Al Chemistry 1995-1998 Paper 1

HKALE Chemistry (AL) 1995-98 Paper I 1995 SECTION A Answer ALL questions in this Section. Write your answers in the spaces provided. 1.

(a)

(i) The first four successive ionization energies of an element A are 578, 1817, 2746 and 10813 kJ mo1-1 respectively. To which group in the Periodic Table does A belong? (ii) The relative atomic mass of bromine is 79.90. It has two isotopes with mass numbers 79 and 81. Calculate the relative abundance of each isotope. (3 marks)

(b)

(i) What can you deduce from the fact that the spectral lines in the atomic emission spectrum of hydrogen are not equally spaced? (ii) In the atomic emission spectrum of hydrogen, the convergence limit for the Lyman series occurs at 3.275 X 1015 Hz. Calculate the ionization energy of hydrogen, in kJ mo1-1. (3 marks)

(c)

Account for the fact that the carbon-oxygen bond lengths in CO, CO2 and CO32- are 0.113, 0.116 and 0.129 respectively. (3 marks)

(d)

The iodination of propanone is catalysed by hydrogen ions. The overall equation is: CH3COCH3(aq)+I2(aq)  CH3COCH2I(aq)+HI(aq) Using four mixtures B, C, D and E, the progress of the reaction was followed by colorimetric measurement. The results are tabulated below. Mixture B C D E

Composition by volume of mixture / cm3 water 1.00 M HCI 60.0 10.0 50.0 10.0 65.0 10.0 65.0 5.0

propanone 10.0 10.0 5.0 10.0

0.05 M I2 in KI 20.0 30.0 20.0 20.0

Initial rate /mol dm-3 s-1 4.96 X 10-6 5.04 X 10-6 2.45 X 10-6 2.47 X 10-6

(i) Determine the effects of the changes in concentration of each of the reactants (iodine and propanone) and the Catalyst (hydrochloric acid) on the reaction rate. Write the rate expression for the reaction. (ii) For mixture B, calculate the rate constant for the reaction at the temperature of the experiment. (Density of CH3COCH3 = 0.789 g cm-3) (4 marks) (e)

The reaction between ethanoic acid and ethanol can be represented by the following equation: CH3COOH(l ) + C2H5OH( l )

CH3COOC2H5(l ) + H2O( l )

12.01g of ethanoic acid are treated with .61g of ethanol in the presence of a catalyst. When the reaction reaches equilibrium at 298K, 5.04g of ethanoic acid are found to have reacted. (i) Name a suitable catalyst for this reaction in the forward direction. (ii) Calculate the equilibrium constant, Kc, for the reaction at 298K. (iii) What additional mass of ethanol would be required in order to use up a further 0.60g of ethanoic acid? (iv) Would the addition of more of the same catalyst affect the value of Kc? Explain. (7 marks) 2.

(a)

Explain why phosphorus can form PC13 and PC15, while nitrogen can form only NC13. (2 marks)

(b)

(i) What is the essential feature of a “redox reaction”? (ii) Is the reaction below a “redox reaction” or an “acid-base reaction”? Explain. CaO + SiO2  CaSiO3 (3 marks) 1

HKALE Chemistry (AL) 1995-98 Paper I

(c)

Manganate(VI) ions readily undergo disproportionation in aqueous solutions, except under very basic conditions. Write a balanced equation for this disproportionation, and give the oxidation state of manganese in the reaction product(s). (3 marks)

(d)

(i) State whether the following hydrides would react with water under room temperature and atmospheric pressure. If there is a reaction, give the balanced equation. CH4 SiH4 H2S HC1 (ii) Explain the difference in reactivity with water between CH4 and SiH4. (iii) Explain the difference in reactivity with water between SiH4 and H2S. (6 marks)

(e)

For each of the following species, draw a three-dimensional structure showing the bond electron pairs and lone electron Pairs of the central atom. State the shape of the species in each case. (i) IC14 (ii) SC12 (3 marks)

(f)

(i) Show the electronic configuration of a ground state Cr2+ ion by filling in the appropriate boxes below. 1s

2s

2p

3s

3p

3d

4s

4p

4d

(ii) What is the highest possible oxidation state of chromium? (iii) Give a chromium compound in which chromium is in its highest oxidation state. (3 marks) 3.

(a)

Arrange the following carbocations in the order of increasing stability. Explain your arrangement. CH2 ,

CH2

and (3 marks)

(b)

Arrange the following carboxylic acids in the order of increasing acidity. Explain your arrangement. CICH2CO2H, CICH2CH2CO2H and FCH2CO2H (3 marks)

(c)

(i) Give the structure of the major product formed from the following reaction: CH3 + HBr

(ii) Outline a mechanism for the above reaction. (Movement of electron pairs should be indicated by curly arrows.) (3 marks) (d)

(i) Give the reactants and conditions for the preparation of benzenediazonium chloride in the laboratory. (ii) Write the structure of the product formed in the diazocoupling of naphthalene-2-ol with benzenediazonium chloride. (iii) If an aqueous solution of benzenediazonium chloride is heated, a solid, which is soluble in dilute NaOH, can be obtained. 2

HKALE Chemistry (AL) 1995-98 Paper I Suggest a structure for the solid obtained and account for its solubility in dilute NaOH. (5 marks)

(e)

Use equations to show how you would carry out the following conversions in the laboratory. For each conversion, Give the reagent(s), conditions and structure of the intermediate compound(s) formed. (i) (CH3)3COH to (CH3)3COCH2CH3 O (ii) CH2=CH2 to

O

COCH2CH2OC (6 marks) END OF SECTION A

SECTION B COMPULSORY question. Write your answers in the spaces provided. 4.

(a)

Devise an experiment to distinguish between KBr(s) and a mixture containing approximately 0% KCI(s) and 60% KBr(s) by mass. (3 marks)

(b)

(i) Describe the experimental procedure by which you would recrystallize a sample of impure benzoic acid. (ii) How would you test the purity of the product obtained in (i)? (4 marks)

(c)

You are provided with a Bunsen burner, a beaker, a thermometer and a set of quickfit apparatus. Draw a labeled diagram to show how selected items from the above are set up for the determination of the boiling point of propanone. (3 marks)

(d)

Name the type of hazard warning label which should be displayed on a bottle containing propanone. (1 mark)

(e)

For each of the volumetric analyses (i) to (iii), state whether an indicator is required. If an indicator is required, select the appropriate one from those given below: litmus; methyl orange; phenolphthalein; potassium dichromate(VI) solution; starch solution (i) ethanedioic and titrated with sodium hydroxide (ii) Sulphuric(VI) acid titrated with aqueous ammonia (iii) Iron(II) sulphate(VI) titrated with potassium manganate(VII) (3 marks)

(f)

In the volumetric determination of chloride ions with silver nitrate(V) in neutral solutions, potassium chromate(VI) can be used as an indicator. (i) Explain the action of this indicator. (ii) Why is this titration not carried out in strongly acidic or strongly basic conditions? (3 marks)

(g)

Give the observations when (i) ammonia solution and (ii) sodium hydroxide solution are added dropwise, until in excess, to aqueous solutions containing Pb2+ and Cu2+ ions respectively. These experiments are carried out at room temperature. (i) ammonia solution

(ii) sodium hydroxide solution

Pb2+(aq) Cu2+(aq) (3 marks) 3

HKALE Chemistry (AL) 1995-98 Paper I

END OF SECTION B

SECTION C Answer ONE question only and write your answers in the AL(D) Answer Book. Marks will be allocated approximately as follows: Chemical knowledge

50%

Organization

30%

Presentation (including proper use of English) 20% Equations, suitable diagrams and examples are expected where appropriate. The examiners are looking for the ability to analyse, to evaluate and to express ideas clearly. 5.

Write an essay on hydrogen bonding. (20 marks)

6. 7.

Write an essay on transition metal complexes, covering their stability, stereochemistry and the quantitative investigation of their stoichiometry. (20 marks) Write an essay on the synthesis and the uses of poly(alkenes). Your essay should include a mechanism for the formation of poly(alkenes) and the reasons why poly(alkenes) are widely used. (20 marks)

END OF PAPER

4

HKALE Chemistry (AL) 1995-98 Paper I 1996 SECTION A Answer ALL questions in this Section. Write your answers in the spaces provided. 1.

