Edexcel Chemistry Unit 5 June 19 2012
Chemistry exam discussion - share revision tips in preparation for GCSE, A Level and other chemistry exams and discuss how they went afterwards.
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Edexcel Chemistry Unit 5 June 19 2012Well, the Unit Four & Five thread has been contaminated with panicking about unit four so thought I'd create a thread SPECIFICALLY for unit five only.
How's everyone preparing for it? Also, if anyone has a list of topics they think will come up, feel free to quote me and I'll edit it into this post.Last edited by Revent; 18-06-2012 at 22:17. -
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Re: Chemistry Unit 5 June 19 2012I haven't started my revision yet so can't help you with the past paper question, but Zwitterions have a high melting temperature because they can form intermolecular ionic bonds which are stronger than other interactions such as hydrogen bonding I believe.(Original post by shahofiran)
Lol i'll ask my question here - i dont get question 11 for unit 5 june 2010. Also, why do zwitterions have a high melting temperature? -
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Re: Chemistry Unit 5 June 19 2012they form hydrogen bonds...(Original post by Revent)
I haven't started my revision yet so can't help you with the past paper question, but Zwitterions have a high melting temperature because they can form intermolecular ionic bonds which are stronger than other interactions such as hydrogen bonding I believe. -
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Re: Chemistry Unit 5 June 19 2012No they don't. Strong electrostatic attractions (ionic bonding) between the COO- and NH3+ of different zwitterions.(Original post by sconter)
they form hydrogen bonds... -
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Re: Chemistry Unit 5 June 19 2012The amino acids are crystalline solids with surprisingly high melting points. It is difficult to pin the melting points down exactly because the amino acids tend to decompose before they melt. Decomposition and melting tend to be in the 200 - 300°C range.(Original post by sconter)
they form hydrogen bonds...
For the size of the molecules, this is very high. Something unusual must be happening.
If you look again at the general structure of an amino acid, you will see that it has both a basic amine group and an acidic carboxylic acid group.
There is an internal transfer of a hydrogen ion from the -COOH group to the -NH2 group to leave an ion with both a negative charge and a positive charge.
This is called a zwitterion.
A zwitterion is a compound with no overall electrical charge, but which contains separate parts which are positively and negatively charged.
This is the form that amino acids exist in even in the solid state. Instead of the weaker hydrogen bonds and other intermolecular forces that you might have expected, you actually have much stronger ionic attractions between one ion and its neighbours.
These ionic attractions take more energy to break and so the amino acids have high melting points for the size of the molecules -
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Re: Chemistry Unit 5 June 19 2012The longer version of what I said.(Original post by Revent)
The amino acids are crystalline solids with surprisingly high melting points. It is difficult to pin the melting points down exactly because the amino acids tend to decompose before they melt. Decomposition and melting tend to be in the 200 - 300°C range.
For the size of the molecules, this is very high. Something unusual must be happening.
If you look again at the general structure of an amino acid, you will see that it has both a basic amine group and an acidic carboxylic acid group.
There is an internal transfer of a hydrogen ion from the -COOH group to the -NH2 group to leave an ion with both a negative charge and a positive charge.
This is called a zwitterion.
A zwitterion is a compound with no overall electrical charge, but which contains separate parts which are positively and negatively charged.
This is the form that amino acids exist in even in the solid state. Instead of the weaker hydrogen bonds and other intermolecular forces that you might have expected, you actually have much stronger ionic attractions between one ion and its neighbours.
These ionic attractions take more energy to break and so the amino acids have high melting points for the size of the molecules
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Re: Chemistry Unit 5 June 19 2012learn somethin new everyday.(Original post by NutterFrutter)
No they don't. Strong electrostatic attractions (ionic bonding) between the COO- and NH3+ of different zwitterions.
the shape of proteins is caused by h bonds tho. -
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Re: Chemistry Unit 5 June 19 2012Yeah
Partly. Hydrogen bonds are one of the multiple interactions that are used to shape a protein.(Original post by sconter)
learn somethin new everyday.
the shape of proteins is caused by h bonds tho. -
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Re: Chemistry Unit 5 June 19 2012I thought it was okay, however, most people will have got low marks on it because they wouldn't have studied breathalysers in depth.(Original post by This Honest)
Thank you Revent for making a new thread.
Can't stand the unit 4 discussion; need to see unit 5 only
Oh btw, june 11 section C was hard! -
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Re: Chemistry Unit 5 June 19 2012And you said you haven't started revision yet....(Original post by Revent)
The amino acids are crystalline solids with surprisingly high melting points. It is difficult to pin the melting points down exactly because the amino acids tend to decompose before they melt. Decomposition and melting tend to be in the 200 - 300°C range.
For the size of the molecules, this is very high. Something unusual must be happening.
If you look again at the general structure of an amino acid, you will see that it has both a basic amine group and an acidic carboxylic acid group.
There is an internal transfer of a hydrogen ion from the -COOH group to the -NH2 group to leave an ion with both a negative charge and a positive charge.
This is called a zwitterion.
A zwitterion is a compound with no overall electrical charge, but which contains separate parts which are positively and negatively charged.
This is the form that amino acids exist in even in the solid state. Instead of the weaker hydrogen bonds and other intermolecular forces that you might have expected, you actually have much stronger ionic attractions between one ion and its neighbours.
These ionic attractions take more energy to break and so the amino acids have high melting points for the size of the molecules -
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Re: Chemistry Unit 5 June 19 2012(Original post by This Honest)
And you said you haven't started revision yet....
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Re: Chemistry Unit 5 June 19 2012(Original post by NutterFrutter)
I thought it was okay, however, most people will have got low marks on it because they wouldn't have studied breathalysers in depth.
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Re: Chemistry Unit 5 June 19 2012Not so much jun10 but jan 11 caused some problems such as the last Q and the dry oil Q(Original post by EffKayy)
I found the June 10 and Jan11 section C really difficult.
Anyone else agree?! :/ Going to fail..
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Re: Chemistry Unit 5 June 19 2012LOL :/ Yeah the dry oil question(Original post by This Honest)
Not so much jun10 but jan 11 caused some problems such as the last Q and the dry oil Q
I hope this paper is OK, im a little scared now as the unit 4 paper seemed quite challenging in some parts
