962/1 STPM TRIAL

STPM TRIAL 962/1

CHEMISTRY (KIMIA)

PAPER 1 (KERTAS 1)

One and a half hours (Satu jam setengah)

SMK BANDAR UTAMA

PEPERIKSAAN PERCUBAAN SEMESTER 1

SIJIL TINGGI PERSEKOLAHAN MALAYSIA

(MALAYSIA HIGHER SCHOOL CERTIFICATE TRIAL EXAMINATION)

Instructions to candidates:

DO NOT OPEN THIS QUESTION PAPER UNTIL YOU ARE TOLD TO DO SO.

Answer all questions in Section A. Marks will not be deducted for wrong answers. For each

question, four suggested answers are given. Choose the correct answer and circle the answer.

Answer all questions in Section B. Write your answers in the spaces provided.

Answer any two questions in Section C. All essential working should be shown. For numerical answers, unit should be quoted wherever appropriate. Begin each answer on a

fresh sheet of paper and arrange your answers in numerical order.

Arahan kepada calon:

JANGAN BUKA KERTAS SOALAN INI SEHINGGA ANDA DIBENARKAN

BERBUAT DEMIKIAN.

Jawab semua soalan dalam Bahagian A. Markah tidak akan ditolak bagi jawapan yang

salah.

Bagi setiap soalan, empat cadangan jawapan diberikan. Pilih jawapan yang betul dan buat

bulatan pada jawapan tersebut.

Jawab semua soalan dalam Bahagian B. Tulis jawapan anda di ruang yang diberikan.

Jawab mana-mana dua soalan dalam Bahagian C. Semua jalan kerja yang sesuai hendaklah ditunjukkan. Bagi jawapan berangka, unit hendaklah dinyatakan di mana-mana yang sesuai.

Mulakan setiap jawapan pada helaian kertas jawapan yang baharu dan susun jawapan anda mengikut tertib berangka.

This question paper consists of 12 printed pages.

(Kertas soalan ini terdiri daripada 12 halaman bercetak.)

SMK BANDAR UTAMA, KP LAU

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Section A [15 marks] Answer all questions in this section.

1. A sample of dichlorodifluoromethane, CF2Cl2, is known to consist of the following

isotopes of equal ratios: 12

C, 19

F, 35

Cl, and 37

Cl. Which of the following sketch spectrum represents part of the mass spectrum of the refrigerant, CF2Cl2?

A)

B)

C)

D)

2. The line spectrum in Figure 1 shows part of the emission spectrum of atomic hydrogen.

Figure 1

Which of the following is TRUE of the above spectrum?

A) Line P has higher frequency than Q

B) Line Q and line R belong to different series.

C) Line Q is the convergence limit of Lyman series.

D) Line S is formed from the electronic transition; n = 3 to n = 2.

3. Each orbital in a d-subshell can accommodate a maximum of _____ electron?

A) 1 B) 2 C) 6 D) 10

Abundance

m/e ratio 120 122 124

P Q R S

Abundance

m/e ratio 120 122 124

Abundance

m/e ratio 120 122 124

Abundance

m/e ratio 120 122 124

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4. The atomic number of nickel is 28. How many unpaired electrons are there in Ni2+

ion in its ground state?

A) 2 B) 3 C) 4 D) 5

5. The first six ionisation energies of four elements; A to D, are given. Which of these elements is most likely to be in Group 14 of the periodic table?

Ionisation Energy/kJ mol-1

1st 2nd 3rd 4th 5th 6th

A 494 4560 6940 9540 13400 16600

B 736 1450 7740 10500 13600 18000

C 1090 2350 4610 6220 37800 47000

D 1400 2860 4590 7480 9400 53200

6.

Two joined vessels containing gas Y and gas Z respectively at s.t.p. is separated by a valve. If both these gasses do not react, calculate the total pressure of the vessels at

equilibrium when the valve is opened.