(a)

(i) Write down the number of neutrons, protons and electrons in one atom of carbon-12, 12C, and in one atom of carbon-13, 13C. (ii) The isotopic mass of 12C is 12.000 atomic mass unit (a.m.u.). Calculate the mass, in kg, of 1 mol of 12 Catoms. (1 a.m.u.=1.6605 X 10-27kg; Avogadro constant, L=6.0221 X 1023 mol-1) (iii) The following data were obtained from the mass spectrum of a carbon-containing compound: Ion

Mass / a.m.u.

Relative intensity

12

12.000

100.000

13

13.003

1.12

C+ C+

Using the above data, calculate the relative atomic mass of carbon. (5 marks) (b)

Carbon-14, 14C, is radioactive, emitting β–particles. (i) Write an equation for the decay of 14C. (ii) A charcoal sample from the ruins of an ancient settlement was found to have a 14C/12C ratio 0.60 times that found in living organisms. (1)

Explain why the 14C/12C ratio in the charcoal sample is smaller than that in living organisms.

(2)

Given that the half-life for the decay of 14C is 5730 years, calculate the age of the charcoal sample. ( Note: The integrated form of the rate expression for radioactive decay can be represented by the following Equation:

where

N0

0.301

log10 Nt

t1/2

t

N0 is the initial number of radioactive nuclei; N1 is the number of radioactive nuclei at time t; t1/2 is the half-life for the decay)

(iii) All radioactive decay has zero activation energy. Comment on the effect of temperature upon the rate of decay. (5 marks) (c)

Explain why (i) The first ionization energy of oxygen is greater than that of sulphur; (ii) The first ionization energy of oxygen is smaller that that of flurine. (2 marks)

(d)

Sketch the pictorial representation of a p orbital and indicate the location of the nucleus in your diagram. (1 mark)

(e)

At 298K, 50cm3 of a solution of I2 in CC14 were mixed and shaken with 200cm3 of distilled water in a separating funnel until equilibrium was attained. The two layers were then separated. 20.0cm3 of the CC14 layer required 12.15 cm3 of 0.105 M S2O32-(aq) for titration, whereas 50.0 cm3 of the aqueous layer required 8.25cm3 of 0.0050 M S2O32-(aq). (i) Calculate the distribution coefficient of I2 between water and CC14 at 298K. (ii) If the 200cm3 of distilled water contain some dissolved KI, will this affect the value of the distribution coefficient? Briefly explain. (3 marks) 5

HKALE Chemistry (AL) 1995-98 Paper I

(f)

So2(g) and O2(g) were mixed in the mole ratio of 3:1 at 1000K in the presence of a catalyst. When equilibrium was attained at 373 kPa pressure, one half of the SO2(g) had been converted into SO3(g). (i) Write an expression for Kp for the reaction of SO2(g) and O2(g) to give SO3(g). (ii) Calculate Kp for the above reaction under the given conditions.

(iii) If the above reaction takes place in the absence of the catalyst, but other conditions remain unchanged, will the value of Kp increase, decrease or remain the same? (4 marks) 2.

(a)

State the method by which sodium hydroxide is produced industrially. Give TWO other products obtained by this industrial process. (2 marks)

(b)

For each of the following chemical species, draw a three-dimensional structure showing the bond electron pairs and lone electron pair(s) of the central atom underlined. State the shape of the species in each case. (i) C1O3(ii) NOF (3 marks)

(c)

What is the oxidation state of the central atom in each of the following compounds? HC1O3

HC1O4

HMnO4

H2CrO4 (2 marks)

(d)

(i) Explain why among the four compounds in (c), only HC1O3 can undergo disproportionation. (ii) Write a balanced equation for the disproportionation of HC1O3 to give HC1O4 and C1O2. (2 marks)

(e)

Which is the stronger acid in each of the following pairs of substances? Briefly explain your choice. (i) [Fe(H2O)6]2+(aq) , [Fe(H2O)6]3+(aq) (ii) HC1O3(aq) , HC1O4(aq) (iii) HMnO4(aq) , H2CrO4(aq)

(f)

The complex ion [Co(H2NCH2CH2NH2)2C12]+ has THREE isomers. These isomers belong to TWO types of isomerism. (i) Draw a three-dimensional structure for each isomer. (ii) What are the two types of isomerism? (iii) State ONE difference in the properties of the pair of isomers in each type of isomerism. (5 marks)

3.

