Name:_______________________________________________ Form: ________________

UPPER SIX FORM

(TINGKATAN ENAM ATAS)

MAY EVALUATION

(PENILAIAN MEI)

Instructions to candidates:

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

Answer all questions in Section A. Write your answer in the space provided.

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.

Answers should be illustrated by large and clearly labeled diagrams wherever suitable.

Answers may be written in either English or Bahasa Malaysia.

Arahan kepada calon:

JANGAN BUKA KERTAS SOALAN INI SEHINGGA ANDA DIBENARKAN BERBUAT DEMIKIAN.

Jawab semua soalan dalam Bahagian A. Tulis jawapan anda dalam ruang yang disediakan.

Jawab mana-mana empat soalan dalam Bahagian B. Tulis jawapan anda pada helaian jawapan yang dibekalkan. Mulakan setiap jawapan anda pada helaian kertas yang baharu dan susun jawapan anda mengikut terbit berangka. Ikat helaian jawapan anda bersama dengan kertas soalan ini.

Jawapan hendaklah disertai gambar rajah yang besar dan mempunyai label yang jelas di mana-mana yang sesuai.

Jawapan boleh ditulis dalam Bahasa Inggeris atau Bahasa Melayu.

Section A [40 marks]

Answer all questions in this section.

1. Nitrogen and phosphorous are in the same group in the Periodic Table. Nitrogen can form NCl3, but phosphorous can form both PCl3 as well as PCl5 molecules.

(a) Write the electron configuration of the nitrogen and phosphorous atoms.[1 mark]

N : ________________________________________________________P : ________________________________________________________

(b) Draw the Lewis diagram for NCl3 and PCl5 and predict their shapes.

[4 marks]

(c) Explain the statement “phosphorous can form PCl5 but nitrogen cannot form NCl5”. [2 marks]_____________________________________________________________________________________________________________________________________________________________________________________________

(d) (i) State whether NCl3 or PCl5 is polar. [1 mark]__________________________________________________________________________________________________________________

(ii) Predict whether NCl3 or PCl3 has higher boiling point. Explain your answer. [2 marks]

___________________________________________________________________________________________________________________________________________________________________________

2. The graph below shows the boiling point-composition curve for two miscible liquids, R and S.

(a) (i) Label the liquid and vapour curves on the on the graph. [1 mark](ii) Determine from the graph, the boiling point of a mixture containing 0.8 mole

fraction of S. [1 mark]

______________________________________________________________________________________________________________________________

(iii) What is the composition of the vapour produced on boiling this mixture?

[1 mark]

______________________________________________________________________________________________________________________________

(b) What will be the composition of the residue left when mixtures of the following compositions are heated under fractional distillation?(i) 0.10 mole fraction of R [1 mark]

____________________________________________________________(ii) 0.32 mole fraction of R [1 mark]

____________________________________________________________(iii) 0.78 mole fraction of R [1 mark]

____________________________________________________________

(c) Based on the graph shown.(i) What type of behaviour is shown by the above liquid mixture? [1 mark]

________________________________________________________________________________________________________________________

(ii) Explain how the interaction between molecules of R and S give rise to this behaviour. [1 mark]________________________________________________________________________________________________________________________

(d) The success of a distillation in separating the components in a mixture depends on the type of fractionating column used and the distillation rate.(i) Why must a long fractionating column packed with glass beads used?

[1 mark]

________________________________________________________________________________________________________________________

(ii) Why is a slow distillation rate used? [1 mark]

________________________________________________________________________________________________________________________

3. Ethene, C2H4 and ethane, C2H6 are both hydrocarbons.(a) (i) State the hybridization of the carbon atoms in ethane and ethane. [2 marks]

Ethene: _______________________ Ethane: _________________________

(ii) Draw the three dimensional shapes of the ethene and ethane molecules.[2 marks]

(b) The carbon-carbon bond in the ethane consists of one sigma bond and one pi bond.(i) Explain what is meant by sigma bond. [1 mark]

______________________________________________________________________________________________________________________________

(ii) Explain what is meant by pi bond. [1 mark]______________________________________________________________________________________________________________________________

(iii) State the type of orbital overlap that produces the carbon-carbon sigma bond and carbon-carbon pi bond. [2 marks]

_____________________________________________________________________________________________________________________________________________________________________________________________

(c) The table below lists the boiling points for three isomers of the hydrocarbon pentane, C5H12.

Isomer Boiling Point/K

Pentane 309

2-methylbutane 301

2,2-dimethylpropane 283

(i) Explain why the boiling point of 2,2-dimethylpropane is lower than 2-methylbutane and pentane. [2 marks]

____________________________________________________________________________________________________________________________________________________________________________________________________________________________________

4. Ammonia is known as Lewis base and also Bronsted-Lowry base. (a) Ammonia gas is evolved when water is added to calcium nitride, Ca3N2.

(i) Write an equation to show the action of water on calcium nitride. [1 mark]_______________________________________________________________

(ii) What is the pH of the solution when 0.020 mol calcium nitride is dissolved in 1dm3 of water? [2 marks]

(b) In an experiment, 25.0 cm3 NH3 0.020 moldm-3 was gradually titrated with 0.050 moldm-3 nitric acid. (Kb of NH3 = 1.8 × 10-5)(i) Calculate the initial pH of NH3 before nitric acid was added. [2 marks]

(ii) Calculate the volume of nitric acid required to completely neutralize NH3.[1 mark]

(iii) Name one suitable indicator that can be used to determine the end point of the titration. [1 mark]_______________________________________________________________

(iv)Sketch a graph to show how the pH of ammonia changes when 20.0 cm3 0.050 moldm-3 nitric acid was gradually added. [3 marks]

Section B [60 marks]

Answer any four questions in this section.

5. (a) Explain the following observations. [10 marks](i) The melting point of water is 0°C while that of hydrogen sulphide is

-83°C.(ii) CI4 decomposes at lower temperature than CCl4.(iii) BH3 is planar but CH4 is not.(iv) The relative molecular mass of butane and propanone are both 58.0.

However, the boiling point of butane is 273K while that of propanone is 330K.

(v) The boiling point of 4-nitrophenol and 2-nitrophenol are 279°C and 216°C respectively.

(b) The proton number of sulphur is 16. [5 marks](i) Write the electron configuration of sulphur.(ii) Sulphur reacts with oxygen to form SO2 and SO3 under suitable

conditions. Draw the Lewis structure for SO2 and SO3 and predict the shape of both molecules.

6. (a) Ethanoic acid is an example of weak acid. [5 marks](i) Describe the properties of ethanoic acid as Bronsted-Lowry acid.(ii) Describe the use of ethanoic acid in the preparation of buffer solution.

(b) Phenolphthalein, HPh, is an acid-base indicator in the pH range between 8.2 and 9.8. The equilibrium equation of phenolphthalein in aqueous solution is as follows.

HPh + H2O H3O+ + Ph−

Explain how phenolphthalein acts in the acid-base titration. [4 marks] (c) A solution is prepared by mixing 250.0 cm3 of 0.05 moldm-3 nitric acid with 250.0

cm3 of 0.05 moldm-3 calcium hydroxide solution. Calculate the pH of the solution. [6 marks]

7. (a) Buffers are essential for homeostasis and many industrial processes. [5 marks](i) Define buffer solution.

(ii) A mixture of aqueous ammonia, NH3 and aqueous ammonium chloride NH4Cl is an example of a buffer solution. Using suitable equations, explain how the buffer solution functions.

(b) The pH of a buffer solution can be calculated by using a formula. [10 marks](i) Derive the following expression for the ethanoic acid/ ethanoate

system.pH = pKn + log

(ii) Calculate the pH of 1.0 dm3 of a buffer solution prepared by dissolving 1.0 mole of CH3COOH and 1.0 mole of CH3COONa in sufficient amount of water. (Ka of CH3COOH is 1.8 × 10-5 moldm-3)

(iii) Calculate the pH of the buffer solution in (ii) above when 0.1 mole of calcium hydroxide, Ca(OH)2, is added to it. Write an equation for the reaction.

8. Benzene and toluene form a solution that obeys Raoult’s law. The vapour pressures of pure benzene and pure toluene are 12.7 kPa and 3.9 kPa respectively at 298K.(a) State Raoult’s law. [2 marks](b) Draw and label, on a graph paper, the vapour pressure-composition graph for a

mixture of benzene and toluene. [5 marks](c) Determine the vapour pressure of solution containing 2.0 moles of benzene

and 3.0 moles of toluene. [3 marks](d) Explain the qualitatively how the vapour pressure of toluene is affected when

benzene is dissolved in it. [2 marks](e) Describe how a mixture of benzene and toluene can be separated. [3 marks]

9. (a) Explain the working of paper chromatography. [9 marks](b) Explain the working of gas-liquid chromatography. [6 marks]

10. (a) Explain in terms of reaction kinetics, why the reaction rate increases when[4 marks]

(i) reactants at higher concentrations are used.(ii) the temperature is increases.

(b) Explain what is meant by the term “homogeneous” and “heterogeneous” catalyst. Give an example of each type and explain how the catalysts work.

[11 marks]

END OF QUESTION PAPER

Prepared By: Mr. Tan Wai Shan