A) 32 kPa B) 44 kPa C) 50 kPa D) 100 kPa

7. What are the hybridizations of the carbon atoms labeled 1 and 2 respectively in glycine?

H

N

C

C

O

H

H H

OH

12

A) C1 : sp2 B) C1 : sp

2 C) C1 : sp

3 D) C1 : sp

3

C2 : sp2 C2 : sp

3 C2 : sp

2 C2 : sp

3

Y Z

V1 = 9.0 L

P1 = 20 kPa

V2 = 6.0 L

P2 = 80 kPa

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8. The time taken for a radioactive element to decay to of its original mass is 60 minutes.

What is the rate constant of this radioactive decay?

A) 0.023 min-1

B) 0.035 min-1

C) 0.050 min-1

D) 20 min-1

9. Phosphorus oxychloride, POCl3, is a product of reaction between an alcohol with PCl5.

Which of the following is TRUE of POCl3?

A) It is a polar molecule.

B) It has a square planar shape.

C) Oxygen is the central atom.

D) There one lone pair electrons on the oxygen atom.

10. In an acid-base titration, a 1.0 mol dm-3

solution of a base is added to a 1.0 mol dm-3

solution of an acid. The graph below shows the variation of pH value of the solution with the volume of the base added.

Which acid-base indicator is best to determine the equivalence point in this titration

exercise?

Acid-Base Indicator pH range Acid-Base Indicator pH range

A) Universal indicator 1.0 14.0 C) Bromothymol blue 6.0 6.6

B) Methyl orange 3.1 4.4 D) Phenolphthalein 8.3 10.00

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11. The equilibrium constants for the reactions are listed below;

HF(aq) + H2O(l) H3O+(aq) + F(aq) Ka = 6.9 x 10

-4

NH3(aq) + H2O(l) NH4+(aq) + OH(aq) Kb = 1.8 x 10

-5

2H2O(l) H3O+(aq) + OH(aq) Kw = 1.0 x 10

-14

Determine the equilibrium constant for the following reaction:

HF(aq) + NH3(aq) NH4+(aq) + F(aq)

A) 1.2 x 10-3 B) 8.1 x 107

C) 1.2 x 106 D) 3.8 x 1015

12. Beaker X contains 100 cm3 water. Beaker Y contains 100 cm

3 aqueous solution with 0.01

mol CH3COOH and 0.01 mol CH3COONa.

When 1.0 cm3 of 1.0 mol dm

-3 hydrochloric acid is added to beakers X and Y

respectively, which of the following takes place? [pKa of CH3COOH is 4.74]

A) pH of the liquid in beaker X changes by 5 units.

B) The concentration of CH3COO increases in beaker Y.

C) The concentrations of H+ in the two beakers are the same.

D) The total volume of the solution in beaker X is slightly higher than 101 cm3.

13. The diagram below shows addition of silver ions to solutions containing Br, Cl , CO32-

and AsO43-

of equal concentrations of 0.10 M.

Which compound will precipitate at the lowest concentrations of silver ions?

A) AgCl (Ksp = 1.8 x 10-10

) B) AgBr (Ksp = 5.0 x 10-13

)

C) Ag2CO3 (Ksp = 8.1 x 10-12

) D) Ag3AsO4 (Ksp = 1.0 x 10-22

)

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14. Calculate the pH of a solution that contains 3.98 x 10-9

mol dm-3

hydroxide ion.

A) 5.60 B) 8.40 C) 3.98 D) 9.00

15. 2-chloro-2-methylpropane is hydrolysed by aqueous sodium hydroxide as shown in the following equations.

CH3 C Cl

CH3

CH3

slowCH3 C

CH3

CH3

+ Cl-

CH3 C OH

CH3

CH3

fastCH3 C

CH3

CH3

+ Cl-

Which of the following diagrams represent the reaction profile for the reaction?

