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Edexcel Chemistry A2 Unit 5 ~ Wednesday 19th June 2013 (Now Closed)

... Did anyone find the June 2012 paper easier than the others? I've just done it (as my last past paper) and have got about 30 raw marks more than I did in the others... Am I actually starting to make improvement?! :smile:

Reply 1801

sounique

Original post by Bubblezzzz

In that question, X is just a repeat monomer of Y i.e. X=2Y
this is why, when it is refluxed with acid to give ONE product, its trying to imply that the bond hydrolyses to give rise to two of the same molecule, hence ONE organic product. :smile:

Oh and its not an ester! its an amino acid

Sorry, but you've completely lost me! Where does it say that X is a repeat monomer of Y?

Also, does conc HCl ALWAYS hydrolyse peptide bonds? I hate that question, I don't feel I have a full understanding of it..

Reply 1802

Bubblezzzz

Original post by Gnome :)

... Did anyone find the June 2012 paper easier than the others? I've just done it (as my last past paper) and have got about 30 raw marks more than I did in the others... Am I actually starting to make improvement?! :smile:

SAME I found that paper easier too, BUT if you have gone up by 30 raw marks, I'm guessing chem unit 5 has finally clicked with you and you have made a tremendous improvement, well done!

Reply 1803

sounique

Original post by Bubblezzzz

SAME I found that paper easier too, BUT if you have gone up by 30 raw marks, I'm guessing chem unit 5 has finally clicked with you and you have made a tremendous improvement, well done!

That paper was the hardest paper I've ever done.

Reply 1804

Bubblezzzz

Original post by sounique

Sorry, but you've completely lost me! Where does it say that X is a repeat monomer of Y?

Also, does conc HCl ALWAYS hydrolyse peptide bonds? I hate that question, I don't feel I have a full understanding of it..

haha same! I would say it always hydrolyses it, although from the question and our previous knowledge, when it said that, I did immediately think esters, but no, I remember in biology, we were discussing how the concentrated HCl in our stomachs breaks down proteins by hydrolysing the amide linkages between amino acid chains.

What I meant by the repeat monomer is effectively that X is two glycenes joined together, hence 2Y. As this happens, a water molecule is lost :smile:

Reply 1805

Bubblezzzz

Original post by sounique

That paper was the hardest paper I've ever done.

Its probably because your too clever, and tend to over-think things :tongue:

x

Reply 1806

randyaloul

Original post by Gnome :)

... Did anyone find the June 2012 paper easier than the others? I've just done it (as my last past paper) and have got about 30 raw marks more than I did in the others... Am I actually starting to make improvement?! :smile:

YES! Thing is compared to Jan 12, it was a much easier paper, yet the boundaries for Jan 12 are higher by like 8 marks! No idea how!

Reply 1807

Bubblezzzz

Original post by randyaloul

YES! Thing is compared to Jan 12, it was a much easier paper, yet the boundaries for Jan 12 are higher by like 8 marks! No idea how!

I think its cos there are so many places here, where one can make mistakes that costs loads of marks. i.e. q14, working out structural formula, you had to be careful with the nitrogen gas at 24cm3 to divide by 24000 then multiply by 2 to get the number of moles of N, whereas I'm assuming many would have forgotten to divide by the 2, which would have messed up the whole question I presume?

Reply 1808

Bubblezzzz

I love the transition on these forums from hope and peaceful revision to complete frustration and anger after the paper

Reply 1809

Hunarench95

13

Original post by sounique

But in the mark scheme it's an amide, not an ester? The structural formula of X.

I may be getting my wires crossed, but the CONH is a peptide link (formed during condensation polymerisation)?

(and it shows two monomers of glycine - amino acid)

Reply 1810

Bubblezzzz

Original post by Hunarench95

I may be getting my wires crossed, but the CONH is a peptide link (formed during condensation polymerisation)?

(and it shows two monomers of glycine - amino acid)

Precisely

Reply 1811

AtomicMan

13

Does anyone know what the advantages and disadvantages of methanol, ethanol and hydrogen fuel cells are?

Reply 1812

Hunarench95

13

Original post by Bubblezzzz

In that question, X is just a repeat monomer of Y i.e. X=2Y
this is why, when it is refluxed with acid to give ONE product, its trying to imply that the bond hydrolyses to give rise to two of the same molecule, hence ONE organic product. :smile:

Oh and its not an ester! its an amino acid

Bugger, didnt mean ester!! Thats COOC!! It's a polymer then :wink:

aka Amino acid..

Reply 1813

Hunarench95

13

Original post by AtomicMan

Does anyone know what the advantages and disadvantages of methanol, ethanol and hydrogen fuel cells are?

Advantages:

•

Hydrogen is abundant (hydrolysis of sea water) - whereas fossil fuels are more scarce

•

Ethanol and methanol are gotten from the decomposition of plant material (again renewable - abundant)

•

Doesn't produce emissions that damages ozone (suitable for airplanes)

•

Only emission is H2O

Disadvantages

•

Rare metals used are expensive

•

Storing hydrogen is expensive/dangerous

•

Hydrogen fuelling stations are not common place

•

Costly for consumer

•

Disposal of decommissioned fuel cells is difficult due to heavy metals.

•

H2O is still a greenhouse gas

(edited 10 years ago)

Reply 1814

sounique

Original post by Hunarench95

Advantages:

•

Hydrogen is abundant (hydrolysis of sea water) - whereas fossil fuels are more scarce

•

Ethanol and methanol are gotten from the decomposition of plant material (again renewable - abundant)

•

Doesn't produce emissions that damages ozone (suitable for airplanes)

•

Only emission is H2O

Disadvantages

•

Rare metals used are expensive

•

Storing hydrogen is expensive/dangerous

•

Hydrogen fuelling stations are not common place

•

Costly for consumer

•

Disposal of decommissioned fuel cells is difficult due to heavy metals.

•

H2O is still a greenhouse gas

Why is hydrogen easily transported not an advantage? It was on one of the multiple choice questions..

Reply 1815

Inspire12

can someone explain Q 14 on the june 12 paper, its the empirical formula and i cant get my head around it!!!

Reply 1816

orange94

Original post by Inspire12

part 15 iii and why do they subtract the no of moles of iodine that you work out from the no of moles of iodine given in the question?

Because you want the amount of iodine that has reacted! That's why duh lol

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Reply 1817

Bubblezzzz

Original post by AtomicMan

Does anyone know what the advantages and disadvantages of methanol, ethanol and hydrogen fuel cells are?

well hydrogen fuel cells are greener compared to their hydrocarbon engine counterparts, because it doesn't use fuel from a finite resource, as hydrogen can be produced from electrolysis of brine and water, provided that the electricity used is also produced by renewable means.
Disadvantage is that it is very difficult to store - need to use liquefaction at ultra-low temperatures or high pressure storage or solid state adsorption, all of which are really expensive and require energy.

Methanol/ethanol - same argument really, they are produced from biomass, i.e. obtained by fermentation of sugars, which can be renewably grown provided that its rate of consumption does not surpass rate of regeneration. This is better again than using finite resources such as crude oil
when plants/crops grow, they act as carbon sinks, i.e. take in carbon dioxide for photosynthesis so reduce carbon footprint.
Disadvantages are that we need land to grow crops from food with a growing population and cannot allocate too much land for biofuel production or this will lead to starvation.

With both fuel cells, no harmful/toxic gaseous emissions evolve AT POINT OF USE as combustion is not taking place, so it is cleaner (although they may use fossil fuels to provide energy to extract or make the fuel)