OCR Salters Chemistry F335 12th June 2013 Exam revision thread

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??

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!

A weak acid partially dissociates in water, it is in equilibrium with its salt and protons.

Generic Answers:

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.

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.

Gas liquid is part of the F335 spec- what question was that because I was gonna ask you to add it to your generic answers :P

But we're expected to know all the experimental techniques for this unit anyway as it's the final unit and very synoptic

Sample X is injected into the carrier gas stream and passes into the column of the gas-liquid chromatograph,

Describe the contents of the column, how the temp is maintained, the measurement that distinguishes the gases.

1) The column consists of a high boiling point liquid
2) that is spread upon a porous support.
3) The temp is maintained using a thermostatically controlled oven.
4) The retention time is used to distinguish between different gases.
5) QOWC

I dont understand jan 2011, question 2 d).

Its asking for an energy level diagram to show why;

- atomic emmision spec of Cu consists of a series of lines
- the lines of arsenic spec are at different frequencies.

I know why I just dont know how I would draw a diagram to show this.. anyone have any idea?!

thanks

I dont understand jan 2011, question 2 d).

Its asking for an energy level diagram to show why;

- atomic emmision spec of Cu consists of a series of lines
- the lines of arsenic spec are at different frequencies.

I know why I just dont know how I would draw a diagram to show this.. anyone have any idea?!

thanks

Are you sure we need to know the experimental techniques? They're not in the F335 spec.