Download 1 [Turn Over Section A For each question there are four possible

1
SAJC H2 Chemistry 2014 Prelims Paper 1
Section A
For each question there are four possible answers, A, B, C and D. Choose the one you
consider to be correct.
1.
A solid hydrocarbon was completely combusted in a closed vessel at 120 oC. The
residual gas had a volume of 64 cm3, which decreased by 24 cm3 after bubbling
through a dehydrating agent. After this, 40% of the final gas volume consisted of
oxygen. What is the empirical formula of the hydrocarbon?
2.
A
CH
B
CH2
C
CH3
D
C2H3
When cobalt metal is reacted with a solution containing cobalt(III) ions, cobalt(II) ions
are formed. How many moles of Co and Co3+(aq) would result in a mixture containing
both cobalt(II) and cobalt(III) ions in the mole ratio of 3:1 after the reaction had taken
place?
Moles of Co
3.
Moles of Co3+
A
1
2
B
1
3
C
1
5
D
2
3
Which graph does not share the same general shape with the other three graphs
according to the ideal gas law for a fixed mass of gas?
A
pV against p (at constant T)
B
V/T against T (at constant p)
C
p against V (at constant T)
D
pV against V (at constant T)
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4.
5.
Which element will possess an empty s orbital after forming a singly-charged cation?
A
Barium
B
Vanadium
C
Copper
D
Gallium
Which of the following reactions will form a product with the same shape as the
reactant with respect to the underlined element?
6.
A
2AlCl3 Al2Cl6
B
2H2O2 2H2O + O2
C
PCl3 + Cl2 PCl5
D
CH3CH2CHO + [O] CH3CH2COOH
Which of the following is arranged correctly in the order of decreasing melting points?
A
Sulfur > Chlorine > Argon
B
Carbon dioxide > Silicon dioxide > Germanium dioxide
C
Beryllium chloride > Magnesium chloride > Calcium chloride
D
Sodium > Magnesium > Aluminium
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7.
A student dissolved 0.238 mol of sodium fluoride in 300 cm3 of water.
Given the following data:
−1
Lattice energy of NaF
Enthalpy change of hydration of F
−918 kJ mol
−
−1
−457 kJ mol
+
Enthalpy change of hydration of Na
−1
−390 kJ mol
What would be the initial temperature of the water if the final temperature of the solution
o
is 20.00 C?
−1
−1
Assume that the specific heat capacity of sodium fluoride solution is 4.18 J g K .
o
A
6.52 C
B
13.48 C
C
20.00 C
D
33.48 C
o
o
8.
o
Ammonia gas and hydrogen chloride gas react to form ammonium chloride as shown in
the equation below:
NH3 (g) + HCl (g) → NH4Cl (s)
∆Ho = −176 kJ mol−1
The standard entropy change of this reaction is −284 J K−1 mol−1.
Which of the following statements is not correct?
A
At room temperature, ∆Go = +84.4 kJ mol−1.
B
The reactants are less stable than the product.
C
The reaction is spontaneous at low temperatures and non-spontaneous at high
temperatures.
D
There is a decrease in the degree of disorderliness.
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9.
The following experimental results are obtained for a reaction with the general rate
equation of:
rate = k [M]x [N]y [L]
Experiment
[M] / mol dm-3
[N] / mol dm-3
[L] / mol dm-3
Relative rate
1
0.1
0.2
0.3
1
2
0.2
0.6
1.2
72
Which of the following are possible values of x and y?
10.
x
y
A
1
1
B
2
1
C
1
2
D
2
2
Which of the following will decrease the rate constant for a reaction?
A
Decrease in concentration
B
Decrease in temperature
C
Decrease in pressure
D
Addition of catalyst
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11.
Phosphorus trichloride and chlorine react according to the following equation:
PCl3(g) + Cl2(g)
PCl5(g)
A mixture of PCl3 and Cl2 was placed in a syringe and brought to equilibrium at time t and
the following graph was obtained.
Which of the following accounts for the drop in [PCl3] at time t?
12.
13.
A
PCl5 was added to the mixture
B
Argon gas was added to the mixture
C
The syringe was heated
D
The plunger of the syringe was withdrawn until the volume was twice the initial
volume
Which of the following statements about phosphoric(V) acid is not correct?
A
HPO42- has a higher Kb value than H2PO4-.
B
PO43- can react as a base.
C
H2PO4- can react both as an acid and as a base.
D
H3PO4 has a higher pKa than HPO42-.
95 cm3 of M2+ ions is mixed with an an equal volume of X- ions at 25oC. Which of the
following initial concentrations of M2+ and X- will result in the precipitation of MX2?
(Ksp of MX2 = 7.67 x 10-13 mol3 dm-9)
[M2+] / 10-4 mol dm-3
[X-] / 10-4 mol dm-3
A
1
1
B
1
2
C
2
1
D
2
2
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14.
Use of the Data Booklet is relevant to this question.
Glucose can be reacted with silver ions to form a silver mirror in the following reaction.
C6H12O6 + 2Ag+ + H2O 2Ag + C6H12O7 + 2H+
Ecell = +0.75 V
Which of the following metal ions cannot be used for a possible reaction with glucose?
15.
A
Mn3+
B
V3+
C
Fe3+
D
Co3+
Use of the Data Booklet is relevant to this question.
The following reaction does not occur under standard conditions.
2NO3─ (aq) + 8H+ (aq) + 6Cl─ (aq)
2NO (g) + 4H2O (l) + 3Cl2 (g)
Which of the following can result in the reaction occuring?
16.
A
Decreasing the volume of the reaction vessel
B
Addition of nitrogen monoxide
C
Decreasing the pH
D
Addition of chlorine
The properties of the oxides of four Period 3 elements W, X, Y and Z are given below.
•
The oxide of W is insoluble in water and in dilute acid but soluble in concentrated
sodium hydroxide.
•
The oxide of X is amphoteric.
•
The oxide of Y reacts with dilute potassium hydroxide at room temperature.
•
The oxide of Z dissolves in water to form a solution of pH = 13.
Which of the following is correct in order of increasing atomic number?
A
Z, X, W, Y
C
Z, W, X, Y
B
W, X, Y, Z
D
Z, Y, W, X
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17.
The following graphs show how two properties of the elements, Na to P, and their
compounds, vary with proton number.
11
12
13
14
15
11
12
13
14
proton number
proton number
Graph 1
Graph 2
15
What properties are shown by the two graphs?
Graph 1
Graph 2
A
Melting point of oxide
Conductivity of element
B
Melting point of oxide
Melting point of chloride
C
Melting point of chloride
Melting point of oxide
D
Melting point of element
Conductivity of element
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18. A student observed the reactions when sodium chloride was added separately to
concentrated sulfuric acid and concentrated phosphoric acid. The experiment was
repeated using sodium iodide.
Reagent
Observation with
sodium chloride
Observation with
sodium iodide
conc. H2SO4
white fumes evolved
purple vapour evolved
conc. H3PO4
white fumes evolved
white fumes evolved
Which deduction can be made from these observations?
A
The reducing power of HI is greater than that of HCl.
B
The bond length of HI is smaller than that of HCl.
C
Concentrated phosphoric acid is a stronger oxidising agent than concentrated
sulfuric acid.
D
Basicity of concentrated phosphoric acid is greater than concentrated sulfuric acid.
19. The following data refer to cobalt as a typical transition element and calcium as an
s-block element.
Which of the following properties shows the correct data for both elements?
Property
Cobalt
Calcium
A
Metallic radius / nm
0.150
0.117
B
Electrical conductivity /
relative units
10.1
50
C
Melting point / oC
1495
1965
D
Density / g cm-3
8.9
1.54
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20. Which of the following cannot act as a ligand?
21.
A
AlH4-
B
N2H4
C
CH3OH
D
CO
The following compound is reacted with LiAlH4 in dry ether.
What is the number of stereoisomers the product would possess?
A
26
B
27
C
28
D
29
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22.
Which statement with regards to the reaction of monobromination of benzene is
correct?
A
This is considered a nucleophilic substitution reaction.
B
The intermediate consists of 4 pi electrons.
C
The intermediate is planar.
D
Upon addition of ethanolic silver nitrate solution to bromobenzene, a cream
precipitate would be observed.
23.
The compound below was reacted with hot alkaline potassium manganate(VII)
solution.
Which statement is correct?
A
The organic products consist of a total of 2 sp2 hybridised carbons.
B
There are 3 chiral centres in the organic products.
C
The organic products would not form a yellow precipitate with warm alkaline
iodine solution.
D
24.
The organic products would not form an orange precipitate with 2,4–DNPH.
In the following synthesis route, which reaction mechanism is not used?
CH3CH2OH CH2=CH2 CH2XCH2X CH2(NH2)CH2NH2
A
electrophilic addition
B
elimination
C
nucleophilic substitution
D
reduction
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25.
A cyclic organic compound has the molecular formula C4H7NO2. Which pair of the
functional groups can be present in this molecule?
26.
A
one ester group and one primary amine group
B
one ester group and one nitrile group
C
one primary alcohol group and one primary amide group
D
one tertiary alcohol group and one tertiary amine group
Which statement about ethanoic acid and its derivatives is correct?
A
Ethanamide is soluble in water to form a neutral solution due to the formation of
equal proportions of ethanoic acid and ammonia.
27.
B
Ethanoic acid has a relative molecular mass of 120 in liquid hexane.
