OCR AS Salters Chemistry F332 - Wednesday 23rd May 2012 1:30pm

Unofficial Mark Scheme
I can remember the majority of questions but I'm missing 4 marks... if anybody could tell me what questions I am missing that would be helpful.
Obviously this mark scheme is not going to be completely correct and the questions are not all in the correct order.

1. a) What are the functional groups present in the molecules? (2)
A. Alkene, ketone (carbonyl)

b) What is the molecular formula of the molecule? (2)
A. C15H22O

c) If bromine water is added, what will the colour change be? (2)
A. brown/red/orange to colourless

d) write the equation of the reaction will excess bromine water. Use the molecular formula from a) (2)
A. C15H220 + 2Br2 = C15H22O(Br2)2

e) What type of reaction is this? (2)
A. Electrophilic addition

g) Bromine reacts with Silver nitrate, what would the student see? (2)
A. cream precipitate

2. What type of alcohol does this molecule contain? (1)
A. Tertiary

b) Explain your answer (1)
A. The carbon atom to which the -OH group is attached is attached to three other carbon atoms.

c) What is the strongest bond that this molecule can form? (1)
A. I'm sure it's P.D - P.D as it contains -OH groups? Or is it H bonding?

d) Draw an OH radical, include the outer shell only. (1)
A. One 'dot' and 'cross' forming a bond between O and H
Then 5 more e- on the O, one on its own

e) What type of reaction produces the hydroxyl radical? (1)
A. Homolytic fission

f) Producing an alcohol from an alkene when water is added. State the reagents and conditions required. (2)
A. Phosphoric acid catalyst (allows sulphuric acid)
High temperatures and pressures / 300C and 60atm

g) Shows two compounds. A contained tertiary alcohols, B contained a primary alcohol. Describe the colour changes when potassium dichromate is added and explain this in terms of the types of alcohol. (5) (1 mark for QWC?)
A. A cannot be oxidised by potassium dichromate as it contains no H on the C atom to which the -OH group is attached.
Thus the colour will not change, it will remain orange
B can be oxidised as it is a primary alcohol and so does contain H atoms on the C to which the -OH group is attached
B will produce a colour change of orange to green and a carboxylic acid will be produced.

3. a) Name the compound CFl3CCl2H (2)
A. 2,2 - dichloro, 1,1,1 - trifluroethene (may ignore numbers)

b) Why is compound A less expensive? (1)
A. Some wrote that it contains no halogen atoms, and thus is less expensive to transport.
Others quoted a fact from the table provided

c) Why can this compound not be used as a cleaning agent (1)
A. Some wrote because it does not contain chlorine and so will not kill bacteria
Others quoted a fact from the table provided

d) Explain why CFCs are not broken down in the troposphere and explain how CFCs deplete ozone (5)
A. The C-F bond is too strong to be broken in the troposphere (1)
In the stratosphere the C-F bond breaks in the presence of high energy (1) UV radiation (1), by photo-dissociation (1?)
This forms Fluorine radicals (1)
Which catalyse ozone break down (1)

ii) Why is ozone a benefit? (3)
A. Ozone absorbs high energy (1) (can also quote specific v) UV radiation (1) which would cause skin cancer (1)
NOTE: mark schemes always say ignore skin DAMAGE

e) Label the partial charges on a CCl3F molecule (1)
A. delta positive on C, delta negative on all chlorine and fluorine atoms

g) explain what these partial charges are (2)
A. The partial charges show the differences in electronegativity values
Chlorine and Fluorine have a greater share of the e- and so have a partial negative charge
C has less of the share of electrons and so has a partial positive charge

h) Draw the 3-D shape of the molecule. (1)
A. Should include a tetrahedral shape with a wedge and a dotted line

i) based on g and h, is this molecule polar? (2)
A. This molecule is polar as fluorine is the most electronegative and so has a greater share of electrons producing a dipole
OR can be that all halogens are more electronegative

j) What are the oxidation states of Sulphur and was it Oxygen? (3)
Sulphur was 0 to +4 i think?


k) what is the formula of the reducing agent? (2)
S as it is itself oxidised and reduces oxygen

l) Name one agricultural source of methane (1)
A. Rice paddies/cattle farming/ mark scheme will include varied options

m) explain how increased conc. of methane are linked to global warming (2)
A. More methane molecules means more IR is absorbed (1) which increases the kinetic energy of the molecules and thus the temperature is increased (1)

4. Explain dynamic equilibrium (2)
A. Rate of forward reaction equals rate of reverse reaction (1) in a closed system/ conc. of reactants and products stay the same (1)

b) Why use nano something or other (2)
A. Provides a larger surface area for reacting particles to react. Thus there will be more frequent collisions, increasing the ROR

c) What is activation enthalpy (2)
A. The minimum energy required for colliding particles to react successfully. The energy needed to overcome the activation enthalpy barrier etc.

d) Effect of increased pressure on rate of reaction (3)
A. Increasing the pressure means the reacting particles are in closer proximity to each other. There will be more collisions. The rate of reaction will increase

e) Increased pressure on yield (3)
A. Position of equilibrium will shift to the .... (what side it was) / side with fewest gas molecules. So there will be increase/decrease in yield

e) Increased temperature on yield (3)
A. POE will shift to the left as the reaction favours the endothermic reaction.So the yield of products will increase

f) How many more times abundant is oxygen compared to methane? (2)
A. Oxygen was 21% methane was 0.00018%
So 20.9?

NOT SURE ABOUT THESE ANSWERS:
5. what is an addition polymer? give an example from the article but not poly(ethene) (3)
A. Many different answers...
I wrote along the lines of.... a large chain made up of many monomers added together
Could of included any polymer from the article, e.g. poly(propene)

b) Infrared spectroscopy (4)
I believe you had to discuss how the bonds absorb specific frequencies of IR

c) what would the people expect if reaction 2.1 had occurred? (2)
I believe you had to quote the absorptions of the functional groups

d) What is an initiation reaction? (1)
A. Produces radicals. There are no radicals at the start of this stage but there are at the end of the stage

e) What does a single headed arrow show? (1)
A. The movement of one electron

g) What type of reaction was the last radical reaction (1)
A. Termination

h) The I.B's question. How they are formed, how the structure link to strength of I.Bs (7)
A. Electrons are constantly moving (1)
This creates an uneven distribution of charge(1)
This creates an instantaneous dipole (1?)
Which induces a dipole in a neighbouring molecule (1)
The two are then attracted (1)

HDPE is un-branched and so has a larger molecular surface area (1)
The chains can pack more closely resulting in stronger I.Bs as they are closer together (1)
Thus, HDPE can whithstand more force than LDPE as it takes more energy to break the bonds (1)

Can also explain LDPE instead of HDPE


NOTE: There are alternative answers to the ones I have wrote, I just cba to include them all. You can use past mark schemes to mark your answers using these questions. There was 5 marks on titration's and 5 marks on E=hv also, i have not included these as i cannot remember the exact figures.

@Alevelstudent1908 - you have good memory! In question 1 though, everyone's saying it was "bromine water" but I only remember it saying "bromine"... does it make a difference?




Same, I literally copied exactly what it said on the sheet, ie. "Ra(CH2)m + (CH2)nRa --->" etc... No idea if that's right!

Okay i think it was C15H21O not 22.

Strongest bonds were hydrogen bonding because it has alcohol groups.

For (d) on CFCs, its not the fluorine i dont think that gets photodissociated but the chlorine. I went on to write a bunch of equations on what could possibly happen and how its removed like:

Molecule dissociates.. Cl radicals formed

Cl + O2 = ClO + O

ClO + O3 -> Cl + 202

So many people said that (i) was non-polar, but if you're right and its polar, thennnnn i'll have 2 marks in the bag hopefully.


(j) +4 to +6 i think. Can't remember, but its defo not zero. The bromine was 0 to -1.

(k) Its not S, its SO2 thats the reducing agent because its oxidation state decreases.

For (m) i think you gotta say that the E is transferred to other molecules by collisions.


e) Increased temperature on yield (3)
A. POE will shift to the left as the reaction favours the endothermic reaction.So the yield of products will increase

No it shifts to the right. The endothermic was the forward reaction, because the enthalpy change was +200 something. Exo woulda been a minus value.


c) What is activation enthalpy (2)
A. The minimum energy required for colliding particles to react successfully. The energy needed to overcome the activation enthalpy barrier etc.

I think you actually had to write the effect of catalysts on the Ae barrier, because there were two parts to the question in my opinion.


b) Infrared spectroscopy (4)
I believe you had to discuss how the bonds absorb specific frequencies of IR

I said:
-When a beam of IR radiation is passed, its absorbed by c.b in molecules
-Increase in vibrational energy
-Different bonds, as well as, bonds in different positions absorb different energies.
-Show up as trough on graph.
-Gave an example on what would come up.

