x Turn on thread page Beta
 You are Here: Home

# OCR Salters Chemistry F335 12th June 2013 Exam revision thread watch

1. (Original post by twizzzzzzter)
Can anyone explain June 2012 1) d) i) ?
You have been given the ratio of nitrogen to oxygen (4:1)

so if you use this to get 5 moles multiplied by 24 dm3 = 120dm3.

1mole oxygen/120dm3 = 8.3x10-3

to get concentration of N2 you multiply [O2] by 4 to get 0.0333...
2. (Original post by tsr1)
Why can't arenes be hydrogenated?
they can can't they?

H2 + finely divided Ni
300degrees and 30 atm

arene to cycloalkane
3. (Original post by gstarwill)
because arenes have a delocalised system of electrons making them very stable, if they are hydrogenated (by addition), they lose stability. Arenes undergo substitution to retain stability

Correct me if I'm wrong but I think thats right
They can be hydrogenated, but just require a lot of energy to do so (300 degrees C) and platinum /finely divided nickel catalyst as mentioned above.
4. (Original post by gstarwill)
You have been given the ratio of nitrogen to oxygen (4:1)

so if you use this to get 5 moles multiplied by 24 dm3 = 120dm3.

1mole oxygen/120dm3 = 8.3x10-3

to get concentration of N2 you multiply [O2] by 4 to get 0.0333...
ahhh thanks very much! I was also getting stuck on this :P
5. (Original post by billybobs)
They can be hydrogenated, but just require a lot of energy to do so (300 degrees C) and platinum /finely divided nickel catalyst as mentioned above.
(Original post by Tikara)
they can can't they?

H2 + finely divided Ni
300degrees and 30 atm

arene to cycloalkane
Thanks
6. (Original post by strawberri)

You know that, because it is in equilibrium:

Ka = [H+][HPO42-]/[H2PO4-]

So....

Ka/[H+] = [HPO42-]/[H2PO4-]

In a solution with pH 7:
pH = -log[H+]
[H+] = 10-pH = 10-7

It tells you what Ka is so you can write this equation:

[HPO42-]/[H2PO4-] = 6.2 x 10-8 / 1 x 10-7
= 0.62

This is how many times the concentration of [H2PO4-] goes into the concentration of [HPO42-] .

The question tells us that the concentration of (Na2)[HPO42-] is 0.1moldm-3.

0.1/0.62 = [H2PO4-] = 0.161
Seeing as this is in a solution of 1.0dm3, we can take this as the number of moles of NaH2PO4-.

number of moles = mass / Mr
mass = number of moles x Mr = 0.161 x 120 = 19.32 = 19.3g

Hope this helped!

Also for 5bi...in a weak acid (indicated by the equilibrium), we assume that [H+] = [A-] because we assume that the amount of H2PO4- has dissociated equally into H+ and HPO42-, due to the 1:1 molar ratio between the products.
Ohhhh! Thank you so muchhh !!!!
Though I'm quite unsure about the weak acid... how would you know if it's a weak acid or not??
7. (Original post by gstarwill)
You have been given the ratio of nitrogen to oxygen (4:1)

so if you use this to get 5 moles multiplied by 24 dm3 = 120dm3.

1mole oxygen/120dm3 = 8.3x10-3

to get concentration of N2 you multiply [O2] by 4 to get 0.0333...
thanks, but how do you get to the 8.3x10-3?
8. (Original post by twizzzzzzter)
thanks, but how do you get to the 8.3x10-3?
conc = mole/volume

mole O2 = 1

vol = 120dm3

1/120 = 8.3x10-3
9. Revision is going well but then i start the June 2012 paper :| Question 2 is so so hard why is this happening

Why does a Dye appeared coloured whereas benzene appears colourless? 5/6 marks

1) A dye has a greater chromophore which has more delocalisation, and
2) therefore requires less energy to excite electrons
3) so can absorb light energy in the visible region of the electromagnetic spectrum
4) transmitting the colour complementary to that of the frequency of light absorbed.
5) Benzene has less delocalisation, so its electrons require more energy to excite
6) So absorbs light in the Ultraviolet region of the electromagnetic spectrum, which appears colourless because we cannot see UV light.
7) Delta E = hv - the frequency of light is proportional to the energy gap.

