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%
This discussion is closed.
LeaX
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#941
(Original post by posthumus)
Hey guys
Just started organic today...

I'm stuck with acylation reactions (with benzene), it states that no further substitution happens as the COCH3 group deactivates the benzene ring? Could someone explain to me what this means

Also for sulfonation the electrophile is SO3 , which I believe has no charge ? But in the diagram it has SO3H substituted onto the benzene ring, so could it be a mistake they said SO3 is the elecrophile ? And meant SO3H+ instead...

I don't like SO3, because its such a weird structure as well !
for the second one, SO3 attacks the benzene ring and then an unstable intermediate forms (where one C is bonded to both a H and the SO3), the H+ then leaves, donating its electron to reform the benzene ring and then the hydrogen bonds onto one of SO3's oxygens. initially, benzene sulfonate forms and then when the H+ is removed it joins on to form benzenesulfonic acid (which is where you get the SO3H from)
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bubblegummer
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#942
(Original post by posthumus)
E on it's own is the electrode potential of that particular half cell ... or "half equation"

Ecell is 2 half cells combined together.... or the sum of two E (electrode potentials) .... or the sum of two half equations However you want to look at it

I've never come across Edelta... but I would assume the change in E would be the E cell....
after asking my teacher and again referring to your explanation, i finally got a clear picture of it. thank you for your help!
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LeaX
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I was wondering if anyone could possibly explain this question? I've circled the correct answer but I'm not sure why it's correct? I put C as the answer because I assumed that D was symmetrical so it wasn't a polar molecule?

Also, another question (sorrrrryyyyyy...) So I know phenylamine is a weak base because the N long pair becomes delocalised which is very stable. But if that's the case, why doesn't phenol become more stable compared to benzene? Because surely the Oxygen's lone pair would also make the molecule more stable? But then with phenol it says that it gets more reactive (hence the multiple substitutions, etc.)

Thank you in advance.
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GeorgeL3
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#944
(Original post by LeaX)
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I was wondering if anyone could possibly explain this question? I've circled the correct answer but I'm not sure why it's correct? I put C as the answer because I assumed that D was symmetrical so it wasn't a polar molecule?

Also, another question (sorrrrryyyyyy...) So I know phenylamine is a weak base because the N long pair becomes delocalised which is very stable. But if that's the case, why doesn't phenol become more stable compared to benzene? Because surely the Oxygen's lone pair would also make the molecule more stable? But then with phenol it says that it gets more reactive (hence the multiple substitutions, etc.)

Thank you in advance.
For your first question, I think the answer is D since it is a chlorofluorocarbon (CFC) and the chlorine and fluorine atoms can be released and then catalyse the breakdown of the ozone layer.
A & B can be ruled out straight away (NaCl is a salt and CO2 is a greenhouse gas rather than an ozone pollutant)
C, although having Fluorine in it is actually a hydrofluorocarbon (HFC) which whilst being a potent greenhouse gas is actually not very damaging to the ozone layer.
Polarity comes more into being a greenhouse gas because it means they can absorb IR and keep in heat whereas it doesn't necessarily mean it damages ozone.

For your second question I didn't know that made it more stable, I thought that just makes phenylamine a weaker base than ammonia because the electrons which would be donated are actually in the benzene ring so it is less basic. However I'm pretty sure phenylamine still has an activated benzene ring though like phenol so it's just as reactive.
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F1's Finest
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(Original post by LeaX)
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I was wondering if anyone could possibly explain this question? I've circled the correct answer but I'm not sure why it's correct? I put C as the answer because I assumed that D was symmetrical so it wasn't a polar molecule?

Also, another question (sorrrrryyyyyy...) So I know phenylamine is a weak base because the N long pair becomes delocalised which is very stable. But if that's the case, why doesn't phenol become more stable compared to benzene? Because surely the Oxygen's lone pair would also make the molecule more stable? But then with phenol it says that it gets more reactive (hence the multiple substitutions, etc.)

Thank you in advance.
All it has to do with, is chlorine radicals. The question was referring to the ozone layer and not the greenhouse effect!
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posthumus
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(Original post by LeaX)
for the second one, SO3 attacks the benzene ring and then an unstable intermediate forms (where one C is bonded to both a H and the SO3), the H+ then leaves, donating its electron to reform the benzene ring and then the hydrogen bonds onto one of SO3's oxygens. initially, benzene sulfonate forms and then when the H+ is removed it joins on to form benzenesulfonic acid (which is where you get the SO3H from)
When the SO3 with neutral charge attacks the benzene ring, has this intermediate also got a neutral charge?
& do you also think this could come up Because it doesn't go to this much detail in George Facer Even though I see the mechanism for this as a kind of exception



(Original post by LeaX)
Name:  chemistryyyyy.png
Views: 127
Size:  16.3 KB

I was wondering if anyone could possibly explain this question? I've circled the correct answer but I'm not sure why it's correct? I put C as the answer because I assumed that D was symmetrical so it wasn't a polar molecule?

