Download 1. Hydrolysis of a dipeptide, W, produces two amino acids, X and Y

1.
Hydrolysis of a dipeptide, W, produces two amino acids, X and Y.
(a)
The chromatogram formed by an aqueous solution of the amino acids X and Y, with a
butan-1-ol/ethanoic acid/water mixture, is shown below.
Calculate the Rf value for each acid, clearly showing any measurements that you make.
(2)
(b)
An aqueous solution of X has no effect on the plane of plane-polarised light.
An aqueous solution of Y rotates the plane of plane-polarised light.
Identify amino acids X and Y. Refer to the table on page 436 of the Students’ Book.
X ..................................................................................................................................
Y ..................................................................................................................................
(2)
(c)
Suggest why each of these amino acids moves a different distance up the chromatogram.
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High Storrs School
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(d)
What feature of the molecule of Y causes its aqueous solution to rotate the plane of
plane-polarised light?
Draw appropriate formulae for Y to illustrate your answer.
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(2)
(e)
Draw the TWO possible structural formulae of the dipeptide, W.
(2)
(Total 9 marks)
High Storrs School
2
2.
(a)
(i)
Draw a fully labelled diagram of the Born-Haber cycle for the determination of the
lattice energy of calcium chloride.
Calculate the lattice energy of calcium chloride using your Born-Haber cycle.
Give your answer to four significant figures.
(5)
(ii)
Give a reason for the difference between your value and the theoretical value, from
the Book of Data, for the lattice energy of calcium chloride.
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(1)
High Storrs School
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(b)
Give the ionic radii, ri, for the germanium ion, Ge4+, and the chloride ion, Cl–, using
Table 4.4 in the Book of Data.
Predict the type of bond between germanium and chlorine, and the structure of
germanium(IV) chloride, using your values and Fajans’ rules.
Justify your answer.
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(4)
(c)
(i)
Write a balanced equation, with state symbols, showing what happens when
calcium chloride is added to water.
(1)
(ii)
Suggest a balanced equation, with state symbols, for the reaction which occurs
when germanium(IV) chloride is added to water.
(1)
(Total 12 marks)
High Storrs School
4
3.
(a)
A liquid hydrocarbon, A, has the molecular formula C6H10.
A has a boiling point of 356.5 K.
On complete combustion, 4.1 g of A forms 7.2 dm3 of carbon dioxide, and 4.5 g of water.
[Molar volume of a gas is 24 dm3 under the conditions of the experiment.]
(i)
Write the empirical formula of A and use the combustion data to show that the
empirical formula is correct.
Empirical formula of A .........................................................................................
(3)
(ii)
A reacts with an excess of bromine water to form B, C6H10Br2. Suggest structural
formulae of A and B.
(2)
(iii)
B reacts with ammonia to produce C, C6H14N2. Give the structural formula for C.
State appropriate conditions, and write the balanced equation, for this reaction.
(4)
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(b)
Compound C reacts with hexanedioyl dichloride to produce a polymer.
Draw the structure of part of the polymer to show TWO repeating units.
State the type of polymerisation involved in making this polymer.
(2)
(Total 11 marks)
4.
This question is about hydrogen peroxide, H2O2, and its decomposition.
(a)
Draw a ‘dot and cross’ diagram to show the electron structure for hydrogen peroxide,
showing outer electrons only.
Draw a displayed formula to show the shape of a molecule of hydrogen peroxide.
State the OOH bond angle.
(3)
(b)
Hydrogen peroxide is a liquid at room temperature. Suggest the principal intermolecular
force between hydrogen peroxide molecules.
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(1)
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(c)
Hydrogen peroxide decomposes slowly at room temperature.
2H2O2(aq) → O2(g) + 2H2O(l)
(i)
Explain, using oxidation numbers, why this is a disproportionation reaction.
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(2)
(ii)
Suggest, with a reason, the sign of the entropy change of the system for this
reaction.
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(1)
(d)
The reaction in (c) is catalysed by iron(II) ions in aqueous solution, Fe2+(aq).
(i)
What type of catalyst are iron(II) ions in this reaction?
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(1)
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(ii)
Add the electrode potentials and half equations relevant to the decomposition of
hydrogen peroxide to the chart below, using the items of data numbered 65 and 102
in Table 6.1 in the Book of Data.
Use the chart to suggest how iron(II) ions catalyse this reaction.
E /V
+0.5
Fe 3+ + e–
Fe 2+
+1.0
+1.5
+2.0
+3
+2
+1
0
–1
–2
Oxidation
number
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(3)
(Total 11 marks)
5.
This question is about the element chromium and its compounds.
(a)
(i)
State the full electronic configuration of a chromium atom in the ground state, using
the s,p,d notation.
(1)
High Storrs School
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(ii)
Apart from differing numbers of electrons, how does the ground state electronic
configuration of chromium differ from those of the two adjacent elements in the
Periodic Table, vanadium and manganese? Suggest the reason for this difference.
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(2)
(b)
Compounds containing the chromium(II) ion, Cr2+, are unstable in aqueous solution
because they are readily oxidised by oxygen in the air.
State the appropriate electrode potentials and half-cells, and use them to explain why this
oxidation takes place.
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(3)
(c)
A useful method of stabilising an unstable oxidation state is to form a complex. You may
have prepared chromium(II) ethanoate, Cr2(CH3CO2)4(H2O)2, where the Cr2+ ion is
stabilised in this way. [Details can be found on pages 464–465 of your Students’ Book.]
(i)
Explain how water acts as a monodentate ligand in this complex.
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(2)
High Storrs School
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(ii)
What type of ligand is the ethanoate ion in this complex?
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(1)
(iii)
Deduce the number of hydrogen peaks in the NMR spectrum of the complex from
the structural formula Cr2(CH3CO2)4(H2O)2. Justify your answer.
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(2)
(iv)
Suggest TWO characteristic absorptions in the infra-red spectrum of the complex.
You should state the bond associated with each absorption and give the
corresponding absorption value in wavenumbers.
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(2)
(d)
(i)
C2H6O +
When first introduced, breathalysers used acidified sodium dichromate(VI) crystals
to detect ethanol on the breath. Using oxidation numbers, or otherwise, balance the
equation for the reaction.
Na2Cr2O7 +
H2SO4 →
C2H4O +
Cr2(SO4)3 +
H2O +
Na2SO4
(2)
(ii)
State the colour change you would expect to see if exhaled air containing an
excessive amount of ethanol reacted with the breathalyser chemicals.
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(1)
High Storrs School
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(iii)
What hazard is associated with the use of sodium dichromate(VI)?
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(1)
(Total 17 marks)
High Storrs School
11