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identifying organic compounds

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Why bother with a post grad? Are they even worth it? Have your say! 26-10-2016
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    questions often ask 'how do you find difference of these two substance 1)acid/alkaline 2)a simple organic compound from 1 of the 4 groups ane, ene, ol, acid'

    so i would say use UI for 1, and i don't know for 2, the markscheme usually says they are imiscible or they are flammable

    are all simple organic coumpounds (first several from 4 main groups) imiscible and flammable or not?? thanks

    You can test for alkenes/unsaturation by adding bromine water, which is brown. In the presence of an alkene, an addition reaction will happen across the double bond, decolourising the bromine water. \

    Simple organic compounds will be immiscible with water, if you added water to the unknown compound, shook the contents and observed what happened, an organic compound would separate from the aqueous layer and form 2 separate layers. However, this is generally not true for alcohols or carboxylic acids as they are polar enough to dissolve in water. A large majority of organic compounds (alkanes, alcohols etc) are flammable as you've stated.

    If you perform the previous two tests and the bromine water is not decolourised and the compound is miscible with water, then you could perform the jones reagent test. If you mix Chromium (VI) oxide and sulfuric acid with your compound, if you have a primary or secondary alcohol, this will be oxidised to the corresponding aldehyde or ketone, respectively. In the process, the chromium is reduced from +6 to +3, changing colour to green.

    If the jones reagent test doesn't work, you may have a tertiary alcohol. Perfoming the Lukas test, by mixing the compound with HCl and ZnCl2 and shaking, will identify a tertiary alcohol. After shaking, allow to settle and you should very quickly see the formation of a cloudy layer.

    If all previous tests come up negative, then you should test for a carboxylic acid by dissolving the unknown compound in methanol and adding saturated NaHCO3 solution. A positive test evolves bubbles of carbon dioxide.

    Hope this helps
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