pahang stpm trial 2010 chemistry [w ans]

1

CONFIDENTIAL*/ SULIT* 962/1

TRIAL STPM 2010

(PEPERIKSAAN PERCUBAAN STPM 2010)

CHEMISTRY (KIMIA)

PAPER 1 (KERTAS 1)

One hour and forty-five minutes (Satu jam empat puluh lima minit)

Instructions to candidates:

DO NOT OPEN THIS BOOKLET UNTIL YOU ARE TOLD TO DO SO.

There are fifty questions in this paper. For each question, four suggested answers are given. Choose one correct answer and indicate it on the multiple-choice answer sheet provided.

Read the instructions on the multiple-choice answer sheet very carefully. Answer all questions.

Marks will not be deducted for wrong answers.

Arahan kepada calon:

JANGAN BUKA BUKU SOALAN INI SEHINGGA ANDA DIBENARKAN BERBUA'T DEMIKIAN.

Ada lima puiuh soalan d a l a m kertas ini. Bagi setiap soalan, empat cadangan jawapan diberikan. Pilih satu jawapan yang betul dan tandakan jawapan itu pada helaian jawapan aneka pilihan yang dibekalkan.

Baca arahan pada helaian jawapan aneka pilihan itu dengan teliti.

Jawab semua soalan. Markah tidak akan ditolak bagi jawapan yang salah.

This question paper consists of 15 printed pages and 1 blank page.

(Kertas soalan ini terdiri daripada 15 halaman bercetak dan 1 halaman kosong.)

TRIAL STPM 962/1 [Turn over (Lihat sebelah) *This question paper is CONFIDENTIAL until the examination is over. CONFIDENTIAL* *Kertas soalan ini SULIT sehingga peperiksaan kertas ini tamat. SULIT*

http://edu.joshuatly.com/ http://www.joshuatly.com/

2

Section A

Four suggest answers labeled A, B, C and D are given for each question. Choose one correct answer. 1. An element X with the electronic configuration of 1s22s22p63s23p5 exists as isotopes mX a nd nX which have 18 and 20 neutrons respectively.What is the percentage abundance of mX ?

[ relative atomic mass of X is 35.5]

A. 25.0 B. 35.0 C. 65.0 D. 75.0

2. A phase diagram of water is shown below.

What can be deduced from the phase diagram?

A. An increase in pressure will increase the freezing point of water. B. In increase in pressure will increase the boiling point of water C. Ice sublimes at a pressure higher than 611 Pa D. Water exists as liquid at a pressure of 611 Pa and a temperature of 298 K.

Pressure/Pa

Temperature/K


3

3. Transition of electrons between energy levels in an atom will cause an absorption or

emission of light.Which energy level diagram shows the transition of electrons that emits light with the lowest frequency?

4. The first, second, third and fourth ionization energies (in kJ mol-1) for an element Y is

given below. 900, 1760, 3240, 19700

The element Y forms a covalent chloride that reacts with water to give an acidic solution.The element Y could be

A. Aluminium B. Beryllium C. Sulphur D. Magnesium


4

5. The first to fourth ionisation energies of four elements are as follows. Elements Ionisation energy/kJ mol-1

First Second Third Fourth P 577 1820 2740 11600 Q 418 3070 4600 5860 R 736 1450 7740 10500 S 494 4560 6940 9540 Which statement about P,Q,R and S is true? A. Q is more electronegative than S. B. Melting point of S is higher than that of R. C. Enthalpy of vapourisation of Q is higher than that of R. D. Oxide Q is more basic than oxide P. 6.Which one of the following pairs of molecular formula and molecular geometry is true? Molecular formula Molecular geometry A. SO4

2- Octahedral B. PCl5 Trigonal bipyramidal C. SO3 Tetrahedral D. H2O Trigonal planar 7. The conductivity of a metal is due to the delocalised electrons in the conduction band. How many electrons are found in the conduction band of a 6.0 g magnesium metal strip? [ Relative atomic mass of Mg is 24.0;Avogadro constant is 6.02 X 1023 mol-1] A. 3.01 x 10 23

B. 3.01 x 10 24 C. 5.02 x 10 23 D. 5.02 x 10 24 8. The rate equation of the reaction 2NO (g) + Cl2(g) → 2 NOCl (g) is Rate = k[NO]2[Cl2] Which of the following statements about this reaction is correct? A.The overall order of reaction is 2 B. The rate constant k decreases when the temperature increases. C. If the concentration of NO is doubled, the rate of reaction is increased by a factor of 2. D. If the concentration of both NO and Cl2 are doubled, the rate is increased by a factor of 8


5

9. Hydrogen peroxide and iodide ion react in the presence of hydrogen ion to produce iodine and water according to the equation. H2O2 + 2I- + 2 H+ → 2 H2O + I2 The rate equation for this reaction can be represented by Rate = k[H2O2]

p[I-]q[H+]r In the kinetic experiment of the reaction above,the following graphs are Obtained.