C
Ethanoyl bromide hydrolyses in water to produce reddish brown fumes.
D
Ethyl ethanoate, upon reaction with 2,4-DNPH, gives an orange precipitate.
Which compound would show the greatest ease of hydrolysis?
A
B
C
D
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28.
The compound above has a total of three nitrogen atoms (NX, NY and NZ). Which
sequence show an increase in pOH?
A
NX, NY, NZ
B
NX, NZ, NY
C
NY, NX, NZ
D
NY, NZ, NX
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29.
Two common drugs administered when a patient experiences headache or fever are
paracetamol and aspirin.
A solution of the two drugs was hydrolysed using hot aqueous sodium hydroxide.
Which organic product would be produced?
A
B
CO2-
O
O
C
30.
D
Which statement about proteins and amino acids is not correct?
A
Amino acids exist as crystalline solids at room temperature.
B
Hydrogen bonds can be found in secondary and tertiary structures of proteins
C
Denaturation of proteins leads to the breaking down of the primary structure.
D
Amino acids can act as buffer solutions.
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Section B
For each of the questions in this section, one or more of the three numbered statements 1 to
3 may be correct. Decide whether each of the statements is or is not correct (you may find it
helpful to put a tick against the statements that you consider to be correct).
The responses A to D should be selected on the basis of
A
B
C
D
1, 2 and 3 are
1 and 2 only are
2 and 3 only are
1 only is correct
correct
correct
correct
No other combination of statements is used as a correct response.
31.
32.
33.
Which of the following are disproportionation reactions?
1
3Cl2 + 6NaOH 5NaCl + NaClO3 + 3H2O
2
IO3- + 5I- + 6H+ 3I2 + 3H2O
3
15Se + SeCl4 + 4AlCl3 2Se8[AlCl4]2
Which of the following pairs are both planar and polar?
1
OCl2 and SO2
2
XeF4 and SO3
3
IF5 and H3O+
Which of the following increase with decreasing temperature for the dissociation of
water?
1
pKb
2
pH
3
pKw
Temperature/ oC
Kw/ mol2 dm -6
50
5.5 x 10-14
25
1.0 x 10-14
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A
B
C
D
1, 2 and 3 are
1 and 2 only are
2 and 3 only are
1 only is correct
correct
correct
correct
No other combination of statements is used as a correct response.
34. Use of the Data Booklet is relevant to this question.
Which of the following statements can be deduced from the diagram below?
Fe
Cu
NaCl(aq)
CuSO4(aq)
Cell 1
1
Size of the anode in Cell 1 decreases.
2
Colour of the electrolyte in Cell 2 remains the same.
3
Effervescence is observed in both cells immediately.
Cell 2
35. 0.5 mol of each of the following was added to 100 cm3 of water. Which of the following
solutions are arranged correctly in the order of increasing pH?
1
SiCl4, MgCl2, NaCl
2
H2SO4, HNO3, CH3CH2COOH
3
NH3, CH3NH2, KOH
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A
B
C
D
1, 2 and 3 are
1 and 2 only are
2 and 3 only are
1 only is correct
correct
correct
correct
No other combination of statements is used as a correct response.
36. Use of the Data Booklet is relevant to this question.
When iron filings are added to nitric acid, a yellow solution and nitrogen dioxide gas are
formed. On the addition of ammonium thiocyanate to the resultant solution, a bloodred colouration due to an iron (III) complex is formed.
Which statements are correct?
37.
1
The oxidation state of N decreases from +6 to +4 in the first reaction.
2
Redox and ligand exchange have taken place.
3
The standard cell potential of the reaction between iron filings and nitric acid is
+0.85 V.
The following steps represent a student’s attempt to synthesise angelic acid from
but-2-ene.
Unfortunately, he was unable to synthesise angelic acid. Which steps were incorrect?
1
HCl(aq), heat
2
limited Cl2, U.V.
3
Ethanolic KCN, reflux
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A
B
C
D
1, 2 and 3 are
1 and 2 only are
2 and 3 only are
1 only is correct
correct
correct
correct
No other combination of statements is used as a correct response.
38.
Which of the following reagents would react with both compounds above?
39.
1
warm alkaline iodine solution
2
warm Fehling’s solution
3
2,4–DNPH
Hydrogen iodide reacts with liquid hex-2-ene to form 2-iodohexane and 3-iodohexane.
When hex-2-ene is mixed with bromine monochloride, BrCl, dissolved in aqueous
sodium methanoate, a similar reaction occurs. Which are the possible products in the
mixture?
1
40.
2
3
Deuterium, D, is the H isotope of hydrogen. Which reactions could give an organic
compound having a chiral centre?
1
2
3
,
CH3CHO C(CH3)2=CH2 , CH3COCH3 ~~~ END ~~~
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SAJC H2 Chemistry 2014 Prelims Paper 1 Worked Solutions
1.
A solid hydrocarbon was completely combusted in a closed vessel at 120 oC. The
residual gas had a volume of 64 cm3, which decreased by 24 cm3 after bubbling
through a dehydrating agent. After this, 40% of the final gas volume consisted of
oxygen. What is the empirical formula of the hydrocarbon?
A
CH
B
CH2
C
CH3
D
C2H3
Vol of H2O = 24 cm3
Vol of CO2 = 0.6 x (64 – 24) = 24 cm3
Mole ratio of CO2 : H2O = 24 : 24 = 1 : 1
Mole ratio of C : H in CxHy = 1 : 2
2.
When cobalt metal is reacted with a solution containing cobalt(III) ions, cobalt(II) ions
are formed. How many moles of Co and Co3+(aq) would result in a mixture containing
both cobalt(II) and cobalt(III) ions in the mole ratio of 3:1 after the reaction had taken
place?
Moles of Co
Moles of Co3+
A
1
2
B
1
3
C
1
5
D
2
3
Co + 2Co3+ 3Co2+
I
1
3
0
C -1
-2
+3
1
3
F
0
(Co3+ was in excess)
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3.
Which graph does not share the same general shape with the other three graphs
according to the ideal gas law for a fixed mass of gas?
A
pV against p (at constant T)
pV = nRT
At constant T,
pV = constant
B
V/T against T (at constant p)
V/T
pV = nRT
At constant p,
nR
V = ( )T
p
C
=
= constant
T
p against V (at constant T)
pV = nRT
At constant T,
p = (nRT)
D
1
V
pV against V (at constant T)
pV = nRT
At constant T,
pV = nRT = constant
V
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4.
Which element will possess an empty s orbital after forming a singly-charged cation?
A
Barium
Ba+: [Xe]6s1
B
Vanadium
V+: [Ar]3d34s1
C
Copper
Cu+: [Ar]3d10
D
Gallium
Ga+: [Ar]4s2
5.
Which of the following reactions will form a product with the same shape as the
reactant with respect to the underlined element?
A
2AlCl3 Al2Cl6
Trigonal planar to Tetrahedral
B
2H2O2 2H2O + O2
Bent to Linear
C
PCl3 + Cl2 PCl5
Trigonal pyramidal to Trigonal bipyramidal
D
CH3CH2CHO + [O] CH3CH2COOH
Trigonal planar to Trigonal planar
6.
Which of the following is arranged correctly in the order of decreasing melting points?
A
Sulfur > Chlorine > Argon
S8 has the largest electron cloud, followed by Cl2 and Ar, hence it has the most
extentive id-id interactions.
B
Carbon dioxide > Silicon dioxide > Germanium dioxide
Silicon dioxide (giant covalent structure) should have a higher m.p than carbon
dioxide (simple covalent structure).
C
Beryllium chloride > Magnesium chloride > Calcium chloride
Beryllium chloride (simple covalent structure due to high charge density of Be2+)
should have a lower m.p than magnesium chloride.
D
Sodium > Magnesium > Aluminium
Al has the largest no. of delocalised electrons, followed by Mg and Na, hence it
has the strongest metallic bonding.
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7.
A student dissolved 0.238 mol of sodium fluoride in 300 cm3 of water.
Given the following data:
−1
Lattice energy of NaF
Enthalpy change of hydration of F
−918 kJ mol
−
−1
−457 kJ mol
+
Enthalpy change of hydration of Na
−1
−390 kJ mol
What would be the initial temperature of the water if the final temperature of the solution
o
is 20.00 C?
−1
−1
Assume that the specific heat capacity of sodium fluoride solution is 4.18 J g K .
o
A
6.52 C
B
13.48 C
C
20.00 C
D
33.48 C
o
o
o
∆H = ∆H − L. E = – 457 – 390 – (–918) = +71 kJ mol-1
(endothermic)
Heat absorbed, q = 71 x 0.238 = 16.898 kJ
∆T = -
!
"#
=-
$%&'&
())(*.$&)
= - 13.48oC
Initial T = 20 + 13.48 = 33.48oC
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8.
Ammonia gas and hydrogen chloride gas react to form ammonium chloride as shown in
the equation below:
NH3 (g) + HCl (g) → NH4Cl (s)
∆Ho = −176 kJ mol−1
The standard entropy change of this reaction is −284 J K−1 mol−1.
Which of the following statements is not correct?
A
At room temperature, ∆Go = +84.4 kJ mol−1.
∆Go = ∆Ho - T∆So = - 176 – 298(-0.284) = -91.4 kJ mol−1
B
The reactants are less stable than the product.
C
The reaction is spontaneous at low temperatures and non-spontaneous at high
temperatures.
At low T, |∆H| , |T∆S|, since both ∆H and ∆S are negative, ∆G < 0.
D
There is a decrease in the degree of disorderliness.
There is a decrease in no. of gaseous moles from 2 to 0.
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9.
The following experimental results are obtained for a reaction with the general rate
equation of:
rate = k [M]x [N]y [L]
Experiment
[M] / mol dm-3
[N] / mol dm-3
[L] / mol dm-3
Relative rate
1
0.1
0.2
0.3
1
2
0.2
0.6
1.2
72
Which of the following are possible values of x and y?
x
y
A
1
1
B
2
1
C
1
2
D
2
2
From expt 1 to 2, [M] increases by 2 times, [N] increases by 3 times and [L]
increases by 4 times, rate increases by 72 times. Order of reaction wrt [L] is 1.
A: 21 x 31 x 41 = 24
B: 22 x 31 x 41 = 48
C: 21 x 32 x 41 = 72
D: 22 x 32 x 41 = 144
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10.
Which of the following will decrease the rate constant for a reaction?
A
Decrease in concentration
B
Decrease in temperature
C
Decrease in pressure
D
Addition of catalyst
From Kinetics lecture notes,
Change
Effect on rate constant, k
Effect on EA
Increase in
concentration
No effect
No effect
Increase in pressure
(gaseous system)
No effect
No effect
Increase in temperature
Increased
No effect
Use of catalyst
Increased
Decreased
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11.
Phosphorus trichloride and chlorine react according to the following equation:
PCl3(g) + Cl2(g)
PCl5(g)
A mixture of PCl3 and Cl2 was placed in a syringe and brought to equilibrium at time t and
the following graph was obtained.
Which of the following accounts for the drop in [PCl3] at time t?
A
PCl5 was added to the mixture
B
Argon gas was added to the mixture
C
The syringe was heated
D
The plunger of the syringe was withdrawn until the volume was twice the initial
volume
Volume increases, resulting in an immediate drop in pressure. Equilibrium then
shifts left to increase the pressure by favouring the backward reaction which
produces less gaseous molecules.
12.
Which of the following statements about phosphoric(V) acid is not correct?
A
HPO42- has a higher Kb value than H2PO4-.
Ka of H3PO4 > Ka of H2PO4- > Ka of HPO42Kb of H2PO4- < Kb of HPO42-
B
since Kb = Kw / Ka
3-
PO4 can react as a base.
In presence of acid, PO43- + H+ HPO42-
C
H2PO4- can react both as an acid and as a base.
In presence of acid, H2PO4- + H+ H3PO4
In presence of base, H2PO4- + OH- HPO42- + H2O
D
H3PO4 has a higher pKa than HPO42-.
Ka of H3PO4 > Ka of H2PO4- > Ka of HPO42pKa of H3PO4 < pKa of H2PO4- < pKa of HPO42-
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13.
95 cm3 of M2+ ions is mixed with an an equal volume of X- ions at 25oC. Which of the
following initial concentrations of M2+ and X- will result in the precipitation of MX2?
(Ksp of MX2 = 7.67 x 10-13 mol3 dm-9)
[M2+] / 10-4 mol dm-3
A
[X-] / 10-4 mol dm-3
1
1
I.P = [M ][X ] = (0.5 x 10 )(0.5 x 10-4)2 = 1.25 x 10-13 mol3 dm-9 < Ksp
B
2+
-
-4
2+
-
-4
2+
-
-4
2+
-
-4
1
2
I.P = [M ][X ] = (0.5 x 10 )(1 x 10-4)2 = 5 x 10-13 mol3 dm-9 < Ksp
C
2
1
I.P = [M ][X ] = (1 x 10 )(0.5 x 10-4)2 = 2.5 x 10-12 mol3 dm-9 < Ksp
D
2
2
I.P = [M ][X ] = (1 x 10 )(1 x 10-4)2 = 1 x 10-12 mol3 dm-9 > Ksp
Precipitation occurs
14.
Use of the Data Booklet is relevant to this question.
Glucose can be reacted with silver ions to form a silver mirror in the following reaction.
C6H12O6 + 2Ag+ + H2O 2Ag + C6H12O7 + 2H+
Ecell = +0.75 V
Which of the following metal ions cannot be used for a possible reaction with glucose?
A
Mn3+
Mn3+ + e-
B
V2+
E = -0.26 V
Fe3+
Fe3+ + e-
D
E = +1.49 V
V3+
V3+ + e-
C
Mn2+
Fe2+
E = +0.77 V
Co2+
E = +1.82 V
Co3+
Co3+ + e-
Ag+ is reduced to Ag while glucose is oxidised.
Ecell = Ered - Eox = +0.75 V
Eox = 0.80 - 0.75 V = + 0.05 V
For a feasible reaction, Ecell < 0, hence Ered (Mx+/M) should be more positive
than +0.05 V.
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15.
Use of the Data Booklet is relevant to this question.
The following reaction does not occur under standard conditions.
2NO3─ (aq) + 8H+ (aq) + 6Cl─ (aq)
2NO (g) + 4H2O (l) + 3Cl2 (g)
Which of the following can result in the reaction occuring?
A
Decreasing the volume of the reaction vessel
B
Addition of nitrogen monoxide
C
Decreasing the pH
Increase in [H+] will cause equilibrium to shift right, favouring the forward reaction.
D
16.
Addition of chlorine
The properties of the oxides of four Period 3 elements W, X, Y and Z are given below.
•
The oxide of W is insoluble in water and in dilute acid but soluble in concentrated
sodium hydroxide.
•
The oxide of X is amphoteric.
•
The oxide of Y reacts with dilute potassium hydroxide at room temperature.
•
The oxide of Z dissolves in water to form a solution of pH = 13.
Which of the following is correct in order of increasing atomic number?
A
Z, X, W, Y
C
Z, W, X, Y
B
W, X, Y, Z
D
Z, Y, W, X
W is Silicon. X is Aluminium. Y is either Phosphorus or Sulfur. Z is Sodium.
[Turn Over
11
17.
The following graphs show how two properties of the elements, Na to P, and their
compounds, vary with proton number.
11
12
13
14
15
11
12
13
14
proton number
proton number
Graph 1
Graph 2
15
What properties are shown by the two graphs?
Graph 1
Graph 2
A
Melting point of oxide
Conductivity of element
B
Melting point of oxide
Melting point of chloride
C
Melting point of chloride
Melting point of oxide
D
NaCl & MgCl2 – giant ionic
NaO, MgO & Al2O3 – giant ionic
AlCl3, SiCl4 and PCl5 – simple
covalent
Si2O3 – giant covalent
Melting point of element
P4O10 – simple covalent
Conductivity of element
[Turn Over
12
18. A student observed the reactions when sodium chloride was added separately to
concentrated sulfuric acid and concentrated phosphoric acid. The experiment was
repeated using sodium iodide.
Reagent
Observation with
sodium chloride
Observation with
sodium iodide
conc. H2SO4
white fumes evolved
purple vapour evolved
conc. H3PO4
white fumes evolved
white fumes evolved
Which deduction can be made from these observations?
A
The reducing power of HI is greater than that of HCl.
NaCl + H2SO4 HCl (white fumes) + NaHSO4
(Cl- is not oxidised at all.)
NaI + H2SO4 HI + NaHSO4
HI produced is readily oxidised by conc. H2SO4 to I2, hence I- has a greater ease of
oxidation and reducing power than Cl-.
8HI + H2SO4 4I2 + H2S + 4H2O
B
The bond length of HI is smaller than that of HCl.
False, as HCl has higher bond strength (smaller bond length) than HI due to smaller
size of Cl and more effective orbital overlap.
C
Concentrated phosphoric acid is a stronger oxidising agent than concentrated
sulfuric acid.
H3PO4 is a non-oxidising acid.
D
Basicity of concentrated phosphoric acid is greater than concentrated sulfuric acid.
True, but cannot be deduced from the above observations.
[Turn Over
13
19.
The following data refer to cobalt as a typical transition element and calcium as an sblock element.
Which of the following properties shows the correct data for both elements?
A
Property
Cobalt
Calcium
Metallic radius / nm
0.150
0.117
Co has more protons than Ca, hence the nuclear charge is higher than Ca. Co also
has more electrons than Ca but the increase in shielding effect is minimal. Although
the additional 2 electrons in Co are added in an inner sub-shell, they still provide a
relatively poor shielding for the outermost 4s electrons. Hence, the valence 4s
electrons in Co experiences a greater effective nuclear charge and are attracted
more strongly to the nucleus than those in Ca, resulting in a smaller radius.
B
Electrical conductivity /
relative units
10.1
50
Cobalt should have higher conductivity than calcium due to more delocalised
electrons from 3d and 4s.
C
Melting point / oC
1495
1965
Cobalt should have higher m.p than calcium. For cobalt, both 3d and 4s electrons
are delocalised to form a ‘sea’ of electrons for strong metallic bonding. Hence, strong
electrostatic forces holding the metallic cations (which has a larger cationic charge
and smaller cationic radius) together.
D
Density / g cm-3
8.9
1.54
While the size of the atom, measured by the metallic radius, decreases slightly from
scandium to zinc, the relative atomic mass increases considerably. This results in an
increase in density from scandium to zinc. The d-block metals are, in general, denser
than the s-block metals.
[Turn Over
14
20. Which of the following cannot act as a ligand?
A
AlH4-
No available lone pair for dative bonding
B
N2H4
C
CH3OH
D
21.
CO
The following compound is reacted with LiAlH4 in dry ether.
What is the number of stereoisomers the product would possess?
A
26
B
27
C
28
D
29
[Turn Over
15
is the product, with no geometric isomers
22.
Which statement with regards to the reaction of monobromination of benzene is
correct?
A
This is considered a nucleophilic substitution reaction.
This should be electrophilic substitution
B
The intermediate consists of 4 pi electrons.
C
The intermediate is planar.
The carbon with four bonds has a tetrahedral shape
D
Upon addition of ethanolic silver nitrate solution to bromobenzene, a cream
precipitate would be observed.
Bromine is directly bonded to the benzene and hence would not likely undergo
nucleophilic substitution to form Br–. Hence no precipitation would occur.
[Turn Over
16
23.
The compound below was reacted with hot alkaline potassium manganate(VII)
solution.
Which statement is correct?
A
The organic products consist of a total of 2 sp2 hybridised carbons.
There is a total of 3 sp2 hybridised carbons.
B
There are 3 chiral centres in the organic products.
There are no chiral centres in the products.
C
The organic products would not form a yellow precipitate with warm alkaline
iodine solution.
D
The organic products would not form an orange precipitate with 2,4–DNPH.
There are 2 ketone functional groups in the products which would form an orange
precipitate with 2,4-DNPH.
[Turn Over
17
24.
In the following synthesis route, which reaction mechanism is not used?
CH3CH2OH CH2=CH2 CH2XCH2X CH2(NH2)CH2NH2
25.
A
electrophilic addition
B
elimination
C
nucleophilic substitution
D
reduction
A cyclic organic compound has the molecular formula C4H7NO2. Which pair of the
functional groups can be present in this molecule?
A
one ester group and one primary amine group
B
one ester group and one nitrile group
C
one primary alcohol group and one primary amide group
D
one tertiary alcohol group and one tertiary amine group
[Turn Over
18
26.
Which statement about ethanoic acid and its derivatives is correct?
A
Ethanamide is soluble in water to form a neutral solution due to the formation of
equal proportions of ethanoic acid and ammonia.
Ethanamide is soluble in water and remains as ethanamide molecules.
B
Ethanoic acid has a relative molecular mass of 120 in liquid hexane.
Ethanoic acid exist as a dimer in non-polar solvents.
C
Ethanoyl bromide hydrolyses in water to produce reddish brown fumes.
HBr are white fumes.
D
Ethyl ethanoate, upon reaction with 2,4-DNPH, gives an orange precipitate.
Esters do not undergo condensation reactions with 2,4-DNPH.
27.
Which compound would show the greatest ease of hydrolysis?
O
A
O
Cl
Cl
C
B
HO
I
D
OH
I
A – presence of ethanoyl chloride (an acyl chloride) which hydrolyses in water
immediately
B – alkyl bromide undergoes hydrolysis slower than acyl chlorides
C – alkyl iodides undergoes hydrolysis faster than alkyl bromide due to the
weaker C – I bond but still slower as compared to acyl chlorides.
D – chlorine is directly bonded to carbon which is part of an alkene. This results
in the C–Cl bond possessing partial double bond character, hence hydrolysis is
unlikely to take place.
[Turn Over
19
28.
The compound above has a total of three nitrogen atoms (NX, NY and NZ). Which
sequence show an increase in pOH?
A
NX, NY, NZ
B
NX, NZ, NY
C
NY, NX, NZ
D
NY, NZ, NX
NX is the nitrogen in an amide, which is neutral.
NY is the nitrogen in a tertiary amine.
NZ is the nitrogen in a N-substituted phenylamine, which has its electrons
delocalised into the benzene ring.
[Turn Over
20
29.
Two common drugs administered when a patient experiences headache or fever are
paracetamol and aspirin.
A solution of the two drugs was hydrolysed using hot aqueous sodium hydroxide.
Which organic product would be produced?
A
B
C
D
The products are:
[Turn Over
21
30.
Which statement about proteins and amino acids is not correct?
A
Amino acids exist as crystalline solids at room temperature.
Amino acids exists as zwitterions which have strong ionic bonds and hence exist
as crystalline solids at room temperature.
B
Hydrogen bonds can be found in secondary and tertiary structures of proteins.
Hydrogen bonds between peptide linkages form the secondary structure and
hydrogen bonds between R-groups form the unique 3D conformation in the
tertiary structure.
C
Denaturation of proteins leads to the breaking down of the primary structure.
Disruption of primary structure occurs during hydrolysis. Denaturation is the
process where secondary, tertiary and quaternary structures are disrupted.
D
Amino acids can act as buffer solutions.
Amino acids, upon dissolving in water, would form zwitterion, which has both
acidic and basic functional groups and hence could maintain the pH of the
solution when small amounts of acid or alkali are added.
31.
Which of the following are disproportionation reactions?
1
3Cl2 + 6NaOH 5NaCl + NaClO3 + 3H2O
2
IO3- + 5I- + 6H+ 3I2 + 3H2O
3
15Se + SeCl4 + 4AlCl3 2Se8[AlCl4]2
Disproportionation reaction is a redox reaction in which a species is
simultaneously reduced and oxidised to form two different products. The second
and third reactions show two species in different oxidation states forming one
product with another oxidation state.
[Turn Over
22
32.
Which of the following pairs are both planar and polar?
1
OCl2 and SO2
Both ben and non-polar
2
XeF4 and SO3
Square planar
Non-polar
3
IF5 and H3O+
Square pyramidal
Polar
33.
Trigonal planar
Non-polar
Trigonal pyramidal
Polar
Which of the following increase with decreasing temperature for the dissociation of
water?
1
Temperature/ oC
Kw/ mol2 dm -6
50
5.5 x 10-14
25
1.0 x 10-14
pKb
At lower T, Kw , [OH-] , Kb , pKb 2
pH
At lower T, Kw , [H+] , pH 3
pKw
At lower T, Kw , pKw [Turn Over
23
34. Use of the Data Booklet is relevant to this question.
Which of the following statements can be deduced from the diagram below?
Fe
Cu
NaCl(aq)
CuSO4(aq)
Cell 1
1
2
3
Cell 2
Size of the anode in Cell 1 decreases.
At the anode:
Cl2 + 2e2ClE = +1.36 V
+
O2 + 4H + 4e
2H2O
E = +1.23 V
2+
Fe + 2e
Fe
E = -0.44 V
3+
Fe + 3e
Fe
E = -0.04 V
Fe has the most negative E , so it will get oxidised at the anode.
Colour of the electrolyte in Cell 2 remains the same.
Electroplating of copper in Cell 2.
Anode: Cu Cu2+ + 2eCathode: Cu2+ + 2e- Cu
Effervescence is observed in both cells immediately.
[Turn Over
24
35. 0.5 mol of each of the following was added to 100 cm3 of water. Which of the following
solutions are arranged correctly in the order of increasing pH?
1
SiCl4, MgCl2, NaCl
SiCl4 (pH = 2 due to HCl fumes), MgCl2 (pH = 6.5 due to high polarising power of
Mg2+), NaCl (pH = 7)
2
H2SO4, HNO3, CH3CH2COOH
H2SO4 (strong dibasic acid), HNO3 (strong monobasic acid), CH3CH2COOH
(weak organic acid)
3
NH3, CH3NH2, KOH
CH3NH2 is more basic than NH3 due to the electron-donating methyl group which
increases the availability of the lone pair of e- on N. KOH is a strong base.
36. Use of the Data Booklet is relevant to this question.
When iron filings are added to nitric acid, a yellow solution and nitrogen dioxide gas are
formed. On the addition of ammonium thiocyanate to the resultant solution, a bloodred colouration due to an iron (III) complex is formed.
Which statements are correct?
1
The oxidation state of N decreases from +6 to +4 in the first reaction.
It should be from +5 to +4.
2
Redox and ligand exchange have taken place.
Redox: Fe is oxidised to Fe3+ and NO3- is reduced to NO2.
Ligand exchange: [Fe(H2O)6]3+ + SCN- [Fe(SCN)(H2O)5]2+ + H2O
yellow
blood-red
3
The standard cell potential of the reaction between iron filings and nitric acid is
+0.85 V.
Fe3+ + 3e-
E = -0.04 V
Fe
NO3- + 2H+ + e-
NO2 + H2O
E = +0.81 V
Ecell = +0.81 – (-0.04) = +0.85V
[Turn Over
25
37.
The following steps represent a student’s attempt to synthesise angelic acid from
but-2-ene.
Unfortunately, he was unable to synthesise angelic acid. Which steps were incorrect?
1
HCl(aq), heat
2
limited Cl2, U.V.
3
Ethanolic KCN reflux
[Turn Over
26
38.
Which of the following reagents would react with both compounds mentioned above?
1
warm alkaline iodine solution
2
warm Fehling’s solution
3
2,4–DNPH
Neither compounds would work with Fehling’s solution as neither have the
aliphatic aldehyde function group, compound B is an acyl iodide which is not a
carbonyl compound and hence would not react with 2,4-DNPH.
[Turn Over
27
39.
Hydrogen iodide reacts with liquid hex-2-ene to form 2-iodohexane and 3-iodohexane.