What is meant by the circular ring in the structure of benzene? 2/3 marks

1) The ring symbolises delocalised electrons
2) That exist above and below the plane of benzene/the ring of carbon atoms
3) And exist over the whole molecule (i.e they are not associated with a single atom)
4) Each carbon atom provides 1 delocalised electron

Explain the origin of colour in transition metal complexes, and why the colour varies with the nature of the ligand (5/6 marks)

1) Delta E = hv - the frequency of light absorbed is proportional to that the difference in energy levels.
2) Transition metals have partially filled d-orbitals (electrons)
3) Ligands cause splitting of the d-orbitals into higher and lower energy levels,
4) When the complex absorbs a frequency of visible light it promotes an electron into the higher energy level
5) Transmitting the colour complementary to that of the frequency of light absorbed
6) Different ligands cause different amounts of splitting = altered differences in energy levels of the d-orbitals.

Describe how you could use a colorimeter to determine the concentraion of X in a sample 5 marks

1) Zero the colorimeter using a cuvette containing distilled water
2) Find a filter that is the complementary colour to that of the sample
3) Make a range of solutions of concentrations above and below that of the sample (by dilution)
4) Measure the absorbance of these solutions
5) Plot a graph of absorbance vs concentration
6) Draw a calibration curve
7) Measure absorbance of sample and read concentration from calibration curve.

Describe how you could purify a sample of X 4/5 marks

1) Find a suitable solvent that a the solid is very soluble in at high temperatures, but is almost insoluble in at low temperatures
2) Dissolve solid in a minimum quantity of hot solvent
3) Cool the sample
4) Filter, and retain fitrate
5) Wash and dry to obtain pure crystals.

Describe how you could use thin-laye chromatography to show X and Y are present in a sample 4/5 marks

1) Draw pencil line 1cm above the bottom of the TLC plate and place sample spots on line
2) Place TLC plate in beaker of solvent, ensuring that solvent doesnt reach the pencil line
3) Cover beaker, and allow time for solvent to rise up TLC plate
4) When solvent reaches the top of the TLC plate, remove plate and dry
5) Apply locating agent (UV light, ninhydrin)
6) Calculate rf value = Distance moved by spot/Distance moved my solvent and compare with known rf values.

Explain the meaning of the term buffer solution and explain its use. 4/5 marks

1) A solution that resists small changes in pH
2) Despite addition of small amounts of acid/alkali
3) Reservoir of [A-]
4) Buffer solutions are useful in instances such as the body
5) Where a required pH is required to be maintained - such as that of the environment that enzymes are found in to prevent the disruption of ionic bonds.
11. (Original post by RainieXD)
Ohhhh! Thank you so muchhh !!!!
Though I'm quite unsure about the weak acid... how would you know if it's a weak acid or not??
A weak acid partially dissociates in water, it is in equilibrium with its salt and protons.
12. OK need help with Q2 June 2012.

Why is CO2 the product in A i, why isn't it methanoic acid.

Why is the answer what it is and not an anhydride in e).

Why is the product ammonia G iv.

Thanks!
13. (Original post by billybobs)
these are awesome thanks!
14. For hydrogen bonding the marks heme says the bond should be O-H-O in straight line but for N-H would it be N-H-O?
15. (Original post by Salmonidae)
OK need help with Q2 June 2012.

Why is CO2 the product in A i, why isn't it methanoic acid.

Why is the answer what it is and not an anhydride in e).

Why is the product ammonia G iv.

