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

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For Question 2C : c) What is the strongest bond that this molecule can form? (1)
Was it Hydrogen bonding or Pd-pd? :\ :confused:
Reply 1401
Original post by hayleyvictoria
For Question 2C : c) What is the strongest bond that this molecule can form? (1)
Was it Hydrogen bonding or Pd-pd? :\ :confused:


Hydrogen bonding.
Reply 1402
Original post by AmirHabeeb
Hydrogen bonding.


damn! I put hydrogen bonding then crossed it out and put pd-pd.
Original post by AmirHabeeb
Hydrogen bonding.


I put hydrogen bonding too! :smile:
Original post by tasniaa
damn! I put hydrogen bonding then crossed it out and put pd-pd.


that is wrong

you should know hydrogen bonding is the stronger intermolecular bond
Original post by hayleyvictoria
I put hydrogen bonding too! :smile:


that is correct
Original post by sharon800
i put copolymerisation because two different unsaturated monomers combined to give A-B+A--B+A--B, ETC
thats what i put...dont know, how they'll mark this, so ambiguous


I understand where you are coming from but I didn't think it was a polymer? I thought it was an imaginary addition reaction ha that they drummed up.
Original post by 4 Mathlete the win
I understand where you are coming from but I didn't think it was a polymer? I thought it was an imaginary addition reaction ha that they drummed up.


i have made so many silly mistakes, especially the reducing agent bit - i put sulphur, so 1 mark gone
then that molecular dipole question where i put the dipoles cancel is eachother out do the symmetry! so that wrong too, and i got the molecular formula wrong!
im sure i've made few other silly mistakes too, but how much is it for an A and can you get an A after all those silly mistakes :afraid:
Original post by Alevelstudent1908
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.


Really rather regretting reading this now!! :')
2C. I thought was HYDROGEN BONDING, not PD-PD.. anyone else think the same? :\
Original post by hayleyvictoria
Really rather regretting reading this now!! :')
2C. I thought was HYDROGEN BONDING, not PD-PD.. anyone else think the same? :\


i think it might have been hydrogen bonding, since the chain contained -OH groups :smile:
Original post by hayleyvictoria
Really rather regretting reading this now!! :')
2C. I thought was HYDROGEN BONDING, not PD-PD.. anyone else think the same? :\


for the CFC's question on why it doesn't go through photodissociation in troposphere, wrote
CFC's are stable and less reactive.
troposphere doesn't have high energy UV radiation to cause photodissociation of the molecule
CFC goes under photodissociation with high energy UV radiation to form cl radicals, which catalyse the breakdown of ozone
and then i involved some reactions like this :-
cl^2----2cl
Cl +O^3----ClO + O^2
ClO +O----Cl +O^2
O+O^2----O^3

is this fine? how many would this get?
Original post by hayleyvictoria
Really rather regretting reading this now!! :')
2C. I thought was HYDROGEN BONDING, not PD-PD.. anyone else think the same? :\


It was hydrogen bonding.
Original post by sharon800
i have made so many silly mistakes, especially the reducing agent bit - i put sulphur, so 1 mark gone
then that molecular dipole question where i put the dipoles cancel is eachother out do the symmetry! so that wrong too, and i got the molecular formula wrong!
im sure i've made few other silly mistakes too, but how much is it for an A and can you get an A after all those silly mistakes :afraid:


Although in real life that molecule does have a dipole.... OCR B Chemistry is far from real life. Some of the mechanisms we learn in the course for example are far from the truth.

I think based on the previous part of the question (the way it got you to mark all symmetrical dipoles on that diagram) that it was non-polar.
But it quite easily could have been polar because it is after all polar in reality.

And don't worry you can make pretty much 20 little mistakes (1 mark a pop) and still get an A. What usually happen will be people make some silly mistakes in which they drop the odd mark here and there and then probably completely miss the mark on one of the explain questions.
Original post by 4 Mathlete the win


I think based on the previous part of the question (the way it got you to mark all symmetrical dipoles on that diagram) that it was non-polar.
But it quite easily could have been polar because it is after all polar in reality.


This is exactly why I wrote 'it is symmertrical so the charges cancel out'. Initially, the first thing that came to mind was 'fluorine is the most electronegative so there must be a dipole'. But then I think I re-read the question way too many times, overanalysed it, so then felt that if they're asking us specifically to use our answers to the previous questions then the symmetry thing makes more sense.

Ah well, we'll see what happens.
Original post by SimpleGirl
This is exactly why I wrote 'it is symmertrical so the charges cancel out'. Initially, the first thing that came to mind was 'fluorine is the most electronegative so there must be a dipole'. But then I think I re-read the question way too many times, overanalysed it, so then felt that if they're asking us specifically to use our answers to the previous questions then the symmetry thing makes more sense.

Ah well, we'll see what happens.


Yeah you're supposed to use art 1 and 2 to answer 3 so I agree. It was only 2 marks anyway :smile:
Original post by hayleyvictoria
Really rather regretting reading this now!! :')
2C. I thought was HYDROGEN BONDING, not PD-PD.. anyone else think the same? :\


Original post by sharon800
i think it might have been hydrogen bonding, since the chain contained -OH groups :smile:


I put hydrogen bonding too. :yy:
Reply 1416
Does anyone remember the titration and energy questions?
Original post by Waki
Does anyone remember the titration and energy questions?


I vaguely remember doing:

a) 340 x 1000 = 340000
340000/(6.02x1023) = 5.65 x 10-19

b) 5.65 x 10-19/(6.62x10-34) = 8.53x1014

Does any of that seem familiar to you?
Or am I just remembering random numbers :colondollar:
Original post by SimpleGirl
I vaguely remember doing:

a) 340 x 1000 = 340000
340000/(6.02x1023) = 5.65 x 10-19

b) 5.65 x 10-19/(6.62x10-34) = 8.53x1014

Does any of that seem familiar to you?
Or am I just remembering random numbers :colondollar:


for the first bit i think i got 6.52 * 10^-4 or was that for different question?
Reply 1419
Original post by dongonaeatu
that is wrong

you should know hydrogen bonding is the stronger intermolecular bond


:frown:

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