k2 soalan kimia stpm 2011 trial sabah

8/4/2019 k2 Soalan Kimia Stpm 2011 Trial Sabah

1/11

Section A[ 40 marks]

Answer all questions

1 Each element has a unique number that identifies how many protons are in one atom of that element. The mass number or nucleon number on the other hand is derived from thesub-atomic particles in the nucleus.

(a) Define the term nucleon number ( mass number ) of an isotope.

............(1 mark )

(b) Write the symbol, including nucleon number ( mass number ) and proton number (atomic number ), for an atom of the isotope which has eight electrons and nineneutrons in each atom.

.............(1 mark )

(c) The table below shows some data about fundamental particles.

Particle Proton Neutron ElectronMass /g 1.6725 10 24 1.6748 10 24 0.0009 10 24

Relative charge

(i) Complete the table by giving a value for the relative charge of each particle.(1 mark )

(ii) Calculate the mass of an atom of hydrogen which is made from a proton andan electron.

..........................................................................................................................(1 mark )

(iii) Calculate the mass of one mole of such hydrogen atoms giving your answer to four decimal places.(The Avogadro constant, L = 6.0225 10 23 mol 1 )

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

.......(1 mark )

(iv) An accurate value for the mass of one mole of hydrogen atoms is 1.0080 g.Give one reason why this value is different from your answer to part (c) (iii).

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

(1 mark )


2/11

(d) The diagram below shows the values of the first ionisation energies of some of theelements in Period 3.

i. On the above diagram, use crosses to mark the approximate positions of thevalues of the first ionisation energies for the element Al and element S.Complete the diagram by joining the crosses.

(2 marks )

ii. From the graph above, state the general trends of the first ionisation energiesof the Period 3 elements. Explain one of the deviations (if any).

.........

.........

.........

.........

..........

(2 mark )

2. The table below shows the results of an investigation of the rate of reaction betweenhydroxide ion, OH and phosphinate ion, PH 2O 2 at 80 C. The overall reaction is

PH 2O2 (aq) + OH (aq) PHO 32(aq) + H 2(g)

No of experimen

t

Initial concentration Initial rate for the productionof H 2 gas (dm 3min -1 ) [PH 2 O 2 ](mol dm -3 ] [OH - ](mol dm -3 ]

1 0.1 6.0 14.42 0.3 6.0 43.23 0.6 1.0 2.44 0.6 2.0 9.6

1600140012001000800600400200

0Na Mg Al Si P S Cl Ar

First ionisationenergy/kJmol 1


3/11

(a)

What is the order of reaction with respect to phosphinate ion?

[2 marks](b)

What is the order of reaction with respect to hydroxide ion?

[2 marks]

(c) What is the overall order of reaction?

[1 mark]

(d)

Write down the rate equation for the reaction above.

[1 mark](e)

Calculate the value of the rate constant at 80 C.

[2 marks]

(f) Predict the rate of production of hydrogen gas when the initial rate of phosphinateions and hydroxide ions are 0.6 mol dm 3 and 3.0 mol dm 3 respectively.

[2 marks]


4/11

3 Group 14 was once also known as tetrels from the Greek tetra which means four .The tetrachlorides of Group 14 are CCl 4, SiCl 4, GeCl 4, SnCl 4, PbCl 4,

(a) (i) State the type of hybridization present in the above tetrachloride

..[1mark](ii) Name the shape of each molecule.

.[1mark]

(b)(i)

From the list of Group 14 tetrachlorides listed above, choose one thatis totally not hydrolysed in water? Explain your answer.

[2 marks]

(ii) has the highest boiling point ? Explain your answer.

[2marks]

(c) Give a reason why carbn tetrachloride is used in fire-extinguishers.

.[1 mark]

(d) (i) Some of the above tetrachlorides decomposed when heated.Name one of the compounds

.[1mark]

(ii) Why is the compound that you have chosen in (d)(i) thermally unstable?

.

[1mark]

(iii) Write an equation for the decomposition of the above-mentioned compound.

.

[1mark].


5/11

4

(a) Menthol is an organic compound made synthetically or obtained from peppermint or other mint oils. It is a common ingredient in cough mixtures. The structuralformula of menthol is shown below.

H3C CH 3

CHOH

CH 3

(i) Name one functional group in menthol.

.[ 1 mark ]

(ii) Give the products formed when menthol reacts with ethanoyl chloride.

[ 2 marks ]

(iii) Give the structural formula of the main product formed when menthol reactswith acidified potassium dichromate (VI) solution

[ 1 mark ]

(iv) Does menthol form a white precipitate with bromine water. Give a reason.

.

.

.[ 1marks ]


6/11

(b) Under suitable conditions, 2-bromo-3 methylbutane can be converted into analcohol or two isomeric alkenes.(i) Name the reagent and conditions for the conversion of 2-bromo-3

methylbutane into an alcohol

.

(ii) State the mechanism for the reaction in (i) above.

(iii) Name the reagent and conditions for the conversion of 2-bromo-3 methylbutane into two isomeric alkenes.

(iv) State the type of reaction that takes place in (iii) above.

[ 4 marks ]

(v) What is the role of the reagent in the reaction in (iii) above.

......[ 1 mark ]


7/11

Section B[60 marks ]

Answer any 4 questions from this section

5 (a) A sample of copper contains the two isotopes, 63Cu and 65Cu. It has a relativeatomic mass, A r , of less than 64. The mass spectrum of this sample shows major peaks with m/e values of 63 and 65, respectively.

(i) Explain why the A r of this sample is less than 64.

(ii) Explain how Cu atoms are converted into Cu + ions in a mass spectrometer.

(iii) In addition to the major peaks at m/e = 63 and 65, much smaller peaks atm/e = 31.5 and 32.5 are also present in the mass spectrum. Identify the ionresponsible for the peak at m/e = 31.5. Explain why your chosen ion has this

m/e value and suggest one reason why this peak is very small.

(6 marks)

(b) The diagram below shows how a water molecule interacts with a hydrogen fluoridemolecule.

O H F

H

H

+

(i) State the value of the bond angle in a single molecule of water and explainyour answer by using the concept of electron pair repulsion.

(5 marks)

(ii) Name the type of interaction between a water molecule and a hydrogenfluoride molecule shown in the diagram above. Explain the origin of the +charge shown on the hydrogen atom in the diagram.

(2 marks)

(iii) When water interacts with hydrogen fluoride, the value of the bond angle inwater changes slightly. Predict how the angle is different from that in a singlemolecule of water and explain your answer.

(2 marks)


8/11

6 (a) A newly discovered fuel cell uses the electrochemical oxidation of ethanol toproduce electrical energy.

(i) Using ethanoic sodium hydroxide, aqueous sodium hydroxide, oxygen gasand graphite electrodes and a permeable membrane.Sketch the set-up of the fuel cell.Label the anode and cathode and indicate the direction of flow of electrons.

[ 3 marks]

(ii) What is the function of the oxygen gas and aqueous sodium hydroxide.

[ 2 marks ]

(iii) Write the ionic equations for the reactions occurring at the anode andcathode.If the standard reduction electrode potential at the anode and cathode is+0.20 V and + 0.40 V respectively. Calculate the emf of the cell.

[ 3 marks ]

(b) (i) State Hesss law.[ 1 mark ]

(ii) Hydrazine, N 2H4, is often used as a liquid fuel. The complete combustion of hydrazine yields nitrogen and steam.

Write an equation for the complete combustion of hydrazine.

[ 2 mark ](iii) Hydrazine reacts with an oxidizing agent such as N 2O 4.

2 N 2H4(l) + N 2O 4 (l) 3N 2(g) + 4 H 2O (g)

Using the data below, calculate the enthalpy change for the above reaction.Hence show that the reaction is violently explosive.

Enthalpy of formation of N 2H4(l) = + 50.63 kJ mol -1Enthalpy of formation of N 2O 4(l) = -19.57 kJ mol -1

Enthalpy of formation of H 2O(g) = - 242.7 kJ mol -1

[ 4 marks]


9/11

7 (a) When aluminium reacts with chlorine gas, aluminium chloride, Al 2Cl6, is formed. Itis a white solid with a low melting and boiling point.

(i) Draw the structural formula of aluminium chloride.[ 1 mark ]

(ii) Write a balanced equation for the above reaction.[ 1 mark ]

(iii) State one important use of aluminium chloride[1 marks]

(iv) When 1.0 g of aluminium was used, 2.3 g of aluminium chloride.wasproduced. Calculate the percentage yield of the product.

[2marks]

(b) With the help of an equation, explain why an aqueous solution of aluminiumchloride is acidic

[4 marks]

(c) An aqueous solution of sodium hydroxide is added slowly until in excess to anaqueous solution of aluminium chloride in a test tube.Explain your observation with the help of chemical equations

[3 marks](d) Aluminium is a reactive metal and yet it is used widely in the industries. For

example, aluminium is used in window panes, rack frames , camping products andcooking utensils. Explain how aluminium as a reactive metal can be made useful inindustries. Use equations to show how it can be done..

[3 marks]

8 The word transition was first used to describe the elements now known as the d-blockby the English chemist Charles Bury in 1921, who referred to a transition series of elements during the change of an inner layer of electrons.(a) Explain why complexes of transition elements are often coloured.

What determines the colour of a particular transition element?

[ 5 marks ](b) Explain the following colour changes as fully as possible.

(i) The addition of thiocyanate ions to aqueous iron (III) ions produces a deepblood-red colour which disappears when aqueous sodium fluoride is added.

[ 3 marks ](ii) The addition of water to blue anhydrous cobalt (II) chloride produces a pale

pink solution.[ 2 marks ]

(c) Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive andtoxic strong acid. During the industrial manufacture of nitric acid, the followingthree processes take place.


10/11

Ammonia and oxygen (in the form of air) are passed over a platinum-rhodium catalyst at 900 C. Nitrogen monoxide and steam are formed.

the gases are cooled and more oxygen is added, which converts thenitrogen monoxide into nitrogen dioxide.

Finally, the nitrogen dioxide is mixed with yet more oxygen and absorbed inwater, forming nitric acid.

(i) Write balanced equations for these three reactions.

(ii) Calculate the maximum mass of nitric acid that can be obtained from 1kilogram of ammonia by this method.

[ 5 marks ]

9 (a) Phenol , also known as carbolic acid , is a toxic , white with a slightly pink tinge,

crystalline solid . Phenol has antiseptic properties, and was used by Sir JosephLister in his pioneering technique of antiseptic surgery.Describe briefly the manufacture of phenol from chlorobenzene in the Dowprocess.Write all relevant equations and give necessary conditions.

[4 marks]

(b) Linalool is a naturally-occurring optically active chemical found in many flowers and spice plants with many commercial applications, the majority of which arebased on its pleasant scent. The (-) enantiomer occurs in rose oil and the (-)enantiomer occurs in orange peels.

(c)

CH 3

CH 3 CH 2 - CH 2 C CH = CH 2 linalool C = C

CH 3 H OH

Mark the chiral carbon atom in linalool by means of an *. State what differencecould be detected experimentally between the (-) and (+) enantiomers of linalool.

[ 3 marks]Draw the structural formula of the principal product formed when linalool reactswith(i) bromine in CCl 4(ii) dry HCl mixed with anhydrous zinc chloride.(iii) cold acidified potassium manganate (VII) solution.(iv) propanoic acid

[ 8 marks ]

10 Esters are widespread in nature. They occur naturally in plants and animals. Smallesters, in combination with other volatile compounds, produce the pleasant aroma of fruits.(a) Write an equation for the formation of methyl propanoate, CH 3CH 2COOCH 3, from

methanol and propanoic acid.
http://en.wikipedia.org/wiki/Toxichttp://en.wikipedia.org/wiki/Crystalhttp://en.wikipedia.org/wiki/Solidhttp://en.wikipedia.org/wiki/Antiseptichttp://en.wikipedia.org/wiki/Joseph_Lister,_1st_Baron_Listerhttp://en.wikipedia.org/wiki/Joseph_Lister,_1st_Baron_Listerhttp://en.wikipedia.org/wiki/Flowershttp://en.wikipedia.org/wiki/Spicehttp://en.wikipedia.org/wiki/Toxichttp://en.wikipedia.org/wiki/Crystalhttp://en.wikipedia.org/wiki/Solidhttp://en.wikipedia.org/wiki/Antiseptichttp://en.wikipedia.org/wiki/Joseph_Lister,_1st_Baron_Listerhttp://en.wikipedia.org/wiki/Joseph_Lister,_1st_Baron_Listerhttp://en.wikipedia.org/wiki/Flowershttp://en.wikipedia.org/wiki/Spice


11/11

[1 mark ](b) Name and outline a mechanism for the reaction between methanol and propanoyl

chloride to form methyl propanoate.[4 marks ]

(c) (i) Give one advantage of the use of propanoyl chloride instead of propanoicacid in the laboratory preparation of methyl propanoate from methanol.

[1 mark ]

(ii) Give one advantage of the use of propanoic anhydride instead of propanoylchloride in the industrial manufacture of methyl propanoate from methanol.

[1 mark ]

(d) An ester contains a benzene ring. The mass spectrum of this ester shows amolecular ion peak at m/e = 136. Deduce the molecular formula of this ester anddraw two possible structures for this ester.

[3 marks ]

(e) Consider the reaction sequence shown below.

(i) Name the mechanism for Reaction 1.[ 1 mark]

(ii)

(iii)

Compound F is the only product formed in Reaction 1. Deduce the structureof compound E.

[ 1mark]

Briefly outline a mechanism for Reaction 2.[3 marks ]

END OF QUESTION PAPER

k2 soalan kimia stpm 2011 trial sabah

Documents