When hex-2-ene is mixed with bromine monochloride, BrCl, dissolved in aqueous
sodium methanoate, a similar reaction occurs. Which are the possible products in the
mixture?
1
40.
2
3
Deuterium, D, is the .$H isotope of hydrogen. Which reactions could give an organic
compound having a chiral centre?
1
/01,1345
CH3CHO 677777778
The product is made of optical isomers of CH3CH(OH)CO2–
2
/09
C(CH3)2=CH2 6777778
The product is made of C(CH3)2ClCH2D
3
13:/; ,0/< 4/
CH3COCH3 677777777778
The product is made of CH3CD(OD)CH3
~~~ END ~~~
[Turn Over
SAJC H2 Chemistry 2014 Prelims Paper 2
1
Answer all the questions
1
Planning (P)
Iron(II) sulfate is one of the most readily available sources of iron(II). Hence it is used to
make iron supplement tablets to treat anaemia and other iron deficiencies. Women are
at a higher risk for iron-deficiency anaemia than men, especially pregnant women.
However, excess iron in the body can lead to health problems, and in severe cases,
death.
The percentage by mass of iron in an iron supplement tablet can be determined by
titrating it with acidified potassium manganate(VII).
(a)
Using the Data Booklet, write an ionic equation for the reaction between
iron(II)
sulfate and acidified potassium manganate(VII).
_________________________________________________________________
[1]
(b)
If the concentration of a standard solution of potassium manganate(VII) is
0.500 mol dm‒3, calculate the range of mass of powdered iron supplement tablets
needed for a suitable and reliable titration. You may assume that the percentage
mass of iron in iron supplement tablets is between 80% to 90%.
[2]
[Turn over
2
1
(c)
Write a plan for the titration that you would carry out to calculate the mass of iron
present in the tablet. You are given a 0.500 mol dm‒3 standard solution of
potassium manganate(VII) and excess powdered iron tablets. You may use the
reagents and apparatus normally found in a school or college laboratory.
In your plan, you should give:
Details, including quantities of all reagents and capacities of apparatus used;
The essential details of the titration procedure.
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
[6]
[Turn over
3
1
d)
Some women take multi-vitamin pills to supplement their diet which often also
contain mineral ions such as Cu2+. However, too much Cu2+ in our body causes
various health problems. In a manufacturing error, a batch of multi-vitamin pills
contained too much Cu2+ and was also contaminated accidentally with a small
amount of Ba2+ ions which are poisonous.
A sample from this batch of multi-vitamin pills is dissolved to form a solution. You
are to devise a series of chemical tests which can be conducted under laboratory
conditions using common laboratory reagents and apparatus to separate the two
cations above, such that each cation is present in a separate precipitate.
Record your plan in the table below.
Test
Expected observation
Identity of cation in
precipitate
[3]
[Total: 12 marks]
[Turn over
4
2
Phosphorus tribromide is a colourless liquid that is commonly used in laboratories for the
manufacture of alkyl bromide from alcohols.
(a)
(i)
Draw a dot and cross diagram of phosphorus tribromide.
(ii)
Draw the structure for the compound formed when phosphorus tribromide
reacts with boron tribromide
(iii)
Suggest whether phosphorus tribromide or boron tribromide has a higher
boiling point. Explain.
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
[5]
(b)
Phosphorus tribromide reacts in a similar way as phosphorus trichloride.
Write an equation, with state symbols, to show the reaction of phosphorus
tribromide with water.
_________________________________________________________________
[1]
[Turn over
5
2
(c)
Using the information from the table below and any relevant data from the Data
Booklet, construct an energy level diagram to calculate the bond energy of the
P-Br bond.
∆H/ kJmol-1
Atomisation energy of phosphorus
+315
Enthalpy change of formation of phosphorus tribromide
-185
Enthalpy
change
of
vapourisation
of
phosphorus +39
tribromide
[4]
[Turn over
6
2
(d)
The general equation for the formation of alkyl bromide from alcohols using
phosphorus tribromide is:
PBr3 + 3ROH 3RBr +H3PO3
The reaction mechanism for the above reaction using ethanol and phosphorus
tribromide is shown below.
(i)
State the type of reaction for the overall reaction
_____________________________________________________________
(ii)
Complete the mechanism above by using partial charges, lone pairs and
curly arrows to represent the electron flow.
(iii)
Suggest a reason why this reaction method cannot be used to prepare
C(CH3)3Br.
_____________________________________________________________
_____________________________________________________________
(iv)
Using the above mechanism in 2(d), suggest the organic compound formed
when ethanoic acid is reacted with phosphorus tribromide.
_____________________________________________________________
[7]
[Turn over
7
2
(e)
PBr3 is used in the following reaction scheme to produce a sweet-smelling
compound D.
(i)
Draw the structures of A to D in the spaces provided above.
[Turn over
8
2
(e)
(ii)
Give the reagents and conditions for Steps II, III, IV and VI.
Step II: ____________________________________________________
Step III:____________________________________________________
Step IV: ____________________________________________________
Step VI: _________________________________________________________
[8]
[Total: 25 marks]
3
Hydrogen peroxide exhibits oxidising and reducing properties, depending on pH.
In acidic solutions, H2O2 is one of the most powerful oxidising agents known and is used
commonly as a bleaching agent and disinfectant.
In one of its reactions, it oxidises potassium iodide to form iodine and water.
(a)
With reference to the Data Booklet, write the balanced equation for the
reaction between hydrogen peroxide and potassium iodide.
_____________________________________________________________
[1]
[Turn over
9
3
(b)
To study the kinetics of the above reaction, two sets of separate experiments
were performed, in which the initial concentrations of each of the reactants
were varied in turn, the other two being kept constant. The results are shown
below.
Graph 1
Graph 2
[H ]
[I-]
0.10
0.10
0.08
0.08
+
0.06
W
0.04
X
0.02
0.06
0.04
Y
0.02
Z
s
2s
time
t
2t
time
W: [H2O2] = 1.0 mol dm-3 and [I-] = 1.0 mol dm-3
X: [H2O2] = 2.0 mol dm-3 and [I-] = 1.0 mol dm -3
Y: [H2O2] = 1.0 mol dm-3 and [H+] = 1.0 mol dm-3
Z: [H2O2] = 2.0 mol dm -3 and [H+] = 1.0 mol dm-3
Use the data above to deduce the rate equation and give the units for the
rate constant.
[5]
[Turn over
10
3
(c)
Two different mechanisms have been proposed for this reaction.
Mechanism A:
H2O2 + I- H2O + OI(slow)
+
(fast)
OI + H HOI
HOI + H+ + I- I2 + H2O (fast)
Mechanism B:
H2O2 + I- + H+ H2O + HIO (slow)
HIO + I- I2 + OH(fast)
OH- + H+ H2O
(fast)
Suggest with reasons which of the two mechanisms, A or B, fits the kinetic
data in (b).
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
[2]
(d)
Draw the energy profile diagram for the reaction based on mechanism A.
[3]
[Total: 11 marks]
[Turn over
11
4
Cobalt has been used for centuries to impart a rich blue color to glass and ceramics.
(a)
A complex of cobalt is prepared by the following method:
Air is bubbled through an aqueous solution containing CoCl2, NH3 and NH4Cl. The
resulting solution was evaporated and crystals of the cobalt compound, P can be
isolated. P has an octahedral cation, and is found to have the following
composition by mass:
Co: 25.2% ; N: 24.0% ; H: 5.1% ; Cl : 45.7%
(i)
Given the molar mass of P is 233.4, calculate the molecular formula of P
and suggest the ligands that are bonded to cobalt.
(ii)
On adding an excess of aqueous solution of silver nitrate to an aqueous
solution of 0.01 mol of P, 1.43 g of silver chloride is precipitated.
Given that P has no overall dipole moment, deduce the structural formula
of P. Draw the full structure of its cation, showing clearly the
arrangement of the ligands that surround cobalt.
[6]
[Turn over
12
4
(b)
A student carried out the following experiment in the laboratory to investigate the
chemistry of cobalt compounds.
Procedures
Step 1 5 g of the potassium sodium tartrate was weighed into a
250 cm3 beaker. 60 cm3 of distilled water was added and the solution
was stirred.
Step 2 20 cm3 of hydrogen peroxide solution was added to the solution in
step 1.
Effervescence was observed after 5 hours.
The student repeated the experiment with the addition of 2 cm3 of cobalt(II)
chloride solution to the mixture. He recorded the following observations:
The solution in the beaker turned from colourless to pink when cobalt(II) chloride
solution was added. The solution then turned green and vigorous effervescence
was observed immediately. When the effervescence stopped, the solution turned
back to pink.
What was the role of cobalt(II) chloride solution in the experiment? Give two
reasons to support your answer using the information above.
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
[3]
[Turn over
13
4
(c)
When a crystal of NH4SCN was added to cobalt(II) chloride solution, the solution
changed colour and the visible absorption spectrum for the resulting solution was
shown below:
Relative
absorbance
300
400
500
600
700
800
Wavelength (nm)
White light spectrum
red
Wavelength(nm) 700
(i)
green
600
500
blue
400
violet
300
What is the colour of the resulting solution?
_____________________________________________________________
(ii)
Explain why the resulting solution is coloured.
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
[4]
[Total: 13marks]
[Turn over
14
5 This question involves various cyclic compounds and their reactions.
(a)
In the Shapiro reaction, a carbonyl group reacts in the presence of an electrophile to
form an alkene. A simplified example of the Shapiro reaction is shown below.
where E represents an electrophile
Shapiro reaction is used on Q.