A)

B)

C)

D)

Energy

Reaction path

Energy

Reaction path

Energy

Reaction path

Energy

Reaction path

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Section B [15 marks] Answer all questions in this section.

16. a) What do you understand by the term order of reaction?

.. [1 mark]

b) Cyanohydrins can be made by reacting ketones with acidified solution of sodium cyanide.

(CH3)2CO + H+ + CN (CH3)2C(OH)CN

In a series of experiments, the reaction was carried out with different concentrations

of the three reagents, and the following relative initial rates were obtained.

Experiment [CH3)2CO]

/mol dm-3

[H+]

/mol dm-3

[CN]

/mol dm-3

Relative initial rate

/mol dm-3

s-1

1 0.020 0.060 0.060 1.00

2 0.020 0.050 0.050 0.833

3 0.020 0.050 0.060 1.00

4 0.025 0.050 0.050 1.042

i) Based on the data in Table 16 to deduce the order of the reaction with respect to

Propanone:

Hydrogen ions:

Cyanide ions: [3 marks]

ii) Hence write the rate equation for this reaction

.... [1 mark]

Two different mechanisms have been suggested for this reaction;

Mechanism A: (CH3)2CO + H+ (CH3)2COH

+

(CH3)2COH+ + CN (CH3)2C(OH)CN

Mechanism B: (CH3)2CO + CN (CH3)2C(O)CH

(CH3)2C(O)CH + H+

(CH3)2C(OH)CN

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iii) Which mechanism is consistent with the rate equation you deduced in (b)(ii), and which step in this mechanism is the slower (rate determining) step? Explain your

answer.

...

...

...

...

.... [3 marks]

Adapted from CGE A-levels Chemistry, Nov. 2002, Cambridge International Examinations

17. Water containing Ca

2+ and Mg

2+ ions is called hard water. Ca

2+ and Mg

2+ ions are

normally removed during water purification process as they are unsuitable for some household and industrial use. One way to remove the Ca

2+ ions from hard water is by

adding washing soda (Na2CO3.10H2O).

a) Why is hard water unsuitable for household or industrial use?

...... [1 mark]

b) Define solubility product, Ksp.

......

...... [1 mark]

c) If the molar solubility of CaCO3 is 9.30 x 10-5

mol dm-3

, determine the solubility

product, Ksp, of CaCO3.

[2 marks]

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d) What is its molar solubility in a 0.0500 mol dm-3

Na2CO3 solution?

[2 marks]

e) Why are Mg2+ ions not removed by this procedure?

......

...... [1 mark]

Adapted from Chang, R., Chemistry, McGraw Hill 2002

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Section C [30 marks]

Answer any two questions in this section

18. a) i) Write the electronic configurations for a stable ion of following three elements:

[3 marks]

ii) Compare the melting points of element Q and R. Provide explanation for your answer.

[3 marks]

b) The normal pH of blood is 7.40, and is controlled in part by the H2CO3/HCO3 buffer system.

i) What is a buffer solution? [1 mark]

ii) Assuming that the Ka value for the carbonic acid, H2CO3, at 25C which is 4.5 x 10-7 applies to blood, what is the [H2CO3]/[HCO3] ratio in normal blood?

[3 marks]

iii) Acidosis is a condition due to excessive acidity of the blood. Explain how the H2CO3/HCO3 system in our blood buffers itself against excessive pH decrease.

[2 marks]

iv) Alkalosis, on the other hand, is a condition due to excessively high pH. Suggest how the human kidney can restore equilibrium to the H2CO3/HCO3 system in our blood.

[3 marks]

Adapted from No. 19.117, p852, Silberberg, Chemistry, McGraw Hill 2003

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19. a) Looking at the phase diagram below for sulphur, answer the following questions:

i) What is a triple point? How many triple points are there? Describe the physical state(s) of matter under these conditions.

[4 marks]

ii) What is the stable phase at room temperature and pressure? Give reasons for your answer.

[1 mark]

ii) Describe the phase changes when sulphur vapour is cooled from 200C to 90C at

3.65 Pa pressure. [2 marks]

b) The energy of the electron in a hydrogen atom is given by the relationship,

J

Based on Planks Quantum Theory, the relationship between energy and the wavelength of an electromagnetic wave can be described as,

whereby, h, is Planks constant (6.63 x 10-34 J); c, is the speed of light (3.0 x 108 ms-1); , is the wavelength of the electromagnetic emission; and n, represents the principal quantum numbers of the hydrogen atom.

i) Describe what happens when an electron falls from the fourth energy level to the second. In which region of the electromagnetic spectrum would this photon have?

[2 marks]

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ii) Calculate the amount of energy contained in the photon released from this electron movement.

[3 marks]

c) Copper crystallizes with a face-centred cubic unit cell. The length of the edge of a

unit cell of copper is 362 pm. Sketch the face of a unit cell, showing the nuclei of the copper atom at the lattice points. The atoms are in contact along the diagonal from

one corner to another. The length of this diagonal is four times the radius of a copper atom. Calculate the radius of the copper atom.

[3 marks]

20. a) When heated to 100C, ammonium carbamate, NH4CO2NH2, decomposes into ammonia and carbon dioxide gas.

NH4CO2NH2(s) 2 NH3(g) + CO2(g)

In a fixed volume vessel, it is found that the equilibrium pressure of the system is

30 kPa.

i) Calculate the both the equilibrium constants for pressure, Kp , and concentration,

Kc, for the reaction above. [6 marks]

ii) Would adding more ammonium carbamate cause the product yield to increase? Discuss.

[2 marks] Adapted from No. 14.71, p597, Chang, R., Chemistry, McGraw Hill 2002

b) Methanal, H2CO, also known as formaldehyde, is a highly toxic organic compound

commonly used as a biological preservative.

i) Draw the Lewis structure, predict and explain the molecular shape for the molecule.

[3 marks]

ii) Describe the bonding that occurs between carbon and oxygen. [2 marks]

iii) Discuss fomaldehydes solubility in water. [2 marks]

END OF PAPER

Prepared by, Verified by, Verified by,

... Lau Kah Pew

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MARK SCHEME 1. C 6. B 11. C

2. B 7. C 12. A

3. B 8. B 13. B

4. A 9. A 14. A

5. C 10. D 15. D

16. a) What do you understand by the term order of reaction?

The power/exponent to which a concentration term is raised in a rate equation

[1 mark]

c) Cyanohydrins can be made by reacting ketones with acidified solution of sodium cyanide.

(CH3)2CO + H+ + CN (CH3)2C(OH)CN

In a series of experiments, the reaction was carried out with different concentrations of the three reagents, and the following relative initial rates were obtained.

Experiment [CH3)2CO]

/mol dm-3

[H+]

/mol dm-3

[CN]

/mol dm-3

Relative initial rate

/mol dm-3

s-1

1 0.020 0.060 0.060 1.00

2 0.020 0.050 0.050 0.833

3 0.020 0.050 0.060 1.00

4 0.025 0.050 0.050 1.042

iv) Based on the data in Table to deduce the order of the reaction with respect to

Propanone: 1st order with regards to propanone

Hydrogen ions: Zero order with regards to H+

Cyanide ions: 1st order with regards to CN.

[3 marks]

v) Hence write the rate equation for this reaction

Rate = k [(CH3)2CO] [H+]

[1 mark]

Two different mechanisms have been suggested for this reaction;

Mechanism A: (CH3)2CO + H+ (CH3)2COH

+

(CH3)2COH+ + CN (CH3)2C(OH)CN

Mechanism B: (CH3)2CO + CN (CH3)2C(O)CH

(CH3)2C(O)CH + H+

(CH3)2C(OH)CN

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vi) Which mechanism is consistent with the rate equation you deduced in (b)(ii), and which step in this mechanism is the slower (rate determining) step? Explain your

answer.

Mechanism B

First step is slow and rate determining

Since H+ is zero order, it should be either not be involved or not present in slow

step, both propanone & CN appear together in same (slow) step in Mech B.

[3 marks]

Adapted from CGE A-levels Chemistry P4-Qs2, Nov. 2002, Cambridge International Examinations

17. Water containing Ca

2+ and Mg

2+ ions is called hard water. Ca

2+ and Mg

2+ ions are

normally removed during water purification process as they are unsuitable for some

household and industrial use. One way to remove the Ca2+

ions from hard water is by adding washing soda (Na2CO3.10H2O).

i) Why is hard water unsuitable for household or industrial use?

these ions react with soap to form insoluble salts, or curds

[1 mark]

ii) Define solubility product, Ksp.

The product of molar cfoncentrations of the constituent ions each raised to the power of its stoichiometric coefficients in the equilibrium equation.

[1 mark]

iii) If the molar solubility of CaCO3 is 9.30 x 10-5

mol dm-3

, determine the solubility

product, Ksp, of CaCO3.

8.6 x 10-9 mol2 dm-6

[2 marks]

iv) What is its molar solubility in a 0.0500 mol dm-3 Na2CO3 solution?

1.73 x 10-7M

[2 marks]

v) Why are Mg2+ ions not removed by this procedure?

MgCO3 is more soluble than CaCO3

[1 mark]

Adapted from No. 16.116, p697, Chang, R., Chemistry, McGraw Hill 2002

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Section C 18. a) i) Write the electronic configurations for a stable ion of following three elements:

: Ion = Q+, e-config. : 1s

2 2s

22p

6

: Ion = R2+

, e-config. : 1s2 2s

22p

6 3s

23p

63d

10

: Ion = W, e-config. : 1s2 2s

22p

6 3s

23p

63d

10 4s

24p

6

[3 marks]

ii) Compare the melting points of element Q and R. Provide explanation for your answer.

Q & R are both metals.

Mp of R > Q.

Metallic bonding R > Q

Valence electron R (2) > than Q (1), metallic bonding of R stronger.

[3 marks]

b) The normal pH of blood is 7.40, and is controlled in part by the H2CO3/HCO3 buffer system.

i) What is a buffer solution?

A buffer solution is a solution of acid and its salt mixture or a base and its salt mixture that has the ability to prevent drastic changes in pH when an acid or a

base is added to the solution. [1 mark]

ii) Assuming that the Ka value for the carbonic acid, H2CO3, at 25C which is 4.5 x 10

-7 applies to blood, what is the [H2CO3]/[HCO3] ratio in normal blood?

pH = pKa log

7.40 = log ( ) log

log = 6.3468 7.40 = 1.0532

= 0.0885

[3 marks]

iii) Acidosis is a condition due to excessive acidity of the blood. Explain how the H2CO3/HCO3 system in our blood buffers itself against excessive pH decrease. When pH decrease, excessive H

+ in the blood combines with HCO3 to form

H2CO3

H+ + HCO3 H2CO3

Small amounts of one buffer component converts into the other resulting in small changes to the relative concentrations of the two components (HCO3 /H2CO3) preventing excessive decrease in pH.

[2 marks]

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iv) Alkalosis, on the other hand, is a condition due to excessively high pH. Suggest how the human kidney can restore equilibrium to the H2CO3/HCO3 system in our blood.

the kidneys remove bicarbonate ion (HCO3 ) from the blood.

As the kidneys decrease the blood's concentration of HCO3 , the equilibrium reaction

H+ + HCO3 H2CO3

is shifted toward the left to compensate for the loss in HCO3 , according to Le Chateliar's Principle, more H

+ ions are generated together with HCO3 ions.

