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OCR Chemistry F322~ 4th June 2013~ AS Chemistry

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Original post by mia_hilton
Hi guys was just marking jun 2010 paper and was confused if i would get a mark or not?
Q 4iii) Give an equation to show the reaction between ethanol and acidified dichromate ions. Use [0] to represent the acidified dichromate ions, the oxidising agent (2 marks)

mark scheme : CH3CH2OH + [O] CH3CHO + H2O
OR CH3CH2OH + 2[O] CH3COOH + H2O
Correct organic product
Balanced equation

i got C2H5OH + [OH] --> C2H4O + H2O ( i never know whether to use simplified formula or structural formula??)
please help - i'll really appreciate it :smile:


I always use structural formulae unless specifically asked for molecular formulae. Also, these oxidation questions in particular always require the structural formula of the oxidation product to get the mark!

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Reply 1361
Avatar for Smko
Smko
Original post by mia_hilton
Hi guys was just marking jun 2010 paper and was confused if i would get a mark or not?
Q 4iii) Give an equation to show the reaction between ethanol and acidified dichromate ions. Use [0] to represent the acidified dichromate ions, the oxidising agent (2 marks)

mark scheme : CH3CH2OH + [O] CH3CHO + H2O
OR CH3CH2OH + 2[O] CH3COOH + H2O
Correct organic product
Balanced equation

i got C2H5OH + [OH] --> C2H4O + H2O ( i never know whether to use simplified formula or structural formula??)
please help - i'll really appreciate it :smile:


Think you'll get the marks. It asked for equation so your fine :smile:


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Original post by Smko
Think you'll get the marks. It asked for equation so your fine :smile:


See my answer above - in these oxidation questions, you never get the mark with the molecular formula of the product!

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Reply 1363
Avatar for chigyy
chigyy
19
May 2012 q 4a iv, how did they get 342kj/mol?
Reply 1364
Avatar for chigyy
chigyy
19
Original post by Hello...
Would there be an intermediate??
Say it's KOH + 1-Iodobutane
I think first step shows nucleophile (in this case OH)"attacking" the slightly positive carbon and the C-I bond breaking.
Second step shows the products Butanol and KI or I-


Yeh, I can't really illustrate it on here, but I might draw it out after I finish revising for a bit.
Reply 1365
Avatar for Cerelaaa
Cerelaaa
I'm re-sitting CH2, but also doing CH4 the week after. I have a massive list of equations but I can't remember which ones will be in CH2.
Is this all of them?

Alcohol -> Carboxylic acid.
Chloroalkane -> Alcohol.
Alkene -> Bromoalkane.
Alkene -> Alcohol.
Alkane -> Chloroalkane.

HELP!!
Reply 1366
Avatar for zangorou
zangorou
Original post by GeneralOJB
sdfghjhgfdsdfg.png

Here's a challenging question for you all - if you can do this you can do any on the exam. :cool:

asdfghj.png

Even harder :eek:


That was crazy complicated! What exam board was that?
Original post by zangorou
That was crazy complicated! What exam board was that?


Its a question from the internet, not an exam :wink:


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Original post by Cerelaaa
I'm re-sitting CH2, but also doing CH4 the week after. I have a massive list of equations but I can't remember which ones will be in CH2.
Is this all of them?

Alcohol -> Carboxylic acid.
Chloroalkane -> Alcohol.
Alkene -> Bromoalkane.
Alkene -> Alcohol.
Alkane -> Chloroalkane.

HELP!!




