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Chemisty C2 - 2015 UNOFFICIAL Markscheme

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For question 1b, I put the concentration of the acid and the size of the marble chips because size affects surface area which affects the rate of reaction!

Reply 101

neon_reaper

Original post by Ankit.B

Last year C2 was 48 and C3 47 do u think they will nuke C3 so much?

Maybe not, but that was much harder than most of the past papers, so i think generally people will do worse and therefore bring down the boundaries

Reply 102

neil20143

Original post by hope99

hi thanks so much for this! For the empirical formula, me and my friend did it wrong and got Pb02, because for lead we got 1 and oxygen 1.5 so rounded up to 2, but is this wrong because we were supposed to at this stage multiply both sides by 2 to get pb203? ahh that's so annoying :frown:

also i'm a bit worried bc for some 1 mark answers like the copper one first i said too flexible but then for some reason i also added after that also because it would conduct electricity which thinking about it now is a ridiculous answer haha, but i looked on the aqa website and it said if you put two reasons and 1 is right and 1 wrong you get 0 marks, and i think for lot of questions i probably added more than necessary which means i'll probably get marked down :frown:

anyway thanks for this, does anyone have an idea of what the grade boundaries might be?

Yeah but you'll get three marks out of four for getting 1 and 1.5

Reply 103

neil20143

Original post by sushiman123

I think this mark scheme is a bit too lenient really, I got 58 according to it o.O

You can't really be lenient with 1-markers as they usually only have one answer. The 3/4-mark questions were all quite straight forward in terms of the marks they were looking for.

Reply 104

hope99

Original post by neil20143

Yeah but you'll get three marks out of four for getting 1 and 1.5

ahh thanks!

Reply 105

sushiman123

Original post by neil20143

You can't really be lenient with 1-markers as they usually only have one answer. The 3/4-mark questions were all quite straight forward in terms of the marks they were looking for.

For example, I said Nitinol was hard, but i really doubt I'd get a mark for it. They probably just want you to say shape memory.

Reply 106

littleheron

Original post by neil20143

You can't really be lenient with 1-markers as they usually only have one answer. The 3/4-mark questions were all quite straight forward in terms of the marks they were looking for.

I had a look through the mark scheme again.

For this question:

5(c) (i). State how lead nitrate can be obtained from lead nitrate oxide (1 mark)
-Crystalisation
-Evaporate and leave to dry.

The question was "State how solid lead nitrate can be obtained fro lead nitrate solution"

Since it was only 1 mark, don't you think its more likely the answer is "Filtration"

Reply 107

littleheron

Original post by sushiman123

For example, I said Nitinol was hard, but i really doubt I'd get a mark for it. They probably just want you to say shape memory.

Do you think if you interchanged the words and said something like "memory shape alloy" or "smart memory alloy" you would still get the mark?

Reply 108

grovyle

welp, according to this i'm screwed
hopefully i've done better in c3 and will do good in c1....

Reply 109

neil20143

Original post by littleheron

Both should be right.

Reply 110

neil20143

Original post by sushiman123

For example, I said Nitinol was hard, but i really doubt I'd get a mark for it. They probably just want you to say shape memory.

This isn't an official mark scheme, just a rough guide.

Reply 111

Palette

Original post by neil20143

This isn't an official mark scheme, just a rough guide.

When will you make the mark scheme for the six marker?

Reply 112

sushiman123

Original post by neil20143

This isn't an official mark scheme, just a rough guide.

Yeah true, certainly better than nothing. Either way I'm pretty sure I got at least 50, should make up for whatever mark I get in C3 xD

Reply 113

Courts99

Original post by eza11

for 4b) I put moles and carbon-12?? Was it just me that didn't put grams?

no i also put moles, but moles i think is the unit for concentation in u3 but i got told it was in relation to hydrogen so i have got both of them wrong!!

