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Chemistry Paper 2,Nov/Dec 2009  
Questions:   1 2 3 4 5 6 7 8   Main
General Comments

Question 4

  1. (i)   What are alkanoates?

(ii)  Write the equation for the preparation of propylethanoate.
(iii) Draw the structural formula of propylethanoate.                           
     [5 marks]

  1. Give the IUPAC names of the following compounds:
      1. CH3CH2CH(CH2)CH3;
      2. CH ≡ CCH2CH3.
  1. Classify the following alkanols as primary, secondary or tertiary

      (i)   CH3 –  C –  OH                                                 

(ii)    CH3  CH2  OH;

(iii)             CH2  CH2  CHCH3  

  1. Consider the following electron arrangements:

    1. What rule/principle is violated in each of the arrangements?  Explain your answer in each case.
    2. Which of the atoms X or Y has a smaller size?  Explain your answer.    [9 marks]
  1. (i)   State the type of bond that would be formed between
      1. 11Na and 8O,
      2. 1H and 8O.

(ii)   Give two characteristic properties of each compound formed in 4(e)(i) I and II  based on their bond types.       [6 marks]


The question was not popular among the candidates and the performance was poor.

In part (a)(i), only few candidates correctly stated that alkanoates compounds formed when alkanoic acids react with alkanols (in the presence of mineral acid). Some of them lost the marks because they referred to alkanoates as “reactions”.

in (a)(ii), candidates correctly wrote the equation for the preparation of propylethanoate however, some of them lost the mark for the reversibility sign. The expected response from them was as written below:
CH3 COOH + CH3 CH2 CH2 OH  ⇌  CH3 COOCH2CH2CH3   + H2O

In (a)(iii), candidates could not draw the correct structure of propylethanoate.  The expected structure was as drawn below:

                            H    O             H     H    H
                             |      | |              |       |      |                                
          H - C  - C  -  O  -  C – C – C - H
                                         |                       |      |      |
                                        H                     H    H    H  


                            H     H     H           O     H     
                             |       |       |             | |      |                                
           H - C  - C  -  C  - O -  C – C –  H
                                         |       |       |                    |     
                                        H     H    H                  H            

In part (b), candidates did not know that the names of the compounds were 2- metylbutane and 1-butyne/ but-1-yne respectively.

In part (c), few candidates correctly classified the compounds as tertiary alkanol, primary alkanol and secondary alkanol in (i), (ii) and (iii) respectively.

In part (d) (i) and (ii), candidates did not know the rule that was violated by each of X and Y nor stated the atom with the smaller size with an explanation.

The expected answers from candidates were as follows:

  1. 14X: Aufbau principle is violated.

3s orbital has a lower energy than 3p orbitals therefore 3s orbitals should be filled before any electrons(s) is/are assigned to the 3p orbitals.

15Y: Hunds rule is violated.
3p orbitals are degenerate/have same energy and electrons must be filled (parallel and) singly before pairing.

  1. 15Y has a smaller size compared to 14X

An additional proton increases the effective nuclear charge hence the outermost electrons are held more tightly leading to smaller size of the 15Y.

In part (e)(i) I and II, only few candidates stated correctly that ionic bond and covalent bond were formed in each case and hence, gave two characteristic properties of each compound based on the bond types in (ii).

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