Alkane → CO2 + H2O
Alkane → Halogenoalkane
Alkane → Alkane + Alkene
Alkane → Cycloalkane
Alkane → Branched Alkane
Alkene → CO2 + H2O
Alkene → Monohalogenated alkane
Alkene → Dihalogenated alkane
Alkene → Alkane
Alkene → Alcohol
Alkene → Poly(Alkene)
Alcohol → CO2 + H2O
Alcohol → Ester
Alcohol → Aldehyde
Alcohol → Carboxylic Acid
Alcohol → Ketone
Alcohol → Alkene
Glucose → Alcohol
Halogenoalkane → Alcohol
Halogenoalkene → Poly(Halogenoalkene)

Ta-daaaaa! :biggrin:
(edited 10 years ago)
Is the CO2 and H2O just the combustion


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Original post by Jimmy20002012
Is the CO2 and H2O just the combustion


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Yeah, oops, it does look a little silly like that as I haven't put the other products in (e.g. alkane -> cycloalkane + H2) - I was just trying to keep it as simple as possible :redface:
Does anyone have all of the functional groups we are suppose to know
EG: carboxylic acid is
R-C=O
....l
...OH
(edited 10 years ago)
Original post by mia_hilton
Hi guys was just marking jun 2010 paper and was confused if i would get a mark or not?
Q 4iii) Give an equation to show the reaction between ethanol and acidified dichromate ions. Use [0] to represent the acidified dichromate ions, the oxidising agent (2 marks)

mark scheme : CH3CH2OH + [O] CH3CHO + H2O
OR CH3CH2OH + 2[O] CH3COOH + H2O
Correct organic product
Balanced equation

i got C2H5OH + [OH] --> C2H4O + H2O ( i never know whether to use simplified formula or structural formula??)
please help - i'll really appreciate it :smile:


the mark scheme normally says accept molecular formula, or don't accept it..was there anything on the right hand side box saying what to accept? I generally use structural formula unless otherwise stated, especially because it clearly shows the functional groups present. just an 'o' on the end could represent an alcohol, ketone etc.
Original post by A guy called Dan
Does anyone have all of the functional groups we are suppose to know
EG: carboxylic acid is
R-C=O
....l
...OH


acid COOH
aldehyde CHO
alcohol OH
alkane C-C
alkene C=C
ketone C=O
Original post by needtosucceed=)
acid COOH
aldehyde CHO
alcohol OH
alkane C-C
alkene C=C
ketone C=O

Thanks mate
Original post by chigyy
May 2012 q 4a iv, how did they get 342kj/mol?


add together the enthalpy change and activation energy. ignore the -ve sign on the enthalpy, make it positive because its for the reverse reaction.
Original post by needtosucceed=)
the mark scheme normally says accept molecular formula, or don't accept it..was there anything on the right hand side box saying what to accept? I generally use structural formula unless otherwise stated, especially because it clearly shows the functional groups present. just an 'o' on the end could represent an alcohol, ketone etc.


I know this because I used to make the same mistake on every single past paper..... for example, the oxidation product the last time I made this mistake was CH3CH2CH2COOH, and on the right hand side it specifically said not to accept C3H7COOH. These particular equations are always two marks, so I was limited to one because of that.
Original post by needtosucceed=)
basically what you do is look at one of the equations, then see whats different about the equation below it (or wherever the arrow from its going to)

so for example, if you look at the equation on the left Ca + 2HCL + C+ 0.5o2
the arrow it goes to underneath it has the equation CaCl2 + h2 + C + 0.5o2
the things that have changed from the top to the bottom equation are the Ca and HCl, they've changed into CaCl2 + h2. so now look at the equations they give you in the table. one of them is Ca + 2hcl = CaCl2 + h2..therefore this value (-168) goes in the first box, inbetween the arrow for the 2 equations we were just looking at.

apply this rule to all the equations.
then to find the final enthalpy change just make all the arrows going in one direction = the arrows in the other direction and rearrange.


A little bit late, but thank you SOOOOOOOOO much!
Original post by needtosucceed=)
add together the enthalpy change and activation energy. ignore the -ve sign on the enthalpy, make it positive because its for the reverse reaction.


If you had a similar question like that, accept the enthalpy change was endothermic and they asked you to find the activation energy if the reverse reaction would do activation energy - enthalpy change or not


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Original post by Jimmy20002012
If you had a similar question like that, accept the enthalpy change was endothermic and they asked you to find the activation energy if the reverse reaction would do activation energy - enthalpy change or not


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yep you would, you asked me this yesterday as well, you probably missed the quote lol

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