Candidates Performance in Paper I (Q1 5) and II B

Transcription

1 HKDSE 2014 Candidates Performance in Paper I (Q1 5) and II B 17, 21 November 2014

2 1 (a) Satisfactory About two thirds of the candidates could apply knowledge of bonding and structure of graphite to explain the properties of graphene. Not able to draw the electron diagram of carbon dioxide.

3 1 (b) Fair; 1 (c) Poor Some candidates could judge the statement correctly, i.e. graphene should NOT have a low melting point. Some candidates were able to describe the structural features of a C 60 molecule. Many candidates could NOT explain why C 60 is soluble in some organic solvents.

4 Combined Science 1 (b) Fair; 1 (c) Poor Some CS candidates could judge the statement correctly, i.e. graphene should NOT have a low melting point. Around a quarter of CS candidates were able to draw the structure of diamond up to an acceptable standard. Again, very few CS candidates could explain whether diamond and graphite would have similar chemical properties.

5 Combined Science 1 (c) Poor The lowest accepted standard of the drawing of diamond.

6 2Satisfactory About half of the candidates could draw the structural formula of ethane 1,2 diol. Most candidates could NOT explain why the molecule is water soluble using both intermolecular hydrogen bond and short carbon chain length.

7 Combined Science 2 Poor Only about a quarter of the CS candidates could draw the structure formula of X (i.e. ethenedioic acid). About half of the CS candidates could state water molecule would be eliminated during the formation of the polymer. Many CS candidates wrongly stated the functional groups as alkene, alcohol, C O and C=O, instead of C=C and COO.

8 3 (a) Satisfactory Many candidates could NOT state the correct means how to carry out a test for unsaturation. For instance, incorrect reagents like bromine, bromine liquid were mentioned instead of bromine water Also, the colour change was NOT correctly described.

9 3 (b) Fair Only a few candidates could write the systematic name for the compound as well as the name for the type of polymerisation involved. As in previous years, many candidates could NOT draw the exact structure of the polymer showing three repeating units. H Cl H Cl H Cl C C C C C C H Cl H Cl H Cl

10 3 (c) (d) Good Candidates demonstrated a good understanding of intermolecular force for explaining why Saran is more suitable than PE to make food wrap for use in microwave ovens. Candidates could explain the pollution problem associated with Saran food wrap.

11 Combined Science 3 (d) Poor Many CS Candidates, around two thirds, could NOT state the effect of heat on thermoplastics, especially when the temperature is very high.

12 4 Good About three quarters of the candidates could describe the methods to be used. Some candidates erroneously considered silver can be extracted by physical methods. Many candidates were less capable of presenting in a logical and systematic manner.

13 5 (a) Satisfactory; (b) Fair About two thirds of the candidates could state the safety measure required for handling concentrated acids. About half of the candidates could correctly comment on the statement. Arguments like concentrated ethanoic acid is not a strong acid and dilute HCl is a strong acid were quite commonly used. Some candidates erroneously linked up the strength of an acid with its basicity / ph value.

14 5 (c) Fair Some candidates wrongly considered the rate of bubble formation in the reaction as a means to distinguish the three concentrated acids. Some candidates correctly recalled the oxidising properties of concentrated HNO 3 and H 2 SO 4, but quite a number of candidates wrongly stated that hydrogen gas would be produced.

15 Thank you for your attention!

16 II 2 (a) Fair; (b) Poor (a) About a quarter of the candidates could NOT distinguish between thermoplastics and thermosetting plastics. (b) Most candidates had limited understanding of silicates and ceramics, and hence could NOT state the answers required.

17 II 2 (c) Fair (c) About two thirds of the candidates could NOT state the correct moulding method to be used, wrong answers like compression moulding were frequently used. (c) Many candidates erroneously state two common types of PE: PVC / PS / PP instead of HDPE and LDPE. (c) Only a few candidates could draw the correct structure of a lactic acid molecule. H H 3 C C C OH O OH

18 Thank you for your attention!