(a)

Arrange the following carbocations in the order of increasing stability. Explain your arrangement. +

+

CH3

CH3 ,

CH3

+

and

(3 marks) (b)

Arrange the following compounds in the order of increasing basic strength. Explain your arrangement. NH2

NH2 ,

and

NH3 (3 marks) 6

HKALE Chemistry (AL) 1995-98 Paper I

(c)

Consider the following structure: H

β C

C

α

γ

C

O C

H

c

b

a

(i) Give the hybridization states of the carbon atoms a, b and c. a

b

c

(ii) Suggest expected values for the bond angles α, β and γ α

β

γ (3 marks)

(d)

Give the structure of the major organic product(s) in each of the following reactions: O

O

(i)

C

O

NaOH(aq) Warm

CH3-C-CH3 + (ii)

H

O

heat

HO-C-CH2-CH2-C-OH CH3

(iii)

CHO

C

Conc. NaOH heat

CH3 (4 marks) (e)

The structure of compounds A and B are shown below: OH

OH

B

A

Outline a laboratory method, based on a difference in their chemical properties, to separate a mixture of A and B. (3 marks) (f)

(i) Give the structures of compounds D and E in the following organic synthesis: O C

HCN

H

D:

D

H3O+ heat

E

E:

(ii) Outline a reaction mechanism for the formation of D. (Movement of electron pairs should be indicated by curly arrows.) (4 marks) END OF SECTION A 7

HKALE Chemistry (AL) 1995-98 Paper I

SECTION B COMPULSORY question. Write your answers in the spaces provided. 4.

(a)

BaO is basic oxide, while CO2 is an acidic oxide. (i) State all observations when dilute HC1(aq) is added to BaO(s). (ii) State all observations when CO2 is bubbled, until in excess, into the following solutions. (1) Dilute HC1(aq) (2) Ca(OH)2(aq) (4 marks)

(b)

Describe the experimental procedures of a chemical test that you would employ in order to demonstrate that a liquid sample is an aromatic primary amine. State the observation of your test. (4 marks)

(c)

In a titration experiment, a H2O2 solution was diluted 25 times. 25.0cm3 of the diluted H2O2 solution, in the presence of excess dilute H2SO4, required 26.45cm3 of 0.00995 M KMnO4 solution for titrated. (i) Describe, with experimental details, how you would dilute the H2O2 solution. (ii) Write a balanced equation for the reaction involved in the titration. (iii) Describe the colour change at the end point of the titration. (iv) Calculate the molarity of the diluted H2O2 solution. (v) What reagent would you use to standardize the KMnO4 solution in this experiment? (8 marks)

(d)

In an experiment to determine the concentration of H2O2 contained in a rainwater sample, 5.0cm3 of the sample were mixed with an excess of a certain transition metal complex solution, giving a coloured mixture. The absorbance of the mixture was measured by a colorimeter and was found to be 0.0273. When 5.0cm3 of 1.46 X 10-6M H2O2 (instead of the rainwater sample) were treated in the same way, an absorbance of 0.0398 was recorded. (i) Calculate the concentration of H2O2 in the rainwater sample assuming that concentration is directly proportional to absorbance. (ii) Why is the method of titration not suitable for the determination of the concentration of H2O2 in the rainwater sample? (iii) Why is it not suitable to collect the rainwater sample for this experiment in an iron container? (4 marks)

END OF SECTION B

8

HKALE Chemistry (AL) 1995-98 Paper I SECTION C Answer ONE question only and write your answers in the AL(D) Answer Book. Marks will be allocated approximately as follows: Chemical knowledge

50%

Organization

30%

Presentation (including proper use of English) 20% Equations, suitable diagrams and examples are expected where appropriate. The examiners are looking for the ability to analyse, to evaluate and to express ideas clearly. 5.

Write an essay on the structures of different types of solid, and the relationship between structure and physical properties of solids. (20 marks)

6.

