GCSE AQA C2 CHEMISTRY UNIT 2 OFFICIAL UNOFFICIAL MARK SCHEME Weds 14 June 2017

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mahmed69
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Sup lads, here's the full Chemistry unit 2 mark scheme. Share and give reps, and don't forget to follow


1ai) draw a smooth curve of best fit on the graph. [1]
goes through all points excluding anomaly, should level off.

1aii) what was the volume of oxygen produced at 25 seconds? [1]
14cm cubed

1aiii) after how many seconds had the reaction stopped? [1]
50

1bi) work out the rate of reaction in the first 10 seconds [1]
6/10 = 0.6 cm cubed per second

1bii) the student concluded that the rate of reaction decreased with time. What evidence is there on the figure to support this statement? [3]
rate increased at first and was very fast until 20 seconds, as there's a steep line. It then began to slow down as less steeper gradient, and then curved off to be level at 50 seconds, thus rate decreased

1c) the catalyst was kept the same in this reaction. Name two other variables the student should control [2]
volume of hydrogen peroxide
temperature of hydrogen peroxide

1d) Explain the effect of increasing the concentration on the rate of reaction [3]
more particles in smaller volume, so closer together. Increases chance of collision so more frequent (and successful) collisions, thus faster rate of reaction

1e) Explain the effect of increasing the amount of catalyst on the rate of this reaction [2]
more catalyst means activation energy lowered even more, thus more faster rate of reaction, so graph would level off quicker, as rate at which volume of oxygen produced would be quicker

2) Metals and thermosoftening polymers have differences in properties. Describe their properties and use their structure to explain why they have these. [6]

Metals have higher MP/BP than TS polymers - have strong layers of metals ions in regular arrangement and have strong electrostatic forces between electrons and ions large amounts of energy needed to overcome these, whereas TS polymers have weak intermolecular forces of attraction between chains so easily overcome by little energy, so easy to melt and remould.
Metals can conduct electricity - sea of delocalised electrons throughout structure, so can carry charge throughout metal, NO ELECTRONS in TS polymers, so dont conduct
Metals better at conducting heat, ions vibrate faster around fixed position, electrons also vibrate more vigorously. Thus, heat is conducted quickly. Thermosoftening melt and don't conduct

3ai) Complete the dot and cross diagram of the molecule of oxygen [2]
4 electron in outer shell of both, 4 in middle - 2 from each atom

3aii) What type of bonding is this? [1]
covalent

3b) Explain why oxygen has a low boiling point [2]
made up of simple molecules and so have weak intermolecular forces between them, easily overcome by small amounts of energy, so gas at rtp

3ci) Magnesium atoms react with oxygen atoms to form Magnesium oxide. Balance the chemical equation for this reaction [2]
....2..Mg + O2 => ...2....MgO


3cii) Describe what happens during this reaction, in terms of electrons to form Magnesium oxide [3]
Magnesium atom needs to lose 2, and oxygen atom needs to gain two, in order to gain full outer shell. Magnesium then donates 2 electrons to the oxygen atom, making Mg2+ and O2-, forming magnesium oxide

3d) Magnesium oxide nanoparticles can be made. What is a nanoparticle? [1]
A particle with the size ranging from 1nm to 100nm

3e) Figure X shows a furnace lined with silicon dioxide. Explain why, in terms of structure, the furnace is lined with SiO2 [3]
each silicon atom is covalently bonded to 2 oxygen atoms and so is very strong. It has a giant lattice structure which makes it very hard, and gives it a high boiling/melting point. This can protect the inside of the furnace, without wearing away

4a) Describe a method by which the student could obtain copper sulfate crystals [4]
react CuO with H2SO4 and heat gently, this forms the crystals, by neutralisation. As the CuSO4 is aqueous, you will have to filter and evaporate in evaporating basin of by heating it. The water then evaporates and leaves behind CuSO4 crystals(blue)

4b) Work out the mass of CuO needed to make 24.95 grams of CuSO4 [3]
The Mr of CuSO4 is 249.5, The Mr for CuO is 79.5
moles = mass/Mr, 24.95/249.5 = 0.1 moles
0.1 x 79.5 = 7.95g

5a) Describe how compounds in substances are separated in gas chromatography [3]
sample is vaporized and carried through the columns by an unreactive gas, usually nitrogen. These have different retention times, and so exit different times, separating them

5b) what do peaks in mass spectrometer show [1]
relative formula/molecular mass

5ci) the student conducts experimen to indentify colours in ink. Describe a method the student could use to find the colours in ink A and B [3]
draw pencil line along solvent paper at bottom, place a dot of A and B on the line, 2 cm apart, put in solvent in container, put lid on to prevent evaporation


5cii) describe the differences between ink A and B. [2]
A and B both have 2 common colours dyes, and A has 2 (or 3-cant remember) dyes, but B has 4


6ai) The student does an experiment (another experiment ffs) where he neutralises HCl with NaOH, to make NaCl and records energy change. Suggest one reason why the energy change was not correct(tickbox) [1]
Third box - initial temperature was inaccurate

6aii) What can you conclude from the data in figure 7? [1]
It is exothermic

6b) the student then electrolysed the sodium chloride solution. Sodium was NOT produced at the cathode. State what was produced and why. [3]
hydrogen gas formed, H+ ions attracted to cathode, and gain 1 electron(reduced), and form hydrogen atoms, thus forming hydrogen gas. This is produced as Sodium is too reactive and is easily discharged in solution.

