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

Poll: How pumped up are you for this exam?-(warning)-(bad jokes arene this poll!)
"Titanium-I'm not going to corrode (even at high temperatures)" (A*) (22)
16.67%
"Benzene's my middle name, give me the paper in a week and I'll ace it!" (A) (27)
20.45%
"Yeah, I'm fairly electrophillic (positively charged) about the exam" (B) (27)
20.45%
"I'm in the middle of the salt bridge, but I will pass-eventually" (C) (21)
15.91%
"I'm feeling rather electroNegative about this exam" (D) (18)
13.64%
"Benzene, what's that?" (E) (6)
4.55%
"Chemistry, what's that?" (F) (11)
8.33%
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shumen9523
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(Original post by AS01)
Nope! Coz now they have ions and no lone pair on N to form any covalent bond

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Thanks for the reply.
Yeah that's what I thought. But how can peptide bonds form between amino acids
in a solution even though, in solutions, these amino acids tend exist as zwitterions. In other words, How is it possible to synthesise a poly-peptide chain from a group of amino acids in a solution ??? (hope my question is clearer now)
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shumen9523
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(Original post by jojo1995)
in some book i read .. maybe GF .. It said something about the zwittzerions being able to undergo reactions of cooh group and nh2 group is acid or base is added to change them back ... ie add acid to turn the coo- in the zwitterion to cooh ... perhaps it is something to do with that

but also another book i read ... maybe GF said that the zwitterion <-> amino acid thing .... they are constantly flicking between states ie one minute they are normal .. then they are in the zwitterion form .. i think


sorry i couldnt be of more help
Thanks for the reply
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Knoyle quiah
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#1363
I have attached qsn and ms, I understand it all but only part I dont get is why structure is B and not A of tiglic acid????? can anyone help please
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Knoyle quiah
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(Original post by jethacan)
So the half equations are

Zn -> Zn2+ +2e-
Fe3+ + e- -> Fe2+

So the electrode for the first one must be Zinc since there's solid Zinc in the reaction.
Electrode 2 involves two ions of Iron Fe2+ and Fe3+, no solid iron is involved. In these cases an inert platinum electrode is used so the reaction can occur on the surface of the platinum electrode without the Pt reacting with the Fe ions.
Ahh thank you makes sense now just remembered seeing that in the book
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LeaX
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(Original post by Knoyle quiah)
I have attached qsn and ms, I understand it all but only part I dont get is why structure is B and not A of tiglic acid????? can anyone help please
Both make iodoform with iodine in alkali. Remember in unit four it was a test and in order to get iodoform you needed a carbonyl group next to a methyl group (CH3CO). B has two methyl groups attached to C=C.
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F1's Finest
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(Original post by LeaX)
Both make iodoform with iodine in alkali. Remember in unit four it was a test and in order to get iodoform you needed a carbonyl group next to a methyl group (CH3CO). B has two methyl groups attached to C=C.
The iodoform works with ethanol and methyl secondary alcohols too!
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jojo1995
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Am or Pm anyone ?
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laurenlou-may
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(Original post by jojo1995)
Am or Pm anyone ?
AM


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Knoyle quiah
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#1369
(Original post by LeaX)
Both make iodoform with iodine in alkali. Remember in unit four it was a test and in order to get iodoform you needed a carbonyl group next to a methyl group (CH3CO). B has two methyl groups attached to C=C.
Thanks, didnt think about thatt
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LeaX
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#1370
(Original post by James A)
The iodoform works with ethanol and methyl secondary alcohols too!
Ooh I never knew that, thank you for letting me know.
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jojo1995
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(Original post by laurenlou-may)
AM


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thank you
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jojo1995
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the anode and the cathode:

you see during a standard reduction potential reaction..... how do you know which half cell is the anode and which one is the cathode?
what happens at the cathode and what happens at the anode please ?
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Knoyle quiah
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NH2CH2CONHCH2COOH (reflux with conc HCl then neutralise) gives NH2CH2COOH(glycine) can someone please explain what is happening here and what type of reaction is it?
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posthumus
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(Original post by jojo1995)
the anode and the cathode:

you see during a standard reduction potential reaction..... how do you know which half cell is the anode and which one is the cathode?
what happens at the cathode and what happens at the anode please ?
This confuses me in the george facer book... like for full cells they claim that zinc is oxidized at the anode, which is negative (thought cathodes were negative)

Well anyway if this is the case, I think the one being tested against a reference electrode will be the anode (being oxidized, according to george).
Because if it's being oxidized... it produces an electron e- Which causes a flow of charge and is read through the volt meter. I don't think reference electrodes such as SHE produce electrons/flow of charge/current .... but I could be wrong


(Original post by Knoyle quiah)
NH2CH2CONHCH2COOH (reflux with conc HCl then neutralise) gives NH2CH2COOH(glycine) can someone please explain what is happening here and what type of reaction is it?
Looks like hydrolysis to me.... but you said concentrated HCl instead of aqueous, so not too sure now
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F1's Finest
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(Original post by posthumus)
This confuses me in the george facer book... like for full cells they claim that zinc is oxidized at the anode, which is negative (thought cathodes were negative)

Well anyway if this is the case, I think the one being tested against a reference electrode will be the anode (being oxidized, according to george).
Because if it's being oxidized... it produces an electron e- Which causes a flow of charge and is read through the volt meter. I don't think reference electrodes such as SHE produce electrons/flow of charge/current .... but I could be wrong




Looks like hydrolysis to me.... but you said concentrated HCl instead of aqueous, so not too sure now
Seems like hydrolysis to me.

One molecule is split into two. Remember that hydrolysis can take place with acids too not just water.

EDIT : There's also such a thing as base hydrolysis too!
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JRP95
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(Original post by posthumus)
This confuses me in the george facer book... like for full cells they claim that zinc is oxidized at the anode, which is negative (thought cathodes were negative)

Well anyway if this is the case, I think the one being tested against a reference electrode will be the anode (being oxidized, according to george).
Because if it's being oxidized... it produces an electron e- Which causes a flow of charge and is read through the volt meter. I don't think reference electrodes such as SHE produce electrons/flow of charge/current .... but I could be wrong




Looks like hydrolysis to me.... but you said concentrated HCl instead of aqueous, so not too sure now
This is why you don't bother with the facer book, it just confuses you and doesn't help at all opposed to cgp...
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Knoyle quiah
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How many nmr peaks for this and how do you know?? I thought only 2 peaks
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Knoyle quiah
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(Original post by posthumus)
This confuses me in the george facer book... like for full cells they claim that zinc is oxidized at the anode, which is negative (thought cathodes were negative)

Well anyway if this is the case, I think the one being tested against a reference electrode will be the anode (being oxidized, according to george).
Because if it's being oxidized... it produces an electron e- Which causes a flow of charge and is read through the volt meter. I don't think reference electrodes such as SHE produce electrons/flow of charge/current .... but I could be wrong




Looks like hydrolysis to me.... but you said concentrated HCl instead of aqueous, so not too sure now
really cant remember whats happening in this reaction
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Knoyle quiah
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what is this question , never seen in my life
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F1's Finest
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(Original post by Knoyle quiah)
How many nmr peaks for this and how do you know?? I thought only 2 peaks
I think it's four. I defo remember that question.

The three -CH3 groups are in their own hydrogen environment. Also the carbon on the far right hand side has a hydrogen attached (it's not showed in the diagram, but they want you to figure it out )
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