AQA further additional chemistry, C3, 15th June 2016 unofficial mark scheme

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username1942323
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Hi everyone,
Hope your chemistry exam went well. how did you find it?
What answers did you put?
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zeldor711
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All I know is that it went much worse than C2 (also the flame tests were potassium, lilac and calcium, red)
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username1942323
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This is the unofficial mark scheme for:
Further addition science, unit 2 chemistry 3, C3
(be aware that there is two similar paper and the other one is chemistry 3, triple science. )

Reps will be appreciated but not necessary 😊

This will be updated regurlarly as i dont remember all the questions and answers. I will start by putting my answers so they might be wrong, but as soon as i know i will update it to correct answers☺

1.Carboxylic acids
Sentence with gaps to fill in:
a) (catalyst)acids,
(pleasant smelling compounds)ester

b) Completing the ethanol diagram: (sorry cant draw the bonds 😕but there is only single bonds)
H H
H C C O H
H H
(note: i can remmeber whether you had to draw ethanol or ethonoic acid, so can anyone confirm please)

c) Balancing-
C2H5OH + 3O2-----> 2CO2 +3H2O


2. Titrations

The method is:
1. use pipette to measure 50cm^2 of hydrochloric acid A and put it the conical flask
2. Put indicator (phenolphthalein) in the conical flask and mix it
3. put the conical flask on the white tile to see the colour change
4. Full the burette with soduim hydroxide up to the 0cm2 mark (making sure the tap is full)
5. Open the tap with one hand and swirl the conical flask with other hand to mix the alkali and acid together
6. Close the tap when the solution in the conical flask goes colourless
7. Work out how much acid was used by substracting the end reading of the burette from the initial reading.
8. repeat step 1-7
9. repeat step 1-8 but using the hydrochloric acid B as the acid in the conical flask

3.hardness of water
How boiling temporary hard water in kettles can reduce efficiency?
temporary hardness is caused by hydrogencarbonate which decomposes into calcium carbonate (a solid) called (lime)scale. this forms on the heating element of the kettle and acts as an insulator so less heat is transferred to the water, reducing efficiency. this means the water has to be heated longer, so more electricity used, and therefore more money used.

ion exchange resins to improve water quality
ion exchange column contain sodium resins. the sodium ions are exchanged for the calcium or magnesium ions (which caused the hardness). these are removed so hardness is removed too.

Table of results for compound testing:
White, the rest is no changes

Pottasium shows lilac flame and calcium red, why won't we able to see any of the colours if potassium and calcium were mixed?

any suggestions?

4. The periodic table

In 19th century, element were aranged in order of atomic mass

The elements are now aranged in order of atomic number. Which particles? electrons/protons

Highest boiling point: fluorine

Why reactivity increases as you down group 1, but decreases as you go down group 7?
Reactivity increases as you go down group 1 because they need to gain an electron. Shielding increases as you go down group 1 meaning the positive charge is felt less by the outer electron and it is therefore lost more easily
Rectivity decreases as you go down group 7 because they need to gain an electron. Shielding increases as you go down the group so it becomes harder for the nucleus to attract an electron.

5.bond energies

Energy change= 212

Reaction endothermic, why?
because the energy required to break the bond is greater than the energy released in making bonds so energy is absorbed.

Labelling energy level diagram (4 marks) :
The products are at higher energy level than the reactant
Line going up from the reactant line and then down to the product line.
Difference between reactant line and product line labelled energy change.
Activation energy- between reactant line to the highest energy reached

6. ammonia

Source of methane: crude oil, natural gas (any other suggestions, they will accept more than one answers btw)

higher yield of ammonia= 1000 atmospheres and 200 degrees

450 degrees, 200 atmospheres? 5 marks
decreasing the temperature encourage the forward reaction which is exothermic so more ammonia would be produced. however, too low temp means the reaction is too slow. therefore a compromise of 450 degrees is well suited.
increasing the pressure shifts the equilibrium to the side where there are fewer molecules so percentage yield of ammonia increases at high pressure. however too high pressure could break the plant/reactor so the reactor need to have thick walls which would be expensive to build. therefore, 200 atmosphere is a compromise; not too high to break the container but not too low so that here is enough percentage yield of ammonia

Mixture of gases, what hapens when they come out of the reactor? (3 marks)
Ammonia is condensed to be stored as a liquid
Hydrogen and nitrogen are recycled so that nothing is wasted (nearly 100% yield)

Any answers would be greatly appreciated. Feel free to correct me if my answers are wrong! Hope you did well
If anyone remembers how many marks a question was, please tell me so i can put it on. Thanks
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tamanna___
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I found c2 so amazing, honestly the best paper ever.. C3 on the other hand wasnr as good as c2 but it didnt go very bad.. It just took some more thinking, like the last question.
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GeorgeMillerr
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Balancing 2,2
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GeorgeMillerr
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Last question, high pressure means more forward reaction to ammonia because there are less moles, pressure not above 200 atomospheres because it is dangerous and explosive, tempreture at 450 degrees celcius because that it the optimun temperature this is because the rate of reaction is fast and the amount of ammonia made isnt too little
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ZaCHH
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Ugh...
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jerrisha 27
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What did u guys get for the bond energy question and also the specific heat capacity question
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username1942323
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(Original post by jerrisha 27)
What did u guys get for the bond energy question and also the specific heat capacity question
i got 212 for bond energy
what was the specific heat capacity question??? cant remember having that.....
do you mean the question where it asks why the student was wrong (dedecane and hexane question...)
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caizk
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(Original post by jerrisha 27)
What did u guys get for the bond energy question and also the specific heat capacity question
For the bond I got 212, and specific heat capacity was something like hexane was around 500 and something, dodecane was around 13100, but hexane burnt up less which is why the conclusion was incorrect.

DON'T TRUST ME BTW.
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Mayfate
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(Original post by mediaya)
i got 212 for bond energy
what was the specific heat capacity question??? cant remember having that.....
do you mean the question where it asks why the student was wrong (dedecane and hexane question...)
Yeah it was harsh As they didnt give the equation for ir or say that 4.2 is the Specific heat capacity of water so lots of people prob didnt realise it was a S.H.C queation.
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loshaw20
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Everything else seems fine apart from the Bond energy question the answer was somewhere around - 1267 something and it was definitely exthermic because it said so in the next question
So this means that ur energy level
Diagram is wrong as well but you would get carry through marks I think


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username1942323
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(Original post by loshaw20)
Everything else seems fine apart from the Bond energy question the answer was somewhere around - 1267 something and it was definitely exthermic because it said so in the next question
So this means that ur energy level
Diagram is wrong as well but you would get carry through marks I think
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No the answer was defo 212 and it was endothermic in MY exam, you just did the other spec, read what i said at the beginning (maybe i should make it more clear?)
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Ms A
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For the hexane question, is it valid to say that both of the hydrocarbons were not of the same mass, so the student conclusion was not correct. To work out the correct calculations I worked out the investigations results by multiplying the hexane results by 3 since the mass of dodecane was 1.5 and hexane was 0. Something? Then I saw that the stydent was wrong with thwse results. Is that ok?

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Ms A
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For the peridoic table question about arranging the elements in order of atomic number and it asked for a particle could you say protons instead of electrons because atomic number is also known as proton number?

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freya.3112
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Ms A YES! thats what i did i didnt do the Q=mcdelta t thing cos i was like theres no need it just needs to be the same mass!
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username1942323
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(Original post by Ms A)
For the peridoic table question about arranging the elements in order of atomic number and it asked for a particle could you say protons instead of electrons because atomic number is also known as proton number?

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Yes, proton would be valid as well i think
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username1942323
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(Original post by Ms A)
For the hexane question, is it valid to say that both of the hydrocarbons were not of the same mass, so the student conclusion was not correct. To work out the correct calculations I worked out the investigations results by multiplying the hexane results by 3 since the mass of dodecane was 1.5 and hexane was 0. Something? Then I saw that the stydent was wrong with thwse results. Is that ok?

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TBH i have no idea, i know i messed up this question in the exam cos i ran out if time but that seems right to me
Sorry am not teally the right person to ask 😅
Btw, which question number was that?
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As101
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Guys I neee an answer quick! On this paper was there a question on diamonds and copper
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