Write an essay on the group of elements carbon to lead, covering the trends in their physical properties as well as the trends in properties of their hydrides and oxides. (20 marks)

7.

Write an essay on amino acids, polypeptides and proteins. Your essay should include the properties of amino acids in aqueous solutions and a method of separation for a mixture of amino acids, as well as the constitution of polypeptides and proteins and their hydrolysis. (20 marks) END OF PAPER

9

HKALE Chemistry (AL) 1995-98 Paper I 1997 SECTION A Answer ALL questions in this Section. Write your answers in the spaces provided. 1.

(a)

At room temperature, iron has a body-centred cubic structure. (i) Draw the unit cell representation of iron. (ii) Deduce the number of atoms in one unit cell of iron. (2 marks)

(b)

In a nickel-plating experiment, after passing a current of 5.0 A through an electroplating bath containing a nickel efficiency is 100%, deduce the oxidation state of nickel in the compound. (3 marks)

(c)

Arrange, with explanation, the following chemical species in the order of decreasing size. F, O and O(3 marks)

(d)

Explain why (i) the boiling point of HF is higher than that of HC1; (ii) the boiling point of HI is higher than that of HBr. (2 marks)

2.

(a)

Consider the following dissociation reaction: PC15(g)

PC13(g)+C12(g)

At 400 K and 101 kPa pressure, the percentage dissociation of PC15(g) is 86%. (i) Calculate Kp for the reaction at 400 K. (ii) State the effect of an increase in pressure (I) (II)

on Kp, and On the percentage dissociation of PC15(g). (4 marks)

(b)

Account for the difference in Ka values given in the following equilibrium reaction: H2SO4(aq) + H2O( l )

H3O+(aq) + HSO4-(aq) Ka=7.94 X 102 mol dm-3

HSO4-(aq) + H2O( l )

H3O+(aq) + SO42-(aq) Ka=0.10 mol dm-3 (2 marks)

(c)

Consider the standard reduction potentials listed below: [FeF6]3-(aq)+eI2(aq)+2eFe3+(aq)+e-

[FeF6]4-(aq) 2I-(aq) Fe2+(aq)

E =+0.40 V E =+0.54 V E =+0.76V

Explain the following observations, giving a balanced equation in each case. (i) When Fe(NO3)3(aq) is added to KI(aq), a brown solution is formed. (ii) When concentrated KF(aq) is added to the resulting solution in (i) above, the brown colour fades. (4 marks) 3.

(a)

For each of the following materials, identify ONE inorganic compound which is an active ingredient: (i) (ii) (iii) (iv)

Photographic film Gun powder Bleaching powder Antacid (3 marks)

10

HKALE Chemistry (AL) 1995-98 Paper I

(b)

For each of the following sulphur-containing chemical species, state its shape and the oxidation state of sulphur. (i) H2S (ii) SO2 (iii) SO42(3 marks)

4.

(c)

The effluent from an electroplating factory contains toxic Cr2O72-(aq). Suggest, with balanced equations, how all chromium-containing species can be removed from the effluent before discharge. (4 marks)

(a)

The formula HO2CCH=CHCO2H Can represent two compounds. (i) Draw a structure for each compound, clearly showing the difference between them. (ii) One of the compounds reacts with P2O5(s) to give compound A. Give the structure of A. (2 marks)

(b)

(i) Draw all possible isomeric structures of dimethylbenzene. (ii) Upon oxidation, one of the isomers of dimethylbenzene produces a compound with the formula C8H6O4. This Compound on condensation with ethane-1,2-diol gives a useful textile material B. Give the structure of B. (3 marks)

(c)

(i) Give the hybridization state of the carbon atoms and the bond angles in ethene. (ii) Outline a free radical mechanism for the conversion of ethene to poly(ethene). Your answer should include Appropriate arrows to show how the new bonds are made. (3 marks)

(d)

5.

