The Student Room Group

C7 OCR 21st Century Science 2016 Exam 22/06/16

Here is where ill attempt to make a rough mark scheme for the exam

:biggrin:First question about differences in processes of making fertilisers and drugs:
Fertilisers need to be made on a large scale as they are bulk and millions of tonnes of them are used
Drugs need to be very pure as they need to be safe for human consumption

Amount of different dyes:
There were either 3 or 4 (up to debate)

Why is a locating agent used:
A locating agent is needed as some of the dyes are invisible to the naked eye therefore the agent makes a coloured spot or makes it glow under UV light

How do you there was more of Dye C:
Dye C had the greatest peak therefore the greatest recorder response which means it was the most detected chemical

How could Alex find out what dyes are being used:
Alex could use the graph results and the results of known chemicals because he can cross-reference the two to find out what combination of known chemicals are in the sweet

What values are needed to calculate the retardation factor:
The measurements needed are the distance between the start line and the centre of the spot (divided by) the distance between the start line and the solvent front

6 mark question about the reaction between methane and steam being unsustainable:
Poor atom economy only 15% of the mass inputted is useful as the rest is wasted carbon dioxide
The reaction requires high temperatures which is expensive to support
Methane is a fossil fuel which is a finite source:biggrin:

The answers between the two :biggrin: came from NiamhM1801 and Username1502 big shoutout to them

Atom economy question: (Thanks to 11207ymir)
4/36 = 11.1%

The question about which one vinegar was:
Circle D as this had COOH group at the end meaning it was the only carboxylic acid

What was the Ester made of:
The ester was made from A and D

Question about the vertical condenser:
This was talking about heating under reflux and how the reaction mixture (reactants + catalyst (sulfuric acid)) needs heat in order to react but the mixture is volatile so vaporizes easily therefore the condenser which is surrounded by cold water cools down the gases to form back into liquids and stay in the flask

Next question about Distillation and Purification:
Distillation - Heating the reaction mixture to the boiling point of the ester so it turns into a gas then funneling this out through a condenser positioned so that the ester can travel to a different container and be separated from the remaining reactants and water.
Purification - This where the ester is shaken with aqueous sodium carbonate this removes any acidic impurities by neutralizing it and moving it to the aqueous layer (lower layer) this is then runoff by a tap leaving the ester (organic layer) which can be removed of ethanol by shaking it with calcium chloride

Question about the bonds in Hydrogen Fluoride:
Reactants:
The H-H bond was 432 KJ/mol
The F-F bond was 155 KJ/mol

The total energy for the reactants was 587 KJ/mol

Products:
The H-F bound was 567 KJ/mol
there was two of these bonds

The total energy for the products was 1134 KJ/mol

What was the energy change:
587 KJ/mol - 1134 KJ/mol = -547 KJ/mol
Reactant + Products = Energy Change

The tick box question about the Haber Process:
Increasing Temperature: Increases rate of reaction
Increasing pressure: Increases Both
Adding a catalyst: Increases (Rate of reaction or Both)
Recycling the reactants: Increases yield

Chromatography what is the qualitative and quantitative analysis:
Qualitative - Whether a certain dye is present or not, identifying a dye bye cross referencing its retention time with known retention times
Quantitative - How much of the dye is present and the percentage make up of the entire compound by looking at the recorder response
(edited 7 years ago)

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Reply 2
Thanks! :smile: i will add answers if needed
Reply 3
add all the answers you have my minds gone blank after that frustration with that len question
What did you guys get for the % atom economy?
Reply 5
Original post by James2021
What did you guys get for the % atom economy?


can u remind me of what was being reacted
Original post by Dr Dead Trim
can u remind me of what was being reacted


I think it was water into hydrogen and oxygen but i can't remember the numbers.
Original post by James2021
What did you guys get for the % atom economy?


i got 4/36*100=11.111111%
Original post by 11207ymir
i got 4/36*100=11.111111%


Somehow i got 20% but everyone else got 11%. Oh well xD

How many marks was this question worth?
Reply 9
Original post by James2021
Somehow i got 20% but everyone else got 11%. Oh well xD

How many marks was this question worth?


I got 20% aswell!
Original post by Dr Dead Trim
Here is where ill attempt to make a rough mark scheme for the exam



Next question about Distillation and Purification:
Distillation - Heating the reaction mixture to the boiling point of the ester so it turns into a gas then funneling this out through a condenser positioned so that the ester can travel to a different container and be separated from the remaining reactants and water.
Purification - This where the ester is shaken with aqueous sodium carbonate this removes any acidic impurities by neutralizing it and moving it to the aqueous layer (lower layer) this is then runoff by a tap leaving the ester (organic layer) which can be removed of ethanol by shaking it with calcium chloride

Btw how many marks is this question I said everything except I said you heat it up but didn't mention heat it above ester boiling point and i said it produces an impure product when the vapour forms and condenses

Also for the tick the boxes question for harbour process won't adding a catalyst also increase yield as the activation energy is lower which therefore suggest more successful collisions occurring so more nh3 made
(edited 7 years ago)
Original post by ritikp
The energy change for the products should be -567 -567 = -1134
Hence the energy change should be 587 subtract (you are meant to subtract because overall energy change = bond breaking - bond making) -1134 so the answer is 1721

Energy is created when bonds are made, it is not negative because you can't create negative energy so 587-1134 is the answer
Original post by ritikp
The energy change for the products should be -567 -567 = -1134
Hence the energy change should be 587 subtract (you are meant to subtract because overall energy change = bond breaking - bond making) -1134 so the answer is 1721


Nah Im sure its -547
[QUOTE="NikhilStephen123;66008598"]
Original post by Dr Dead Trim
Here is where ill attempt to make a rough mark scheme for the exam



Next question about Distillation and Purification:
Distillation - Heating the reaction mixture to the boiling point of the ester so it turns into a gas then funneling this out through a condenser positioned so that the ester can travel to a different container and be separated from the remaining reactants and water.
Purification - This where the ester is shaken with aqueous sodium carbonate this removes any acidic impurities by neutralizing it and moving it to the aqueous layer (lower layer) this is then runoff by a tap leaving the ester (organic layer) which can be removed of ethanol by shaking it with calcium chloride

Btw how many marks is this question I said everything except I said you heat it up but didn't mention heat it above ester boiling point and i said it produces an impure product when the vapour forms and condenses

Also for the tick the boxes question for harbour process won't adding a catalyst also increase yield as the activation energy is lower which therefore suggest more successful collisions occurring so more nh3 made


not too sure
(edited 7 years ago)
Original post by NikhilStephen123
Energy is created when bonds are made, it is not negative because you can't create negative energy so 587-1134 is the answer


negative energy is right. negative means its exothermic as energy is lost and positive is endothermic as energy is gained.
Original post by Jashi1999
negative energy is right. negative means its exothermic as energy is lost and positive is endothermic as energy is gained.

I meant the answer is 587-1134 which is a negative number when you do the calculation but the bond of the products is not negative but positive (+567+567) I was replying to message which said its (-567-567):smile:
(edited 7 years ago)
Where's the rest of the mark scheme?
How did everyone find that? I'm so mad at myself. I revised so hard, and I got As and A*s in the past papers, but when it got down to the actual exam, I didn't finish it! I didn't finish the last double spread page, which was 7 marks :frown: and it looks like I've made a lot of mistakes in the parts I did do. This is probably the worst exam I've done so far. It wasn't even that difficult in retrospect. Ugh...
Reply 18
Original post by babznd
I got 20% aswell!


So did I !!!
Reply 19
Shall we make a full mark scheme?

For the bonds energy for come reason I got 40kj:frown:

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