6c) complete the half equation for the positive electrode [2]
2Cl- => 2e- + Cl2

6d) the pH of the remaining solution was 14. Explain why [2]
Sodium Hydroxide(NaOH) discharged in solution as sodium ions and OH- react to form it. This is a base so is alkaline, and causes pH to rise.

All i can remember off top of my head... Pls comment below as there is some missing or marks are incorrectly allocated to each question...regardless please comment and don't forget to FOLLOW
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richageorge
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5cii) describe the differences between ink A and B. [2]
it was 3 marks not 2
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richageorge
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What can you can conclude about this reaction? (1 mark)
It is exothermic
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richageorge
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i'm not too sure but i think the balancing equation was 1 mark
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richageorge
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dot and cross was 2 marks
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Fabrice811
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For 5b, I'm sure it's Relative molecular mass, is that the same as Relative formula mass?
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Debbypoz
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(Original post by Fabrice811)
For 5b, I'm sure it's Relative molecular mass, is that the same as Relative formula mass?
I wrote that too, apparently for gcse molecular mass and formula mass are the same thing but not for A level
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monster_ej
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For the adding extra catalyst one I wrote it doesn't effect the rate of reaction because it is not used up in the reaction- I saw that somewhere I think in a past paper question
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Adaytoremember
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(Original post by monster_ej)
For the adding extra catalyst one I wrote it doesn't effect the rate of reaction because it is not used up in the reaction- I saw that somewhere I think in a past paper
question
I thought that too one of my teachers said it yesterday I think
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Fortitude2001
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(Original post by richageorge)
What can you can conclude about this reaction? (1 mark)
It is exothermic
because heat energy is given out so the surrounding temperature increases.
Examples of an exothermic reaction include combustion and respiration.


Endothermic- heat energy taken in and surrounding temperature decreases. An example of an endothermic reaction would be photosynthesis.
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Fortitude2001
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(Original post by Adaytoremember)
I thought that too one of my teachers said it yesterday I think
A catalyst can be used more than once but if it becomes poisoned it has to be replaced.
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mahmed69
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(Original post by Fortitude2001)
because heat energy is given out so the surrounding temperature increases.
Examples of an exothermic reaction include combustion and respiration.


Endothermic- heat energy taken in and surrounding temperature decreases. An example of an endothermic reaction would be photosynthesis.
Infacr, you could go one better and say that this experiment was a neutralisation reaction because it was acid plus base and thus its exothermic
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hogfe001
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(Original post by monster_ej)
For the adding extra catalyst one I wrote it doesn't effect the rate of reaction because it is not used up in the reaction- I saw that somewhere I think in a past paper question
You're right about how it isn't used up but it speeds up the rate of reaction, so it does change the rate
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Ahmed365
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the ethene question
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monster_ej
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(Original post by hogfe001)
You're right about how it isn't used up but it speeds up the rate of reaction, so it does change the rate
but if there is catalyst already, then adding extra amount of catalyst would not increase the rate of reaction
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cricinfo
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can you have the relative atomic mass for the mass spectrometer question?
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cricinfo
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Would about 54 in Paper 1, 48 or 49 ish in Paper 2, 48/49 ish in Paper 3 plus 47/50 in the ISA be enough to get A star?
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maya555
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(Original post by mahmed69)
Sup lads, here's the full Chemistry unit 2 mark scheme. Share and give reps, and don't forget to follow


1ai) draw a smooth curve of best fit on the graph. [1]
goes through all points excluding anomaly, should level off.

1aii) what was the volume of oxygen produced at 25 seconds? [1]
14cm cubed

1aiii) after how many seconds had the reaction stopped? [1]
50

1bi) work out the rate of reaction in the first 10 seconds [1]
6/10 = 0.6 cm cubed per second

1bii) the student concluded that the rate of reaction decreased with time. What evidence is there on the figure to support this statement? [3]
rate increased at first and was very fast until 20 seconds, as there's a steep line. It then began to slow down as less steeper gradient, and then curved off to be level at 50 seconds, thus rate decreased

1c) the catalyst was kept the same in this reaction. Name two other variables the student should control [2]
volume of hydrogen peroxide
temperature of hydrogen peroxide

1d) Explain the effect of increasing the concentration on the rate of reaction [3]
more particles in smaller volume, so closer together. Increases chance of collision so more frequent (and successful) collisions, thus faster rate of reaction

