POK OI HOSPITAL TANG PUI KING MEMORIAL COLLEGE

SECOND TERM TEST ( 1997-1998 )

S6 CHEMISTRY I

 

Class                :           6 S                                           Date     :           __________________

Name               :           ________________                Time allowed: 60 minutes

Class Number  :           ________________                ( P.1 - P.7 /38 )

 

Instructions to students:

 

1. There are TWO sections in this paper, Section A and Section B.

2. Section A carries 20 marks and Section B carries 20 marks The total score is 40

   marks.

3. All questions in Sections A and B are COMPULSORY. Write your answers in the

   spaces provided in this Question/ Answer Book.

4. A Periodic Table is printed on the last page of the question paper.

________________________________________________________________________

 Section A

 Answer ALL questions in this Section. Write your answers in the spaces provided.

 

1. (a)

 

 

        The above apparatus was used to determine the relative molecular mass of

        propanone ( acetone), by measuring volumes of known masses of propanone. The propanone was

        introduced into the gas syringe by means of a hypodermic springe ( not shown ).

 

        (i)    Where exactly should the propanone be introduced?

 

 

        (ii)   How could the amount of propanone introduced be determined?

 

 

        (iii)  Suggest two precautions that should be taken in order to achieve the best  result.

 

                                                                                                     ( 4 marks )

  

    (b) (i)    Draw the shape of the molecule PF5.

 

   

         (ii)   What is the hybridisation in the bonding of nitrogen in the NH4+ ions?

  

                                                                                                    ( 2 marks )

 

    (c) The diagram shows the distribution curve for the energies of reactants molecules

         in a given system at constant temperature.

 

 

         (i)    Sketch on the diagram a distribution curve representing the same sample of reactant molecules at a

                higher temperature.

          (ii)   What does the area under either curve represent?

  

         (iii)  If E1 represents the activation energy in the absence of a catalyst, mark on the graph ( and label it E2 )

                an appropriate value for the activation energy in the presence of a catalyst. Briefly explain your

                answer.

 

　

　

                                                                                                                        ( 4 marks )

2. (a)

 

        (i)    What are the co-ordination numbers of the black sphere and of the white

               sphere.

 

  

 

        (ii)   Calculate the number of white spheres and black spheres in the above unit   cell. Briefly show your calculation.

 

  

 

 

                                                                                                                          ( 3 marks )

 

    (b) When 10 cm3 of 1.5 M hydrofluoric acid HF and 20 cm3 of 0.3 M sodium fluoride NaF are mixed, the pH

        of the resulting solution is 3.9. Calculate the acid dissociation constant of HF.

 

 

 

 

                                                                                                                                 ( 3 marks )

     (c) Define the following terms:

          (i)    Acid-base indicator

 

  

         (ii)   Buffer

  

 

         (iii)  End point

 

  

         (iv)  Equivalence point

 

 

                                                                                                                              ( 4 marks ) 

  Section B

 Write your answers in the spaces provided.

 Marks will be allocated approximately as follows:

                       chemical knowledge                                       50%

                       organization                                                     30%

                       presentation ( including proper use of English )20%

 

Equations, suitable diagrams and examples are expected whereas appropriate.

 The examiners are looking for the ability to analyse, to evaluate and to express ideas

clearly.

  

3. Write an essay on hydrogen bonding.

   ( Your essay should include the condition for hydrogen bond formation, the types of

    hydrogen bond and its effect on the properties of compounds.)

                                                                                                                ( 20 marks )

 

 _______________________________________________________________________

Chemical knowledge

Organization :

Pesentation :                                                                

 

 

 

END OF PAPER

  

POK OI HOSPITAL TANG PUI KING MEMORIAL COLLEGE

SECOND TERM TEST ( 1997-1998 )

S6 CHEMISTRY II

 

Class                :6S                                           Date     :           __________________

Name               :           ________________                Time allowed: 90 minutes

Class Number  :           ________________                ( P.1 - P.3 /38 )

 

Instructions to students:

1. Answer ALL questions.

2. Write your answers on the foolscap papers provided.

3. The total score is 60 marks.

4. A Periodic Table is printed on the last page of this paper.

 

1. (a) Nitrogen and phosphorus are members of group V, but these elements and their

         compounds have different properties. Briefly explain their differences.