As a result, the pH decreases

[3 marks]

Adapted from No. 19.117, p852, Silberberg, Chemistry, McGraw Hill 2003

19. a) Looking at the phase diagram below for sulphur, answer the following questions:

i) What is a triple point? How many triple points are there? Describe the physical state(s) of matter under these conditions.

Triple point is a state, at a certain temperature and pressure whereby three different phases of the substance exist together at equilibrium.

3 triple points At 95.4C, 578Pa, Sulphur exist as vapour, solid rhombic and solid

monoclinic phases at equilibrium At 119C, 365Pa, Sulphur exist as vapour, solid monoclinic , and liquid

phases at equilibrium At 151C, 130.5kPa, Sulphur exist as liquid, solid rhombic and solid

monoclinic , and liquid phases at equilibrium [4 marks]

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ii) What is the stable phase at room temperature and pressure? Give reasons for your answer.

Rhombic solid crystal phase. At this temperature, and pressure, sulphur can only exist stably as this state.

[1 mark]

iii) Describe the phase changes when sulphur vapour is cooled from 200C to 90C at

3.65 Pa pressure.

Sulphur vapour will cool until 119C, at this point, solid monoclinic and liquid

sulphur would form and coexist together with sulphur vapour at equilibrium

When sulphur cool further from 119c to 90C, the liquid would freeze and the

vapour would deposit as solid monoclinic sulphur. [2 marks]

b) The energy of the electron in a hydrogen atom is given by the relationship,

J

Based on Planks Quantum Theory, the relationship between energy and the wavelength of an electromagnetic wave can be described as,

whereby, h, is Planks constant (6.63 x 10-34 J); c, is the speed of light (3.0 x 108 ms-1); and , is the wavelength of the electromagnetic emission.

i) Describe what happens when an electron falls from the fourth energy level to the second. In which region of the electromagnetic spectrum would this photon have?

Energy is lost/released

in a form of Electromagnetic waves in the visible light region (Balmer)

[2 marks]

ii) Calculate the amount of energy contained in the photon released from this electron movement.

= 4.87 x 10-7 m

[3 marks]

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c) Copper crystallizes with a face-centred cubic unit cell. The length of the edge of a unit cell of copper is 362 pm. Sketch the face of a unit cell, showing the nuclei of the

copper atom at the lattice points. The atoms are in contact along the diagonal from one corner to another. The length of this diagonal is four times the radius of a copper

atom. Calculate the radius of the copper atom.

Radius of Cu = = 9.05 x 10-11 m

[3 marks]

20. a) When heated to 100C, ammonium carbamate, NH4CO2NH2, decomposes into

ammonia and carbon dioxide gas.

NH4CO2NH2(s) 2 NH3(g) + CO2(g)

In a fixed volume vessel, it is found that the equilibrium pressure of the system is 30 kPa.

i) Calculate the both the equilibrium constants for pressure, Kp , and concentration, Kc, for the reaction above.

NH4CO2NH2(s) 2 NH3(g) + CO2(g)

Initial W - -

Change -x +2x +x

Equilibrium W - x 2x x

PT = 30 000 Pa = 2x + x x = 10 000 Pa

PNH3 = 20 000 Pa, PCO2 = 10 000 Pa

Kp = PNH32. PCO2

= (20 000)2 (10 000) = 4.0 x 1012

Kc = [CO2] [NH3]2

= Kp/(RT)3

= 134 [6 marks]

ii) Would adding more ammonium carbamate cause the product yield to increase? Discuss.

No. NH4CO2NH2 is a solid. Concentration is constant. Adding more will not disturb equilibrium.

[2 marks]

Adapted from No. 14.71, p597, Chang, R., Chemistry, McGraw Hill 2002

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b) Methanal, H2CO, also known as formaldehyde, is a highly toxic organic compound commonly used as a biological preservative.

i) Draw the Lewis structure, predict and explain the molecular shape for the molecule.

C

O

H

H

>120o