1e) Explain the effect of increasing the amount of catalyst on the rate of this reaction [2]
more catalyst means activation energy lowered even more, thus more faster rate of reaction, so graph would level off quicker, as rate at which volume of oxygen produced would be quicker

2) Metals and thermosoftening polymers have differences in properties. Describe their properties and use their structure to explain why they have these. [6]

Metals have higher MP/BP than TS polymers - have strong layers of metals ions in regular arrangement and have strong electrostatic forces between electrons and ions large amounts of energy needed to overcome these, whereas TS polymers have weak intermolecular forces of attraction between chains so easily overcome by little energy, so easy to melt and remould.
Metals can conduct electricity - sea of delocalised electrons throughout structure, so can carry charge throughout metal, NO ELECTRONS in TS polymers, so dont conduct
Metals better at conducting heat, ions vibrate faster around fixed position, electrons also vibrate more vigorously. Thus, heat is conducted quickly. Thermosoftening melt and don't conduct

3ai) Complete the dot and cross diagram of the molecule of oxygen [2]
4 electron in outer shell of both, 4 in middle - 2 from each atom

3aii) What type of bonding is this? [1]
covalent

3b) Explain why oxygen has a low boiling point [2]
made up of simple molecules and so have weak intermolecular forces between them, easily overcome by small amounts of energy, so gas at rtp

3ci) Magnesium atoms react with oxygen atoms to form Magnesium oxide. Balance the chemical equation for this reaction [2]
....2..Mg + O2 => ...2....MgO


3cii) Describe what happens during this reaction, in terms of electrons to form Magnesium oxide [3]
Magnesium atom needs to lose 2, and oxygen atom needs to gain two, in order to gain full outer shell. Magnesium then donates 2 electrons to the oxygen atom, making Mg2+ and O2-, forming magnesium oxide

3d) Magnesium oxide nanoparticles can be made. What is a nanoparticle? [1]
A particle with the size ranging from 1nm to 100nm

3e) Figure X shows a furnace lined with silicon dioxide. Explain why, in terms of structure, the furnace is lined with SiO2 [3]
each silicon atom is covalently bonded to 2 oxygen atoms and so is very strong. It has a giant lattice structure which makes it very hard, and gives it a high boiling/melting point. This can protect the inside of the furnace, without wearing away

4a) Describe a method by which the student could obtain copper sulfate crystals [4]
react CuO with H2SO4 and heat gently, this forms the crystals, by neutralisation. As the CuSO4 is aqueous, you will have to filter and evaporate in evaporating basin of by heating it. The water then evaporates and leaves behind CuSO4 crystals(blue)

4b) Work out the mass of CuO needed to make 24.95 grams of CuSO4 [3]
The Mr of CuSO4 is 249.5, The Mr for CuO is 79.5
moles = mass/Mr, 24.95/249.5 = 0.1 moles
0.1 x 79.5 = 7.95g

5a) Describe how compounds in substances are separated in gas chromatography [3]
sample is vaporized and carried through the columns by an unreactive gas, usually nitrogen. These have different retention times, and so exit different times, separating them

5b) what do peaks in mass spectrometer show [1]
relative formula/molecular mass

5ci) the student conducts experimen to indentify colours in ink. Describe a method the student could use to find the colours in ink A and B [3]
draw pencil line along solvent paper at bottom, place a dot of A and B on the line, 2 cm apart, put in solvent in container, put lid on to prevent evaporation


5cii) describe the differences between ink A and B. [2]
A and B both have 2 common colours dyes, and A has 2 (or 3-cant remember) dyes, but B has 4


6ai) The student does an experiment (another experiment ffs) where he neutralises HCl with NaOH, to make NaCl and records energy change. Suggest one reason why the energy change was not correct(tickbox) [1]
Third box - initial temperature was inaccurate

6aii) What can you conclude from the data in figure 7? [1]
It is exothermic

6b) the student then electrolysed the sodium chloride solution. Sodium was NOT produced at the cathode. State what was produced and why. [3]
hydrogen gas formed, H+ ions attracted to cathode, and gain 1 electron(reduced), and form hydrogen atoms, thus forming hydrogen gas. This is produced as Sodium is too reactive and is easily discharged in solution.

6c) complete the half equation for the positive electrode [2]
2Cl- => 2e- + Cl2

6d) the pH of the remaining solution was 14. Explain why [2]
Sodium Hydroxide(NaOH) discharged in solution as sodium ions and OH- react to form it. This is a base so is alkaline, and causes pH to rise.

All i can remember off top of my head... Pls comment below as there is some missing or marks are incorrectly allocated to each question...regardless please comment and don't forget to FOLLOW
How many marks of out 60 do you think you'll need to get a B?
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mahmed69
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(Original post by cricinfo)
Would about 54 in Paper 1, 48 or 49 ish in Paper 2, 48/49 ish in Paper 3 plus 47/50 in the ISA be enough to get A star?
Deffo


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mahmed69
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(Original post by maya555)
How many marks of out 60 do you think you'll need to get a B?
Roughly 36 or 37


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