GCSE C1-C3 Unofficial Mark Scheme 10/06/2016

1 c) I think it was C8H18

Please help me with the questions lol, I don't remember half of them.1. (a) Alkene = (I think it was E or F) - it was basically an ethene molecule.
(b) - (It was one where there were 3 carbon atoms and 8 hydrogen atoms so the propane molecule and then the one with the weird structure where carbon and hydrogen atoms were all over the place - the last on the diagram) Someone just tell me the letters please lol.
(c) C₈H₁₈
(d) if there was a part d - i think it was the polymer of it.
It was basically

[ F F ]
[ C C ]
[ F F ] n

The dashes between the C and F and extended bonds through the bracket. like this } lol kind of.

Why is an ester not a hydrocarbon? [1]

It contains an oxygen atom.

Do you think pentyl ethanoate is suitable as a solvent or something?

No bloody idea... I didn't even read the table properly - but I predicted the boiling point as similar to the one before. (130 degrees I think). I wrote that it has a high boiling point so it is suitable, I have no idea - I was thinking to say it is not, but rather C is suitable because it is soluble in water and therefore it can dissolve the substance that needs to be removed.
[I believe I wrote no, as the melting point was low, therefore it requires less energy to overcome the bond between the molecules. I predicted a volume between the two lines.]
Air Quality 6 marker:

Talk about respiration, combustion and photosynthesis - balanced.
Talk about nitrogen's low reactivity.
Talk about increase in demand - more fossil fuels burnt, more tropical rainforests cut down - less photosynthesis.

Colloid:

The particles are too small to settle out at the bottom and they always remain dispersed throughout the whole liquid without dissolving in it, instead - they are mixed and all over the solution, so they do not separate.

Gore-Tex (Advantage and breathable):

It allows water vapour to pass through so that the wearer doesn't become wet when the sweat condenses. Also, it doesn't allow wind through its membrane - so the wearer isn't cold. It has a microporous membrane so it allows water vapour through but not rainwater.
[Advantages of Gore-Tex over nylon- Nylon is not breathable, as water vapor is unable to pass through the material, therefore sweat condenses and makes the inside of the jacket damp. I believe this question was 1 mark, though it may have been 2.]

Incomplete Combustion of Methane:

CH4 + O2 --> C + 2H2O

Question on sodium hydrogencarbonate (can't remember it):

Might have missed it out accidentally...
[It may have been a balancing the equation question? I'm not sure what answer I wrote.]

How do oil pants dry?:

The solvent evaporates and the oil is oxidised by the atmospheric oxygen allowing it to form a protective skin over the surface.Wegener's theory - why it is accepted:

Sea floor spreading evidence was found.
Subsequent research led to his theory becoming accepted and developed.
It explains a wide range of evidence ^.
It has been discussed and tested by many scientists.

Alloys:

Mercury for amalgam
brass for copper and zinc
solder - lead and tin

Iron equation:

Iron + oxygen + water --> Hydrated iron (III) oxide

Aluminium - how do you know its that metal:

It didn't corrode in damp air because it has a protective layer of aluminium oxide.
I wrote dry air!!

Aeroplane wings evaluation literally was about density and relative hardness and cost.

Low density - advantage [As it is more fuel efficient.]
High density - disadvantage
High cost - disadvantage [More expnsive to manufacture and mass produce.]
Low cost - advantage
Low relative hardness - disadvantage
High relative hardness - advantage

(part b) was either A or D - A is expensive but low density and relative hardness high. D - cheap, less dense but low relative hardness. [Personally, I chose D.]

6 marker on Haber Process:

They aim for the most economical yield and the most daily product - a high pressure increases energy costs.
A low temperature - even though it decreases the cost, not enough ammonia will be made - low rate of reaction. Ammonia is in large demand and therefore, a low temperature won't meet the demand.
The unreacted starting materials are recycled, so the percentage yield is technically 100% overall.
A catalyst can compensate for the low temperature but it is costly.
A low percentage yield can be accepted if the reaction can be repeated with recycled starting materials.

Did it ask for why they don't use those or just in general why they don't aim for the highest percentage yield? I only answered why - economical yield etc, didn't say the what the conditions do - decrease yield or whatever. [It asked why these conditions are used, and what the optimum conditions were on the graph.]

potassium hydroxide + nitric acid word equation --> potassium nitrate and water

fertiliser - why it needs to be dissolved

the plants absorb the minerals in the fertiliser through the water they absorb from their roots - so it must be dissolved in water for the plant to absorb it through the roots. Also, only the dissolved substances are small enough to be absorbed, forgot that .

