17 Limonene is an oil extracted from the skin of citrus fruits such as oranges or lemons. It is found in some cleaning products such as those used to remove chewing gum. Limonene has the structure shown
(a) Deduce the molecular formula of limonene.
(2)
ANSWER
Total number of Carbon atom = 10
Total number of Hydrogen atom = 16
Therefore the molecular formula is C10H16
(b) (i) A few drops of acidified potassium manganate(VII) solution are mixed with a
sample of limonene.
State the colour change.
(1)
From....................... To.......................
ANSWER
Color Changes from purple to colorless.
(ii) Draw the skeletal formula of the structure of the organic product formed when the reaction in (b)(i) is carried out with excess acidified potassium manganate(VII).
(1)
ANSWER
(iii) Name the type of reaction that limonene undergoes in (b)(i).
(1)
ANSWER
Oxidation or Electrophilic Addition.
(c) On heating, limonene reacts to form two molecules of a smaller hydrocarbon, Q.
Q can be polymerised to form R, a polymer used to improve the grip of car tyres.
A section of R is shown
Draw the structure of Q.
(1)
ANSWER
(d) Give two ways in which chemists can help minimise problems caused by the disposal of polymers.
(2)
ANSWER
Develop biodegradable polymers
Remove toxic gases produced by incineration of polymers.
(e) Limonene is extracted from orange peel using a solvent.
Possible solvents are hexane and liquid carbon dioxide.
Liquid carbon dioxide can be obtained by allowing solid carbon dioxide to melt under high pressure.
(i) Suggest one advantage and one disadvantage of using liquid carbon dioxide rather than hexane to dissolve the limonene. Assume that the carbon dioxide does not escape into the atmosphere.
(2)
Advantage………………………………………………………………………………………………………………………………………….
Disadvantage……………………………………………………………………………………………………………………………………..
ANSWER
Advantage: CO2 is non-toxic and non-flammable
Disadvantage: Melting requires high pressure which is expensive.
(ii) Orange peel contains 1.63% of limonene by mass.
A chewing gum remover contains 30cm3 of limonene per bottle.
Calculate the mass of orange peel, in kg, needed to obtain 30cm3 of limonene.
[Density of limonene = 0.841gcm–3]
(3)
ANSWER
Now by using ratio method,
100gram of orange peel contain 1.63gram of limonene
X gram of orange peel contain 25.23 gram of limonene
Therefore
