AQA Chemistry C3 - Unofficial Mark Scheme

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TheAnon121
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#1
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#1
Post your answers below, and we'll get an unofficial mark scheme!

Random answers:
Bond energies: -1276/-1623 (some uncertainty here)
Explain why: Energy needed making bonds was greater than energy released breaking bonds
Balance equation: 2 and 2 somewhere
Efficiency of Kettle: Hydrogencarbonate ions thermally decompose to carbonate, then react with calcium ions to product a precitipates of calcium carbonate (limescale). Limescale is a bad conductor of electricity - more energy needed to heat water
Hard water cleaner q: Calcium and magnesium ions replaced by sodium and hydrogen ions
Benefits of hard water: contains calcium which strengthens teeth and bones
Element that has low boiling point: Flourine
What happens in the mixture of gases? Ammonia is liquified, then cooled - Nitrogen and Hydrogen are recycled
Specific heat capacity: 3444J (you had to use the mass of water (50g), not the 0.8g mass of fuel
How is methane obtained: Natural gas
Why air shouldn't be allowed in reactor: Air is a mixture of gases, the elements in air could have reacted with nitrogen and hydrogen in the reactor; wasting reactants, reducing yield. Other gases/elements entering the chamber also contaminates it.
Two boiling tubes: Tube A: fizzing/effervescence because acid is dissolving calcium carbonate
Tube B: calcium carbonate produced, solution goes cloudy
Sentence completion: - acid catalyst, ester
-Forward reaction is exothermic, so opposite reaction is endothermic
Filling in boxes: white precipitate for the halide test, no change for the others
What conditions are needed for highest yield of ammonia: 200 degrees, 1000 atm
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milolj
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#2
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#2
Will you lose a mark for saying 1623 rather than -1623?
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lou_isa
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#3
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#3
Benefit of Hard Water - Contains Calcium which is good for teeth and bones

What happens after the reactor? - Goes to a condenser which liquefies Ammonia which is then removed. Nitrogen and Hydrogen is recycled.
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lilacpotato
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#4
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Last question: Using graph, suggest and explain why 450 degrees C and 200 atmospheres are the conditions for the Haber Process (5 marks)


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lilacpotato
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#5
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Filling in table about non metal ion testing: white precipitate in first box, the rest were no change I think
(2 marks)

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pixiefuller
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#6
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What did you get for the specific heat capacity question? (the one before the bond energies question)

There was also the question on the Periodic table where you had to say which element had the lowest boiling point - I put F
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chelseafc141
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#7
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#7
I got -1276 for the bond energies
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RayRay99
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#8
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#8
Last question:

Low temp is needed for a higher yield of ammonia as the forward reaction is exothermic.
But this would decrease the rate of reaction too much so a comprise temp of 450'c is used.

A high pressure would also give a higher yield as there are fewer molecules in the right than on the left.
But a higher pressure costs too much money so a compromise pressure is used. (200atm)
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ProbablyJade
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#9
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#9
(Original post by lilacpotato)
Filling in table about non metal ion testing: white precipitate in first box, the rest were no change I think
(2 marks)

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Yea thats what i got
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Sadxa
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#10
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#10
me too
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CaptErin
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#11
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(Original post by milolj)
Will you lose a mark for saying 1623 rather than -1623?
They usually put the minus in brackets on the mark scheme like '(-) 1623' so you should be fine
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arj2104
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#12
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#12
I got the last bit of the Bond Energy wrong and wrote -1176 by making an arithmetic mistake. How many marks did you lose?
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Roquebrune2014
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#13
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(Original post by chelseafc141)
I got -1276 for the bond energies
So did I is -1276 wrong?


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TheAnon121
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#14
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#14
(Original post by pixiefuller)
What did you get for the specific heat capacity question? (the one before the bond energies question)

There was also the question on the Periodic table where you had to say which element had the lowest boiling point - I put F
For specific heat capacity, I got 3444J. And some people said it was F for that and some Rb - not sure which one was right
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CaptErin
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#15
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#15
(Original post by pixiefuller)
What did you get for the specific heat capacity question? (the one before the bond energies question)

There was also the question on the Periodic table where you had to say which element had the lowest boiling point - I put F
Fr?
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user2k16
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#16
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#16
the bond energy question I didn't get a minus (-) as it was an endothermic reaction ?
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etata
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#17
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(Original post by Roquebrune2014)
So did I is -1276 wrong?


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I got that too
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TheAnon121
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#18
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#18
(Original post by user2k16)
the bond energy question I didn't get a minus (-) as it was an endothermic reaction ?
It said in the question that it was an exothermic reaction
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bod247
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#19
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#19
Its Rb because in group 1 (alkali metals), the Boiling point and Melting Point decrease as you go down. Rb was the last Alkali Metal so its the lowest Boiling Melting/Point.
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user2k16
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#20
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#20
(Original post by TheAnon121)
It said in the question that it was an exothermic reaction
oh no no 3 marks for me
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