stpm percubaan 2008 sabah chemistry paper 2

8/14/2019 STPM Percubaan 2008 Sabah Chemistry Paper 2

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Section A

[40 marks]

Answer all questions

1. (a) The following figure shows the principal energy levels of the hydrogen atom.

(i) The figure shows that as the quantum numbers of the energy level

increases, the separate lines of the energy levels becomes closer until

they converge, at n =

State the magnitude of the nuclear force towards the electron in the

hydrogen atom at this point.

....

[ 1 mark ]

(ii) Calculate the minimum energy required to ionise a hydrogen atom in its

ground state.

[1 mark ]

(iii) Calculate the frequency of the electromagnetic radiation emitted if theelectron at n = 2makes a transition to n = 4.

[ 2 marks ]

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(b) Hydrogen combines with chlorine to form hydrogen chloride. The mass

spectrum of hydrogen bromide is shown below.

Intensity

P2

30 35 40 45 m/e

(i) Identify the ions that causes the peaks P1 and P3

(ii) Calculate the ratio of the peak heights, P2 and P4.State one significance of this ratio value.

[ 3 marks ]

(c) The figure below shows the plot of pV/RT against pressure for hydrogen

pV/RT

1.0

Pressure/atm

(i) Give a reason why hydrogen gas deviates from the ideal behaviour at high

pressure.

.

.

2

100

0

50P1

P3

P4


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(ii) Unlike hydrogen gas, hydrogen chloride gas shows a very marked negative

deviation from ideal behaviour at medium pressure. Give two reasons.

1.

.

.

2.

.

[ 3 marks ]

2. Chlorine dioxide gas, ClO2, which is a reddish yellow gas. It is used for thedisinfection and the principal agent used in the decontamination of buildings in the

United states after the 2001 anthrax attack.

(a) Chlorine dioxide gas can be prepared in the laboratory by the following

reactions:

2AgClO3 (s) + Cl2 (g) 2AgCl (s) + 2ClO2 (g) + O2 (g); H = zero

[ Hf(AgClO2) = -25kJ mol-1; Hf (AgCl) = -127 kJ mol

-1]

(i) Calculate the value of Hf(ClO2)

(ii) From the value obtained in a (i) above; comment on the relative stability

of chlorine dioxide.

...

...

[ 3 marks ](b) Chlorine dioxide is a strong oxidizing agent in acidic solution. This is why it is

used as a bleaching agent.

ClO3 (aq) + 4H+ (aq) + 5e Cl- (aq) + 2H2O ; E

= + 1.50 V

Predict the reactions if any, of chlorine dioxide in acidic solution with

(i) aqueous iron (II)

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(ii) Aqueous hydrogen sulphide, H2S

[4 marks ]

(iii

)

Draw a labeled diagram to show how the redox potential of

E(ClO2/ Cl- ) might be measured in the laboratory.

[2 marks]

(c) Chlorine dioxide undergoes disproportionation in alkaline solution to give a

mixture of chlorate (III) and chlorate (V) ions.

Write an ionic equation for the reaction.

...

[ 1 mark ]

3. The first ionization energies of some Group 2 and group 3 elements are given as

follows.

Group 2

elements

Ionisation energy

(kJmol-1)

Group 13

elements

Ionisation energy

(kJmol-1)

Be 900 B 798Mg 726 Al 575

Ca 592 Ga 575

Sr 546 In 556

Ba 502 Tl 589

(a) Define the first ionization energy of an element.

[ 1 mark ]

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(b) The first ionization energy of the Group 2 elements decreases down the group.

State the 2 factors that contribute to the decrease in 1 st ionization energy from

Be to Ba.

1. ..

2. ..

[2 marks]

(c) Explain why the 1st ionization energy of magnesium is higher than that of

aluminium.

...

...

...

[ 2 marks ]

(d) The 1st ionization energy of boron and barium do not show a marked difference,

however, barium compounds are ionic whereas boron compounds are

predominately covalent. Give an explanation for this observation.

...

.......

...

[ 2 marks ]

(e) Burning of magnesium in air produces magnesium oxide and a little

magnesium nitride

(i) Draw a Lewis structure for magnesium nitride.

(ii) When magnesium nitride is warmed with water, a gas that turns moist red

litmus paper blue is liberated.

Write a balanced equation for the reaction between magnesium nitride

and water.

..

[ 3 marks]

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4. An organic compound X of molar mass of 136.9g mol-1 has the following

composition by mass:

(a) Determine the molecular formula of X.

[ 2 marks ]

(b) When X is boiled under reflux with aqueous sodium hydroxide, 2-methyl-1-

propanol is formed.

(i) Draw the structural formula of X.

(ii) State the mechanism of the reaction.

...

[ 2 marks ]

(c) When X is treated with an alcoholic solution of sodium hydroxide, an alkene Y

is formed. Y reacts with hydrogen bromide to form Z which is an isomer of X

(i) Y has four isomers. Give the structural formula for the isomer that

exhibits geometrical isomerism.

(ii) Draw the structural formula for Z

6

C, 35.2%; H, 6.5 %; Br, 58.3%


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(iii) State one isomer of alkene Y that produces carbon dioxide when heated

with concentrated acidified KMnO4? Give an equation for the reaction.

Isomer:

Equation:

[ 4 marks]

(d) Z reacts with aqueous sodium hydroxide to form an alcohol P.Suggest a simple chemical test to differentiate between alcohol P and

2-methyl-1-propanol

....

[ 2 marks]

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SECTION B

(60 marks)

Answer any four questions.6. (a) The following are all equilibrium processes. In each case, write a chemical

equation to show the equilibrium, and use Le Chateliers principle to explain the

observations described.

(i) When potassium nitrate dissolves in water, the temperature drops. If a

saturated solution of potassium nitrate at 100 C is cooled to room

temperature, crystals are formed.

(ii) When a small volume of a concentrated solution of sodium sulphate is added

to a saturated solution of calcium sulphate, a white precipitate is formed.

(iii

)

When brown NO2 gas is cooled, colourless N2O4 gas is formed. A gas

syringe is filled with NO2 gas and the end sealed. When the gas is

compressed, the brown colour fades. Warming the syringe restores the

colour.

[ 8 marks ]

(b) The following reaction is used industrially to produce a combustible gas from coal.

H2O(g) + C (s) H2(g) + CO (g)

A mixture of powdered coal and steam at a pressure of 1 atm and a temperature of

1300 C was allowed to reach equilibrium. It was found that the total pressure had

increased to 1.9 atm but the remaining steam had a partial pressure of only 0.1 atm.

Use the data given to calculate the partial pressures of hydrogen and carbon

monoxide, and hence calculate a value for Kp[ 3 marks ]

(c) Hydrangeas are flowering plants which commonly have pink flowers. Theyproduce blue flowers in soils which contain high concentrations of Mg 2+ (aq). The

pH of well limed soil is 9.0, whereas the pH of peat-based soil is 6.5. The

numerical value of the solubility product, Ksp of magnesium hydroxide is 1.8 x 10-

12

Deduce and explain which of these types of soil favours good cultivation of blue

hydrangeas.

[ 4 marks]

7. (a) A solid halide reacts with concentrated sulphuric acid to form HX gas which is

5. (a) What do you understand by the terms

(i) relative atomic mass

(ii) isotope [ 3 marks]

(b) The mass spectrum of ethanol contains peaks at m/e values of 15, 28, 31, 45

and 46. Account for the appearance of these peaks as fully as you can.

[ 5 marks]

(c) Explain clearly and concisely the meaning of each underline terms and

indicate the significance of each of the numerical values.

(i) The ionic product of water is equal to 1.0 x 10-14 mol2dm-6 at 250C

and increases as the temperature increases[ 4 marks]

(ii) The standard electrode potential of calcium (Ca2+ / Ca) is -2.87V

[ 3 marks]

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then oxidized to X2 gas. The solid plays an important role in black-white

photography. Identify the solid halide. Explain your answer.

[5 marks]

(b)

A coordination compound triamminetrichlorocobalt(III) exists as two isomers.

(i) What is the chemical formula of triamminetrichlorocobalt(III)?

(ii) Draw the structures of the two isomers and name them.

[5 marks]

(c) Explain the observations when an aqueous solution of silver nitrate is added to

(i) triamminetrichlorocobalt(III)

(ii) triamminedichlorocobalt(III) chloride

[5 marks]

8. (a) (i) Suggest reasons why magnesium gives the nitride, Mg3N2, in addition to its

oxide when burned in air.

(ii) A 1.00g sample of the powder obtained from burning magnesium in air was

boiled with water. The ammonia that was evolved neutralizes 12.00 cm3 of

0.5 mol dm-3 hydrochloric acid. Construct balanced equations for the reaction

of magnesium nitride with water.

Calculate the percentage of magnesium nitride in the 1.00g sample.

[ 6 marks]

(b)NaCl AlCl3 CCl4 SiCl4

Describe the reaction, if any, of each of the four chlorides with water, stating the

appropriate pH of any solution formed, and writing balanced equation for any

reaction that takes place. Offer an explanation for any differences that occur in

their reactivity.

[6 marks ]

(c) Articles made from copper and its alloys can be cleaned of their oxides tarnish by

the use of metal polishes containing aqueous ammonia and an abrasive.

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Assuming the tarnish copper contains copper(II) ions, suggest with an equation, how

the aqueous ammonia might react with the tarnish, and suggest the colour of the

resultant solution.

[ 3 marks ]

9. The amino acids tyrosine, lysine and glycine are constituents of many proteins.

(a) State the reagents and conditions you could use to break proteins down into amino

acids.

[ 2 marks ]

(b) Draw a ring around each chiral centre in the above molecules.

[ 2 marks]

(c) In aqueous solution amino acids exist as zwitterions. Draw the zwitterionic

structure of glycine.

[ 1 mark ]

(d) For each of the following reactions, draw the structure of the organic compound

formed.

(i) glycine + excess NaOH(aq).

(ii) tyrosine + excess NaOH(aq)

(iii) lysine + excess HCl(aq)

(iv) tyrosine + excess Br2(aq)

[ 5 marks ]

(e) Draw the structural formula of a tripeptide formed from all three of these amino

acids, showing clearly the peptide bonds.

[ 2 marks ]

(f) The formula of part of the chain of a synthetic polyamide is shown below.

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(i) Identify the repeat unit of the polymer by drawing square brackets around it on

the above formula.

(ii) Draw the structures of the two monomers from which the polymer could be

made.

(iii) Name the type of polymerisation of the polymer shown above.

[ 3 marks ]

10 This question is concerned with organochlorine compounds.

(a) State the conditions needed to produce the two compounds A and B.

[ 2 marks ]

(b

)State the reagent needed to carry out the following reaction.

[ 1mark ]

(c) The three chloro-compounds A, B and C vary in their ease of hydrolysis.

(i) Arrange the reactivity of the above compounds in decreasing order

(ii) Suggest an explanation for these differences in reactivity

[ 3 marks ]

(d

)

Draw the structural formulae of the organic products X, Y and Z of the followingreactions of compound C.

OH in NaOH (aq)

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X

Y

Z


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COCl

CH3NH2

C

H2O

(e) Compounds D and E are both ketones.CH3CH2COCH2CH3

D E

(i) State which one of these compound reacts with alkaline aqueous iodine, and drawthe structural formulae of the products formed during this reactions.

[ 3 marks ]

(ii) The reduction ofD with NaBH4produces just one alcohol, but a similar reductionofEproduces two isomers in equal amounts. Explain these observations, drawingstructures where appropriate.

[ 3 marks ]

12

CH3CH2CH2COCH3

[ 3 marks ]


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stpm percubaan 2008 sabah chemistry paper 2

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