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OCR A2 CHEMISTRY F324 and F325- 14th and 22nd June 2016- OFFICIAL THREAD

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Anyone got a link to the 2015 F325 and MS ? Thanks
Original post by Walkerz7
Hey guys could you help me with this question?
"You are providednwi I three alcohols that are structural isomers
CH3CH2CH2CH2OH
CH3CH2CHOHCH3
(CH3)3OH
You have access to normal lab apparatus and an infrared spectrometer
You should provide structural formula for any reaction and a description of how you will identify the three alcohols from any observations" it's a 6 marker plz help


Firstly, identify the alcohols

The fist alcohol is a primary alcohol

The second alcohol is a secondary alcohol

The third alcohol is a tertiary alcohol

Testing the compounds ----->

So you know that a primary alcohol can be oxidised to a carboxylic acid and a secondary alcohol can only be oxidised to a ketone.

We use (H2SO4/K2Cr2O7) as reagents to carry out the oxidation of alcohol under reflux

The third alcohol will have no change as it is a tertiary alcohol so it can't be oxidised.

So we will see solution change from orange to green for the first 2 alcohols

From the first alcohol we get a carboxylic acid, and for the second alcohol we get a ketone.

Using a infrared spectrometer to analyse the compounds

For the product(carboxylic acid) of the first alcohol you will find:

Very broad absorption at 2500-3300 cm^-1 for O-H bond
Absorption at 1640-1750 cm^-1 for C=O bond

For the product(ketone) of the second alcohol you will only find:

Absorption at 1640-1750 cm^-1 for the C=O bond
(edited 7 years ago)
Original post by M.Branson98
Ok, so the butanoic acid is mixed with NaOH and an acid-base reaction would obviously occur.
CH3(CH2)2COOH + NaOH --> CH3(CH2)2COO-Na+ + H2O

You work out the number of moles of butanoic acid: n= c x v/1000
n(butanoic acid) = 0.0125mol
n(NaOH) = 0.0025mol

NaOH is the limiting reactant, so all of it is used up and forms 0.0025mol of the salt, CH3(CH2)2COO-Na+

Because butanoic acid is in excess, only some of it is used up: 0.0125 - 0.0025= 0.01mol
You then work out the new concentrations using c=n/v
c(butanoic acid)= 0.01/(100/1000) = 0.1 mol dm^-3
c(CH3(CH2)2COO-)= 0.0025/(100/1000) = 0.025 mol dm^-3

Then you plug these concentrations into the buffer equation and you get a concentration of H+ of 6.04x10^-5.
Then -log that answer and you get a pH of 4.22


Thanks very much!
Original post by Walkerz7
Hey guys could you help me with this question?
"You are providednwi I three alcohols that are structural isomers
CH3CH2CH2CH2OH
CH3CH2CHOHCH3
(CH3)3OH
You have access to normal lab apparatus and an infrared spectrometer
You should provide structural formula for any reaction and a description of how you will identify the three alcohols from any observations" it's a 6 marker plz help
Is this F325? Looks like an F324 question.

1. Primary alcohol
2. Secondary alcohol
3. I think you mean (CH3)3COH. Tertiary alcohol.

1. Distil it to give carbonyl (aldehyde) (orange to green = oxidised). Positive test with Tollens therefore primary
2. Distil/reflux it to give carbonyl (ketone) (orange to green = oxidised). Negative test with Tollens therefore secondary
3. Distil/reflux it. No oxidation (no orange to green) therefore tertiary
I've seen the predictions have been posted on twitter and I'm confused what exactly is meant by "Effect of equilibrium shift on electrode potential". Please can someone explain, possibly with an example? Thanks!
Original post by marioman


You seem like an A/A* candidate. Are there any areas or types of questions that you struggle with in particular? Any tips you might have. Thanks

Aiming for A/A*
Original post by sophay_
I've seen the predictions have been posted on twitter and I'm confused what exactly is meant by "Effect of equilibrium shift on electrode potential". Please can someone explain, possibly with an example? Thanks!


Got to so with electrode potentials when the standard conditions has been changed
Original post by Rust Cohle
You seem like an A/A* candidate. Are there any areas or types of questions that you struggle with in particular? Any tips you might have. Thanks

Aiming for A/A*


No areas in particular. The application of knowledge questions are the hardest. Tips would be to ensure that you know all of the little details in the specification so that you can pick up as many of the 'easy' marks as possible.
Original post by KB_97
Well f***. after the aqa core 3 disaster my only hope for a* is chemistry. It's never gonna happen.


Gonna join you on that boat after the ocr core 3 disaster... Literally our entire uni offer depends on tomorrows paper wow
is the cathode the positive electrode?
2SO2 + O2 > 2SO3

Explain what would happen to the pressure as the system was allowed to reach equilibrium

I wrote the pressure would decrease as wquilibrium would shift to the left, but the MS says pressure decreases and fewer moles? Could anyone explain what Is meant by this?
Why is it difficult to use Born-Haber cycles to find the lattice enthalpy of sodium carbonate? I know it's something to do with the formation of the carbonate ions right?
Original post by thesuperdark
Why is it difficult to use Born-Haber cycles to find the lattice enthalpy of sodium carbonate? I know it's something to do with the formation of the carbonate ions right?


Cos carbonate contain 2 different atoms, you would have to work out the enthalpy change of formation of the carbonate ions first.
Can anyone explain how you work out the element from the 'average mass' like in this question:
Screen Shot 2016-06-21 at 14.39.57.png10.8KB
Original post by CalistaJupiter
Can anyone explain how you work out the element from the 'average mass' like in this question:


Just times that value by the Avogadro constant to get the Mr of the element
Jan 13 Q8(c)(ii) explained and worked through

Original post by AqsaMx
2SO2 + O2 > 2SO3

Explain what would happen to the pressure as the system was allowed to reach equilibrium

I wrote the pressure would decrease as wquilibrium would shift to the left, but the MS says pressure decreases and fewer moles? Could anyone explain what Is meant by this?


you start off with no SO3 so as it reaches equilibrium, more SO3 forms. There's fewer moles of gas on this side which also means pressure decreases (remember how if you increase the pressure, the position of equilibrium shits to the side with fewest moles of gas to decrease the pressure). hope that makes sense
Original post by AqsaMx
2SO2 + O2 > 2SO3

Explain what would happen to the pressure as the system was allowed to reach equilibrium

I wrote the pressure would decrease as wquilibrium would shift to the left, but the MS says pressure decreases and fewer moles? Could anyone explain what Is meant by this?


Yes, pressure would decrease because position of equilibrium would shift to the right, which has fewer moles of gas.
Does anyone have any tips on how to put together ionic equations? It's pretty much the one thing I have no idea about, I never know which ions to use and which ones get left out

As an example Q;

http://www.ocr.org.uk/Images/144762-question-paper-unit-f325-01-equilibria-energetics-and-elements.pdf

Question 7bii

Any tips would be greatly appreciated :smile:
Original post by megafidget
Gonna join you on that boat after the ocr core 3 disaster... Literally our entire uni offer depends on tomorrows paper wow


Lmao I don't even have an offer. I'm taking a gap year but still, I need the grades to maximise my chances. And it just feels like after all this hard work, I'm still not gonna get the grades I want. If only I was born 4 years earlier...the 2012 papers for all my subjects were so easy, I would've had 3A*. But Life's a b****. Good luck to you and everyone else for tomorrow anyway.

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