Anal symptoms to anal obliteration: quackery in proctology ...
Option a Modern Anal
14
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Transcript of Option a Modern Anal
1. Phenolphthalein is colourless at pH 7 but its structure changes at pH 11 and it becomes pink.
The structures of the compound at these two pH values are shown below.
Deduce the colours of the two structures and explain, in terms of the bonding, why one is
coloured and the other is not.
Structure A:
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Structure B:
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Explanation:
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2. Copper(II) sulfate forms a pale blue aqueous solution. When aqueous ammonia is added to this,
initially a pale blue precipitate forms; this precipitate then dissolves in excess ammonia to form
a deep blue solution. Explain why these solutions are coloured and the colour with excess
ammonia is a deeper blue.
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3. Gas-liquid chromatography (GLC) is a powerful analytical technique. Outline the principles of
this technique, from the injection of the sample.
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4. The structures of retinol and cholesterol are given in Table 21 of the Data Booklet.
Both are slightly soluble in a colourless non-polar solvent. Explain why retinol forms a
coloured solution whereas the solution of cholesterol remains colourless.
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5. When excess ammonia solution is added to a solution of copper(II) sulfate the oxidation
number of the copper ion does not change but there is a noticeable colour change.
Outline the reasons for this change in colour.
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6. A mixture of two alcohols was analysed using high-performance liquid chromatography,
HPLC, and produced chromatogram 1 below. In the space provided in chromatogram 2, sketch
the chromatogram if the column of the chromatograph was less tightly packed and all other
variables were kept constant.
(Total 2 marks)
7. (a) Identify a possible mobile phase and stationary phase for HPLC and gas-liquid
chromatography, GLC.
Chromatographic
techniqueStationary phase Mobile phase
HPLC
GLC
(4)
(b) Deduce which technique, HPLC or GLC, can be used to analyse the urine sample of an
athlete for the anabolic steroid, tetrahydrogestrinone, THG.
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(c) Outline how the technique selected in part (b) would be carried out to confirm the
presence of the steroid THG in the urine sample.
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(Total 7 marks)
8. β-carotene is involved in the formation of vitamin A. Its sources include carrots, broccoli and
dark, leafy vegetables. Its structure is shown below.
Explain whether β-carotene absorbs ultraviolet or visible radiation.
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9. Although both lead, Pb, and chromium, Cr, are metals, only chromium is classified as a
transition metal and forms transition metal complexes, such as [Cr(H2O)6]3+.
(i) The energy level diagram showing the electrons in the five 3d orbitals of a chromium
atom is represented below. Draw the completed diagram showing the d orbitals in
[Cr(H2O)6]3+ after splitting.
(1)
(ii) State and explain what happens to the splitting of the d orbitals if the ligand is changed
from H2O to NH3.
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(Total 3 marks)
10. A feature of some 1H NMR spectra is the electron-withdrawing effect of electronegative atoms.
These atoms cause nearby protons to produce peaks at higher chemical shift values, often in the
range 2.5 to 4.5 ppm.
Consider the 1H NMR spectrum of an unknown compound, D, which has a molecular formula
C4H8O2 and is known to have an absorption in its IR spectrum corresponding to a C=O
absorption.
Use this information and the values in Table 18 of the Data Booklet to deduce the structure of
D.
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11. The wavelength of colour absorbed by a transition metal complex can be explained in terms of
the splitting of the d orbitals in the metal ion.
(i) For the complex, [Ni(NH3)6]Cl2, draw a diagram showing the splitting of the d orbitals.
(2)
(ii) Outline why colour depends on the oxidation state of the transition metal.
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(iii) The complex [Ni(NH3)6]Cl2 is purple. Predict the colour of the [Ni(H2O)6]Cl2 complex
and explain your answer.
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(Total 5 marks)
12. Describe briefly how a double-beam IR spectrometer operates.
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(1)
(iii) The complex [Ni(NH3)6]Cl2 is purple. Predict the colour of the [Ni(H2O)6]Cl2 complex
and explain your answer.
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(Total 5 marks)
13. (a) Identify the feature that allows some organic molecules to absorb UV radiation.
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(b) The wavelengths at which three compounds absorb UV radiation most strongly are given
in the following table.
Compound Wavelength / nm
1,4-pentadiene 177
1,3-pentadiene 223
1,3,5-hexatriene 258
Explain why the wavelength increases down the table.
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(Total 5 marks)
14. The complex ion [Ni(H2O)6]2+ is green and [Ni(NH3)6]2+ is blue. Explain why the [Ni(H2O)6]2+
complex ion is coloured and outline why changing the identity of the ligand changes the colour
of the ion.
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15. The colours of transition metal complexes depend on several factors.
(a) Use [Mn(H2O)6]2+ and [Fe(H2O)6]2+ as examples to outline why the colours depend on
the identity of the transition metal.
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(b) Outline why the colour depends on the oxidation state of the transition metal.
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(Total 4 marks)
16. An analgesic tablet contains 400 mg of aspirin and 80 mg of caffeine. The molecular formula of
aspirin is C9H8O4 and that of caffeine is C9H10N4O2.
(a) State and explain which method, gas-liquid chromatography (GLC) or high performance
liquid chromatography (HPLC), would be best for the separation and mass determination
of aspirin and caffeine in the tablet.
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(b) State and explain which of the two components would have the shorter retention time.
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(c) Sketch a chromatograph for the separation of the aspirin and caffeine in the analgesic
tablet.
time
(2)
(Total 6 marks)
