O-Level-Chemistry-Notes

Copyrights AF/PS/2009/2010 59
To produce margarine:
Hydrogen is reacted with vegetable oil with presence of nickel catalyst and heat,
which adds to C=C bond, increasing the molecular mass of the compound
- With increase in mass, the compound has higher boiling point. Therefore,
margarine is solid at room temperature.
- Since only some C=C bonds react with hydrogen, margarine is partially
hydrogenated and each has different hardness, depending on the number of C=C
bonds.
The Cracking of Alkanes
Alkanes can be cracked into shorter chain hydrocarbons because of the higher
value it has that it can create more variety of products in petrochemical industries.
We crack alkane by catalytic cracking, which is, using catalyst to break alkane into
simpler hydrocarbons. We crack alkane to get more valuable hydrocarbons. The
total number of carbon and hydrogen atoms from products should equal to the
total number of carbon and hydrogen atoms in cracked alkane.
E.g. Octane can be cracked into simpler hydrocarbons such as the reaction below.
Suggest the possible identity of product x.
C8H18(l) C2H4(g) + x + CH4(g)
Number of C atoms in x = 8 – 2 – 1
= 5
Number of H atoms in x = 18 – 4 – 4
= 10
Product x is C5H10
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Isomers
Hey, I’m
C6H14!
No, you poser!
I’M C6H14!
Look at the figure above and count the number of carbon and hydrogen atoms in
each case. You will end up with the same C6H14. We can’t deny that they have the
same molecular formula. However, their structures are different. Therefore:
Isomers are compounds with same molecular formula but different structural
formula. Due to different chain length, they have different physical properties (e.g.
boiling point). Isomerism can occur in both alkanes and alkenes.
We therefore can’t just say that C6H14 is simply hexane because there are more
variations of C6H14 and each variation has its own name. The figure below shows
the nomenclature (i.e. how to name) these isomers.