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Related Topic: Organic Chemistry 1

Related Subtopic: Recommended practice of topic summary

Questions 3.4(a)

1. Name the specific addition reactions and processes labelled I, II, III, IV, V, VI in Figure 3.4.

2. Prepare a condensed summary together with a reaction scheme for alkanes, using ethane as an example.




Sample Answers to Questions 3.4(a)




1. I. Bromination II. Dehydration III. Self-addition polymerization IV. Combustion V. Hydrogenation VI. Cracking



2. Alkanes

   Are saturated hydrocarbons; that is, with only single bonds between carbon atoms
   

   Sources of alkanes

   Fractional distillation of crude oil.
   Cracking of higher alkanes
   

   Laboratory preparation

   Reacting a sodium salt of an organic acid.
   Example: CH₃CH₂COONa + NaOH → Na₂CO₃ + CH₃CH₃
   

   General formula

   Belong to a homologous series with the general formula, C_nH_2n+2
   

   Naming

   Take the form Alk-x-ane, where x is the position of branch
   

   Physical properties

   Low melting and boiling points (due to simple molecular structures)
   Low density and float on water
   

   Chemical properties

   Low reactivity because they are saturated and stable
   Neutral to litmus paper
   Burn in air in gaseous phase, producing steam (H₂O(g)) and carbon (IV) oxide (CO₂).
   Eample: CH₄(g) + 2O₂(g) → 2H₂O(g) + CO₂(g)
   Undergo substitution reaction with halogens in presence of ultraviolet light
   Examples
   CH₄ + Cl₂ u.v. light→ CH₃Cl + HCl
   CH₃CH₃ + Cl₂ u.v. light→ CH₃CH₂Cl + HCl
   (successively till all hydrogen atoms are substituted)
   Undergo cracking to produce lower alkanes and alkenes
   Example
   
   

   Uses of alkanes

   Used as fuel (for domestic and motor traffic), source of hydrogen, manufacture of printing ink, body oil manufacture of methanal, the body preservative