Thanks!
Just did that paper and got the same answers as you!
Edit:
For 2a(i) you start with C4H6O5 and end up with C3H6O3 so you can see that CO2 is lost
16. Also in question 3/e iv How has glycerin have 4 peaks when there are clearly not 4 electron environment?? (JUN 13)
17. (Original post by billybobs)
A weak acid partially dissociates in water, it is in equilibrium with its salt and protons.
Ahhh thank you haha feel dumb for asking that now haha ^^! Rep for you :3
18. (Original post by billybobs)

Why does a Dye appeared coloured whereas benzene appears colourless? 5/6 marks

1) A dye has a greater chromophore which has more delocalisation, and
2) therefore requires less energy to excite electrons
3) so can absorb light energy in the visible region of the electromagnetic spectrum
4) transmitting the colour complementary to that of the frequency of light absorbed.
5) Benzene has less delocalisation, so its electrons require more energy to excite
6) So absorbs light in the Ultraviolet region of the electromagnetic spectrum, which appears colourless because we cannot see UV light.
7) Delta E = hv - the frequency of light is proportional to the energy gap.

What is meant by the circular ring in the structure of benzene? 2/3 marks

1) The ring symbolises delocalised electrons
2) That exist above and below the plane of benzene/the ring of carbon atoms
3) And exist over the whole molecule (i.e they are not associated with a single atom)
4) Each carbon atom provides 1 delocalised electron

Explain the origin of colour in transition metal complexes, and why the colour varies with the nature of the ligand (5/6 marks)

1) Delta E = hv - the frequency of light absorbed is proportional to that the difference in energy levels.
2) Transition metals have partially filled d-orbitals (electrons)
3) Ligands cause splitting of the d-orbitals into higher and lower energy levels,
4) When the complex absorbs a frequency of visible light it promotes an electron into the higher energy level
5) Transmitting the colour complementary to that of the frequency of light absorbed
6) Different ligands cause different amounts of splitting = altered differences in energy levels of the d-orbitals.

Describe how you could use a colorimeter to determine the concentraion of X in a sample 5 marks

1) Zero the colorimeter using a cuvette containing distilled water
2) Find a filter that is the complementary colour to that of the sample
3) Make a range of solutions of concentrations above and below that of the sample (by dilution)
4) Measure the absorbance of these solutions
5) Plot a graph of absorbance vs concentration
6) Draw a calibration curve
7) Measure absorbance of sample and read concentration from calibration curve.

Describe how you could purify a sample of X 4/5 marks

1) Find a suitable solvent that a the solid is very soluble in at high temperatures, but is almost insoluble in at low temperatures
2) Dissolve solid in a minimum quantity of hot solvent
3) Cool the sample
4) Filter, and retain fitrate
5) Wash and dry to obtain pure crystals.

Describe how you could use thin-laye chromatography to show X and Y are present in a sample 4/5 marks

1) Draw pencil line 1cm above the bottom of the TLC plate and place sample spots on line
2) Place TLC plate in beaker of solvent, ensuring that solvent doesnt reach the pencil line
3) Cover beaker, and allow time for solvent to rise up TLC plate
4) When solvent reaches the top of the TLC plate, remove plate and dry
5) Apply locating agent (UV light, ninhydrin)
6) Calculate rf value = Distance moved by spot/Distance moved my solvent and compare with known rf values.

Explain the meaning of the term buffer solution and explain its use. 4/5 marks

1) A solution that resists small changes in pH
2) Despite addition of small amounts of acid/alkali
3) Reservoir of [A-]
4) Buffer solutions are useful in instances such as the body
5) Where a required pH is required to be maintained - such as that of the environment that enzymes are found in to prevent the disruption of ionic bonds.
Are you sure we need to know the experimental techniques? They're not in the F335 spec.
19. (Original post by AmirHabeeb)
Are you sure we need to know the experimental techniques? They're not in the F335 spec.
Indeed they aren't, but I just thought I'd throw them in anyways!
20. (Original post by AmirHabeeb)
Are you sure we need to know the experimental techniques? They're not in the F335 spec.
I just found a question on what's required for Gas Liquid chromatography, from the June 2008 design paper, although it is the old spec.

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: February 3, 2014
Today on TSR

### Been caught plagiarising...

...for the 2nd time this year

### More snow?!

Discussions on TSR

• Latest
Poll
Useful resources

Can you help? Study Help unanswered threadsStudy help rules and posting guidelines

## Groups associated with this forum:

View associated groups
Discussions on TSR

• Latest

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE