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Chemistry Paper 2,Nov/Dec 2008  
Questions:   1 2 3 4 5 6   Main
General Comments

Question 6

(a)        (i)         Give one example of

I.          a deliquescent substance;
II.         a hygroscopic substance;
III.       an efflorescent substance;

(ii)        Name three products of the destructive distillation of coal.

(iii)       Give two uses of graphite.                                                              [8 marks]

(b)        (i)         Write a balanced chemical equation for the complete reaction between
                        dilute tetraoxosulphate (VI) acid and aqueous sodium hydroxide.

(ii)        State the type of reaction involved in 8(b)(i) above.

(iii)       If 20cm3 of 0.125 moldm-3 of tetraoxosulphate(VI) acid solution reacted with a solution of sodium hydroxide, calculate the number of moles of sodium hydroxide required for a complete reaction.

(iv)       Outline how a solid sample of the product of the reaction in 8(b)(iii) could be obtained.                                                                                   [11 marks)

(c)        (i)         Draw two resonance structures of benzene.
(ii)        Give two types of reactions that benzene undergoes
(iii)       Give two physical properties of benezene.                                     [6 marks]


This question was attempted by most  candidates and the performance was good.
In(a)(i), candidates correctly gave one example each of I – III from the list of examples thus: 
            I.          FeCl3 /KOH/CaCl2/NaOH/MgCl2/P2O5.
            II.         CuO/CoCl2/conc H2SO4/ silica gel/CuSO4.
            III.       Na2CO3 IOH2O/ Na2SO4  IOH2O /MgSO4   7H2O .

IUPAC names of any of the compound was accepted instead of the formula.

In (a)(ii), candidates gave three products of the destructive of coal from the following:

  1. coke
  2. ammoniacal liquor
  3. coal tar
  4. coal gas


In(a)(iii), candidates correctly gave two uses of graphite from among the following uses:

  1. as lubricant
  2. as electrodes
  3. for making lead pencils
  4. moderators in nuclear reactors


In(b)(i), candidates correctly wrote a balanced chemical equation for the complete reaction thus:

            H2SO4(aq)  +    2NaOH(aq) →   Na2SO4(aq) +  2H2O(l), 

In(b)(ii), candidates correctly stated that the reaction is neutralization.

In(b)(iii), majority of the candidates could correctly calculate the number of moles of sodium hydroxide required for a complete reaction as follows:

No. of moles of H2SO4   =   20 x 0.125
                                       =    0.0025 moles

1 mole of H2SO4  Ξ       2  moles of NaOH
∴   0.005 moles of  H2SO4  Ξ       2 x  0 . 0025   moles of NaOH
                                         =    0.005 moles of NaOH.

Other correct method were accepted.

In (b)(iv), only few candidates could correctly outline how a solid sample of the product of the reaction in (b)(iii) could be obtained.  The expected answer from candidates is as stated below:

  1. put solution into evaporating dish
  2. heat to concentrate/evaporate
  3. obtain the solid/allow to cool and crystallize.


In (c)(i), most candidates could not draw resonance structure of benzene.  The correct structures expected from candidates are as follows:







In (c)(ii), only few candidates knew that benzene undergoes substitution and addition reactions.

In (c)(iii), most candidates gave chemical properties of benzene instead of physical properties:  The expected answers were as follows:

  1. colourless liquid
  2. less dense than water
  3. insoluble in polar solvents/soluble in organic solvents
  4. has boiling point of 80ºC.


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