sajc h2 chemistry 2014 prelims paper 1 -...

1

[Turn Over

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?

A CH

B CH2

C CH3

D C2H3

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

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)

SAJC H2 Chemistry 2014 Prelims Paper 1

2

[Turn Over

4. Which element will possess an empty s orbital after forming a singly-charged cation?

A Barium

B Vanadium

C Copper

D Gallium

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

B 2H2O2 � 2H2O + O2

C PCl3 + Cl2 � PCl5

D CH3CH2CHO + [O] � CH3CH2COOH

6. 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

3

[Turn Over

7. A student dissolved 0.238 mol of sodium fluoride in 300 cm3 of water.

Given the following data:

Lattice energy of NaF −918 kJ mol−1

Enthalpy change of hydration of F −

−457 kJ mol−1

Enthalpy change of hydration of Na+

−390 kJ mol−1

What would be the initial temperature of the water if the final temperature of the solution

is 20.00o

C?

Assume that the specific heat capacity of sodium fluoride solution is 4.18 J g−1

K−1

.

A 6.52o

C

B 13.48o

C

C 20.00o

C

D 33.48o

C

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.

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.

4

[Turn Over

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

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

5

[Turn Over

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

12. 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-.

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 [X-] / 10-4 mol dm-3

A 1 1

B 1 2

C 2 1

D 2 2

6

[Turn Over

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+ E�

cell = +0.75 V

Which of the following metal ions cannot be used for a possible reaction with glucose?

A Mn3+

B V3+

C Fe3+

D Co3+


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

D Addition of chlorine

16. 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

7

[Turn Over

17. The following graphs show how two properties of the elements, Na to P, and their

compounds, vary with proton number.

proton number proton number

Graph 1 Graph 2

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

11 12 13 14 15

11 12 13 14 15

8

[Turn Over

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

9

[Turn Over

21. 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

20. Which of the following cannot act as a ligand?

A AlH4-

B N2H4

C CH3OH

D CO

10

[Turn Over

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 The organic products would not form an orange precipitate with 2,4–DNPH.

24. 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

11

[Turn Over

25. 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

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.

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.

27. Which compound would show the greatest ease of hydrolysis?

A

B

C

D

12

[Turn Over

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

13

[Turn Over

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

D

30. 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.

14

[Turn Over

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

correct

1 and 2 only are

correct

2 and 3 only are

correct

1 only is correct

No other combination of statements is used as a correct response.

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

32. Which of the following pairs are both planar and polar?

1 OCl2 and SO2

2 XeF4 and SO3

3 IF5 and H3O+

33. Which of the following increase with decreasing temperature for the dissociation of

water?

Temperature/ oC Kw/ mol2 dm-6

50 5.5 x 10-14

25 1.0 x 10-14

1 pKb

2 pH

3 pKw

15

[Turn Over

A B C D

1, 2 and 3 are

correct

1 and 2 only are

correct

2 and 3 only are

correct

1 only is correct



Which of the following statements can be deduced from the diagram below?

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.

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

CuSO4(aq)

Cu

NaCl(aq)

Fe

Cell 1 Cell 2

16

[Turn Over

A B C D

1, 2 and 3 are

correct

1 and 2 only are

correct

2 and 3 only are

correct

1 only is correct


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


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 blood-

red 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.

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.

17

[Turn Over

A B C D

1, 2 and 3 are

correct

1 and 2 only are

correct

2 and 3 only are

correct

1 only is correct


38.

Which of the following reagents would react with both compounds above?

1 warm alkaline iodine solution

2 warm Fehling’s solution

3 2,4–DNPH

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

2

3

40. Deuterium, D, is the H�� isotope of hydrogen. Which reactions could give an organic

compound having a chiral centre?