Reply 114

varun1212

According to the rough guides, i got about 32 in B2 and 35 in C2, (with official maybe 1-2 marks more)and i got B in isa, how much more would I roughly need to get B overall in additional science, considering im doing double? Any response would be appreciated

Reply 115

fabsafxo

Original post by neil20143

I tried to make an unofficial mark scheme for this. Please be free to add things :smile:

c. Why does a catalyst reduce costs?
-Because less energy is needed to start the reaction (as it has a lower activation energy)

2(b).Improves the investigation? (2 marks)
Improvement: Use a lid/ insulate the container
Reason: Prevents heat from being transferred to the surroundings/escaping.

Could the answer to the first one be that the catalyst is biodegradable and can the second one be add a stopwatch to see how fast it reacted???

Reply 116

fabsafxo

Original post by neil20143

I tried to make an unofficial mark scheme for this. Please be free to add things :smile:

1a. State one conclusion about the effect of temperature on the rate of reaction? (1 mark)
-An increase in temperature increases the rate of reaction

aii. One reason why? (1 mark)
-Because the volume of gas being produced at 40 degrees was more rapid than at 20 degrees.

a(iii). Average rate (1 mark)
-2 cm cubed per second (I think)

1 (b) two students should the student keep constant? (2 marks)
-Mass of Marble Chips
-Concentration of acid

b ii. Increasing the surface area affect the rate of reaction? (2 marks)

-Increases the rate of reaction
-As the particles are colliding more frequently (more successful collisions)

c. Why does a catalyst reduce costs?
-Because less energy is needed to start the reaction (as it has a lower activation energy)

(there may be alternatives)

2 (a). What could the student see? (1 mark)
-Copper being formed (brown) or zinc disappearing

2(b).Improves the investigation? (2 marks)
Improvement: Use a lid/ insulate the container
Reason: Prevents heat from being transferred to the surroundings/escaping.

2c (6 marker - will do later at some point)

3 (a). How does a metal conduct electricity? (4 marks)
-Delocalised electrons can move through the metal
-Transfer electrical charge
-Sea of moving electrons (structure)
-Lattice of positive ions (structure)

3(b). Describe the structure of an alloy is different to a metal (2 marks)
-Different elements with different sizes
-Distort layers in the mixture, preventing them from sliding over each other.
OR
-Irregular pattern of atoms.

3(c). Why is Nitinol used in braces? (1 mark)
-Hard/strong/corrosive-resistant/smart-alloy

3(c) (ii). Why are coins not made out of pure copper? (1 mark)
-Because it is too soft so will corrode

3 (c) (iii)). Aluminium Oxide

3 (c) (iv). How can the reaction produce two different products? (1 mark)
-Made using different reaction conditions / any specified reaction condition (e.g. pressure, temperature).
-Using different catalysts

3(d). Instrumental methods are used to detect impurities? (2 marks)
Any two from:
-They use very little samples.
-Accurate
-Sensitive
-Fast

4 (a). Why does Lithium have 7 as it's atomic number? (3 marks)
-3 protons
-4 neutrons
-3 + 4 = 7 which is its mass
-electrons have a very small mass.

4(b). Complete the sentences (2 marks)
-Grams
-Carbon-12

4(c). Isotope differences (3 marks)
-18-Oxygen had 2 more neutrons than 16-Oxygen
-Same number of protons
-Same number of electrons

5 (a). Name a soluble compound that contains silver
(1 mark)
-Silver Nitrate

5(a) ii Compound containing carbonate ions (1 mark)
-Potassium or Sodium Carbonate

5(b) (1 mark)
-(insoluble)Base

5(c) (i). State how lead nitrate can be obtained from lead nitrate oxide (1 mark)
-Crystalisation
-Evaporate and leave to dry.