It was such an ambiguous question.

Okay i think it was C15H21O not 22.

No, it was C15H22O.

No, it does favor the forward reaction, the position of the equilibrium shifts to the right. Yield increases.
(have another look at what you wrote and you will see. unless your under the impression that the question said describe the effect of decreasing the temperature.)

For k) i'm not sure whether is was S or SO2, i guess we won't know to the mark schemes are released :/
Also, a reducing agent become oxidised itself, not reduced.

e) I realised I put to the left, i didn't mean too. Cant tell my left from my rights :')

I was so unsure what to write for the IR spectroscopy q.! I hope i've picked up a few marks :/
I think your answer will get 4/4

For the rest, i think your correct. How did you find the paper? I thought it was okay, especially compared to the bio exam -.-

C15H22O

what did people write for the type of reaction in figure 1? I wrote electrophilic addition which i know must be wrong as electrophilic addition was mentioned earlier on in the paper but i didnt know what else it could be. At school someone wrote copolymer addition or something similar.

I had no clue for that question and now i realise there was a reversible reaction arrow as well but still dont know :/

I wrote addition polymerisation, but I misinterpreted the question. It was actually equilibrium.

ahh right. What did you write as your example of an addition polymer? I wrote poly(ethene) but am not sure if this counts as it would be too easy?

You coulda said, PVC or poly(propene).



The question said that you have to state an addition polymer other than poly(ethene).

Its only one mark though!

Dang it! why did i write that! And i remember reading it now as well. FML

Na they are symmetrical so they cancel out

i have a feeling it was question 3?! haha! i really can't remember!

question 1: was all about electrophillic addition - oxidation of alcohols etc

question 2: ???? - was it the titration malarky and bromide ions with chlorine??

question 3: CFC's?

question 4: equilibrium question - rate/ pressure etc

question 5: advanced notice


its really bugging me!

I wrote addition polymerisation, but I misinterpreted the question. It was actually equilibrium.

Unofficial Mark Scheme
I can remember the majority of questions but I'm missing 4 marks... if anybody could tell me what questions I am missing that would be helpful.
Obviously this mark scheme is not going to be completely correct and the questions are not all in the correct order.

1. a) What are the functional groups present in the molecules? (2)
A. Alkene, ketone (carbonyl)

b) What is the molecular formula of the molecule? (2)
A. C15H22O

c) If bromine water is added, what will the colour change be? (2)
A. brown/red/orange to colourless

d) write the equation of the reaction will excess bromine water. Use the molecular formula from a) (2)
A. C15H220 + 2Br2 = C15H22O(Br2)2

e) What type of reaction is this? (2)
A. Electrophilic addition

g) Bromine reacts with Silver nitrate, what would the student see? (2)
A. cream precipitate

2. What type of alcohol does this molecule contain? (1)
A. Tertiary

b) Explain your answer (1)
A. The carbon atom to which the -OH group is attached is attached to three other carbon atoms.

c) What is the strongest bond that this molecule can form? (1)
A. I'm sure it's P.D - P.D as it contains -OH groups? Or is it H bonding?

d) Draw an OH radical, include the outer shell only. (1)
A. One 'dot' and 'cross' forming a bond between O and H
Then 5 more e- on the O, one on its own

e) What type of reaction produces the hydroxyl radical? (1)
A. Homolytic fission

f) Producing an alcohol from an alkene when water is added. State the reagents and conditions required. (2)
A. Phosphoric acid catalyst (allows sulphuric acid)
High temperatures and pressures / 300C and 60atm

g) Shows two compounds. A contained tertiary alcohols, B contained a primary alcohol. Describe the colour changes when potassium dichromate is added and explain this in terms of the types of alcohol. (5) (1 mark for QWC?)
A. A cannot be oxidised by potassium dichromate as it contains no H on the C atom to which the -OH group is attached.
Thus the colour will not change, it will remain orange
B can be oxidised as it is a primary alcohol and so does contain H atoms on the C to which the -OH group is attached
B will produce a colour change of orange to green and a carboxylic acid will be produced.