Q
(i)
State the number of chiral centers in Q
Number of chiral centers = ____________________
(ii)
In the diagram below, circle the sp2 hybridised carbons.
[Turn over
15
5 (a)
(iii)
Draw the structures of the product formed when Q reacts with each of the
following reagents in the Shapiro reaction.
H2O
(iv)
Chloroethane
Cyclic esters R and S are possible products of the Shapiro reaction.
R
S
Suggest reagents and conditions to distinguish between esters R and S. State
the observations for each ester.
Reagents and conditions:
______________________________________________________________
Observations:
______________________________________________________________
______________________________________________________________
[6]
[Turn over
16
(b)
The structure of a dicarboxylic acid J is shown below.
J
(i)
The pKa values of the two acidic groups in J are 2.2 and 6.4. In the diagram
above, circle the acidic group which has a pKa value of 2.2. Explain your
answer.
______________________________________________________________
______________________________________________________________
______________________________________________________________
K is an isomer of J.
K
(ii)
State the type of isomerism exhibited in J and K.
______________________________________________________________
[Turn over
17
5 (b)
(iii)
With the aid of a diagram, explain why J has a more stable mono-anion than
the mono-anion of K.
______________________________________________________________
______________________________________________________________
______________________________________________________________
[5]
[Total: 11 marks]
~~~END~~~
[Turn over
SAJC H2 Chemistry 2014 Prelims Paper 2 Worked Solutions
1
(a)
5Fe2+ + MnO4‒ + 8H+ 5Fe3+ + Mn2+ + 4H2O
[1]
(b)
If volume of titre is assumed to be 25 cm3:
Amount of KMnO4 required = 0.5 x 0.025 = 0.0125 mol
Amount of Fe2+ = 0.0125 x 5 = 0.0625 mol
Mass of Fe2+ = 0.0625 x 55.8 = 3.4875 g
Maximum mass of tablet = (100/80) x 3.4875 = 4.36 g
Minimum mass of tablet = (100/90) x 3.4875 = 3.88 g
[2]
(c)
• Weigh a dry and clean weighing bottle.
• Add iron supplement tablet into the weighing bottle and weigh the bottle + tablet.
• Tip the tablet into a small beaker and reweigh the emptied weighing bottle to
determine the actual mass of tablet used.
• Add excess dilute sulfuric acid to the small beaker containing the tablet.
• Stir with a glass rod to dissolve the tablet.
• Transfer the solution with several washings into a clean 250 cm3 volumetric
flask.
• Make up to the mark with distilled water.
• Stopper the volumetric flask and shake well to obtain a homogeneous solution.
• Pipette 25.0 cm3 of the iron solution prepared into a 250 cm3 conical flask.
• Fill the burette the standard solution of KMnO4.
• Titrate the iron solution against KMnO4 from the burette, with continuous
swirling.
• Stop when one drop of solution from the burette causes a colour change from
colourless to pale pink.
[6]
(d)
Step
Expected observation
Identity of cation in ppt
Add NaOH(aq)
Pale blue ppt formed in
Cu2+
dropwise until excess.
colourless solution.
3
Pour 2 cm of the
solution into a test tube.
Filter the mixture into a
separate test tube.
Add excess H2SO4(aq)
White ppt formed. [½]
Ba2+
to the filtrate.
* Can identify Ba2+ first
[3]
2
a)
i)
ii)
iii)
Both compounds are simple covalent. Phosphorus tribromide is polar with
permanent dipole-permanent dipole while boron tribromide is non polar with
induced dipole-induced dipole. More energy required to break the stronger
pd-pd interactions of phosphorus tribromide so PBr3 has a higher boiling
point.
[5]
b)
PBr3(l) +3H2O(l) H3PO3(aq) +3HBr(aq)
[1]
-1
c)
Energy/ kJ mol
P(g) + 3Br(g)
3/2 x (+193)
P(g) + 3/2Br2(l)
+315
3 x BE
P(s) + 3/2Br2(l)
0
PBr3(g)
-185
+39
PBr3(l)
BE = +250 kJmol-1
[4]
d)
i)
Nucleophilic substitution
ii)
iii)
To form C(CH3)3Br would require the starting alcohol to be a tertiary alcohol
which is not feasible for a SN2 reaction due to steric hindrance/large bulky
groups/electron donating methyl groups.
iv)
e)
CH3COBr
[7]
(i)
(ii)
[8]
Total: 25 marks
3
a)
H2O2 +2 I- + 2H+ 2H2O + I2
b)
From graph 1, since graph is a straight line graph, rate of reaction is constant
when [H+] changes. Therefore zero order wrt [H+].
From graph 1, when [I-] is constant, [H2O2] is doubled, rate (gradient) is
doubled from 0.02/2s to 0.02/s.
Therefore first order wrt [H2O2].
From graph 2,
When [H+] = 1.0 mol dm−3, [H2O2] = 2.0 mol dm−3, t1/2 is constant at ½ t.
Therefore first order wrt [I-].
Rate = k [H2O2] [I-]
c)
units for k: mol-1dm3s-1
Mechanism A.
Step 1 is the rate determining step as the stoichiometric coefficient of the
reactants matches the power of the [H2O2] and [I-] in the rate equation.
d)
Energy
∆H
Reaction Pathway
[Total: 11 marks]
4
a)
i)
Co
N
H
Cl
%
25.2
24.0
5.1
45.7
Mole ratio
0.428
1.71
5.1
1.29
Simplest ratio
1
4
12
3
n (CoN4H12Cl3 ) = 233.4,
n=1
molecular formula = CoN4H12Cl3 . Ligands: NH3 and Clii)
0.01 mol of P contains 9.965 x 10-3 mol of free chloride ions
1mol of P contains 1 mol of free chloride ions
formula of P : [Co(NH3)4Cl2]+ Cl-
[6]
b)
i)
Catalyst
The reaction becomes faster when it is added as seen from the vigorous
effervescences
The solution turns from pink to green and back to pink colour as the catalyst
is regenerated
4c)
i)
Violet
ii)
In the isolated gas phase, the d orbitals of the Co2+ is degenerate. In the
complex, partially filled 3d orbitals split into two groups with a small energy gap
between them. When light shines, the complex absorbs light energy from the
visible light spectrum to promote electrons from the lower to the higher energy
group, (d-d transition). The light not absorbed will be reflected and seen as the
colour of the complex.
[7]
[Total: 13marks]
5 a)
i)
ii)
Number of chiral centers = 2
iii)
iv)
H2O
Chloroethane
Reagents and conditions: KMnO4, aq. H2SO4, heat
Observations: S decolourise purple KMnO4 but purple KMnO4 remains in R
*K2Cr2O7 accepted.
[6]
(b)
J
(i)
It is further from the electron donating cyclopentane group which destabilise
the carboxylate anion.
(ii)
5 (b)
Geometric isomer/ cis-trans
(iii)
Anion after dissociation is stabilised by intra hydrogen bonding of the
carboxylate group with –OH
[5]
[Total: 11 marks]
~~~END~~~
SAJC H2 Chemistry 2014 Prelims Paper 3
1 (a)
1
Phosphorus pentachloride, PCl5, is a useful reagent in organic synthesis. It can
undergo auto-ionisation in polar solvents according to the following equilibrium:
2PCl5
PCl4+ + PCl6‒
Draw the dot-and-cross diagrams for PCl4+ and PCl6‒ ions and state the shapes
around the central atom for each ion.
[3]
(b)
PCl5 exists in equilibrium with PCl3 and chlorine gas as shown below:
PCl5 (g)
PCl3 (g) + Cl2 (g)
∆H = +124 kJ mol‒1
At equilibrium, at 200 °C and a total pressure of 5 atm, 40% of PCl5 is dissociated.
(i)
Write an expression for Kp for the above equilibrium.
(ii)
Calculate a value for Kp at 200 °C and state its units.
(iii)
Predict and explain the effect of increasing the temperature on the value of Kp.
[5]
(c)
Aluminium oxide is insoluble in water. However, it is able to dissolve in an aqueous
solution of PCl5.
(i)
Explain why aluminium oxide is insoluble in water.
(ii)
Explain why aluminium oxide can dissolve in an aqueous solution of PCl5 and
write balanced equations for any reactions that occur.
[4]
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2
1 (d)
5-hydroxy-2-coumaranone can be synthesised using compound F as the starting
material. The structural formulae of 5-hydroxy-2-coumaranone and compound F are
shown below.
HO
O
O
5-hydroxy-2-coumaranone
Compound F
Suggest a synthesis to convert compound F into 5-hydroxy-2-coumaranone in not
more than five steps. State all reagents and conditions used and all intermediates
formed.
[4]
(e)
G and H have the following structure:
OH
CO2H
O
CHO
O
Compound G
Compound H
Describe a chemical test which would distinguish between F and G and a different
chemical test to distinguish between F and H.
[4]
[Total: 20]
[Turn Over
3
2. (a)
Hydroxyapatite, Ca5(PO4)3OH, is a group of phosphate minerals which can be
found in the teeth and bones of the human body. Thus, it is commonly used as a
filler to replace amputated bone or as a coating to promote bone ingrowth into
prosthetic implants.
(i)
Write an equation to illustrate what is meant by the term enthalpy change
of formation of hydroxyapatite.
