Recapitulation on Chemistry Experiments (Expt 23.1, 25.1, 25.2)

 

The following students (as 03/10/2001) still haven’t hand in their experiment workbook for marking:

2,4,9,12,13,17,19,21,26,27,28,32,35,38

For those have handed in the Expt workbook, most of them forget to finish the Expt 23.1.

 

Frequent mistakes

p.5

Q13: Yes, higher-boiling fractions contain larger molecules with greater intermolecular forces that attraction between molecules is stronger. Hence the molecules move past each other with greater difficulty.

 

p.6

Q.15: Crude oil itself is too complex a mixture to be any use. After refinery, each of the fractions is used as raw material for various industries, e.g. medicine and plastics.

 

p.15

Write an equation for a possible reaction.

C₆H_14(l) + Br_2(g)→C₆H₁₃Br_(l) or C₆Br_14(l) (HBr could be omitted and equations for organic reaction may not be balanced)

 

Section D

6. light, 7. substitution, 8. similar, 9. similar

 

p.18

Q3(a): If so, the medicinal paraffin absorbed by the rocksil would vaporize too fast. And only hot pumice stones have catalytic function on cracking, and then most of the vapour passes over the hot pumice stones without reaction.

 

p.19

Q.4:(c) A yellow flame is observed, which is a little sooty.

Q.7: heat, smaller, more.