3. a) Name the compound CFl3CCl2H (2)
A. 2,2 - dichloro, 1,1,1 - trifluroethene (may ignore numbers)

b) Why is compound A less expensive? (1)
A. Some wrote that it contains no halogen atoms, and thus is less expensive to transport.
Others quoted a fact from the table provided

c) Why can this compound not be used as a cleaning agent (1)
A. Some wrote because it does not contain chlorine and so will not kill bacteria
Others quoted a fact from the table provided

d) Explain why CFCs are not broken down in the troposphere and explain how CFCs deplete ozone (5)
A. The C-F bond is too strong to be broken in the troposphere (1)
In the stratosphere the C-F bond breaks in the presence of high energy (1) UV radiation (1), by photo-dissociation (1?)
This forms Fluorine radicals (1)
Which catalyse ozone break down (1)

ii) Why is ozone a benefit? (3)
A. Ozone absorbs high energy (1) (can also quote specific v) UV radiation (1) which would cause skin cancer (1)
NOTE: mark schemes always say ignore skin DAMAGE

e) Label the partial charges on a CCl3F molecule (1)
A. delta positive on C, delta negative on all chlorine and fluorine atoms

g) explain what these partial charges are (2)
A. The partial charges show the differences in electronegativity values
Chlorine and Fluorine have a greater share of the e- and so have a partial negative charge
C has less of the share of electrons and so has a partial positive charge

h) Draw the 3-D shape of the molecule. (1)
A. Should include a tetrahedral shape with a wedge and a dotted line

i) based on g and h, is this molecule polar? (2)
A. This molecule is polar as fluorine is the most electronegative and so has a greater share of electrons producing a dipole
OR can be that all halogens are more electronegative

j) What are the oxidation states of Sulphur and was it Oxygen? (3)
Sulphur was 0 to +4 i think?

k) what is the formula of the reducing agent? (2)
S as it is itself oxidised and reduces oxygen

l) Name one agricultural source of methane (1)
A. Rice paddies/cattle farming/ mark scheme will include varied options

m) explain how increased conc. of methane are linked to global warming (2)
A. More methane molecules means more IR is absorbed (1) which increases the kinetic energy of the molecules and thus the temperature is increased (1)

4. Explain dynamic equilibrium (2)
A. Rate of forward reaction equals rate of reverse reaction (1) in a closed system/ conc. of reactants and products stay the same (1)

b) Why use nano something or other (2)
A. Provides a larger surface area for reacting particles to react. Thus there will be more frequent collisions, increasing the ROR

c) What is activation enthalpy (2)
A. The minimum energy required for colliding particles to react successfully. The energy needed to overcome the activation enthalpy barrier etc.

d) Effect of increased pressure on rate of reaction (3)
A. Increasing the pressure means the reacting particles are in closer proximity to each other. There will be more collisions. The rate of reaction will increase

e) Increased pressure on yield (3)
A. Position of equilibrium will shift to the .... (what side it was) / side with fewest gas molecules. So there will be increase/decrease in yield

e) Increased temperature on yield (3)
A. POE will shift to the right as the reaction favours the endothermic reaction.So the yield of products will increase

f) How many more times abundant is oxygen compared to methane? (2)
A. Oxygen was 21% methane was 0.00018%
So 20.9?

NOT SURE ABOUT THESE ANSWERS:
5. what is an addition polymer? give an example from the article but not poly(ethene) (3)
A. Many different answers...
I wrote along the lines of.... a large chain made up of many monomers added together
Could of included any polymer from the article, e.g. poly(propene)

b) Infrared spectroscopy (4)
I believe you had to discuss how the bonds absorb specific frequencies of IR

c) what would the people expect if reaction 2.1 had occurred? (2)
I believe you had to quote the absorptions of the functional groups

d) What is an initiation reaction? (1)
A. Produces radicals. There are no radicals at the start of this stage but there are at the end of the stage

e) What does a single headed arrow show? (1)
A. The movement of one electron

g) What type of reaction was the last radical reaction (1)
A. Termination

h) The I.B's question. How they are formed, how the structure link to strength of I.Bs (7)
A. Electrons are constantly moving (1)
This creates an uneven distribution of charge(1)
This creates an instantaneous dipole (1?)
Which induces a dipole in a neighbouring molecule (1)
The two are then attracted (1)

HDPE is un-branched and so has a larger molecular surface area (1)
The chains can pack more closely resulting in stronger I.Bs as they are closer together (1)
Thus, HDPE can whithstand more force than LDPE as it takes more energy to break the bonds (1)

Can also explain LDPE instead of HDPE


NOTE: There are alternative answers to the ones I have wrote, I just cba to include them all. You can use past mark schemes to mark your answers using these questions. There was 5 marks on titration's and 5 marks on E=hv also, i have not included these as i cannot remember the exact figures.

Well you should have known that.