CHAPTER 1. ORGANICMOLECULES 1.7
- Give the structural formula for each of the following compounds:
(a) octane
(b) 3-methyl-hexane
- Methane is one of the simplest alkanes andyet it is an important fuel source.
Methane occurs naturally in wetlands, naturalgas and permafrost. However,
methane can also be produced when organic wastes (e.g. animal manureand de-
caying material) are broken down by bacteria under conditions that are anaerobic
(there is no oxygen). The simplified reaction is shown below:
Organic matter→ Simple organic acids→ Biogas
The organic matter could be carbohydrates, proteins or fats which arebroken
down by acid-forming bacteria into simple organic acids such as aceticacid or
formic acid. Methane-forming bacteria then convert these acids into biogases
such as methane and ammonia.
The production of methane in this way is veryimportant because methane can
be used as a fuel source. One of the advantagesof methane over other fuels like
coal, is that it producesmore energy but with lower carbon dioxide emissions.
The problem however, is that methane itself is agreenhouse gas and hasa much
higher global warmingpotential than carbon dioxide. So, producingmethane
may in fact have an evenmore dangerous impacton the environment.
(a) What is the structural formula of methane?
(b) Write an equation to show the reaction that takes place when methane is
burned as a fuel.
(c) Explain what is meant by the statement thatmethane ’has a greaterglobal
warming potential thancarbon dioxide’.
- Chlorine and ethanereact to form chloroethane and hydrogen chloride.
(a) Write a balanced chemical equation for thisreaction, using molecular for-
mulae.
(b) Give the structural formula of chloroethane.
(c) What type of reaction has taken place in thisexample?
- Petrol (C 8 H 18 ) is in fact not pure C 8 H 18 but a mixture of various alkanes. The
’octane rating’ of petrolrefers to the percentageof the petrol which is C 8 H 18.
For example, 93 octanefuel contains 93% C 8 H 18 and 7% other alkanes.The
isomer of C 8 H 18 referred to in the ’octane rating’ is in fact not octane but 2,2,4-
trimethylpentane.
(a) Write an unbalancedequation for the chemical reaction which takesplace
when petrol (C 8 H 18 ) burns in excess oxygen.
(b) Write the general formula of the alkanes.
(c) Define the term isomer.
(d) Use the informationgiven in this question and your knowledge of naming
organic compounds to deduce and draw the fullstructural formula for 2,2,4-
trimethylpentane. (IEB pg 25)