(a)

Suggest, with explanation, a chemical reaction which would enable 4-methylbenzoic acid and 4-methylphenol to be distinguished from each other. (2 marks) Give a structure for each of the compounds D, E, F, G and H : (1) LiAlH4 (2) H2O

(i) CH3CH2CONH2

Br2/NaOH(aq) (ii) CH3CH2CONH2

SOCl2

(iii) CH3CH2CO2H

(1) O3 (iv) C8H16 G

(2) Zn/CH3CO2H

D

E

F

Butanal only

I2/NaOH(aq) (v) C4H8O H

triiodomethane + sodium salt of a carboxylic acid

(5 marks) 11

HKALE Chemistry (AL) 1995-98 Paper I

(b)

Consider the following reactions: conc. H2SO4 heat

HBr

J

CH3CH2COC1

L

CH3CH2CH2OH Na2Cr2O7 H3O+

K

NHNH2 NO2 NO2

M

N

Give structures for J, K, L, M and N. (5 marks) 6.

(a)

(i) Vegetable oils (e.g. peanut oil) can undergo the following chemical reactions to give useful solid products P and Q. Excess H2/Pt Vegetable oil

P

NaOH(aq)

Q

heat Give one use each for P and Q. Suggest a possible structure for P. (ii) What is meant by the ‘iodine value’ of a fat/oil? (3 marks) (b)

Consider the reaction: R C12H22O11 Disaccharide S

C6H12O6 glucose only

(i) Give a chemical reagent R for the reaction. (ii) Draw a possible structure for S, clearly showing the linkage between the monosaccharide units. (2 marks) (c)

(i) Explain with the help of chemical equations, why ozone in the stratosphere is important to life on earth. (ii) Show, with the help of chemical equations, how the presence of chlorofluorocarbons (CFCs) can influence the amount of ozone in the stratosphere. (iii) What have CFCs been widely used for in the past? Suggest a more environmentally acceptable chemical to replace CFCs. (5 marks) END OF SECTION A

SECTION B Answer ALL questions in this section. Write your answers in the spaces provided. 7.

(a)

Briefly describe how a sample of dry chlorine gas can be prepared in the laboratory. Draw a labeled diagram of the laboratory set-up and state the safety precaution(s) that is/are required. (6 marks)

(b)

An aqueous solution contained 0.40 g of a complex salt Cr(NH3)5Cl3. The free chloride ions present in the solution required 21.90cm3 of 0.150 M silver nitrate(V) solution for complete precipitation. Deduce the structural formula of the complex ion present in the salt. (4 marks) 12

HKALE Chemistry (AL) 1995-98 Paper I

8.

(a)

(i) Give the reaction conditions and the necessary chemicals/reagents required for the formation of benzenediazonium ion from phenylamine. (ii) Benzenediazonium ion reacts with naphthalene-2-ol to give compound T. Give the structure of T. (3 marks)

(b)

You are provided with a mixture of two liquids, hexan-1-amine (U) and ethyl ethanoate (W). Outline an experimental procedure, based on a solvent extraction process, to enable U to be separated from W. (3 marks)

(c)

For each of the following groups of compounds, suggest a chemical test which would enable each compound to be distinguished from the other(s). In your answer also give the changes that you would expect to observe for each compound. (i) CH3CH2CH2OH, (CH3)2CHOH and (CH3)3COH (ii) C6H5CH2I and C6H5CH2C1 (4 marks)

END OF SECTION B

SECTION C Answer ONE question only and write your answers in the AL(D) Answer Book. Marks will be allocated approximately as follows: Chemical knowledge

50%

Organization

30%

Presentation (including proper use of English) 20% Equations, suitable diagrams and examples are expected where appropriate. The examiners are looking for the ability to analyse, to evaluate and to express ideas clearly. 9.

Write an essay on the variation in properties of the Group II elements and their compounds. (20 marks)

10. Write an essay on the chemistry of amines. (20 marks) END OF PAPER

13

HKALE Chemistry (AL) 1995-98 Paper I 1998 SECTION A Answer ALL questions in this Section. Write your answers in the spaces provided. 1.

(a)

Arrange the following chemical species in the order of increasing ionization enthalpy. Explain your arrangement. N+, N and O (3 marks)

(b)

(i) An iodine molecule can be represented by the diagram below, with each dot ‘‧’ representing an atomic nucleus.

(I)

Using one or more diagrams of this kind, illustrate your understanding of the two terms ‘covalent radius’ and ‘van der Waals’ radius’.