1 CH3CHO

��,��

� �

2 C(CH3)2=CH2

��

� �

3 CH3COCH3

��,��

� �

~~~ END ~~~

1

[Turn Over

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 (Co3+ was in excess)

C -1 -2 +3

F 0 1 3

SAJC H2 Chemistry 2014 Prelims Paper 1 Worked Solutions

2

[Turn Over

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)

pV = nRT

At constant p,

V = (nR

p)T

=

��

= constant

C p against V (at constant T)

pV = nRT

At constant T,

p = (nRT)1

V

D pV against V (at constant T)

pV = nRT

At constant T,

pV = nRT = constant

V/T

T

V

3

[Turn Over

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.

4

[Turn Over

7. A student dissolved 0.238 mol of sodium fluoride in 300 cm3 of water.

Given the following data:

Lattice energy of NaF −918 kJ mol−1

Enthalpy change of hydration of F −

−457 kJ mol−1

Enthalpy change of hydration of Na+

−390 kJ mol−1

What would be the initial temperature of the water if the final temperature of the solution

is 20.00o

C?

Assume that the specific heat capacity of sodium fluoride solution is 4.18 J g−1

K−1

.

A 6.52o

C

B 13.48o

C

C 20.00o

C

D 33.48o

C

∆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

5

[Turn Over

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.

6

[Turn Over

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

7

[Turn Over

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

8

[Turn Over

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 HPO4

2-

Kb of H2PO4- < Kb of HPO4

2- since Kb = Kw / Ka

B PO43- can react as a base.

In presence of acid, PO43- + H+ � HPO4

2-

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- � HPO4

2- + H2O

D H3PO4 has a higher pKa than HPO42-.

Ka of H3PO4 > Ka of H2PO4- > Ka of HPO4

2-

pKa of H3PO4 < pKa of H2PO4- < pKa of HPO4

2-

9

[Turn Over

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 [X-] / 10-4 mol dm-3

A 1 1

I.P = [M2+][X-] = (0.5 x 10-4)(0.5 x 10-4)2 = 1.25 x 10-13 mol3 dm-9 < Ksp

B 1 2

I.P = [M2+][X-] = (0.5 x 10-4)(1 x 10-4)2 = 5 x 10-13 mol3 dm-9 < Ksp

C 2 1

I.P = [M2+][X-] = (1 x 10-4)(0.5 x 10-4)2 = 2.5 x 10-12 mol3 dm-9 < Ksp

D 2 2

I.P = [M2+][X-] = (1 x 10-4)(1 x 10-4)2 = 1 x 10-12 mol3 dm-9 > Ksp

Precipitation occurs


Glucose can be reacted with silver ions to form a silver mirror in the following reaction.

C6H12O6 + 2Ag+ + H2O � 2Ag + C6H12O7 + 2H+ E�

cell = +0.75 V

Which of the following metal ions cannot be used for a possible reaction with glucose?

A Mn3+

Mn3+ + e- Mn2+ E� = +1.49 V

B V3+

V3+ + e- V2+ E� = -0.26 V

C Fe3+

Fe3+ + e- Fe2+ E� = +0.77 V

D Co3+

Co3+ + e- Co2+ E� = +1.82 V

Ag+ is reduced to Ag while glucose is oxidised.

E�cell = E�

red - E�

ox = +0.75 V

E�ox = 0.80 - 0.75 V = + 0.05 V

For a feasible reaction, E�cell < 0, hence E�

red (Mx+/M) should be more positive

than +0.05 V.

10

[Turn Over


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 Addition of chlorine

16. 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.

11

[Turn Over

17. The following graphs show how two properties of the elements, Na to P, and their

compounds, vary with proton number.

proton number proton number

Graph 1 Graph 2

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

NaCl & MgCl2 – giant ionic

AlCl3, SiCl4 and PCl5 – simple

covalent

Melting point of oxide

NaO, MgO & Al2O3 – giant ionic

Si2O3 – giant covalent

P4O10 – simple covalent

D Melting point of element Conductivity of element

11 12 13 14 15

11 12 13 14 15

12

[Turn Over

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.

13

[Turn Over

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

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.

14

[Turn Over

21. 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

20. Which of the following cannot act as a ligand?

A

AlH4- No available lone pair for dative bonding

B

N2H4

C

CH3OH

D CO

15

[Turn Over

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.

16

[Turn Over

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.

17

[Turn Over

24. 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

25. 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

18

[Turn Over

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?

A

Cl Cl

OO

B

C HO OH

II

D

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.

19

[Turn Over

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.

20

[Turn Over

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:

21

[Turn Over

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.

22

[Turn Over

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 Trigonal planar Non-polar Non-polar

3 IF5 and H3O+

Square pyramidal Trigonal pyramidal Polar Polar

33. Which of the following increase with decreasing temperature for the dissociation of

water?

Temperature/ oC Kw/ mol2 dm-6

50 5.5 x 10-14

25 1.0 x 10-14

1 pKb

At lower T, Kw �, [OH-] �, Kb �, pKb �

2 pH

At lower T, Kw �, [H+] �, pH �

3 pKw

At lower T, Kw �, pKw �

23

[Turn Over


Which of the following statements can be deduced from the diagram below?

1 Size of the anode in Cell 1 decreases.

At the anode:

Cl2 + 2e- 2Cl

- E� = +1.36 V

O2 + 4H+ + 4e- 2H2O

E� = +1.23 V

Fe2+ + 2e- Fe E� = -0.44 V

Fe3+ + 3e- Fe E� = -0.04 V

Fe has the most negative E�, so it will get oxidised at the anode.

2 Colour of the electrolyte in Cell 2 remains the same.

Electroplating of copper in Cell 2.

Anode: Cu � Cu2+ + 2e-

Cathode: Cu2+ + 2e- � Cu

3 Effervescence is observed in both cells immediately.

CuSO4(aq)

Cu

NaCl(aq)

Fe

Cell 1 Cell 2

24

[Turn Over

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.


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 blood-

red 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- Fe E� = -0.04 V

NO3- + 2H+ + e- NO2 + H2O

E� = +0.81 V

E�cell = +0.81 – (-0.04) = +0.85V

25

[Turn Over

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

26

[Turn Over

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.

27

[Turn Over

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

2

3

40. Deuterium, D, is the H$. isotope of hydrogen. Which reactions could give an organic

compound having a chiral centre?

1 CH3CHO

/01,1345677777778

The product is made of optical isomers of CH3CH(OH)CO2–

2 C(CH3)2=CH2

/096777778

The product is made of C(CH3)2ClCH2D

3 CH3COCH3

13:/;,0/<4/677777777778

The product is made of CH3CD(OD)CH3

~~~ END ~~~

1

[Turn over

1

Answer all the questions

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]


2

[Turn over

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]

3

[Turn over

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]

4

[Turn over

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]

5

[Turn over

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

tribromide

+39

[4]

6

[Turn over

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]

7

[Turn over

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.

8

[Turn over

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]

9

[Turn over

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

s 2s t 2t

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]

time

[H+]

0.10

0.08

0.06

0.04

0.02

W

time

[I-]

0.10

0.08

0.06

0.04

0.02

X Y Z

10

[Turn over

3 (c) Two different mechanisms have been proposed for this reaction.

Mechanism A:

H2O2 + I- � H2O + OI- (slow)

OI- + H+ � HOI (fast)

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]

11

[Turn over

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]

12

[Turn over

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]

13

[Turn over

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:

(i) What is the colour of the resulting solution?

_____________________________________________________________

(ii) Explain why the resulting solution is coloured.

_____________________________________________________________

_____________________________________________________________

_____________________________________________________________

_____________________________________________________________

[4]

[Total: 13marks]

White light spectrum

Wavelength(nm) 700 600 500 400 300

red green blue violet

Relative

absorbance

300 400 500 600 700 800

Wavelength (nm)

14

[Turn over

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.

15

[Turn over

5 (a) (iii) Draw the structures of the product formed when Q reacts with each of the

following reagents in the Shapiro reaction.

H2O

Chloroethane

(iv) 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]

16

[Turn over

(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.