5c(ii) (1 mark)

Pbo + 2HNO3 = PB(NO3) + H2O

5c (iii). number of atoms in the compound
-9

5(d). Empirical Formula (4 marks)
Pb2O3

6(a). Structure and bonding in sodium chloride (4 marks)
-Ionic Bonding
-Sodium atoms lose one electron to form positive ions
-Chloride ions gain one electron to form negative ions
-Opposites attract
-Giant ionic structure
-Cubic Lattice
-Electrostatic forces

Any of these should get the mark I think

6(b). Other products when brine is electrolysed (2 marks)
-Sodium Hydroxide
-Hydrogen

6(c). Ethical reason for not putting Iodine in food (1 mark)
-People may not want to have these extra Iodine amount (no choice)

6(d) (i). (2 marks)
-3 electrons lone pairs and one covalent bond

6(d) (ii). Why does Iodine have a low melting point (3 marks)
-Simple molecules
-Weak intermollecular forces
-Little energy needed to break them down

6(d) (iii). Why does iodine not conduct electricity? (2 marks)
-No overall charge so can't carry electrical charge

(I'm not sure about this question)

can you do one for biology B2 please??

Reply 117

MoshBosh

Both exams were quite simple tbf, same standard as previous years imo. Therefore it seems most likely that the grade boundaries will replicate those of last year, i.e. 47/48 for C2 and 45-47 for C3.

(edited 8 years ago)

Reply 118

Decklan

Original post by fabsafxo

can you do one for biology B2 please??

Cardiac output.

148x38=5624 volume ml/blood min, units were given dw.

Explain why person two had a lower cardiac output? (2 mark)

Because his stroke volume was much lower, which meant a lower cardiac output.

Explain why person one ran faster than person two? (5 marks)

Because person one had a greater cardiac output this meant more blood flow to the muscles from the heart. Therefore a constant supply of glucose and oxygen reached the muscles allowing aerobic respiration to release energy compared to anaerobic which releases less energy and lactic acid. More energy released for running.

Fossils

Explain he formation of the fossil archaeopteryx? (2 marks)

The animal must first die, and the hard parts of the animal were not able to decay leaving a fossil.

Give two reasons why there were gaps in the record? (2 marks)

i) More fossils are yet to still be discovered.
ii)Fossil couldn't be formed because of decay.

Explain how species could be formed from the ancestor archaeopteryx? ( 4 marks)

You must first explain natural selection, and then speciation. So something like for e.g Variations in gene caused certain characteristics to be better suited for the environment these animals survived (natural selection) and passed their genes to the future generations. These animals would become so different that interbreeding successfully would not be viable so a specie has been formed. Isolation must be said at the start of this question though.

Alleles & genetics.

Describe where the dna is found in human cells? (2 marks)

Dna found in the nuclear cells as nuclear Dna.

Minimum allele that needs to be present for polydactyly to be expressed?(1 mark)

Well considering it is a dominant condition, only one needs to be present.

Minimum allele that needs to be present for cystic fibrosis to be expressed? (1 mark)

It's recessive, so two.

Mendel's experiment.

The ratio I personally think it's 3:1 as the experiment is directly from his work which consisted of the same ratio esp from the genetic diagram. Also 729/228 = 3.1 makes sense for the ratio to be 3:1. (1 mark)

Give two reasons why his work wasn't accepted or on those lines which is what they were essentially asking for. (2 marks)

i) Because he wasn't a renowned scientist, a monk his work wasn't accepted.
ii) At the time inheritance factors weren't known and hence they didn't really appreciate how important Mendeleev work.

For the tick boxes, if you do the genetic diagram it was most definitely.(3 marks)

-Homo
-Homo
-Hetero

Cell structure

Mitochondria - Sight at which respiration occurs. (1 mark)

Ribosome - Where protein synthesis occurs. (1 mark)

Muscle cell magnification is 400. idk how many marks.

Explain why muscle cells cover the stomach? (2 marks)

Help to churn the food which would mix with the digestive enzymes.

Some answers could be wrong tbf, but here you go.