(II)

Account for the difference between the covalent radius and van der Waals’ radius for iodine.

(ii) Explain why the carbon-oxygen bond lengths in CO and CO2 are different. (4 marks) (c)

The theoretical lattice enthalpies of NaCl(s) and AgCl(s), and the experimental lattice enthalpy of AgCl(s) are given in The table below. Compound NaCl(s)

Theoretical lattice enthalpy /kJ mol-1y -770

Experimental lattice enthalpy /kJ mol-1 ?

AgCl(s)

-833

-905

(i) Calculate the experimental lattice enthalpy of NaC1(s) using the following thermochemical data. △H /kJ mol-1 108 495 239 -349 -411

Atomization enthalpy of Na(s) First ionization enthalpy of Na(g) Bond dissociation enthalpy of C12(g) Electron affinity of C1(g) Enthalpy change of formation of NaCl(s) (a)

The phase diagram for carbon dioxide is shown below. D

12 10 pressure/atm

2.

8

C

6

B

4 2 0

A 100

200 temperature/K

300

(i) Identify points B and C. (ii) What is the physical meaning of point C? (iii) Starting with a sample of CO2(g) at room temperature and atmospheric pressure, suggest how the following can be obtained. (I) Solid CO2 (dry ice) (II) Liquid CO2 (4 marks) 14

HKALE Chemistry (AL) 1995-98 Paper I

2.

(b)

Which compound, H2O or F2O, would you expect to have a higher boiling point? Explain your answer. (2 marks)

(c)

At 4200K, the equilibrium constant for the following reaction is 1.2 X 10-2. N2(g) + O2(g)

2NO(g)

1.0 mol of O2(g) and 2.0 mol of N2(g) are allowed to react in a 2.0 dm3 closed container. Calculate the concentration of N2(g), in mol dm-3, in the equilibrium mixture at 4200 K. (3 marks) (a)

For each of the nitrogen-containing chemical species below, state its shape and the oxidation state of nitrogen. (i) NO2+ (ii) NH3 (iii) NO3(3 marks) Sketch the trends for the properties mentioned in (i), (ii) and (iii) below, and account for the trend in each case.

Melting point

(i) Melting point of the alkali metals, Li, Na and K

Li

Na

K

(ii) Boiling point of the Period 3 elements, Na, Mg and Al

Boiling point

(b)

Na

Mg

Al

(iii) Solubility in water of the Group II sulphates(VI), MgSO4, CaSO4, SrSO4 and BaSO4. Solubility in water

3.

MgSO4

CaSO4

SrSO4

BaSO4

15

HKALE Chemistry (AL) 1995-98 Paper I (7 marks) 4.

Alcohol E has the structure CH3CH(OH)C2H5. (a)

(i) Draw a three-dimensional representation of E. (ii) What type of isomerism can be exhibited by E? (2 marks)

(b)

(i) Draw the structures of three structural isomers of E, all of which are alcohols. (ii) Describe how the reagent Zn/concentrated HCl can be used to distinguish E from the three structural isomers. (3 marks)

(c)

On treatment with dilute H2SO4(aq), E gives mainly two isomeric compounds, F and G, both of which have the Formula C4H8. On treatment with bromine, both F and G give a product H with formula C4H8Br2. (i) Draw structures for F, G and H. (ii) What is the isomeric relationship between F and G? (iii) Outline the mechanism for the formation of H from either F or G. (5 marks)

5.

Consider the five reactions of butanone (C4H8O) J shown in the reaction scheme below: ?

K (C4H10O)

HCN

L (C5H9NO)

NaHSO3

butanone (C4H8O) J

M

I2/NaOH(aq) 2,4-C6H3(NO2)2NHNH2

(a)

N+P

R (a red precipitate)

Suggest a reagent by which K may be formed and give the structure for K. (1 mark)

(b)

State the type of reaction involved in the formation of L and outline the mechanism of the reaction. (3 marks)

(c)

Give structures for compounds M, N, P and R. (4 marks)

(d)

(i) S is a structural isomer of J. S also reacts with 2,4-C6H3(NO2)2NHNH2 to give a red precipitate. Draw the structure of S. (ii) How many J and S be identified by making use of their reactions with 2,4-C6H3(NO2)2NHNH2 ? (2 marks)

6.

