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Distinguish between polyunsaturated vegetable oil and petroleum oil

  1. Jan 11, 2009 #1
    1. Which of the following chemical reaction could be used to Distinguish between polyunsaturated vegetable oil and petroleum oil containing a mixture of saturated and unsaturated hydrocarbon?
    Explain your answer.

    i.addition of bromine in CCl4
    ii. hydrogenation
    iii.saponification
    iv.ozonolysis

    2.The attempt at solution:

    i.addition of bromine in CCl4

    polyunsaturated oil will be becomes colourless; whereas saturated and unsaturated mixture hydrocarbon will not become colorless

    ii. hydrogenation

    polyunsaturated oil becomes solidified after treated with Hydrogen , whereas saturated and unsaturated mixture hydrocarbon will not become solidified

    iii.saponification

    polyunsaturated oil will produce 3 unsaturated fatty acid, whereas saturated and unsaturated mixture hydrocarbon form a mixture of saturated and unsaturated fatty acid
     
    Last edited: Jan 11, 2009
  2. jcsd
  3. Jan 12, 2009 #2

    chemisttree

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    No. You know nothing about the color of the petroleum oil... before or after treatment with bromine. The color of vegetable oils would come from carotenoids perhaps but you don't know if the veggie oil has been refined and is therefore initially colorless or nearly so.

    How do you know that petroleum unsaturate won't crystallize? You are correct in that it does tend to be true that petroleum unsaturates won't solidify but it isn't a definitive test.

    Do petroleum oils contain triglycerides or esters?
     
  4. Jan 14, 2009 #3
    I assume by "petroleum oil" they are referring to either a paraffinic or naphthenic mineral oil. These do not contain triglycerides or esters, they are a mixture of paraffinic and naphthenic hydrocarbons, with somewhere between 0 and 15% aromatic hydrocarbons. There may also be some very minor concentrations of polar species (nitrogen or sulphur containing molecules) but this is very minor (<0.5%).

    I would suggest that some form of quantitative hydrogenation would be a good way to distinguish the two. It is possible to measure the amount of hydrogen taken up by a sample of oil using a pressure-drop method, converting back to STP. You will find that a petroleum oil takes up virtually nothing, whereas a veg oil takes up about 0.1 - 0.2 cc of hydrogen per gram of oil.
     
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