Eutrophication:

- increased nitrate and phosphate levels in lakes/streams
- algal bloom occurs
- blocks sunlight and plants die
- no photosynthesis so no oxygen produced for aquatic organisms to respire using
- aerobic bacteria starves on remaining oxygen
- aquatic organisms die as they can't respire and produce energy [This was a three mark question, so you may only need three of these points.]Rate of reaction question at end:

44 / 30 = 22 / 15 = 1.46 recurring cm^3/s

Concentration affect on rate of reaction:

more crowded particles - more collisions - increased rate of reaction

Relative atomic mass Q:

add up both reactants and products - show both are equal to 168 relative formula mass
reactant was only one - so 168. - i think this was the sodium hydrogen carbonate question lol right?
[One of the following questions required you to prove that a certain amount of a compound will create the predicted amount. I multiplied the given compound my 2.5 I believe. Something like that.]
percentage yield and other q:

something like 0.61/1 * 2.51 = answer depends on actual values
percentage yield = actual yield / 2.51 or whatever = 78% or something idek

bond making question - exothermic:

bond making - releases energy
bond breaking - uses / absorbs energy
overall, exothermic because more energy is released than needed.

question on the energy:

i think it was 16000, but whatever it was *2 = answer
[I think I got something like 8000j, though I think that I did this one wrong, as I didn't multiply it by 2.]

second part = 76 degrees something like that

32000 / (100*4.2) = 32000 / 420 = 76
[You had to round it to one decimal place. It was definitely 70-something.]
sample of a drug 6 marker:

Extracting the sample of the drug:
- crushing to disrupt and break the cell walls where the chemical/drug is located
- boiling in a suitable solvent to dissolve the compounds
- chromatography to separate and identify individual compounds
- isolating, purifying and testing potentially useful compounds
The melting point was not the same as a pure chemical, so the drug was not pure - it had a few impurities.
The chromatography - not sure, either the distance from the start line and solvent front between the two dots was not the same - shows the speed of one sample was faster than the pure sample - means it was not pure.

pharmaceuticals - 2/3 marker

- thousands of compounds often need to be tested to find effective ones
- likely compounds need to be tested on living tissue to ensure safety
- lone term trials on humans anre needed to identify possible effects
- many similar compounds need to be developed to try to reduce side effects
- the recommended doses need to be shown to be effective
- the research needs to be independently verified
- patents expire before costs and recpoured and others can make a version.

got none of them, didn't revise C3 - messed up on it badly!!

Aluminium oxide balanced symbol equation

4Al + 3O₂ --> 2Al₂O₃

INFO:

give your thoughts on the test too and help me build the mark scheme - correct me in wrong places.

I think I've got 5/075 marks, losing around 10 on C3 itself .. or more

Hope this helps.

The answer seems better - (no) for the solvent, I can't believe I forgot this ffs - well I only revised 2 hours before the exam but still...

Wait, for the percentage yield... Did i read the question wrong again?...Do you remember the exact question about the C2 6 marker. [It was something along the lines of; 'Use the graph to figure out which conditions would produce the highest yield, and why the second set of conditions [High temperature and low pressures] are used for the industrial manufacture of ammonia.]

in terms of eutrophication, it will have a wide range of stages of eutrophication and will give 1mark of each - hence why i wrote all of them.

Yeah, that's what I done right below where you quoted it (the rounding and *2.5 question).

For the energy released, I think you divided it by 2, it was 32 or 33k or something. [I wrote 32k in y working out- darn! At least I'll get 2 out of the three marks. ]

For the part (b) temperature part, I don't remember, but I got it correct in the exam lolz (quite sure).I think it was to 3 significant figures, but I doubt it was 70 i don't remember. All depends on what the first value was for the energy released in part (a).

Confirmed with friends, the energy was 32k. Now, it's all about what the mass of the water actually was lol. If you think about it, change in temperature = energy released or transferred / (mass * shc) = 32,000 / (mass * 4.2).
I don't know what the mass of the water was, but, I feel confident it was 100g though.

It definitely was 100g.

- Amount that should be made prove that its 1.578g: minus 39.6% off 2.something

- Average amount of hydrogen produced was 60cm^3

Energy released question you divide by two not times by 2 its even in the revision guide, there is no equation that states you times to get the energy released, it was 8000j and 19% this percentage was also on the dot.

Energy released question you divide by two not times by 2 its even in the revision guide, there is no equation that states you times to get the energy released, it was 8000j and 19% this percentage was also on the dot.

I thought I did okay until I saw the mark scheme. To be fair, I only started revising the night before. I completely messed up the nail varnish section and got all of that wrong, forgot details in each question, such as deforestation and stuff in the question about the gases in the air and how a rising population effects it. Also, for some reason I put that as well as hydrated iron (III) oxide being produced, carbon dioxide is as well, even though I knew as soon as the exam was over that it is not. I'm actually really worried because I'm predicted an A* and I think I've lost 20-30 marks.

Thanks :P.
Regarding that question, how did you work it out? I had 5 minutes to complete 15 marks of C3 so I didn't really have time lol to answer any questions, so I didn't even read them properly.

The amount from iron was 62 cm^3 i think and the other one was 58 cm^3 so it said how much would be produced from a mix so i took the average (62+58)/2 = 60cm^3.

Hope that helps

in the incomplete combustion question, wasn't carbon monoxide also produced?