become colourless. In presence of Alkane, the solution will remain brown.

5) Reagents and conditions for conversion of alcohol into alkene: CONCENTRATED H2SO4, 170 Degrees C

6) Reagents and conditions to convert alcohol into an acid: Acidified Potassium dichromate; You will observe a colour change from Orange to Green

7) Conditions & reagents for CATALYTIC Cracking: 500 Degrees C, Low pressures, Zeolite catalyst

8) Conditions for THERMAL Cracking: 450-750 Degrees C, 70 atm.

9) Conditions for polymerisation of Ethene: 250 Degrees C, 2000 atm, traces of O2 to initiate.

10) 3 Catalysts that can be used in hydrogenation of an alkene into an alkane: Platinum or Palladium or Nickel

11) Test for a Carboxylic Acid, what would you observe: Adding Sodium Carbonate/Bicarbonate then testing for CO2 with lime water

Learn all that (along with your mechanisms) and that your CH2 done my friend. Well 90% done anyway. :wink:

Reply 13

PrimeLime

Original post by Faisalshamallakh

Thanks a lot, repped. :smile:

Reply 14

Faisalshamallakh

Original post by PrimeLime

Thanks a lot, repped. :smile:

Thank you,

I really hope that a mathematical based paper comes up. Because I just did a May 2011 paper, it consisted of complete memorisation which was horrible. There were a few maths questions but not nearly as much compared to other papers. Fingers crossed.

Reply 15

PrimeLime

Original post by Faisalshamallakh

Did you do the CH1 Jan 2012 paper? Oh my god, that was a COMPLETE GIFT. I wish that was our paper. I managed to get 98% raw in it!
And yeah, anything mathsy in my exams will definitely be a huge bonus for me. :biggrin:

Reply 16

Faisalshamallakh

Original post by PrimeLime

I haven't tried it yet, i will do it tonight though see how i do.

Posted from TSR Mobile

Reply 17

PrimeLime

Original post by Faisalshamallakh

I haven't tried it yet, i will do it tonight though see how i do.

Posted from TSR Mobile

Oh and the maths involved in CH1 isn't really maths anyway. It's basically 'we tell you the numbers, you plug them into formula', which is in no way worthy of being considered maths. I wish chemistry could be a bit more mathsy like its superior cousin physics.

Reply 18

Faisalshamallakh

Original post by PrimeLime

That's enough maths for me! :biggrin:

Physics is just too complicated. I think it's because you have to accept everything and learn formulas rather than understand why it works. Well that was the case at GCSE anyway!

Reply 19

PrimeLime

Original post by Faisalshamallakh

That's enough maths for me! :biggrin:

Physics is just too complicated. I think it's because you have to accept everything and learn formulas rather than understand why it works. Well that was the case at GCSE anyway!

Woaaah, wait a second. I'm pretty sure that's more the case in chemistry. In physics, I can assure you that every single thing you learn, you can (and should!) understand. If you just learn formulas and use them without understanding how they work (the 'GCSE method') in A Level, you won't get too far.
Admittedly even in GCSE you could understand everything if you tried/had the maturity to try. I didn't XD! But I do in A Level, and it's so satisfying when it all clicks in. :biggrin: