ATAR Notes: Forum
VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: crayolé on May 14, 2010, 06:09:59 pm
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-CH2O-
It was in the SAC today and i can't really remember what was branching off it but it's doing my head in ;]
I wrote aldehyde as a wild guess (are they tested in VCE?), everyone else wrote carboxylic acid
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yeah..you should get it right
-CH2O-,that's the simplest aldehyde, FORMALDEHYDE
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Is that part of the VCE course?? I've never seen it before.
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this is hard stuff! D:
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Carboxylic acid is R-COOH, so it can't be carboxylic acid
Aldehyde is R-CHO, so yea it can be an aldehyde
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"• structure and systematic nomenclature of alkanes, alkenes, amines, chloroalkanes, alkanols and
carboxylic acids up to C10;"
No mention of aldehydes in study design...
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aldehydes and ketones arent in the study design.
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Yea but my Chem teacher said that there was a ketone molecule on a VCAA exam a few years ago
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Ohhh shit ;]
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Yea but my Chem teacher said that there was a ketone molecule on a VCAA exam a few years ago
In the old syllabus? The new syllabus (ie. the one you are doing now) only started in 2008 and by a "few years ago", could that mean pre-2008?
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Yea but my Chem teacher said that there was a ketone molecule on a VCAA exam a few years ago
In the old syllabus? The new syllabus (ie. the one you are doing now) only started in 2008 and by a "few years ago", could that mean pre-2008?
It was in 2008 exam. U didnt need to know the molecule was called a keytone
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They're just another group, as kyzoo said R-COH is aldehyde, but a ketone is the isomer of it with the C=O bond not on the terminal ends, so R-CO-R.
And Yea CH2O is an aldehyde (end in al), it's methanal. And I'm guessing the dashes don't represent R groups?
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They're just another group, as kyzoo said R-COH is aldehyde, but a ketone is the isomer of it with the C=O bond not on the terminal ends, so R-CO-R.
And Yea CH2O is an aldehyde (end in al), it's methanal. And I'm guessing the dashes don't represent R groups?
One side of the dash was the a huge ass molecule and I'm pretty sure the other side was just a H or CH3
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Then I don't think it can be a C=O because then it wouldn't have four bonds?
O-H
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-C-
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H
that's the only way I see it works (Carbon having four bonds).
Mao where art thou.
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Then I don't think it can be a C=O because then it wouldn't have four bonds?
O-H
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-C-
|
H
that's the only way I see it works (Carbon having four bonds).
Mao where art thou.
Yeah thats the way i ended up drawing it :/
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It does seem like that's the only option.
But it would usually be written as -CH(OH)- wouldn't it?
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Secondary alkanol:
R-CH2O-R, or R(CHOH)R
Ketone:
R-CO-R, or R(C=O)R
Aldehyde:
R-COH, or R(C=O)H
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Okay, so it was a secondary alkanol, thanks Mao,
What makes it secondary?
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A secondary alkanol is one where the -OH group is attached to a C atom which is attached to two other C atoms. E.g. CH3.CHOH.CH3
A tertiary alkanol is one where the associated C atom is attached to three other C-atoms. E.g. CH3.COH(CH3).CH3
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Primary alkanol has OH at terminal C, while secondary doesn't.
Primary can be oxidised to form aldehyde, secondary to form ketone.
Aldehyde goes on further to be oxidised to form carboxylic acids, ketones do not.
Bit of unnecessary info, but it can't hurt to know :).
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Primary alkanol has OH at terminal C, while secondary doesn't.
Primary can be oxidised to form aldehyde, secondary to form ketone.
Aldehyde goes on further to be oxidised to form carboxylic acids, ketones do not.
Bit of unnecessary info, but it can't hurt to know :).
On the contrary, that is important information. That is one of the chemical tests to distinguish a primary alcohol (e.g. propan-1-ol) from a secondary alcohol (e.g. propan-2-ol).
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Primary alkanol has OH at terminal C, while secondary doesn't.
Primary can be oxidised to form aldehyde, secondary to form ketone.
Aldehyde goes on further to be oxidised to form carboxylic acids, ketones do not.
Bit of unnecessary info, but it can't hurt to know :).
On the contrary, that is important information. That is one of the chemical tests to distinguish a primary alcohol (e.g. propan-1-ol) from a secondary alcohol (e.g. propan-2-ol).
So what's the test?
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Primary alkanol has OH at terminal C, while secondary doesn't.
Primary can be oxidised to form aldehyde, secondary to form ketone.
Aldehyde goes on further to be oxidised to form carboxylic acids, ketones do not.
Bit of unnecessary info, but it can't hurt to know :).
On the contrary, that is important information. That is one of the chemical tests to distinguish a primary alcohol (e.g. propan-1-ol) from a secondary alcohol (e.g. propan-2-ol).
