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Test for functional groups
Testing for primary, secondary and tertiary alcohols
Potassium dichromate (VI) is an oxidising agent
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Can use the notation [O] to
represent an oxidising agent when you write out a reaction
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This is
accompanied by a colour change
Orange dichromate (VI) ions are reduced

green chromium (III) ions are formed

You can use this colour change to test for presence of primary, secondary or tertiary alcohols
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No colour change seen with tertiary alcohols
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Fehling’s and Benedict’s solution:
Fehling’s solution is blue solution of copper (II) ions dissolved in sodium hydroxide
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Method:
1) Add 2cm3 of Fehling’s or Benedict’s solution to a test tube
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No reaction happens with ketones, so solution will stay blue
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10 mol dm-3 silver nitrate solution in test tube
2) Add few drops of dilute sodium hydroxide solution
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3) Add drops of dilute ammonia solution until brown precipitate dissolves completelythis solution is Tollens’ reagent
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Silver will coat the inside of the apparatus to form a silver mirror
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Aldehydes and ketones should always be warmed using a water bath, rather than
using a Bunsen burner, to prevent them from catching alight
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When
carbon dioxide is bubbled through limewater, limewater turns cloudy
Careful- this test will give positive result with any acid, so you can only use it to
distinguish between organic compounds when you already know that one of them is a
carboxylic acid
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1) Add 2cm3 of the solution that you want to test to a test tube
2) Add 2cm3 o bromine water to the test tube
3) Shake the test tube
If an alkene is present, the bromine water will turn from orange to colourless



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