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AQA Chemistry C3 - Unofficial Mark Scheme

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any idea what the grade boundaries would be?
It was exothermic so it had to have a negative sign.
Original post by user2k16
the bond energy question I didn't get a minus (-) as it was an endothermic reaction ?
That's what I put too
Original post by TheAnon121
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


the answer is 1000000000000% 1276 the people who got 1623 forgot to include the c-c bond in the reactants http://www.avogadro.co.uk/h_and_s/bondenthalpy/bondenthalpy.htm
Original post by bod247
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.


but then as you go up the group 7 table, the boiling point also decreases, with F being at the top
Original post by Emilybirch
I got the same, the next question said it was endothermic


exactlyhaha
Original post by miles354
but then as you go up the group 7 table, the boiling point also decreases, with F being at the top


no its fluorine because it's a gas so obvs it has the lowest bp.
Original post by Guest99999
Phew! someone who did the same exam as me, was worried they were the same exam as some questions are similar/same. I also got 212, and 2,3,2 for balancing, thank you so much you've saved my worries

omg thank god!!! i thought i had got the exam entirely wrong. yeah i got 212 too and also 2,3,2 after twenty years of attempting to balance it
"How is methane obtained: Natural gas"

That wasn't the question

The question was "What else can be obtained from the same source as Hydrogen"

The answer being Carbon as methane is CH4 (consisting of hydrogen and carbon)

I am certain of this as my first answer was Natural Gas then when I double checked I realised I had read the question wrong
Original post by Fractite
The next part said that the reaction was exothermic - it was a combustion reaction (which always gives out heat if you think about it lol.)


you did a different exam to me which is we didnt get the same answers. there are 2 science specs.
also its definitely -1276
This wasn't no where near as hard as last year's paper, so don't expect low grade boundaries. Chem 1 and C2 were harder than our papers last year and that was 50/60 for A* so I predict 53/60 for A* for our unit.
Original post by Oblivion99
This wasn't no where near as hard as last year's paper, so don't expect low grade boundaries. Chem 1 and C2 were harder than our papers last year and that was 50/60 for A* so I predict 53/60 for A* for our unit.


53/60 for what ... lool ur clueless
Original post by dh12345
53/60 for what ... lool ur clueless


For our Unit's* (C1 & C2) dumbass.
Original post by Oblivion99
For our Unit's* (C1 & C2) dumbass.


no it won't your actually mentally challenged if you think that, just because you think you did well dosen't mean the grade boundaries will jump up by 3 mate
Original post by dh12345
no it won't your actually mentally challenged if you think that, just because you think you did well dosen't mean the grade boundaries will jump up by 3 mate


the whole country found the paper's easy, pipe down lad.
Original post by Oblivion99
the whole country found the paper's easy, pipe down lad.


oi kid i know people who found it quite hard, and also people last year found the paper just as easy most likely the grade boundaries will be the same so hush little man
Original post by dh12345
oi kid i know people who found it quite hard, and also people last year found the paper just as easy most likely the grade boundaries will be the same so hush little man


"hush" little man, seriously, i'd slap you back to your mom's uterus which I played with last night, stfu.
For the sources of methane, would saying crude oil get a mark?
Thank You
Original post by NancyMassingham
"How is methane obtained: Natural gas"

That wasn't the question

The question was "What else can be obtained from the same source as Hydrogen"

The answer being Carbon as methane is CH4 (consisting of hydrogen and carbon)

I am certain of this as my first answer was Natural Gas then when I double checked I realised I had read the question wrong


I think the question was asking to name one source of methane, but I might be wrong.

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