What is the order of the reaction with respect to H2O2, I

- and H+ ? H2O2 I

- H+ A. 0 1 2 B 1 1 0 C 1 1 2 D 2 1 0

Concentration, Mol/dm3


6

10. When 0.20 mol of iodine and 0.20 of hydrogen are heated to equilibrium at 650C in a 1 dm3 vessel, the equilibrium mixture contains 0.044 mol of iodine. I2(g) + H2(g) 2 HI (g) What is the numerical value Kc for the reaction? A. 0.30. B. 19.3 C. 50.3 D. 10.3 11.Which of the following reactions is represented by the graph shown in figure which shows the effect of pressure on percentage yield? Pressure (atm) Percentage yield A. W(g) 2 Z (g) B. W(g) + V(g) 2 Z (g) C. W(g) + V(s) Z(g) D. W(g) + 2V(s) Z(g) 12. Phosphorus pentachloride dissociates when heated to produce to produce an equilibrium mixture PCl5 (g) < ==== > PCl3 (g) + Cl2 (g) When m g of PCl5 is heated at a constant pressure,p and a fixed temperature,T its partial pressure at equilibrium is 1/7 p.What is the equilibrium constant,Kp at this temperature? A. 9/7 p B. 18/7 p C. 6p D. 7p


7

13. A solution contains propanoic acid and sodium propanoate. Which of the following expressions can be used to calculate the concentration of hydrogen ions in the solution? A. [H+] = Ka[acid] B. [H+] = lg Ka C. [H+] = Ka [acid] [salt] D. [H+] = Ka [salt] [acid] 14. The degree of dissociation of 0.20 mol dm-3 solution of an acid HA is 0.018 %.The pH of the acid is 1.0.What is the value of Ka (mol dm-3) for HA? A. 0.1 x 0.1 0.2 B.0.4 x 10 -5 C 0.9 x 10-5 D.1.8 X 10-5 15.A solution containing 7 x 10-7 mol dm-3 Ag + ions is required for a reaction. Which of the following saturated solutions can be used for this purpose?

Saturated solution of the silver salt

Ksp of the silver salt

A AgCl 2.0 x 10-10 mol2 dm-6 B AgBr 5.0 x 10-13 mol2dm-6 C Ag2SO4 2.0 x 10 -5 mol3dm-9 D Ag2CrO4 1.3 x 10 -12 mol3dm-9

16. Which of the following statements about electrolysis is correct? A.Oxidation occurs at the cathode B. Electrons flow from the cathode to the anode in the external circuit. C. The more reactive the metal,the less readily the metal is discharged during electrolysis. D. The number of moles of a metal deposited during electrolysis is proportional to the quantity of electricity used and the charge on the metal ion. 17. If 0.125 A of electric current is passed through concentrated copper(II)sulphate solution for 5.0 hours,what mass of copper and volume of chlorine( at stp) are produced? ( 1F = 9.65 x 104 Cmol-1 ; molar volume of gas at stp = 22.4 dm3)

Mass of copper (g) Volume of chlorine (dm3) A 0.74 0.26 B 0.74 0.52 C 0.37 0.26 D 0.37 0.52


8

18. The standard electrode potential for nickel and zinc are given below Zn2+(aq) + 2e = Zn(s) E = -0.76V Ni2+ (aq) + 2e = Ni (s) E = - 0.25 V Based on the data given above,we can conclude that A.nickel is a stronger reducing agent than zinc B. the Zn2+ (aq) ion is a stronger reducing agent than the Ni2+ (aq) C. zinc will displace nickel from a solution of Ni2+ (aq) ions D. nickel is the positive pole when it is connected to the standard hydrogen electrode. 19. The standard electrode potentials for three half-cells are given below: J2+ /J E = - 0.44 V L2+/L E = - 0.76 V T2+/T E = + 0.34 V Which of the following can reduce Sn2+(aq) to Sn(s) at 298 K ( The standard electrode potential for Sn2+ (aq)/Sn(s) at 298 K is -0.14V) A. J and L only B. J,L and T C. J2+ and L2+ D. L2+ and T only 20. Calculate the emf of a Daniell cell at 25 C if the concentration of Zn2+(aq) is 0.25 mol dm-3 and the concentration of Cu2+(aq) is 0.15 mol dm-3. Given that Cu2+ + 2e = + 0.34 V Zn2+ + 2e = - 0.76 V A. + 1.10 V B. + 1.09 V C. – 1.06 V D. - 1.09V 21. Which of the following elements belongs to Group 2 in the Periodic Table?

Element Melting point / C Density/ g cm-3 A 98 0.97 B 180 0.53 C 850 1.54 D 3500 2.25


9

22. Aluminium chloride reacts with an ether, (CH3)2O to form a compound with the formula, (CH3)2.AlCl3 .In this reaction aluminium acts as a

A. Lewis acid B. Lewis base C. Bronsted acid D. Bronsted base

23. Aluminium is used for making carbonated soft drink cans.Which of the following is the most important reason explaining why aluminium is used?

A. Aluminium can be recycled B. Aluminium has a low density C. Aluminium is a good conductor of heat D. Aluminium is resistant to corrosion by weak acids.

24.A group 14 tetrachloride,XCl4 has the following properties. The tetrachloride is

A. SiCl4 B. PbCl4 C. SnCl4 D. GeCl4

25. Nitrogen oxides have high positive standard enthalpies of formation, ∆Hf .Which of the following is the major factor for the high positive value of ∆Hf ?

A. The tendency of oxygen to form oxides B. The high electron affinity of the oxygen atom C. The high bond energy of the nitrogen,N2 molecules. D. The nitrogen and oxygen atom have similar electronegativities.

26. Which element forms the complex ion ,[ XCl4]

- ?

A. Manganese B. Chromium C. Copper D. Lead

Undergoes hydrolysis readily Decomposes at room temperature to produce chlorine


10

I II 27. Butan-2-ol → But-2-ene → 2- chlorobutane What are the chemical needed for the conversion of I and II ? I II A H2SO4 Chlorine gas B High concentrated H2SO4 Hydrogen chloride gas C Liquidify HNO3 aqueous Hydrogen chloride D Acidified KMnO4 HCl aqueous

28. Chlorination of benzene is carried out by using iron as catalyst.The function of iron in this reaction is to produce A. chlorine free radicals B. chloride ions C. nucleophiles D. electrophile 29. Which of the following compound is expected to have the highest boiling point? A. CH3CH2CH2CH2Cl B. CH3CH2CH2CH3 C. CH3CH(OH)CH2CH3 D. CH3CH2OCH2CH3

30. CH3CH2Br reacts with an aqueous solution of potassium hydroxide forming CH3CH2OH, whereas (CH3)3CBr reacts with an ethanolic solution of potassium hydroxide forming CH2 =C(CH3)2 as the major product. Which statement is true of the two reactions? A The reactions occur at room temperature. B The reactions occur through the formation of carbocation. C The reactions are nucleophilic substitution and elimination respectively.

D The rate of each reaction is independent of the concentration of OH– ions.

31.A compound has the following chemical properties.

(i) It gives a positive iodoform test. (ii) It decolourises acidified aqueous potassium manganate (VII). (iii) It reacts with phosphorus pentachloride to produce hydrogen chloride gas. The compound is

A CH3CH2OH B CH3COCH3

C (CH3)3COH

D (CH3CH2)2CHOH


11

32. The structural formula of progesterone, a sex hormone, is shown as follows.

CH3 H3C C=O

H3C

O

H H Which of the following statements is true of progesterone? A It has a planar ring structure. B It has three chiral carbon atoms. C It reacts with Fehling solution. D It reacts with aqueous potassium manganate (VII).

33..Which of the following compounds reacts by nucleophilic addition? A CH3CH2OH B CH3CH2Br

C CH3CHO D C6H6

34 2-Chloro-2-methylbutane and 1-chlorobutane are separately reacted with aqueous potassium hydroxide. The reagent that can be used to distinguish the products of the reactions is A Na B Br2 /CCl4 C concentrated H2SO4 D concentrated HCl /ZnCl2

35. Compound Z has the composition percentage by mass: carbon, 40.0%; hydrogen, 6.7%; oxygen, 53.3%. Compound Z also has a chiral carbon atom and relative molecular mass 90.0. Which of the following statements is not true of compound Z? [Relative atomic mass: C = 12.0, H = 1.0, O = 16.0]

A It can be prepared from propanenitrile. B It produces effervescence with aqueous sodium hydrogen carbonate. C It produces a yellow precipitate when heated with alkaline iodine solution.

D. It decolourises acidified potassium manganate(VII) solution when heated 36 Which of the following could not be used to differentiate between CH3CHO and CH3COCH3? A Tollen’s reagent B Fehling’s solution C Iodoform test D Mass spectrometry


12

37. Hydrocarbons undergo various reactions. One of the reactions involving 3, 3-dimethyloctane is shown below.

X 3,3-dimethyloctane -------- > products

X could be A 450 C, Al2O3/SiO2 B H2SO4(conc.), 180 C C NaOH(aq), reflux D KCN(aq)/ ethanol, reflux

38. Which of the following compounds can form condensation homopolymers?

A CH2 = CHCl B CH2 = C(CH3)COOCH3 C H2NCH2CH2CH2CH2NH2 D H2NCH2CH2CH2CH2COOH

39.Plastic can be classified as thermoplastic and thermosetting plastic based on its thermal properties. Which is a thermosetting plastic?

A. Bakelite B. Perspex

C. Polystyrene D. Polyvinyl chloride

40. Ziegler-Natta catalyst is used in addition polymerisation of ethene Which statement is not true of the process? A It requires a low pressure. B It requires a low temperature. C I t p r o d u c e s h i g h d e n s i t y poly(ethene). D It is an example of free radical polymerisation.


13

Section B

For each of the questions in this section, one or more of the three numbered statements 1 to 3 may be correct the responses A to D should be selected as follows:

A B C D

1 only is correct 1 and 2 only are correct

2 and 3 only are correct

1,2 and 3 are correct

41. An enzyme found in the stomach operates at a maximum efficiency when in an aqueous solutions buffered at pH 5.Which combination of substances when dissolved in 10 dm3 of water give the necessary buffer solution? 1.5 mol of CH3COOH and 5 mol of CH3COONa 2. 10 mol of NH3 and 10 mol of NH4Cl 3. 1 mol of HCl and 1 mol of CH3COONa 42.

The boiling point-composition diagram for two pure liquids P and R is given above. Which of the following statements could be correct? 1. R is less volatile than P 2. The liquid with composition Q boils at T2

3. The liquid with composition Q can be separated into pure P and pure R by fractional distillation. 43. Which statements about the reaction given are correct? IO3

- (aq) + 2I- (aq) + 6H+(aq) + 6 Cl-(aq) → 3ICl2-(aq) + 3 H2O (l)

1.There is no change in oxidation number of chlorine 2.The oxidation number of iodine in iodate ion,IO3