Also, another question (sorrrrryyyyyy...) So I know phenylamine is a weak base because the N long pair becomes delocalised which is very stable. But if that's the case, why doesn't phenol become more stable compared to benzene? Because surely the Oxygen's lone pair would also make the molecule more stable? But then with phenol it says that it gets more reactive (hence the multiple substitutions, etc.)

Thank you in advance.
d) I would have thought purely because its a chlorofluorocarbon (CFC) - and Under UV light Cl free radicals are produced, which then react with ozone
If what you say is true, the others are greenhouse gases due to polarity then I don't think that necessarily means they react with Ozone, just that they absorb radiation which is reflected by the earth and warm up the atmosphere Not too sure about that though, still need to go over Unit 2

I'm not sure what you mean by your second question, phenol and phenylamine both become more vulnerable to electrophilic substitution. Also because the Lone pairs on the Nitrogen and Oxygen interact with the delocalised ring, the Phenylamine becomes less effective as base and the Phenol becomes less effective as an alcohol.
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AtomicMan
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#947
(Original post by LeaX)
Name:  chemistryyyyy.png
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I was wondering if anyone could possibly explain this question? I've circled the correct answer but I'm not sure why it's correct? I put C as the answer because I assumed that D was symmetrical so it wasn't a polar molecule?

Also, another question (sorrrrryyyyyy...) So I know phenylamine is a weak base because the N long pair becomes delocalised which is very stable. But if that's the case, why doesn't phenol become more stable compared to benzene? Because surely the Oxygen's lone pair would also make the molecule more stable? But then with phenol it says that it gets more reactive (hence the multiple substitutions, etc.)

Thank you in advance.
C-F bond is too strong to be broken by UV light, whereas the C-Cl bond can be broken to produce Cl free fradicals which can attack the ozone layer.
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LeaX
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(Original post by GeorgeL3)
For your first question, I think the answer is D since it is a chlorofluorocarbon (CFC) and the chlorine and fluorine atoms can be released and then catalyse the breakdown of the ozone layer.
A & B can be ruled out straight away (NaCl is a salt and CO2 is a greenhouse gas rather than an ozone pollutant)
C, although having Fluorine in it is actually a hydrofluorocarbon (HFC) which whilst being a potent greenhouse gas is actually not very damaging to the ozone layer.
Polarity comes more into being a greenhouse gas because it means they can absorb IR and keep in heat whereas it doesn't necessarily mean it damages ozone.

For your second question I didn't know that made it more stable, I thought that just makes phenylamine a weaker base than ammonia because the electrons which would be donated are actually in the benzene ring so it is less basic. However I'm pretty sure phenylamine still has an activated benzene ring though like phenol so it's just as reactive.

(Original post by James A)
All it has to do with, is chlorine radicals. The question was referring to the ozone layer and not the greenhouse effect!

(Original post by posthumus)
When the SO3 with neutral charge attacks the benzene ring, has this intermediate also got a neutral charge?
& do you also think this could come up Because it doesn't go to this much detail in George Facer Even though I see the mechanism for this as a kind of exception





d) I would have thought purely because its a chlorofluorocarbon (CFC) - and Under UV light Cl free radicals are produced, which then react with ozone
If what you say is true, the others are greenhouse gases due to polarity then I don't think that necessarily means they react with Ozone, just that they absorb radiation which is reflected by the earth and warm up the atmosphere Not too sure about that though, still need to go over Unit 2

I'm not sure what you mean by your second question, phenol and phenylamine both become more vulnerable to electrophilic substitution. Also because the Lone pairs on the Nitrogen and Oxygen interact with the delocalised ring, the Phenylamine becomes less effective as base and the Phenol becomes less effective as an alcohol.

(Original post by AtomicMan)
C-F bond is too strong to be broken by UV light, whereas the C-Cl bond can be broken to produce Cl free fradicals which can attack the ozone layer.
Thank you everyone! You can tell I haven't looked back over AS stuff yet hahaha.
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GeorgeL3
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There's a part in the syllabus that says we have to understand 'purification by washing, eg with water and sodium carbonate solution'.
Does anybody know what they mean?
Is like using polar solvents to clean stuff away from a non polar product maybe?
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F1's Finest
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(Original post by GeorgeL3)
There's a part in the syllabus that says we have to understand 'purification by washing, eg with water and sodium carbonate solution'.
Does anybody know what they mean?
Is like using polar solvents to clean stuff away from a non polar product maybe?
Yeah, solvent extraction where you use a separating funnel.