(ii)
Using the following information and with the aid of the Data Booklet,
construct a Born Haber cycle to calculate the enthalpy change of lattice
energy of hydroxyapatite.
Value / kJ mol-1
(iii)
∆Hformation Ca5(PO4)3OH (s)
-12 969
∆Hformation OH- (g)
-230
∆Hformation PO43- (g)
-1913
∆Hatomisation Ca (s)
+178.2
Hydroxyapatite thermally decomposes to produce calcium phosphate,
calcium oxide and steam. Write a balanced equation to show the thermal
decomposition of hydroxyapatite. Hence, calculate the mass of calcium
oxide that could be obtained by decomposing 9 g of hydroxyapatite.
(iv)
Al2PO4(OH)3 is a recently discovered phosphate mineral found in high
pressure metamorphic rocks. Suggest, using the Data Booklet, why it has
been found that Al2PO4(OH)3 decomposes at a lower temperature than
hydroxyapatite.
[8]
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4
2
(b) An organophosphate is the general name for esters of phosphoric acid. Acephate
is an organophosphate which is used in many insecticides and herbicides.
Acephates are acutely toxic where recent studies suggest a possible link to
adverse effects in the neurobehavioral development of foetuses and children.
(i)
Experts have recommended that the concentration of acephate in fruits
should not exceed 7 ppm (1 ppm = 1 mg of acephate in 1 kg of fruits).
Calculate the maximum mass in grams of acephate that a fruit weighing
50 g can contain before it is deemed hazardous.
(ii)
Alkyl phosphates are phosphate esters that are formed when 1 mole of
phosphoric acid combines stepwise with 3 moles of an alcohol as shown in
the reaction below.
State the type of reaction in the formation of the phosphate esters.
[Turn Over
5
2
(b)
(iii)
Alkyl phosphates play a central role in biochemistry. Phosphate ester
linkages compose the backbone of the nucleic acid, RNA, which performs
multiple vital roles such as genetic expression. Ribose, an alcohol, forms
part of the RNA backbone.
Using the segment of the RNA molecule above and (b)(ii), suggest the
structural formula of the alcohol which reacted with phosphoric acid.
(iv)
Name three functional groups in the segment of the RNA molecule.
[6]
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6
2
(c)
An aldose is an alcohol that contains only one aldehyde group per molecule. The
Killiani-Fischer synthesis lengthens an aldose carbon chain by adding one
carbon to the aldehyde end of the aldose. An example of the synthesis of tetrose
from triose is illustrated below.
(i)
Outline the mechanism of the reaction in Step I.
(ii)
Tetrose is reacted with NaBH4 to form compound X. Tetrose is reacted with
acidified potassium dichromate to form compound Y.
Using the structural formulae of X and Y, write balanced equations to
explain each of the above reactions.
[6]
[Total: 20 marks]
[Turn Over
7
3
(a)
Electrophoresis is a technique used to separate a mixture of amino acids. Often, this
process is carried out using a gel which is soaked in a buffer solution to ensure pH is
kept at a relatively constant value. A small well is etched on the gel and the solution
containing the mixture of amino acids is dropped carefully in the well. An electric field
is then applied across the gel.
The table below shows three amino acids to be separated by electrophoresis and
their isoelectric points.
Amino acid
Formula of side chain Isoelectric point
(R in RCH(NH2)CO2H)
Cysteine (Cys)
‒CH2SH
5.07
Lysine (Lys)
‒(CH2)4NH2
9.74
Serine (Ser)
‒CH2OH
5.58
(i)
Explain what is meant by a buffer solution.
(ii)
Draw the predominant species of each amino acid when the pH of the buffer
solution is 7.20.
(iii)
Illustrate two ways in which vinegar might interact with a protein that contains
the three amino acids in the table above to bring about denaturation. You may
find that including sketches or diagrams will help you in your answer.
[8]
(b)
Keratin is an important protein which is a major component in hair. Keratin contains
large amounts of cysteine which gives strength to our hair. Perming hair involves
creating permanent waves in hair. This process includes forming new disulfide bonds
via oxidation. Hydrogen peroxide is often used as the oxidising agent.
(i)
Briefly explain how the presence of cysteine in keratin strengthens hair.
(ii)
Using the Data Booklet, write the half-equations involved in the formation of
new disulfide bonds using hydrogen peroxide.
[3]
[Turn Over
8
3
(c)
Hydrogen peroxide can also act as a reducing agent. It is used to react with sodium
hypochlorite, NaClO, to produce oxygen gas. The resulting solution is then reacted
with aqueous silver nitrate and a white precipitate is seen. The white precipitate
disappears on addition of dilute aqueous ammonia.
(i)
Using the Data Booklet, write the overall equation that produces oxygen gas.
(ii)
Identify the white precipitate and explain its subsequent disappearance with the
aid of relevant equations.
(iii)
Sodium hypochlorite can be prepared using chlorine in the laboratory. Suggest
a reason why this preparation should not involve heating.
(iv)
A 250 cm3 solution contains 0.05 mol dm‒3 silver nitrate and 0.04 mol dm‒3
copper(I) nitrate. By carefully adding solid NaCl, it is possible to precipitate Ag+
while keeping Cu+ in solution.
Compound
Ksp value
AgCl
1.8 x 10‒10
CuCl
1.2 x 10‒6
Using the data in the table above, determine the maximum mass of NaCl that
can be added before Cu+ starts to precipitate.
[9]
[Total: 20]
[Turn Over
9
4
(a)
Electrosynthesis in organic chemistry is the synthesis of chemical compounds in
an electrochemical cell using inert electrodes. In 1932, Gordon Alles reported his
investigations into the electrolysis of an aqueous solution of nitroalkene to an
amine. 1-phenyl-2-aminopropane can be obtained from the cathode by the
following reaction.
(i)
Suggest the products of the reaction at the anode. Hence, construct an
equation for the overall reaction.
(ii)
Calculate the mass of 1-phenyl-2-aminopropane produced when a current
of 0.25 A is passed through an aqueous solution of phenyl nitropropylene
for a day.
[4]
(b)
On
completion
of
the
electrosynthesis
reaction,
the
purification
of
1-phenyl-2-aminopropane is effected by exactly neutralising the impure product
with aqueous hydrochloric acid.
(i)
Write a balanced chemical equation between 1-phenyl-2-aminopropane
and hydrochloric acid.
(ii)
1-phenyl-2-aminopropane crystals are dissolved in ethanol and made up to
250 cm3 in a volumetric flask. 25 cm3 of this solution is then pipetted and
required 27.4 cm3 of 0.05 mol dm-3 aqueous hydrochloric acid for reaction.
Calculate the concentration of the solution of 1-phenyl-2-aminopropane in
g dm-3.
(iii)
Hence, determine the percentage purity of the 1-phenyl-2-aminopropane
crystals produced during the electrosynthesis reaction in (a)(ii).
[4]
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10
4
(c)
(i)
1,4-diaminobutane is a bidentate ligand which can be synthesised from a
suitable nitroalkene.
1,4-diaminobutane
Using information from (a), suggest the structural formula of this
nitroalkene.
(ii)
What do you understand by the term bidentate ligand?
(iii)
Addition of 1,4-diaminobutane to an aqueous solution containing Cu2+ ion
causes the formation of a violet complex. Account for this change in colour
of the copper-containing compounds.
(iv)
Suggest the formula of this violet complex ion.
[5]
(d)
(i)
2-aminopropane
can
be
synthesised
using
NH3
and
a
suitable
chloroalkane. Draw the displayed formula of this chloroalkane.
(ii)
A by-product in the formation of 2-aminopropane from (d)(i) gives an
immediate precipitate with ethanolic silver nitrate and is able to conduct
electricity in the molten and aqueous state. Suggest a structure for this
by-product given that its molecular formula is C12H28NCl.
[2]
[Turn Over
11
4
(e)
Amines react with carbonyl compounds to yield imines as shown in the following
reaction.
One of the pathways by which organisms make alanine involves the addition of
ammonia to alpha-keto acids such as pyruvic acid.
(i)
Using the above information, suggest the structural formula of imine W.
(ii)
With reference to structure and bonding, explain why alanine has a higher
melting point than pyruvic acid.
(iii)
Propose a two-step synthetic pathway for the synthesis of pyruvic acid from
propene.
[5]
[Total: 20 marks]
[Turn Over
12
5 (a)
J has the following structural formula:
The pKa1 and pKa2 values of J are 3.25 and 7.60 respectively.
(i)
Calculate the pH of a 0.025 mol dm‒3 solution of J (ignore the effect of pKa2 on
the pH).
(ii)
30 cm3 of 0.025 mol dm‒3 NaOH is added to 10.0 cm3 of 0.025 mol dm‒3 of J.
Draw the structural formulae of the predominant organic species when 15 cm3
of NaOH is added.
(iii)
Sketch the shape of the pH curve you would expect to obtain from (ii) and
briefly describe how you have calculated the various key points on the curve.
[8]
(b)
A, C10H14O2NI, dissolves in aqueous HNO3. A is formed, along with a brown
precipitate, when B reacts with potassium manganate(VII) at 0°C. On addition of
ethanolic silver nitrate to A, a yellow precipitate is formed. When aqueous bromine is
added to A, the orange-red solution decolourises and a white precipitate, C,
C10H11O2NIBr3, is formed. 0.125 mol of A produces 2800 cm3 of gas at s.t.p. when
sodium metal is added. D, C10H13O2NICl, is produced when potassium dichromate
and hot dilute hydrochloric acid is added to A. D reacts with 2,4-DNPH but not with
Tollen’s reagent. E and a yellow precipitate are formed when warm aqueous iodine
and aqueous sodium hydroxide are added to both A and D separately.
