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Reply 300
~Adel~
What do you mean by ''overall grade boundary''? I was talking about the UMS..lol. I need 113 UMS score altogether for the last two units..


Yes the grades boundaries for the UMS changes it doesnt stay the same each year
Reply 301
Urm...are you sure..480/600 will always be an A no matter how the RAW marks fluctuate...
Reply 302
yes u need 480/600 for an A. So u can lose a total of 120 marks!!! wow thats a lot!
Reply 303
No..i need to get 113/210 for the last two units in order to get an A..i'm not that brilliant to be able to afford that many marks!!
Reply 304
~Adel~
Urm...are you sure..480/600 will always be an A no matter how the RAW marks fluctuate...



That cant be true?...because the UMS grades for Unit exams change?
Reply 305
Oxy
That cant be true?...because the UMS grades for Unit exams change?


No, UMS always stays the same. The amount of raw marks needed to get a certain UMS mark changes though.
Reply 306
yes u r right fait!
i'll upload the file and you can state what question you were on about because its a little unclear
I am not too sure with my 2b)ii), about the collision theory in respect to temperature and catalyst.

For temperature, I spoke about how an increase in temperature provides more energy to the molecules. More energy means that there is larger proportion of successful reactions to unsuccessful reactions.

For catalyst, I commented about how it provides a reaction surface for the reaction to occur (the first "law" of collision theory is that the particles collide) and also commented how the catalyst also provides attack on the right orientation of the molecules (I'm thinking about steric factor here).

Can anyone elaborate on my explanation?

------

And for the question that everyone has been discussing, about the 1,2-dibromoethane elimination reaction with Potassium Hydroxide, the following are allowed (as far as I think):

Bromoethene
Ethyne
Potassium Bromide (*)
Water (*)
Hydrogen Bromide (**)

(*) The question does not specify whether it has to be organic or not. It only says compound, so I think a side product would even be allowed. But I don't think that there is anyone who would have gotten this.

(**) I'm so sure of this. The hydroxy ion from the KOH would cause an attack on a hydrogen, causing an electron to push off from the C-H bond onto the Carbon, and then the electron from the C-Br bond would move to the Bromine, forming a Bromide ion, and it may JUST be possible to make HBr as a product.

Not so sure on this.

------

Otherwise I feel okay with the rest of the paper.
for catalyst i put it provides an alternative path with a lower activation energy therefore more particles have energy greater than Ea, hence more successful collisions, hence a faster rate of reaction..
temp one seems ok i think
and for the 1 2 dibromoethane question - your forgot about ethene!
Reply 310
eug.galeotti
I am not too sure with my 2b)ii), about the collision theory in respect to temperature and catalyst.

For temperature, I spoke about how an increase in temperature provides more energy to the molecules. More energy means that there is larger proportion of successful reactions to unsuccessful reactions.

For catalyst, I commented about how it provides a reaction surface for the reaction to occur (the first "law" of collision theory is that the particles collide) and also commented how the catalyst also provides attack on the right orientation of the molecules (I'm thinking about steric factor here).

Can anyone elaborate on my explanation?

------

And for the question that everyone has been discussing, about the 1,2-dibromoethane elimination reaction with Potassium Hydroxide, the following are allowed (as far as I think):

Bromoethene
Ethyne
Potassium Bromide (*)
Water (*)
Hydrogen Bromide (**)

(*) The question does not specify whether it has to be organic or not. It only says compound, so I think a side product would even be allowed. But I don't think that there is anyone who would have gotten this.

(**) I'm so sure of this. The hydroxy ion from the KOH would cause an attack on a hydrogen, causing an electron to push off from the C-H bond onto the Carbon, and then the electron from the C-Br bond would move to the Bromine, forming a Bromide ion, and it may JUST be possible to make HBr as a product.

Not so sure on this.

------

Otherwise I feel okay with the rest of the paper.


I think you are right on the products, what do you think they will allow for the products of the oxidation of the diol.

I think they will allow an aldehyde with an alcohol group, an organic with two aldehyde groups, a ketone with an alcohol and an organic with two ketone groups.

Thanks
Reply 311
hey what did u pple write for Q1b (i) and (ii) Identify Y and Z

and Q3b(ii) Kp : calculate the total pressure required to reduce the the mole fraction of N2O4 to 0.10

and Q4b(ii) explain why the the values of theoritical and experimental lattice energies are diff??
Is AgF soluable or insoluable?

pH of pure water at 50degrees?
Explain why pure water at 50degrees is neutral despite the fact that its pH is not pH 7??

pls someone tell me what u wrote for these...
um, for the catalyst thing, i also commented on the lower activation energy, i just forgot to mention it here.

about the diol, i made a dialdehyde and a dicarboxylic acid. a ketone can't be made if it forms an aldehyde (primary alcohol)...
Reply 313
But can an aldehyde be made with an extra OH group?

Thanks
Reply 314
Sorry, i meant carboxylic acid, can one be made with an OH group?

Thanks
yeah, because reactions can be controlled in ways to make acids like that that still may contain a hydroxy group.

it's possible, i don't see why not. but i think that we are all too familiar with how sometimes examiners are picky, and won't allow for certain answers, so i ended up giving my 2 possible compounds as a dialdehyde and dicarboxylic acid, in order to avoid any possible conflict with the mark scheme.
Reply 316
Hi

I think to avoid any conflict, the 4 compounds will be allowed as the reactions of diols aren't even on the syllabus to my knowledge, like for the KOH one, in 2001, as someone posted, they allowed bromoethene and ethene.

Thanks
sounds fair then...

It was only Unit 2, and for most of you (at least I think), this is your first time sitting this paper.

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