- changes from +5 to +1 3. The iodide ion is reduced to ICl2

-

Boiling point


14

44. Which of the following reactions does the value of ∆ H represents both enthalpy change of formation and enthalpy change of combustion ? 1. S(s) + O2(g) → SO2 (g) 2. C(s) + O2(g) → CO2(g) 3. H2 (g) + ½ O2(g) → H2O (l) 45. Which of the following steps in the Born-haber cycle for the enthalpy change of formation of calcium oxide has a negative ∆ H value? 1. O(g) + e → O-(g) 2. ½ O2(g) → O (g) 3. Ca(s) → Ca(g) 46. Compound X has the formula [CoCl3(NH3)3].The properties of X include 1. X has an octahedral structure 2. Oxidation state of Cr is +3 3. X exhibits geometric isomerism,fac and mer 47. The colour changed from pale blue to deep blue when ammonia is added to an aqueous solution of copper(II) salt as shown in the reaction below is caused by [Cu(H2O)6]

2+ → [Cu(NH3)4]2+

Pale bule deep blue

1.NH3 is a stronger ligand than H2O. 2.The central copper ion has the same oxidation number. 3.The central copper atom has same number of electrons 48. Adrenaline is a hormone with the formula OH

Which of the following statements about adrenaline is correct? 1.It is a secondary amine 2.It forms a salt when it reacts with dilute nitric acid 3. It produces nitrogen gas when it reacts with nitrous acid.

CH(OH)CH2NHCH3

HO


15

49. Glutamine has the formula H2N-CH-CH2CH2-CONH2

COOH

Based on the formula,we can deduce that 1. glutamine is soluble in water 2. glutamine shows optical isomerism 3. ammonia is liberated when glutamine is heated with aqueous sodium hydroxide. 50. The physical properties of a polymer can be altered by cross-linking.Cross-linking 1.makes the polymer harder 2.increases the melting point of the polymer. 3. causes the polymer to be insoluble in organic solvents.

End of the question paper


Identity card number ................................................ Centre number/index number: ........................... (Nombor kad pengenalan) (Nombor pusat/angka giliran)

962/2

TRIAL STPM 2010

(PEPERIKSAAN PERCUBAAN STPM 2010)

CHEMISTRY (KIMIA)

PAPER 2 (KERTAS 2)

Two and a half hours (Dua jam setengah)

For examiner’s use

1

2

3

4

5

6

7

8

9

10

Total

This question paper consists of 10 printed pages.

Instructions to candidates: DO NOT OPEN THIS QUESTION PAPER UNTIL YOU ARE TOLD TO DO SO. Answer all questions in section A.Write your answers in the spaces provided.All working should be shown.For numerical answers,units should be quoted wherever they are appropriate. Answer any four questions in section B.Write your answers on the answer sheets provided.Begin each answer on a fresh sheet of paper and arrange your answers in numerical order.Tie your answer sheets to this question paper.


1

SECTION A

Answer all question in this section

1. The reaction between hydrogen and iodine can be represented by the following equation:

H2(g) + I2(g) 2HI(g) H = +52 kJ mol–1

Kinetic data are available for both forward and reverse reactions. A series of experiments to investigate the kinetics of the forward reaction was carried out at a constant temperature. The results are shown in Figure 1.

Experiment Initial concentration of

H2 / mol dm–3

Initial concentration of

I2 / mol dm–3

Initial rate

/ mol dm–3 s–1

1 2.0 × 10–3 3.0 × 10–3 l.2 × 10–6

2 6.0 × 10–3 3.0 × 10–3 3.6 × 10–6

3 6.0 × 10–3 6.0 × 10–3 7.2 × 10–6

Figure 1

(a) Explain the meaning of each of the following terms:

(i) rate constant;

(1)

(iii) overall order of reaction.

(2)


2

(b) (i) Use the results in Figure 1 to work out the order of the forward reaction with respect to both hydrogen and iodine, explaining your reasoning.

(3)

(ii) Write the rate equation for the reaction between hydrogen and iodine.

(1)

(iii) Calculate the value of the rate constant for the forward reaction and give its units.

(2)

(c) The experiment was repeated with the following initial concentrations for reactants:

[H2] = 4.0 × 10–3 mol dm–3 [I2] = 5.0 × 10–3 mol dm–3

Calculate the initial rate of the reaction.

(1)

(Total 10 marks)


3

2. (a) Write an equation for the reaction which occurs when the weak acid HA is added to water.

........................................................................................................................

(1)

(b) Write an expression for the dissociation constant, Ka, for the weak acid HA.

........................................................................................................................

(1)

(c) The dissociation of the acid HA is an endothermic process. Deduce the effect, if any, of

(i) an increase in temperature on the value of the dissociation constant, Ka

..............................................................................................................

(ii) an increase in temperature on the pH of an aqueous solution of the acid

..............................................................................................................

(iii) an increase in the concentration of the acid on the value of Ka

...............................................................................................................

(3)

(d) Identify a compound which could be added to aqueous ethanoic acid so that the pH of the resulting solution would not change significantly if a small volume of dilute hydrochloric acid were added. State the name given to solutions which behave in this way.

Compound......................................................................................................

Name..............................................................................................................


4

(2)

(e) The diagram below shows the trend in the first ionisation energies of the elements from neon to aluminium.

(i) Draw crosses on the graph to show the first ionisation energies of silicon, phosphorus and sulphur.

(1)

(ii) Explain why the first ionisation energy of neon and that of magnesium are both higher than that of sodium.

Explanation for neon

.......................................................................................................................

Explanation for magnesium

...................................................................................................................... (2)

(Total 10 marks)

Ne Na Mg Al Si P S

First ionisationenergy

Element


5

3. a. The ionic radius of the Group 2 element is given in the table below.

Ion Be2+ Mg2+ Ca2+ Sr2+ Ba2+ Ionic radius (nm) 0.027 0.072 0.099 0.113 0.136

(i) Write the electronic configuration of Mg2+ ion and Sr2+ ion.

Mg2+ion :....................................................................................................................

Sr2+ion :.....................................................................................................................

(ii) How would you expect the ionic radius of Al3+ ion to be compared to that of Mg2+

ion. Explain your answer. ...................................................................................................................................

..................................................................................................................................

..................................................................................................................................

(iii) The hydrated Be2+ ion has the formula, [Be(H2O)4]2+. State one property shown by

beryllium salts in water.

..................................................................................................................................

(5)

b. The carbonates of the Group 2 elements decompose on heating.

(i) Write the chemical equation for the decomposition of magnesium carbonate.

...................................................................................................................................

(ii) Explain why magnesium carbonate does not decompose spontaneously.

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

(iv) The thermal stability of the carbonates increases with the proton number of the element. Suggest an explanation for the effect of the size of the cation on the thermal stability of the carbonates.

..................................................................................................................................

..................................................................................................................................

..................................................................................................................................

(5)


6

4. a. Benzene undergoes electrophilic substitution reaction. In the nitration process, nitrobenzene is obtained by the mixture of two acids and benzene.

(i) Name the two acids, the condition and write a balanced equation for the reaction.

��Nameofacids:............................................................................................................

Condition:...................................................................................................................

Equation:....................................................................................................................

(3)

(ii) State the electrophile in the above reaction.

...................................................................................................................................

(iii) Using balanced equations, describe the mechanism for the substitution reaction.

(iv) State one importance of benzene in the chemical industry.

.......................................................................................................................................

(4)

b. Give the structural formulae of the organic products formed from the following reactions.

(i) CH3COCl + C6H5NH2

(ii) CH3 + H2SO4 conc

(iii) (CH3)2CCHCH3 + Br2(aq)

(3)

H20


7

SECTION B

Answer any 4 question in this section.

5. (a) Define the term electronegativity and explain why the electronegativity values of the Group II elements Be–Ba decrease down the group.

(4)

(b) Name the strongest type of intermolecular force between hydrogen fluoride molecules and draw a diagram to illustrate how two molecules of HF are attracted to each other. In your diagram show all lone pairs of electrons and any partial charges. Explain the origin of these charges. Suggest why this strong intermolecular force is not present between HI molecules.

(7)

(c) Crystals of sodium chloride and of diamond both have giant structures. Their melting points are 1074 K and 3827 K, respectively. State the type of structure present in each case and explain why the melting point of diamond is so high.

(4)

6. Methanol, CH3OH, is a convenient liquid fuel.

(a) An experiment was conducted to determine the enthalpy of combustion of liquid methanol. The energy obtained from burning 2.12 g of methanol was used to heat 150 g of water. The temperature of the water rose from 298

(i) Define the term standard enthalpy of combustion.

(ii) Use the data above to calculate a value for the enthalpy of combustion of one mole of liquid methanol.

(7)

(b) Methanol can be synthesised from methane and steam by a process that occurs in two stages.

Stage 1 CH4(g) + H2O(g) 3H2(g) + CO(g) is

Stage 2 CO(g) + 2H2(g) CH3OH(g)

(i) Explain why, in Stage 1, a higher yield of hydrogen and carbon monoxide is not obtained if the pressure is increased.

(ii) Stage 2 is carried out at a compromise temperature of 500K. By considering what would happen at higher and lower temperatures, explain why 500 K is considered to be a compromise for Stage 2.

(5)

H = +206 kJ mol–1

H = –91 kJ mol–1


8

(c) The standard enthalpies of combustion of carbon monoxide and of hydrogen

are –283 kJ mol–1 and –286 kJ mol–1, respectively. Use these data and the enthalpy change for Stage 2 to calculate a value for the standard enthalpy of combustion of gaseous methanol. (3)

7. (a) An solution of sodium chloride of concentration 2.00 mol dm-3 is electrolysed for 25 minutes using graphite electrodes. The resulting solution is then treated with hydrochloric acid of concentration 0.25 moldm-3. If the volume of hydrochloric acid needed to complete titration is15.50 cm3, calculate the magnitude of the current used during the electrolysis. (7)

(b) the partition coefficient for a solute S between ether and water is 12.50.

(i) Referring to solute S, ether and water, explain what is meant t by partition law.

(ii) suggest the conditions at which the partition law holds true.

(iii) calculate the mass of S remaining in 25.0 cm3 of water that originally contains 8.00 g of S after separate extraction with 25.0 cm3 of ether and two separated portion of 12.50 cm3 of ether. (8)

8. (a) By referring to the physical and chemical properties of aluminium, describe the

property of an aqueous solution of aluminium salt. (5)

(b) By writing equations for the reactions involved, explain;

(i) the reaction of anhydrous aluminium chloride with water. (2)

(ii) why aluminium carbonate cannot be prepared from a solution containing the Al3+ ion. (4) (iii) Aluminium chloride is a white solid that fumes in moist air and sublimes at 180

°C. (4)

9. (a) The table below shows the molecular formulae and dissociation constants, Kb at 250C for ammonia, ethylamine and phenylamine.