______________________________________________________________

17

[Turn over

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~~~

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

Pour 2 cm3 of the

solution into a test tube.

Add NaOH(aq)

dropwise until excess.

Pale blue ppt formed in

colourless solution.

Cu2+

Filter the mixture into a

separate test tube.

Add excess H2SO4(aq)

to the filtrate.

White ppt formed. [½]

Ba2+

* Can identify Ba2+ first

[3]

SAJC H2 Chemistry 2014 Prelims Paper 2 Worked Solutions

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]

c) Energy/ kJ mol-1

BE = +250 kJmol-1

[4]

d) i) Nucleophilic substitution

PBr3(l)

PBr3(g)

P(g) + 3/2Br2(l)

P(g) + 3Br(g)

P(s) + 3/2Br2(l)

0

-185

+39

3 x BE

3/2 x (+193)

+315

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) CH3COBr [7]

e)

(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-] units for k: mol-1dm3s-1

c) 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 Cl-

ii) 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) Number of chiral centers = 2

ii)

iii) H2O

Chloroethane

iv) 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) Geometric isomer/ cis-trans

5 (b) (iii)

Anion after dissociation is stabilised by intra hydrogen bonding of the

carboxylate group with –OH

[5]

[Total: 11 marks]

~~~END~~~

1

[Turn Over

1 (a) 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]


2

[Turn Over

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:

CO2H

CHO

O

O

OH

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]

3

[Turn Over

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

∆Hformation Ca5(PO4)3OH (s) -12 969

∆Hformation OH- (g) -230

∆Hformation PO43- (g) -1913

∆Hatomisation Ca (s) +178.2

(iii) 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]

4

[Turn Over

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.

5

[Turn Over

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]

6

[Turn Over

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]

7

[Turn Over

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

(R in RCH(NH2)CO2H)

Isoelectric point

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]

8

[Turn Over

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]

9

[Turn Over

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]

10

[Turn Over

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]

11

[Turn Over

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]

12

[Turn Over

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 ~~~

1 [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]

2 [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]

3 [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) 2Ca5(PO4)3OH � 3Ca3(PO4)2 + CaO + H2O

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

4 [Turn Over

(b) (iii)

(iv) Alkene, (secondary or tertiary) amide, secondary alcohol OR ether

[6]

(c)

(i)

(ii)

[6] [Total: 20 marks]

5 [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

COOH2N

CH2SH

H

COOH2N

CH2OH

H

(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+ + 2e-

H2O2 + 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]+ + Cl-

AgCl 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.

6 [Turn Over

(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)

7 [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)

8 [Turn Over

(ii)

[2]

(e) (i)

C

NH

CH3COOH

(ii) 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]

9 [Turn Over

(b) Observations Deductions

A dissolves in aqueous HNO3. A contains amine or phenylamine group.

Neutralisation

B reacts with cold KMnO4 to

form A.

Mild oxidation.

B contains C=C.

A is a diol.

Brown ppt is MnO2.

A forms yellow ppt on addition of

ethanolic silver nitrate.

Nucleophilic substitution.

A contains iodoalkane.

Yellow ppt is AgI

A decolourises aqueous

bromine and white ppt is formed.

B contains 3 Br atoms.

Electrophilic substitution.

A is phenylamine.

A produces 0.125 mol of gas

when sodium metal is added.

Gas is H2.

Redox reaction.

1 mol of A produces 1 mol of H2.

Two –OH group present in A.

D is produced when hot acidified

K2Cr2O7 is added to A.

Oxidation.

Primary or secondary alcohol present in A.

Carboxylic acid or ketone in D

D reacts with 2,4-DNPH but not

with Tollen’s.

D contains ketone.

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 RCOO-

Yellow ppt is CHI3.

Oxidation.

A:

B:

10 [Turn Over

C:

D:

E:

[12]

[Total: 20]

END OF PAPER

sajc h2 chemistry 2014 prelims paper 1 -...

Documents