CCEA A2 2 Chemistry May 2012

Original post by lopikase123

i said yellow oily liquid but who knows like, what is a kekule structure??

I said a white solid :tongue:

It's the structure of benzene with no delocalised pi electrons, it forms double and single bonds instead between the carbons. What was the name of the monomer on the very last question??? I got 3-methylprop-2-ene :tongue:

Reply 23

I thought it was good enough as a paper. Although which has less basic character phenylamine or ethanamide? Also, I wasn't sure which poisiton the NO2 would go on so I said position 3 when it asked and put a side not saying that there were isomers and named them. Would that be okay?

For the benzenes I first drew kekulé's structure which was hexan-1,3,5-triene and then our normal benzene, but because it said to show the p-orbitals I gave the shape of how they would overlap and drew the p orbitals in instead of drawing just a ring. Would this be acceptable?

Thanks guys!

Reply 24

Original post by Who_Is_It?

I said a white solid :tongue:

It is, it's a white crystalline solid :smile:

Reply 25

Original post by d3ano

It is, it's a white crystalline solid :smile:

Ohhh yeaaa, I feel like a lord for guessing that :biggrin:

I'm not completely sure about your NO2 question but if you put both the p orbitals and the benzene structures I'm sure that would be fine :smile:

They can't penalise you for giving extra information.

Also I think ethanamide has more basic character?? Although I'm probably wrong, cause the lone pair could be drawn into the delocalised ring in phenylamine reducing its availability even more so than in ethanamide :s

(edited 11 years ago)

Reply 26

Original post by Who_Is_It?

Ohhh yeaaa, I feel like a lord for guessing that :biggrin:

I'm not completely sure about your NO2 question but if you put both the p orbitals and the benzene structures I'm sure that would be fine :smile:

arent amides neutral?

Reply 27

I agree that the order was phenylamine first because it's delocalisation was most stable, and more stable than that given by the pi electron in an amide, so although both have negligable basic character, it was greater in ethanamide.

Reply 28

Original post by ms607

arent amides neutral?

Ohhh yea your right sorry... I was thinking of something completely different :tongue:

Yea they're neutral, so phenylamine will have more basic character. Slightly embarrassing after just doing a test on this stuff :colondollar:

Reply 29

They're only neutral because of the delocalisation, which there is more of in phenylamine though.

Reply 30

Original post by d3ano

They're only neutral because of the delocalisation, which there is more of in phenylamine though.

yes but amides are neutral whilst phenylamine still has weak basic character

also I just looked up some pKb values and they agree that methylamine > phenylamine > ethanamide in basicity

Reply 31

Okay, pKb values are accepted :P
Do you guys think the marks will be scaled up much, because in A21 I got 102 and it scaled up to 111. Do you think it'll be similar?

(edited 11 years ago)

Reply 32

Original post by d3ano

Okay, pKb values are accepted :P
Do you guys think the marks will be scaled up much, because in A21 I got 102 and it scaled up to 111. Do you think it'll be similar?

ooh, lucky you :O I never found out my raw mark but it mustn't have been that great because I got 98 in january

as for this paper, I can see it being scaled up, as there were some questions that were unusual and probably caught a lot of people out, though I couldn't make a good enough guess as to how much it would...

Reply 33

Original post by ms607

Yea, I can see why it might be scaled up, there were a few questions that would have tripped quite a few people up. Fingers crossed the scaling is nice for this one :tongue:

How many marks do you reckon I would have lost for drawing the mechanism with methyl benzene instead of methyl benzoate?? :s-smilie:

Cause that means i got the name of the thing wrong after... damn!!

Reply 34

callumbm

Original post by ms607

yes but amides are neutral whilst phenylamine still has weak basic character

also I just looked up some pKb values and they agree that methylamine > phenylamine > ethanamide in basicity

I concur. Amides are actually slightly acidic in nature. Phenylamine is only slightly basic because the benzene ring draws in the electrons from N. Whilst amines are the most basic as the alkyl groups push electrons onto N, increasing its electron density.

(edited 11 years ago)

Reply 35

Original post by Who_Is_It?

Yea, I can see why it might be scaled up, there were a few questions that would have tripped quite a few people up. Fingers crossed the scaling is nice for this one :tongue:

How many marks do you reckon I would have lost for drawing the mechanism with methyl benzene instead of methyl benzoate?? :s-smilie:

Cause that means i got the name of the thing wrong after... damn!!

hmm... no idea... maybe 1 or 2 marks because it's showing a correct electrophilic substitution mechanism with NO2(+)

I drew methyl benzoate correctly but drew the nitronium ion joining onto position 2 of the benzene ring instead of 3 (I assume it was 3 because then the product would have been methyl 3-nitrobenzoate?) meaning my product name was wrong :frown:

Reply 36

Original post by ms607

Thank god, its not all lost then :smile:

You'll probably get follow through marks for the name though.

Another question:
See for the half equation for VO2+ to V2+ did you include water, hydrogen ions and electrons?
And the emf calculation for the zinc and aluminium did you have to multiply the each emf value by 2 or 3 based on your equation?? :s-smilie:

Reply 37

Original post by Who_Is_It?

Thank god, its not all lost then :smile:

for the emf values, you never change the numbers, only the signs if you use the reverse reaction, regardless of whether a reaction needs to be multiplied to balance charges, so no

for VO₂⁺ to V²⁺ I just balanced it as I normally would, so it would have been VO₂⁺ + 4H⁺ + 3e^- > V²⁺ + 2H₂O ???? (assuming it was VO₂⁺ and not VO²⁺, can't really remember)

(edited 11 years ago)

Reply 38