During organic synthesis, you need to obtain a pure sample of a product, however impurities will be present. Sodium Carbonate solution of course, absorbs any acidic impurities, e.g. maybe an acid that was used in the preparation of the product.

Water then removes any unreacted sodium salts and water soluble organic substances.

Basically the spec is implying that those are the only two features we will be required to know about what to wash our product with.....

just be wary about the fact that polar substances dissolve in polar substances. Also, non-polar substances dissolve in non-polar substances!
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posthumus
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(Original post by GeorgeL3)
There's a part in the syllabus that says we have to understand 'purification by washing, eg with water and sodium carbonate solution'.
Does anybody know what they mean?
Is like using polar solvents to clean stuff away from a non polar product maybe?
I haven't read everything yet of organic chemistry, but I think it may be referring to preparation of organic substances such as 2-methylnitrobenzene.
(page 255 if you are using the George Facer book)

When you nitrate methylbenzene, it won't be pure... so you pour the mixture (from the reflux apparatus) into a separating funnel and you will get a bottom layer of methylnitrobenzenes Discard top layer.... you wash your impure methylnitrobenzene with Sodium carbonate solution.... I believe this is a very strong base and will react with any acids in the solution Then you wash with water to remove any sodium carbonate. After that you try it by adding anhydrous CaCl2... after that you distill of the 2-methylnitrobenzene
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GeorgeL3
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(Original post by James A)
Yeah, solvent extraction where you use a separating funnel.

During organic synthesis, you need to obtain a pure sample of a product, however impurities will be present. Sodium Carbonate solution of course, absorbs any acidic impurities, e.g. maybe an acid that was used in the preparation of the product.

Water then removes any unreacted sodium salts and water soluble organic substances.

Basically the spec is implying that those are the only two features we will be required to know about what to wash our product with.....

just be wary about the fact that polar substances dissolve in polar substances. Also, non-polar substances dissolve in non-polar substances!
(Original post by posthumus)
I haven't read everything yet of organic chemistry, but I think it may be referring to preparation of organic substances such as 2-methylnitrobenzene.
(page 255 if you are using the George Facer book)

When you nitrate methylbenzene, it won't be pure... so you pour the mixture (from the reflux apparatus) into a separating funnel and you will get a bottom layer of methylnitrobenzenes Discard top layer.... you wash your impure methylnitrobenzene with Sodium carbonate solution.... I believe this is a very strong base and will react with any acids in the solution Then you wash with water to remove any sodium carbonate. After that you try it by adding anhydrous CaCl2... after that you distill of the 2-methylnitrobenzene
Ah okay then, that makes more sense now. Thanks guys.
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F1's Finest
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Feeling good for this exam, but I'm relying more on Unit 2 to get me my A. Unit 5 can throw anything tbh.
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JoshL123
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(Original post by James A)
Feeling good for this exam, but I'm relying more on Unit 2 to get me my A. Unit 5 can throw anything tbh.
You definitely seem like the kind of person with the potential to get A*!

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(Original post by JoshL123)
You definitely seem like the kind of person with the potential to get A*!

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Nah, I would have needed to have gotten 108 in Unit 4, got 101 ums back in June 2012. So an A* is off the cards but an A, that's my aim I need 15 ums more though (from either unit 2 or 5 :sigh: )

You?
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JoshL123
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(Original post by James A)
Nah, I would have needed to have gotten 108 in Unit 4, got 101 ums back in June 2012. So an A* is off the cards but an A, that's my aim I need 15 ums more though (from either unit 2 or 5 :sigh: )

You?
A* is out of the cards for me as well. I got 98 in January (ran out of time in the last nmr question) :/. So yeah I would need 118 in unit 5 to get the a star (doesnt seem possible :L). So I am going for the A. I need like 48 or something ums for it though so hopefully should get it. Its just that I have seen you in the biology thread as well and you defo aound prepared!

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(Original post by JoshL123)
You definitely seem like the kind of person with the potential to get A*!

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Anyone who can get an A* in this beast of a unit has my full respect tbh
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(Original post by JoshL123)
A* is out of the cards for me as well. I got 98 in January (ran out of time in the last nmr question) :/. So yeah I would need 118 in unit 5 to get the a star (doesnt seem possible :L). So I am going for the A. I need like 48 or something ums for it though so hopefully should get it. Its just that I have seen you in the biology thread as well and you defo aound prepared!

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Don't they add up what you got from your assessed practical when totalling whether you got an A*?
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JoshL123
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(Original post by James A)
Don't they add up what you got from your assessed practical when totalling whether you got an A*?
Hold on a minute. Just had a stupid moment (as you do :P)...I need 110 ums!

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(Original post by JoshL123)
Hold on a minute. Just had a stupid moment (as you do :P)...I need 110 ums!

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Did your teacher tell you what they reckon you would pick up on the practical?

Usually all teachers do it for the Chem ISA's.
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