Compound Formula Kb / moldm-3 Ammonia NH3 1.8 x 10-5

Ethylamine CH3CH2NH2 5.4 x 10-4 Phenylamine C6H5NH2 5.0 x 10-10

(i) Arrange the compounds according to increasing basic strength. (ii) Discuss the factors that determine the relative base strength of the compounds

above. (5)


9

b. Give reagents, condition, and equations to show how each of the following compounds can be prepared from methylbenzene in the laboratory.

(i) CONH2

(ii) CH2OH

Explain one simple test to show the presence of hydroxyl group, -OH in compound (ii).

Write equations for reactions occurred. (10)

10. a. A sweet smelling liquid organic compound X has a molecular formula of C10H12O2 undergoes acidic hydrolysis to produce an acid and an alcohol,Y. The alcohol Y reacts with bromine water to produce a white precipitate. Reduction of X with lithium tetrahydridoaluminate (III) followed by acid hydrolysis produces two alcohols Y and Z. On dehydration by concentrated sulphuric acid, Z produces 2-methylpropene.

Determine the structures of X, Y and Z. Write equation for all the reactions involved. Name compound X. (11) b. Grignard reagents are organometallic compounds that are very important in the

synthesis of organic compounds. (i) State how ethyl magnesium bromide can be prepared from a named haloalkane.

(ii) Write the reaction sequence in the preparation of 2-methyl-2-butanol from ethyl magnesium bromide. (4)

END OF THE QUESTION PAPER


Trial STPM 2010 Chemistry paper 1 Answers 1 D 26 B 2 B 27 B 3 B 28 D 4 A 29 C 5 D 30 C 6 B 31 A 7 A 32 D 8 D 33 C 9 B 34 D 10 C 35 A 11 A 36 C 12 A 37 A 13 C 38 D 14 D 39 A 15 B 40 D 16 C 41 B 17 A 42 D 18 C 43 B 19 A 44 D 20 B 45 A 21 C 46 C 22 A 47 B 23 A 48 B 24 B 49 D 25 C 50 D


ANSWER AND MARK SCHEME

QUESTION 1

1. (a) (i) sum of dependent on 2nd mark or reference to ‘orders’ (1)

powers in rate equation (1) allow reference to annotated rate equation 2

(b) (i) (H2) – 1 (1)

eg rate trebles as [H2] trebles not rate doubles as [H2] doubles (1)

(I2) – 1 (1)

eg rate doubles as [I2] doubles (1)

mark these points independently allow 1 mark for orders if not clear that both are first order 4

(ii) rate = k[H2][I2] (1)

must be [H2] not [H] allow e.c.f from (b)(i) allow mark for correct answer for (b)(ii), even if (b)(i) wrong 1

(iii) rearrange correctly

correct substitution and correct consequential answer (1)

correct units (mol–1 dm3 s–1) (1)

allow e.c.f. from (b)(ii) allow e.c.f. for incorrect arrangement 2

(c) 4 × 10–6 (1) allow e.c.f. from (b)(ii) and (b)(iii) could be worked by ratio from values in table or from rate equation 1

[10]

QUESTION 2

2. (a) HA H+(aq) + A–(aq) or HA + H2O H3O+ + A– (1) 1


1

(b) Ka = [H+][A–]/[HA] or Ka = [H3O+][A–]/[HA] (1) 1

(c) (i) Increases (1)

(ii) Decreases (1)

(iii) No change (1) 3

(d) Sodium ethanoate or sodium hydroxide (1)Buffer solution (1) 2

(e) (i)

(1)

(ii) Explanation for neon

Neon’s electron is in a lower (2p) shell attracted more strongly to (or less shielded from) the nucleus (1)

Explanation for magnesium

more protons electrons in same shell or similar shielding (1)

(Total 10 marks)

Ne Na Mg Al Si P S

Firstionisationenergy (1)

(1)

(1)

Element


2

QUESTION 3

3. a. (i) Mg2+ ion: 1s22s22p6 [ 1 ]

Sr2+ ion: 1s22s22p63s23p63d104s24p6 [ 1 ]

(ii) Al3+ ion is smaller than Mg2+ ion. [ 1 ]

Al3+ ion and Mg2+ ion are isoelectronic. However the nuclear charge in Al3+ is [ 1 ]

higher than that in Mg2+ ion. Hence the size of Al3+ ion is smaller.

(iii) An aqueous solution of beryllium salt shows acidic properties due to the

dissociation of the dehydrated Be2+ ion. [ 1 ]

b. (i) MgCO3 (s) MgO(s) + CO2(g) [ 1 ]

(ii) The activation energy for the reaction is high. [ 1 ]

At room temperature the particles do not have enough energy to overcome

the activation energy. [ 1 ]

(iii) As the size of the cation increases, the charge density and the polarising [ 1 ]

power towards the CO32- decreases. Hence the carbonates become more

stable. [ 1 ]

Total : [ 15 ]

QUESTION 4

4. a. (i) Concentrated nitric acid and concentrated sulphuric acid. [ 1 ]

Temperature not exceeding 550C [ 1 ]

C6H6 + HNO3 2HSO4-- + NO2

+ + H3O+ [ 1 ]

(ii) Nitronium ion, NO2+ [ 1 ]

(iii) Step 1

+ NO2+ H [ 1 ]

NO2

Step 2

H NO2 + H+ [ 1 ]

NO2

(iv) Benzene is used as a solvent for oils and fats / can be converted to

Cumene, used for making phenol. [ 1 ]

+

+


3

b. (i) CH3CONHC6H5 [ 1 ]

