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AQA Chemistry C3 - Unofficial Mark Scheme

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Original post by LiamCollins
How many marks could you pick up without referring to equilibrium and exothermic\endothermic reactions?

probs 3 maybe 4
Original post by Purplepizza988
For the last question, what would happen if the pressure was too high?


the reaction vessle bursts and also it's sooooooooooooo expesnive, literally it wou;dn't be profitable.
Original post by dausa99

nah-its-for-a-fricken-F.-It-obviously-for-an-A*-hahaha.-Its-chill-dude
Original post by Fr3dg
could be hit or miss really, first mark is right, but you probably wanted to talk about it being a compromise, i think it migt be down to tghe marker?


Well I talked about how it's a compromise between yield and rate of reaction for both temperature and pressure
Original post by Purplepizza988
For the last question, what would happen if the pressure was too high?


I just talked about how it was cost lots of money to make a container that can withstand that high pressure or something :s-smilie:
Original post by Fr3dg
yeah its a bit of a piss take really, especially since there is wuite a high chance to get it wrong, i didnt even get the result i wrote down in the exam :[


I should have been like 5 marks, smh that took me so long! :biggrin:
Reply 166
Original post by Roquebrune2014
I've just had a thought, for the energy change with specific heat capacity question, I put 3,444J but 4.2 is the SHC for water to change ONE gram of water, should 3,444 therefore be multiplied by 0.8 to scale it down to 0.8g from 1g?


Posted from TSR Mobile


no, if it was one gram of water, you would have 1*4.2*16.4, which is 68.88J, but since it is the heating of 50g of water, then you times this by 50, to get 3444, if they wanted to know how much energy was released by 1 gram of FUEL rather than the 0.8g listed in the question, thenm you wouuld divide by 0.8, but thye didnt ask for this.
Original post by Edgerulezs
I just talked about how it was cost lots of money to make a container that can withstand that high pressure or something :s-smilie:


Also dangerous as it's explosive (hydrogen is).
Reply 168
Chemical Analysis and Ethanoic Acid
Test tube 1 - effervescence/fizzing as the calcium carbonate reacted the ethanoic acid
Test tube 2 - limewater turns cloudy as calcium carbonate + ethanoic acid -> calcium ethanoate + carbon dioxde. The carbon dioxide makes the limewater cloudy.

Silver nirate in the presence of dilute nitric acid: white precipitate and no change
Barium chloride in the presence of hydrochloric acid: no change and no change

An acid(ic) catalyst is the production of esters

Bond Energies
-1276kJ/mol

More energy used in bond breaking than in bond making. Surplus energy released to the surroundings as heat energy.

The specific heat capacity question
Q=mcΔT
Q= 50 x 4.2 x 16.4
Q= 3444J
3444/50 = 68.88J per gram of alcohol burned
68.88/10 = 6.888
6.888 x 8 = 55.104J

The Periodic Table

Elements were in order of relative atomic mass in Mendeleev's Periodic Table.

The discovery of the proton led to elements being arranged in order of the atomic number. (I'm wrong here? but that's what i wrote)

The element with the lowest bp is Fluorine.

Group 1 elements react by donating electrons. Group 7 elements react by accepting electrons. The electrons are attracted to the positive charge of the atomic nucleus. Down Group 1 and Group 7 the number of electron shells that are occupied increases this shields the nucleus from the electrons in the highest energy level, diminishing the attraction. This makes it easier for electrons to be donated and more difficult for them to be accepted.

The Haber Process
Methane is obtained from natural gas or crude oil

All the gases are cooled in a condenser. Ammonia liquefies. The unreacted hydrogen and nitrogen are recycled and piped back into the reactor.

The optimum conditions are 200 degrees Celsius and a pressure of 1000atm

A temperature of 450 degrees is used because too high a temperature would favour the endothermic reaction and the reaction to produce ammonia is exothermic, this was reduce the yield of ammonia. Too low a temperature would decrease the rate of the reaction. A pressure of 200atm is used as it is too expensive to build a reaction vessel that can withstand pressures of 1000atm.

This is all I can remember if you want I can wrack my brain for more
(edited 7 years ago)
Original post by vishantu_success
nah-its-for-a-fricken-F.-It-obviously-for-an-A*-hahaha.-Its-chill-dude


Calma Calma 😂


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Reply 170
Original post by LiamCollins
Well I talked about how it's a compromise between yield and rate of reaction for both temperature and pressure


thats good then! fingers crossed for you
Original post by Fractite
Also dangerous as it's explosive (hydrogen is).


Rawrrr forgot about that... Lol all well :biggrin:
Reply 172
For the limescale question I mentioned both Calcium Carbonate and Magnesium Carbonate. I just discovered that it's Magnesium Bicarbonate. Would I still get full marks, keeping in mind that I still talked about calcium carbonate?
Original post by k0chia


The discovery of the proton led to elements being arranged in order of the atomic number. (I'm wrong here? but that's what i wrote)



Nah that's correct.
Original post by BW999
For the limescale question I mentioned both Calcium Carbonate and Magnesium Carbonate. I just discovered that it's Magnesium Bicarbonate. Would I still get full marks, keeping in mind that I still talked about calcium carbonate?