(a)

Most natural fats and oils are mixed glycerides, and may be characterized by their ‘iodine value’, two examples of which are shown below: Fat/oil Butter fat Corn oil

Iodine value 30 120

(i) Draw the structure of a typical natural fat or oil. (ii) Assuming that butter fat and corn oil glycerides have similar relative molecular masses, suggest what information About their chemical structures may be deduced from the iodine values in the above table. 16

HKALE Chemistry (AL) 1995-98 Paper I (3 marks)

6.

(b)

With the help of formulae, outline the chemical reaction involved in each of the following processes: (i) Saponification of an animal fat (ii) Hardening of a vegetable oil (2 marks)

(c)

There are two processes which cause rancidity in fats and oils. Complete the table below by stating the type of chemical reaction involved in each process, the expected products, and a method to prevent each process from occurring. Type of chemical reaction involved

Expected products

Method to prevent the process from occurring

(1) (2)

(3 marks) (d)

When Fehling’s solution is added to glucose, HOCH2(CHOH)4CHO, a red precipitate is observed. Give the formulae of the products formed from the reaction, including the red precipitate. (2 marks) END OF SECTION A

SECTION B Answer ALL questions in this section. Write your answers in the spaces provided. 7.

(a)

Briefly describe how you would test for the presence of the following chemical species in a sample of iron alum, (NH4)2SO4‧Fe2(SO4)3‧24H2O. (i) ammonium ions (ii) iron (III) ions (iii) sulphate (VI) ions (iv) water of crystallization (4 marks)

(b)

The sulphur dioxide content in white wine was determined by an experiment described below: 25.0cm3 of a sample of white wine was transferred to a conical flask. 15cm3 of 1M NaOH(aq) was added to the flask and the mixture was allowed to stand for 15 minutes. 15cm3 of 2M H2SO4(aq) was then added and the resulting solution was quickly titrated with 0.0050M I2(aq). 12.9cm3 of the I2(aq) was required to reach the titration end point. (i) What is the purpose of adding the 2M H2SO4(aq)? (ii) Why should the titration be carried out quickly? (iii) Briefly describe how the end point of the titration can be determined. (iv) Calculate the sulphur dioxide content, in mg dm-3, in the sample of white wine. (6 marks) 17

HKALE Chemistry (AL) 1995-98 Paper I

8.

(a)

Show how you would (i) Determine whether a sample of C2H5CH(OH)CH3 is in the (+) form or (±) form. (ii) Distinguish between propan-2 and propanone using spectroscopy, (iii) Distinguish between C6H5COCl and C6H5COBr using a chemical test. (3 marks)

(b)

20.0g of 4-nitrobenzoic acid (C7H5NO4) reacted with PC15 to give a product which reacted exothermically with NH3 to give T. After treatment with Br2( l ) ad NaOH(aq), T gave a solid. Crystallization of the solid from ethanol gave 9.3g of U (C6H6N2O2). (i) Calculate the percentage yield of U formed from 4-nitrobenzoic acid. (ii) Give the structures of T and U. (iii) Briefly give three reasons which could explain why the yield of U in the above preparation is not quantitative (i.e.100%). (4 marks)

(c)

You are provided with a mixture of two liquids, heptanoic acid and hexan-3-one. Outline an experimental procedure, Based on a solvent extraction process, to isolate pure heptanoic acid in good yield. (3 marks) END OF SECTION B

SECTION C Answer ONE question only and write your answers in the AL(D) Answer Book. Marks will be allocated approximately as follows: Chemical knowledge

50%

Organization

30%

Presentation (including proper use of English) 20% Equations, suitable diagrams and examples are expected where appropriate. The examiners are looking for the ability to analyse, to evaluate and to express ideas clearly. 9.

Write an essay on the possible boiling point-composition relationships of a mixture of two miscible liquids. (20 marks)

10. Write an essay on the compound, CH3CH(NH2)CO2H. Your essay should include such topics as its expected chemical reactions and physical properties, and how the compound may Be obtained from natural sources. (20 marks)

END OF PAPER

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