OH

(ii) CH3 [ 1 ]

(iii) (CH3)2C(OH)CH2CH3 [ 1 ]

TOTAL : [15]

SECTION B

5(a) Tendency or strength or ability or power of an atom/element/nucleus to 1

attract/withdraw electrons / e– density / bonding pair / shared pair

In a covalent bond 1 (tied to M1 – unless silly slip in M1)

(If molecule/ion then = CE = 0) (NOT electron (singular) for M1) Mark as 2 + 2

Increase in size or number of shells or increased shielding or bonding 1 electrons further from nucleus

[NOT ‘increase in number of electrons’]

Decreased attraction for (bonding) electrons 1 (tied to M3)

(If ‘ion’ here, lose M3 and M4) (NOT ‘attraction of covalent bond’)

(Ignore reference to proton number or effective nuclear charge)

(b) Hydrogen bonding (full name) 1

Diagram shows at least one δ+H and at least one δ–F 1 (If full charges shown, M2 = 0)

3 lone pairs shown on at least one fluorine atom 1 H-bond indicated, between H and a lone pair on F

(If atoms not identified, zero for diag)

(‘Fl’ for fluorine - mark to Max 2)

(Max 1 if only one HF molecule shown, or HCl shown)

Dipole results from electronegativity difference or values quoted 1 (‘difference’ may be inferred)

H F H F

+ +– –

: :

: :

. .. .


4

(Allow explanation – e.g. F attracts bonding electrons more strongly than H)

Fluorine more/very electronegative or iodine less electronegative 1 or electronegativity difference too small in HI Comparison required, may be implied.

HI dipole weaker or bonding e– more equally shared - wtte 1 (c) NaCl is ionic (lattice) 1

(Treat atoms/molecules as a contradiction)

(Accept ‘cubic lattice’)

Diamond is macromolecular/giant covalent/giant atomic/giant molecular 1 (NOT molecular or tetrahedral)

(Ionic/van der Waals’ = CE = 0)

(Many) covalent/C-C bonds need to be broken / overcome 1 (NOT just ‘weakened’ etc.)

(‘Covalent’ may be inferred from diagram)

(Treat diagram of graphite (without one of diamond) as a contradiction – lose M2 but allow M3/M4])

Which takes much energy or covalent bonds are strong 1

[15]

QUESTION 6

(a) (i) enthalpy change when 1 mol of a substance (or compound) 1 is (completely) burned in oxygen (or reacted in excess oxygen) 1 at 298 K and 100 kPa (or under standard conditions) 1

(ii) heat produced = mass of water × Sp heat capacity x ∆T (or mc∆T) 1 = 150×4.18×64 (note if mass = 2.12 lose first 2 marks then conseq) = 40100 J or = 40.1 kJ (allow 39.9-40.2 must have correct units) 1 moles methanol = mass/Mr = 2.12/32 (1) 1

= 0.0663

∆H = – 40.1/0.0663 = – 605 kJ (mol–1) 1 (allow –602 to –608 or answer in J)

(note allow conseq marking after all mistakes but note use of 2.12 g loses 2 marks

(b) (i) equilibrium shifts to left at high pressure 1 because position of equilibrium moves to favour fewer moles (of gas) 1

(ii) at high temperature reaction yield is low (or at low T yield is high) 1 at low temperature reaction is slow (or at high T reaction is fast) 1 therefore use a balance (or compromise) between rate and yield 1


5

(c) ∆H = ∆Hcο(reactants) – ∆Hc

ο (products) (or correct cycle) 1

∆Hcο (CH3OH) = ∆Hc

ο(CO) + 2 × ∆Hcο(H2) – ∆H 1

= (–283) + (2 × –286) – (–91) (mark for previous equation or this)

= –764 (kJ mol–1) ( units not essential but lose mark if units wrong) 1 (note + 764 scores 1/3)

[15]

7. (a) During the electrolysis of aqueous sodium chloride, hydrogen is liberated at the

cathode (1) While chlorine is liberated at the anode. (1) At the cathode, 4OH- 2H2O + O2 + 4e Hence for every mole of electron that passes through the electrolyte, one mole of

NaOH will be produced. (1) NaOH + HCl NaCl + H2O 0.25 x 15.50 No of moles of HCl used in titration = ------------------- = 3.88 x 10-3 mol (1) 1000 No of moles of NaOH produced = 3.88 x 10-3 mol (1) Quantity of charge required , Q = 3.88 x 10-3 mol x 96500 C = 374.4 C Using Q = It, 374.4 = I x 25 x 60 I = 0.25 A/ (1)

(b) (i) The partition law states that a solute, s distributes itself between the two Immiscible solvents, ether and water in such a way that the ration of the concentrations in the two solvent is constant. (1) Concentration of S in ether --------------------------------- = 12.50 Concentration of S in water (1)

(ii) The partition law only holds when the temperature is constant and the molecular condition in both solvents. (2)

(iii) single extraction Let a be the amount of S left in the aqueous layer, 8.00 – a ---------- = 12.50 a

a = 0.59 g (1)

1st portion in 2 extractions, Let b be the amount of S left in the aqueous layer,

(8.00 – b)/12.50 -------------------- = 12.50 b/25.0

b = 4.00 g (1)


6

2nd portion in 2 extractions, Let b be the amount of S left in the aqueous layer,

(8.00 – 1.10 - c)/12.50 ----------------------------- = 12.50 c/25.0

c = 2.00 g [ 1 ]

total extraction = 4 + 2 = 6.00 g [ 1 ] ______ [ 15 ]

8. a. In aqueous solution, the Al3+ ion which has the empty valence orbitals [ 1 ]

forms coordinate bond with water molecules producing [Al(H2O)6]3+ [ 1 ]

complex ions.