I think if you have the whole idea about limescale and the kettle with it needing more energy to boil the water, you should be able to get full marks.
Reply 175
Original post by k0chia

The specific heat capacity question
Q=mcΔT
Q= 50 x 4.2 x 16.4
Q= 3444J
3444/50 = 68.88J per gram of alcohol burned
68.88/10 = 6.888
6.888 x 8 = 55.104J



i think that the question was asking for the the energy released by the fuel combusted, not per 1 gram of fuel, youd therfore stop after finding 3444J. futhermore if u wanted to find the energy released by 1 gram, youd just divide the 3444 by 0.8, since what you did was find the energy required to heat 0.8 grams of water by 16.4 degrees, which is definately not what the question asked for... good effort thogh!!
Reply 176
I think an issue here is that some people have done AQA GCSE Further Additional Science Unit 2 (Chemistry) and others have done AQA GCSE Chemistry Unit 3 (Further Unit 2 equivalent). Despite the specification being similar the exam papers are also similar but not exactly the same; the biology paper is a prime example as one exam had a 6 marker on the same thing however with a different factor (too hot, too cold). If I recall correctly, my Further Additional Unit 2 (C3) paper was asking which was the most reactive metal on the given periodic table (on the question) which was Rubidium.
Original post by k0chia
Chemical Analysis and Ethanoic Acid
Test tube 1 - effervescence/fizzing as the calcium carbonate reacted the ethanoic acid
Test tube 2 - limewater turns cloudy as calcium carbonate + ethanoic acid -> calcium ethanoate + carbon dioxde. The carbon dioxide makes the limewater cloudy.

Silver nirate in the presence of dilute nitric acid: white precipitate and no change
Barium chloride in the presence of hydrochloric acid: no change and no change

An acid(ic) catalyst is the production of esters

Bond Energies
-1276kJ/mol

More energy used in bond breaking than in bond making. Surplus energy released to the surroundings as heat energy.

The specific heat capacity question
Q=mcΔT
Q= 50 x 4.2 x 16.4
Q= 3444J
3444/50 = 68.88J per gram of alcohol burned
68.88/10 = 6.888
6.888 x 8 = 55.104J

The Periodic Table

Elements were in order of relative atomic mass in Mendeleev's Periodic Table.

The discovery of the proton led to elements being arranged in order of the atomic number. (I'm wrong here? but that's what i wrote)

The element with the lowest bp is Fluorine.

Group 1 elements react by donating electrons. Group 7 elements react by accepting electrons. The electrons are attracted to the positive charge of the atomic nucleus. Down Group 1 and Group 7 the number of electron shells that are occupied increases this shields the nucleus from the electrons in the highest energy level, diminishing the attraction. This makes it easier for electrons to be donated and more difficult for them to be accepted.

The Haber Process
Methane is obtained from natural gas or crude oil

All the gases are cooled in a condenser. Ammonia liquefies. The unreacted hydrogen and nitrogen are recycled and piped back into the reactor.

The optimum conditions are 200 degrees Celsius and a pressure of 1000atm

A temperature of 450 degrees is used because too high a temperature would favour the endothermic reaction and the reaction to produce ammonia is exothermic, this was reduce the yield of ammonia. Too low a temperature would decrease the rate of the reaction. A pressure of 200atm is used as it is too expensive to build a reaction vessel that can withstand pressures of 1000atm.

This is all I can remember if you want I can wrack my brain for more


WOW! How could you remember all that?!
I put the exact same for the SHC question but lots of people are saying that you have to use 50g instead of 0.8g... :frown:
Original post by Wisbey
I think an issue here is that some people have done AQA GCSE Further Additional Science Unit 2 (Chemistry) and others have done AQA GCSE Chemistry Unit 3 (Further Unit 2 equivalent). Despite the specification being similar the exam papers are also similar but not exactly the same; the biology paper is a prime example as one exam had a 6 marker on the same thing however with a different factor (too hot, too cold). If I recall correctly, my Further Additional Unit 2 (C3) paper was asking which was the most reactive metal on the given periodic table (on the question) which was Rubidium.


That was on our exam too (Unit 3) - with the nine elements - but it wasn't a 6 marker.
We had 'how to carry out a titration' for our 6 marker - which was kinda easy, since they basically gave the answer to us.
Reply 179
Original post by Fr3dg
i think that the question was asking for the the energy released by the fuel combusted, not per 1 gram of fuel, youd therfore stop after finding 3444J. futhermore if u wanted to find the energy released by 1 gram, youd just divide the 3444 by 0.8, since what you did was find the energy required to heat 0.8 grams of water by 16.4 degrees, which is definately not what the question asked for... good effort thogh!!


It asked for the amount of energy released when 0.8g of the alcohol was burned. I found out the amount of energy released by heating up 50g of water. then finding how much energy would be released for each gram of water, then for 01.g of water and then when 0.8g of water was heated

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