         (i)    The melting point of N2 is -210 oC, whereas that of P4 is 44 oC.

         (ii)   P4 burns spontaneously in air, but N2  reacts with O2 at high temperature or lightning.

         (iii)  The bond angle of PH3 is 90 o, but the bond angle of NH3 is 107 o.

         (iv)  NH3 is very soluble in water, but PH3 is only sparingly soluble in water.

         (v)  The boiling point of NH3 is -36 oC, but that of PH3 is -87 oC.

                                                                                                    ( 10 marks )

 

     (b) Given:

                                 Ka for CH3(CH2)2COOH = 1.5 x 10-5 mol dm-3 at 298 K.

       Calculate the pH of

          (i)    an aqueous solution of 0.10 M CH3(CH2)2COOH;

          (ii)   an aqueous solution of 0.050 M CH3(CH2)2COONa and 0.050 M

               CH3(CH2)2COOH; and

          (iii)  1.0 dm3 of the solution in (ii) after the addition of 1.0 x 10-3 mol of solid

               NaOH.

                                                                                                      ( 10 marks )

 2. (a) Iodine reacts with propanone according to the equation:

                        CH3COCH3 (aq) + I2 (aq) ® CH3COCH2I (aq) + H+ (aq) + I- (aq)

         The following data were obtained for the reaction at 300 K:

 

Experiment

Initial concentration / mol dm-3

Relative Rate

 

CH3COCH3

I2

H+

 

1

0.50

1.25 x 10-3

1.25

2

2

0.50

1.25 x 10-3

0.625

1

3

0.25

1.25 x 10-3

1.25

1

4

0.50

6.25 x 10-4

1.25

2

         (i)    Determine the rate equation for this reaction.

         (ii)   What is the unit of the rate constant for this reaction?

         (iii)  The reaction occurs in several steps, with each step involving a collision

              between two particles. Name the two particles involved in the  rate-determining step. Explain your

               choice.                                                                            ( 7 marks )

 

     (b) The rate constant of the following reaction at various temperatures are

         given below:

                                                            X (g) + Y (g) ® Z (g)

 

         At T1 = 700 K, k1 = 1.3 dm3 mol-1 s-1

         At T2 = 800 K, k2 = 23 dm3 mol-1 s-1

 

         Determine the activation energy of the above reaction.

         ( Given : gas constant, R = 8.314 J K-1 mol-1)                        ( 4 marks )

 

 

    (c) The rate constant for the reaction of                                                                I

 

      with CN- was measured at various temperatures and the results are shown below: 

T / K

300

310

320

330

k / s-1

3.72 x 10-5

9.42 x10-5

5.48 x 10-4

2.01 x10-3

         (i)    What is the overall order of this reaction?

          (ii)   By using the Arrhenius equation and plotting a suitable graph, determine the activation

                  energy, Ea of the reaction.

                ( Given : gas constant, R = 8.314 J K-1 mol-1)                        ( 9 marks )

  

3. In the Contact Process, the sulphur dioxide is converted into sulphur trioxide. The

    standard enthalpy changes of formation of SO2 (g) and SO3 (g) are -297 and

    -395 kJ mol-1 respectively.

     (a) Calculate DH o for the reaction 

2SO2 (g) + O2 (g) ==== 2SO3 (g)            ( 2 marks )

 

    (b) Give and explain the effect of

         (i)    increasing the temperature and

         (ii)   increasing the pressure

         on the rate and the position of equilibrium for this reaction.        ( 8 marks )

     (c) Comment on the fact that in industry a temperature of about 800 K, a pressure of

         one to two atmospheres and a catalyst are used for the Contact Process.

                                                                                                             (6 marks )

    (d) At a certain temperature, the equilibrium partial pressures were, in atmospheres,

                                                 P ( SO2 ) = 0.27, P ( O2 ) = 0.40, P ( SO3 ) = 0.32.

          (i)    Calculate the equilibrium constant, Kp, at this temperature.

         (ii)   This equilibrium mixture was obtained from oxygen and sulphur dioxide

               only, in a sealed container at this temperature. What were the initial pressures of O2 and SO2?

                                                                                                               ( 4 marks )

        

 

END OF PAPER