The Al3+ ion has a small ionic radius and a high charge density. [ 1 ]

In the coordinated H2O molecule, the O-H bond is weakened as the

electrons of the oxygen atom are strongly attracted towards the Al3+ ion.

The complex ion acts as a Bronsted- Lowry acid by donating a proton

to an uncoordinated H2O molecule forming the H3O+ ion which makes [ 1 ]

the solution acidic.

[Al(H2O)6]3+ (aq) + H2O(l) [Al(H2O)5OH]2+(aq) + H3O

+(l) [ 1 ]

(i) Al2Cl6 (s) + 12H2O(l) 2[Al(H2O)6]3+ (aq) + 6Cl- [ 1 ]

Anhydrous aluminium chloride exists as a dimer which dissolves [ 1 ] in water forming [Al(H2O)6]

3+ and Cl- ions.

(ii) 2[Al(H2O)6]3+ (aq) + 3CO3

2- (aq) 2[Al(H2O)3(OH)3](s) + [ 1 ] 3 CO2 (g) + 3H2O(l)

The Al3+ ion solution contains the [Al(H2O)6]3+ complex ion which

forms the solid aluminium hydroxide with a strong base such as [ 1 ] a carbonate or a sulphide. Aluminium carbonate and aluminium sulphide are not formed in [ 1 ] the reaction between the Al3+ (aq) solution with sodium carbonate or sodium sulphide solutions. 2[Al(H2O)6]

3+ (aq) + 3S2- (aq) 2[Al(H2O)3(OH)3](s) + [ 1 ] 3H2S (g)

(iii) Aluminium chloride is a simple covalent compound. The molecules are

held by weak van der Waals forces. [ 1 ]

It has a low melting point and sublimes at 1800C. [ 1 ]

It fumes in moist air because of hydrolysis. [ 1 ]

The white fume is hydrogen chloride gas.

AlCl3 (s) + 3H2O (l) Al(OH)3 ( s) + 3HCl (g) [ 1 ]

_______

[ 15 ]


7

9. a (i) phenylamine < ammonia < ethylamine [ 1 ]

(ii) The strength of a base depends on its ability to donate its lone pair [ 1 ]

electrons for sharing with a proton.

In phenylamine, the lone pair electron on N atom is delocalised into [ 1 ]

the ring.

The p orbital of N atom overlaps with those of the carbon atoms in

the ring. Thus it is not readily shared with protons. [ 1 ]

In ethylamine, the ethyl group has an electron donating effect. [ 1 ]

This makes the lone pair electron on N atom more available for

sharing with protons.

b. (i) Add acidified KMnO4 to methylbenzene and heat. [ 1 ]

Benzoic acid is formed.

C6H5CH3 + 3[O] C6H5COOH + H2O [ 1 ]

Add PCl5 and heat, benzoyl chloride is formed [ 1 ]

C6H5COOH + PCl5 C6H5COCl + POCl3 [ 1 ]

Add concentrated ammonia

C6H5COCl + NH3 C6H5CONH2 + HCl [ 1 ]

(ii)Chlorine gas , sunlight and boiling methylbenzene [ 1 ]

Chloromethylbenzene is formed

C6H5CH3 + Cl2 C6H5CH2Cl + HCl [ 1 ]

Add aqueous sodium hydroxide and reflux

C6H5CH2Cl + NaOH C6H5CH2OH + NaCl [ 1 ]

To prove the presence of –OH group in (ii), add PCl5 [ 1 ]

White fumes of hydrogen chloride is observed

C6H5CH2OH + PCl5 C6H5CH2Cl + HCl + POCl3 [ 1 ]

_____

[ 15 ]

10. a. X is an ester ( sweet smelling liquid ) [ 1 ]

Y is phenol ( formation of white precipitate with bromine water ) [ 1 ]

Reduction of X would produce two alcohols. Y is a tertiary alcohol [ 1 ]

And Z is a primary alcohol.

Structure of X

CH3 O

CH3 C C O [ 1 ]

H

Name of X : phenyl-2-methylpropanoate [ 1 ]


8

Hydrolysis of X :

CH3 O

CH3 C C O + H2O [ 1 ]

H

(CH3)2CHCOOH + OH

(Y) [ 1 ]

Reaction of Y with bromine water

Br

OH + 3 Br2 Br OH + 3HBr [ 1 ]

Br

Reduction of X :

CH3 O

CH3 C C O + 4[H] (CH3)2CHCH2OH (Z) [ 1 ]

H

+ OH [ 1 ]

Dehydration of Z :

(CH3)2CHCH2OH (CH3)2C= CH2 + H2O [ 1 ]

b. (i) Ethyl magnesium bromide can be prepared by heating

bromoethane with magnesium metal [ 1 ]

at 350C in dry ether [ 1 ]

(ii)CH3CH2MgBr + CH3COCH3 CH3CH2C(CH3)2 + MgBr+ [ 1 ]

O-

CH3CH2C(CH3)2 + MgBr+ + H2O CH3CH2C(CH3)2 + Mg(OH)Br [ 1 ]

O- _____

[ 15 ]


9


pahang stpm trial 2010 chemistry [w ans]

Documents