Chemisty C2 - 2015 UNOFFICIAL Markscheme

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

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)

for 1 a (ii) i said because the steep gradient showed a fast reaction, would i still get the mark?!! help please!

for 1 a(ii) i said because there is a steeper gradient which shows the fast reaction? would i still get a mark? help!!!!!

Just checking For what did the student see, is seeing copper being produce the right answer?

Would I get a mark if for the first question I said increasing the temp increases the rate of reaction TO AN EXTENT
and my justification was at (x) seconds they both reach the same volume of gas/?????

hi,

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

a better answer would be

there are no delocalised electrons to carry the current


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

i believe that another reason is

too high maluability as of structure

6 mark question?
i think i made an error in this
was the reaction endothermic?

hi,

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

a better answer would be

there are no delocalised electrons to carry the current


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

i believe that another reason is

too high maluability as of structure

6 mark question?
i think i made an error in this
was the reaction endothermic?

For the bonding in sodium chloride, i mentioned that is an ionic structure, has positive sodium ions (Na+) and negative chloride ions (Cl-). I also mentioned there's electrostatic forces of attraction between the ions so a high mp/bp is needed to break the bonds. But i didnt mention sodium ions lose 1 electron and chlorine atoms gainan electron Will i still be able to get 4 marks?

Do you guys think the grade boundaries will be on the higher side or the lower side?

6 (d) iii, I put because there are no free ions to conduct the electricity, pretty confident on that. and for 1 (b) I put the concentration and mass of marble chips. could be wrong though!

*Slightly* lower for both C2 and C3.

can someone explain carbon 12 to me please i do not see how that's the answer LOL

Do you guys think the grade boundaries will be on the higher side or the lower side?