Deduce the structures of A to E, and explain the reactions described.
[12]
[Total: 20]
~~~ END OF PAPER ~~~
[Turn Over
SUGGESTED ANSWERS SAJC PRELIM 2014 PAPER 3 (H2 CHEMISTRY)
1 (a)
[3]
(b)
(i) Kp =
(ii)
PCl5
PCl3
Cl2
I / mol
Z
0
0
C / mol
-0.4 z
+0.4 z
+0.4 z
E / mol
0.6 z
0.4 z
0.4 z
Total moles = 1.4 z
PPCl5 = (0.6 z / 1.4 z) x 5 = 2.143 atm
PPCl3 = PCl2 = (0.4 z / 1.4 z) x 5 = 1.429 atm
Kp = 0.953 atm
(iii)
When temperature increases, the equilibrium will favour the endothermic reaction to
absorb the excess heat / to decrease the temperature. Hence, rateforward increases
more than ratebackward. Hence, Kp increases.
[5]
(c)
(i)
The energy released from forming ion-dipole interaction between aluminium oxide
and water is insufficient to overcome ionic bonds in aluminium oxide.
(ii)
Aluminium oxide is amphoteric.
Aqueous solution of PCl5 is acidic.
PCl5 + 4 H2O H3PO4 + 5 HCl
Al2O3 + 6HCl →2AlCl3 + 3H2O
[4]
1
[Turn Over
(d)
[4]
(e)
Between F and G
Add Tollen’s reagent to both compounds and warm.
No silver mirror seen for compound F, while silver mirror is seen for G.
OR
Add neutral FeCl3
F forms a violet solution (complex) whilst G forms no violet solution.
OR
Add Br2 (aq)
F orange will turn to colourless with white ppt and G will remain orange.
OR
Add 2, 4-DNPH.
Orange ppt formed for G and no orange ppt formed for F.
Between F and H
Add 2, 4-DNPH.
Orange ppt formed for H and no orange ppt formed for F.
OR
Add hot aq H2SO4 K2Cr2O7
F turns from orange to green whilst H remains orange.
[4]
[Total: 20]
2
[Turn Over
2. (a)
(i)
5 Ca(s) + 3 P(s) + 13/2 O2 (g) + ½ H2 (g) Ca5(PO4)3OH (s)
(ii)
5(178.2) + 5(590+1150) – 230 – 3(1913) + x = - 12969
x = -16 591 kJ mol-1
(iii) 2Ca (PO ) OH 3Ca (PO ) + CaO + H O
5
4 3
3
4 2
2
Moles of hydroxyapatite = 9 / 502.5 = 0.01791 mol
Moles of calcium oxide = 8.96 x 10-3 mol
Mass of calcium oxide = 8.96 x 10-3 x (40.1+16) = 0.502 g
(iv) Quote: Ca2+: 0.099 nm and Al3+: 0.050
Al3+ ion has a higher charge density, and higher polarising power than Ca2+.
Thus, there is more distortion of the electron cloud of the anion, hence
requiring less energy to break.
[8]
(b) (i) Given that 1 kg of fruits can contain 7mg of acephate,
1g of fruit = 7 x 10-6 g
Hence, 50 g of fruit = 3.5 x 10-4 g of acephate
(ii)
Nucleophilic substitution / Condensation
3
[Turn Over
(b)
(iii)
(iv) Alkene, (secondary or tertiary) amide, secondary alcohol OR ether
[6]
(c)
(i)
(ii)
[6]
[Total: 20 marks]
4
[Turn Over
3
(a)
(i)
A buffer solution is a solution whose pH remains almost unchanged when a small
amount of H+ or OH- is added to it.
(ii)
Cysteine
Lysine
Serine
H
H2N
H
COO
H 2N
CH2SH
COO
CH2OH
(iv)
AND
[8]
(b)
(i)
Cysteine can form disulfide linkages which are strong covalent bonds which are
hard to break.
(ii)
2 -CH2SH -CH2S-SCH2- + 2H+ + 2eH2O2 + 2H+ + 2e- 2H2O
[3]
(c)
(i)
H2O2
O2 + 2H+ + 2e-
2e- + 2H+ + ClO-
Cl- + H2O
Overall eqn: H2O2 + ClO- O2 + H2O + Cl(ii)
White ppt is AgCl.
AgCl + 2NH3 [Ag(NH3)2]+ + ClAgCl
Ag+ + Cl- (Eqm 1)
The decrease in [Ag+] due to formation of complex shifts eqm 1 to the right. Also,
decrease in [Ag+] also decreases I.P. of AgCl which becomes lower than Ksp of
AgCl, hence ppt dissolves.
5
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(iii)
ClO- can undergo disproportionation at higher temperatures to form ClO3-.
(iv)
For CuCl:
[Cu+][Cl‒] = 1.2 x 10‒6
[Cl‒] = (1.2 x 10‒6) / 0.04 = 3.00 x 10‒5 mol dm‒3
For AgCl @ the point where IP CuCl = Ksp CuCl
Hence, [Ag+][Cl‒] = 1.8 x 10‒10
[Ag+] = 6.00 x 10‒6 mol dm‒3
No of moles of AgCl formed = 250 / 1000 x 0.05 – 250 / 1000 x 6.00 x 10‒6
= 0.012499 mol
Total moles of Cl- needed = Cl- in AgCl + Cl- in saturated solution
= 0.012499 + 250 / 1000 x 3.00 x 10-5 = 0.012507 mol
Maximum mass of NaCl that can be added = 0.012507 x (35.5 + 23) = 0.732g
[9]
[Total: 20]
4
(a)
(i)
Product are H+ and O2
Overall equation
(ii)
Q = (0.25) x (24 x 60 x 60) = 21, 600 C
From the above half equation, 1 mole of 1-phenyl-2-aminopropane requires
8F (772 000C).
Mol of 1-phenyl-2-aminopropane formed by 21,600 C = 0.0280 mol
Mass of 1-phenyl-2-aminopropane =
0.0280 x [ 9 (12) + 13 (1) + 14 (1) ] = 0.280 x 135 = 3.78 g
[4]
(b)
(i)
6
[Turn Over
(ii)
Moles of HCl = moles of 1-phenyl-2-aminopropane in 25 cm3 = 1.37 x 10-3.
moles of 1-phenyl-2-aminopropane in 250 cm3 = 1.37 x 10-2 mol
[1-phenyl-2-aminopropane] in g dm-3 = (4 x 1.37 x 10-2 x 135) =
7.40 g dm-3
(iii)
Mass in 250 cm3 = 1.85 g
percentage purity of the 1-phenyl-2-aminopropane crystals =
1.85 / 3.78 x 100 = 49.0 %
[4]
(c)
(i)
(ii)
Bidentate ligand can form 2 dative bonds to a central atom or ion.
(iii)
When 1,4-diaminobutane is added, the colour of the complex changes from
blue to violet as there is a ligand exchange of water by 1,4-diaminobutane.
The energy absorbed for the excitation of d electrons changes as different
ligands are bonded to Cu2+.
(iv)
[5]
(d)
(i)
7
[Turn Over
(ii)
[2]
(e)
NH
(i)
C
CH3
(ii)
COOH
Pyruvic is a simple covalent molecule whilst alanine is a zwitterion with
giant ionic lattice structure. Intermolecular forces between the pyruvic acid
molecules is hydrogen bonding while in alanine, it’s held by strong
electrostatic forces of attraction between oppositely charged ions. More
energy is needed to break the stronger ionic bonds in alanine than the
hydrogen bond in the acid.
(iii)
[5]
5 (a)
(i)
[H+] = (10-3.25 x 0.025)1/2 = 3.7494 x 10-3 mol dm-3
pH = 2.43
(ii)
(ii)
[8]
8
[Turn Over
(b)
Observations
Deductions
A dissolves in aqueous HNO3.
A contains amine or phenylamine group.
Neutralisation
B reacts with cold KMnO4 to
Mild oxidation.
form A.
B contains C=C.
A is a diol.
Brown ppt is MnO2.
A forms yellow ppt on addition of
Nucleophilic substitution.
ethanolic silver nitrate.
A contains iodoalkane.
Yellow ppt is AgI
A decolourises aqueous
Electrophilic substitution.
bromine and white ppt is formed. A is phenylamine.
B contains 3 Br atoms.
A produces 0.125 mol of gas
Gas is H2.
when sodium metal is added.
Redox reaction.
1 mol of A produces 1 mol of H2.
Two –OH group present in A.
D is produced when hot acidified
Oxidation.
K2Cr2O7 is added to A.
Primary or secondary alcohol present in A.
Carboxylic acid or ketone in D
D reacts with 2,4-DNPH but not
D contains ketone.
with Tollen’s.
Secondary alcohol present in A. (no double
award)
D undergoes condensation.
A and D both form yellow ppt
with aqueous alkaline iodine.
A contains
and D contains
.
E has a RCOOYellow ppt is CHI3.
Oxidation.
A:
B:
9
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C:
D:
E:
[12]
[Total: 20]
END OF PAPER
10
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