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Edexcel Chemistry IGCSE 1C Unofficial Mark Scheme 19th May 2016

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Original post by conradliebers
1. No, it asked for a compound.
2. It is CaCO3.
Original post by MMay2000
that makes no sense?


It does, the acid is in excess in both experiment 1 and 2 so the magnesium is all reacting in both. The magnesium is giving a 'set amount of energy' out and this means that in the second experiment, it is having to heat up twice the amount of volume of acid as before with the same energy. Therefore the rise in temperature is less. If you topped up a bath or a swimming pool with a kettle, same amount of heat energy in the kettle, but the temperature of bath is obviously going to increase more.
I think the empirical formula qu. has been missed out?? Sorry, cant remember which question is was...
Original post by deardood
It does, the acid is in excess in both experiment 1 and 2 so the magnesium is all reacting in both. The magnesium is giving a 'set amount of energy' out and this means that in the second experiment, it is having to heat up twice the amount of volume of acid as before with the same energy. Therefore the rise in temperature is less. If you topped up a bath or a swimming pool with a kettle, same amount of heat energy in the kettle, but the temperature of bath is obviously going to increase more.


Thank you omg so many people didn't get it.
Original post by conradliebers
I already went through this. They doubled to volume of acid used, so even though its already in excess, because the reaction will give of the same amount of energy, because the volume has doubled, it requires more energy for the same increase in temperature, so the rise in temperature is less.


I'm sure the wording of the question was as follows: "The experiment is repeated again, this time using a volume of 50cm3 of dilute acid, describe the diffrence in temperature"

If this is indeed the wording, then the anwser will be no change, and the acid is in excess, and therefore the reaction completes at the same rate and thus temperature. Your argument that there is more acid to heat is fair, but unfortunately as it asks for the temperature of the reaction, I'm sorry to say it is incorrect.
Original post by Togarty12
I'm sure the wording of the question was as follows: "The experiment is repeated again, this time using a volume of 50cm3 of dilute acid, describe the diffrence in temperature"

If this is indeed the wording, then the anwser will be no change, and the acid is in excess, and therefore the reaction completes at the same rate and thus temperature. Your argument that there is more acid to heat is fair, but unfortunately as it asks for the temperature of the reaction, I'm sorry to say it is incorrect.


Yes, but it doesn't reach the same temperature because it has to heat twice as much acid?
Original post by deardood
Yes, but it doesn't reach the same temperature because it has to heat twice as much acid?


As stated in my post, the question asked for the temperature of the reaction, not the temperature of the acid after the reaction. If you heat up a pool of water at the centre, and we go by your theory, then the water furthest from the pool should be as hot as that next to the heat source? That's not how water works, it's in a beaker and so is not flowing. The same ammount of acid comes into contact with the metal in experiment 1 as in experiment 2.
Reply 247
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Original post by Togarty12
I'm sure the wording of the question was as follows: "The experiment is repeated again, this time using a volume of 50cm3 of dilute acid, describe the diffrence in temperature"

If this is indeed the wording, then the anwser will be no change, and the acid is in excess, and therefore the reaction completes at the same rate and thus temperature. Your argument that there is more acid to heat is fair, but unfortunately as it asks for the temperature of the reaction, I'm sorry to say it is incorrect.


You are wrong it doesn't matter if it's in excess or not. The fact is that the same heat is generated but this heat has to be transferred through a larger volume of liquid so the overall temperature will be less as the heat will have to be shared out through more particles of solution.
my thinking behind that question was to do with concentration, - does doubling the volume of acid decrease its concentration- so less collisions per second etc and lower rate of reaction? not completely sure
whats the answer to the one about the mass of water produced with the 5H20
when it said the mass of one side is 2.50 grams
Answer to calculating mass in reactions, "0.9"?!
Original post by HKHASSAN
Im pretty sure it is CH2


I agree with Pedaly7, it was a double bond so CH2 couldn't possible exist
Original post by Gdmn
You are wrong it doesn't matter if it's in excess or not. The fact is that the same heat is generated but this heat has to be transferred through a larger volume of liquid so the overall temperature will be less as the heat will have to be shared out through more particles of solution.


The reason I base my argument as on doing a past paper last night, this exact question came up. http://qualifications.pearson.com/content/dam/pdf/Edexcel%20Certificate/Chemistry/2011/Exam%20materials/4CH0_1C_que_20140114.pdf

See Q10 which is almost identical to today. Then look at the mark scheme for that question!

http://qualifications.pearson.com/content/dam/pdf/Edexcel%20Certificate/Chemistry/2011/Exam%20materials/4CH0_1C_msc_20140306.pdf
Original post by Gdmn
You are wrong it doesn't matter if it's in excess or not. The fact is that the same heat is generated but this heat has to be transferred through a larger volume of liquid so the overall temperature will be less as the heat will have to be shared out through more particles of solution.



I thought it wasn't the heat of the acid? it's the heat given off/temperature change.
Original post by Robertarthur
I agree with Pedaly7, it was a double bond so CH2 couldn't possible exist

it does
Reply 255
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Gdmn
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Original post by MMay2000
I thought it wasn't the heat of the acid? it's the heat given off/temperature change.


The heat given off is the temperature of the acid
Original post by Robertarthur
I agree with Pedaly7, it was a double bond so CH2 couldn't possible exist


Doesn't matter whether it can 'exist' or not, the empirical formula is the simplest ratio of atoms therefore the empirical formula of Propene is CH2


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Original post by Robertarthur
I agree with Pedaly7, it was a double bond so CH2 couldn't possible exist


It doesn't matter where it exists or not, it's the empirical formula - the lowest ratio - regardless
Original post by Togarty12
I'm sure the wording of the question was as follows: "The experiment is repeated again, this time using a volume of 50cm3 of dilute acid, describe the diffrence in temperature"

If this is indeed the wording, then the anwser will be no change, and the acid is in excess, and therefore the reaction completes at the same rate and thus temperature. Your argument that there is more acid to heat is fair, but unfortunately as it asks for the temperature of the reaction, I'm sorry to say it is incorrect.


Yeah its asking for the difference in temperature of the acid, because thats whats being measured. If the same amount of energy is being release and is transferred to the acid of a higher volume, the average kinetic energy of the particles will be less overall due to having more particles.

Anyway, its all up for debate now, however, the outcome will be the outcome.
Original post by conradliebers
Yeah I can't think of them and I've done this mark scheme for so long I'm just tired right now.

I understand you're tired but perhaps later on in the night you could update it. I really appreciate what you're doing as I was really doubtful of my answers and this unofficial mark scheme reassures me thus relieving stress. Thank you :smile:

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