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Ocr f321 , f322 retakes on 27/05/16 and 10/06/16

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How the hell did I get 2 point something gram on the percentage yield question TOT
hey whats the twitter account username?
Original post by jirapat121
How the hell did I get 2 point something gram on the percentage yield question TOT


I got 2 point something and so did my friends. It was a 45% percentage yield and I had time at the end so I checked and it seemed to work


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Would some explain to me how they got there answer for the litres one??
I got 40.1 which is wrong

I think I worked out:
- Moles of c02
- did stoichiometry 1:8 ratio
- then worked out litres after I found the Grams???
Original post by AJtheconfusedcat
hey whats the twitter account username?


It's @ChemistryALevel. :smile:
Original post by fastandfurious
It's @ChemistryALevel. :smile:


they said yesterday they're not allowed to or something
Original post by Lion2121
Would some explain to me how they got there answer for the litres one??
I got 40.1 which is wrong

I think I worked out:
- Moles of c02
- did stoichiometry 1:8 ratio
- then worked out litres after I found the Grams???


Not sure if I got it right but I worked out the moles of CO2 and then compared it to the octane which was 8 times less, so I divided the moles by 8 to get the moles of octane. I then found the mass in g by multiplying the moles by the Mr and then divided it by the value (I think it was 700?) to find the litres. I got 200 and something, can't remember the exact figure.

Not sure if it's right as maths is not my strong point but that was my thought process!


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What did everyone get for the enthalpy mcat thing??? I got -317 something like that
Original post by emem2011
Not sure if I got it right but I worked out the moles of CO2 and then compared it to the octane which was 8 times less, so I divided the moles by 8 to get the moles of octane. I then found the mass in g by multiplying the moles by the Mr and then divided it by the value (I think it was 700?) to find the litres. I got 200 and something, can't remember the exact figure.

Not sure if it's right as maths is not my strong point but that was my thought process!


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I must have got the conversion to litres wrong....

I'm sure il only drop a mark for that though
Original post by Lion2121
I must have got the conversion to litres wrong....

I'm sure il only drop a mark for that though


Yeah honestly you won't lose more than one mark as you had all the hard stuff right :smile:


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Original post by jirapat121
How the hell did I get 2 point something gram on the percentage yield question TOT


I got 2 point something too at the beginning but then I think I got 12 afterwards(or maybe 14 lol don't remember)
You're suppose to do 5.00g/68 to get the mols
(If 68 is the Mr of the product) then divide it 0.45 (45%/100) and then times the Mr of the reactant to get the mass.
I could be wrong though!
Unofficial Markscheme anyone?
Does anyone know if anybody has done an unofficial mark scheme? Would be much appreciated!
I thought exam was great. I've seen different answers for it but I got 1062 for CO bond enthalpy question
Original post by emem2011
I got 2 point something and so did my friends. It was a 45% percentage yield and I had time at the end so I checked and it seemed to work


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Yeah I think we are right because people were saying they got 11-14g and I was like it's not possible because the question stated that they want to make 5 g. So yeah we're correct hahaha
Original post by PeterMJP
Does anyone know if anybody has done an unofficial mark scheme? Would be much appreciated!
I thought exam was great. I've seen different answers for it but I got 1062 for CO bond enthalpy question


i got 1062 too
Original post by lolliillol
I got 2 point something too at the beginning but then I think I got 12 afterwards(or maybe 14 lol don't remember)
You're suppose to do 5.00g/68 to get the mols
(If 68 is the Mr of the product) then divide it 0.45 (45%/100) and then times the Mr of the reactant to get the mass.
I could be wrong though!


No we're definitely correct because the question stated that they want to make 5g that's mean 5g is the theoretical mole.
Generally when the AS are ok or easy,they make the A2 vice versa so GL for everyone who is doing OCR A chem a2 :P
Today's exam was awesome, so happy with it ngl. Grade boundaries will be high like.

I didn't like the petrol question, in the first sentence it said per mile, but the car obviously isn't going to emit 10 to the 5 grams more or less per mile. That was confusing imo.
I was a little disappointed that the analysis question wasn't very meaty.
Original post by jirapat121
Yeah I think we are right because people were saying they got 11-14g and I was like it's not possible because the question stated that they want to make 5 g. So yeah we're correct hahaha


You can't make 5g with 2g or something. That's not enough. It makes sense for it to be between 11-14g as only 45% of that was used making the 5g, if ygm? what's your thought process?
Original post by jirapat121
Yeah I think we are right because people were saying they got 11-14g and I was like it's not possible because the question stated that they want to make 5 g. So yeah we're correct hahaha


Yeah I think you got the Q the wrong way round...


think about it logically surely there'd be more reactant than product
....

the value of 5g was for the product so you had ti find the reactant mass

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