So what's the test?
Alkanol can either be primary, secondary or tertiary.
When you have a mixture of alkanols [e.g. mixture of propan-1-ol, propan-2-ol and t-butanol], fractional distillation will give you pure [or almost pure] fractions [e.g. pure propan-1-ol, pure propan-2-ol and t-butanol]. However, their identity is not known, since boiling point is often difficult to predict, thus, chemical tests are needed to characterise these fractions.
One of the chemical test is to oxidize the fraction, usually with acidified solution of permanganate or dichromate (you should be familiar with these).
Primary alkanol will be oxidized to an aldehyde, then carboxylic acid. This oxidation process will decolourize the permanganate solution (purple -> clear). Addition of an alkanol (such as ethanol) will give an ester, which tends to have a distinct fragrance [fruity smell usually].
Secondary alkanol will be oxidized to a ketone. This oxidation process will decolourize the permanganate, however, since the oxidized carbon doesn't have any more hydrogen, it cannot become an acid. Addition of an alkanol (such as ethanol) will do nothing.
Tertiary alkanol will not oxidize, and the permanganate does not decolourize.
So by adding the same chemical (permanganate then another alkanol), these three very similar compounds will give three distinctively different results: 1o = decolourization and fruit scent, 2o = decolourization, 3o = no reaction.
You should be familiar with a range of chemical tests, such as the bromine test, the test for acidity using sodium bicarbonate.
*note, t-butanol is the lazy way of saying 2-methylpropan-2-ol, I don't recommend you using it in an exam, but I am lazy.
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hey mao, did you learn this at uni?
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hey mao, did you learn this at uni?
nah mate, learnt this in year 12.
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wow ... which book? heinemann?
i am sure it's no in the jacaranda book
also (Primary alkanol will be oxidized to an aldehyde, then carboxylic acid. )
the aldehyde transform to aldehyde hydrate, is that important?
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Genius explanation as always Mao ;D thanks
And Simon, I'm pretty sure you wont need to know the aldehyde step, just the alkanol ---> carboxylic acid
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wow ... which book? heinemann?
i am sure it's no in the jacaranda book
also (Primary alkanol will be oxidized to an aldehyde, then carboxylic acid. )
the aldehyde transform to aldehyde hydrate, is that important?
I use Heinemann and I never seen that test before 0.o I would guess that Mao most likely obtained this info from an external company's Chem practice exam solutions.
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wow ... which book? heinemann?
i am sure it's no in the jacaranda book
also (Primary alkanol will be oxidized to an aldehyde, then carboxylic acid. )
the aldehyde transform to aldehyde hydrate, is that important?
I'm so glad my teacher hates the textbooks and doesn't teach using them, else I wouldn't have known that!
But I don't think it's critical to know this stuff.
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wow ... which book? heinemann?
i am sure it's no in the jacaranda book
also (Primary alkanol will be oxidized to an aldehyde, then carboxylic acid. )
the aldehyde transform to aldehyde hydrate, is that important?
I use Heinemann and I never seen that test before 0.o I would guess that Mao most likely obtained this info from an external company's Chem practice exam solutions.
His teacher might have taught him it?
I don't think teachers always strictly follow the textbook, well atleast they shouldn't?
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True, I've learned a lot from my Chem and Physics teachers that wasn't in the textbook
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lol.....jacaranda has heaps of mistakes...
looks like i have to read over heinemann as well
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I use Heinemann and I never seen that test before 0.o I would guess that Mao most likely obtained this info from an external company's Chem practice exam solutions.
It's pretty much applying your knowledge of organic pathways anyway.
Alkanol -----Cr2O7 Catalyst------->> Carboxylic acid
and then esterification
All the in between steps arent really needed are they?
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http://en.wikipedia.org/wiki/Alcohol_oxidation
have a look~~!
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I don't think you should leave the aldehyde step out.
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pretty sure our teacher has NEVER mentioned this aldehyde + ketone stuff, thank god for vce notes :D
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I don't think you should leave the aldehyde step out.
Yeah it will probably make you look a more competent student thus more deserving of marks but I was at a tsfx lecture and the lady said that the intermediate step with aldehydes and ketones werent needed in the exam?
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As far as I know, you won't need to know any intermediates. However, you should be aware of what aldehydes and ketones are, how they are derived, what chemical pathways they can undergo, and what chemical pathways lead to them.
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I don't really understand how the textbooks, with so much irrelevant information (such as bus companies and their efforts to be environmentally friendly), can miss these more relevant aspects such as aldehydes.
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I don't really understand how the textbooks, with so much irrelevant information (such as bus companies and their efforts to be environmentally friendly), can miss these more relevant aspects such as aldehydes.
Aha true tbh theres so much bs in the green chemistry