testing for functional groups - Unit 4 AOS 2 Flashcards
1
Q
testing for carbon to carbon double bonds
A
- bromine water test
- potassium permanganate test
2
Q
bromine water test
A
- It can be used to determine whether a compound contains double or triple bonds, as these unsaturated bonds react with bromine water,
causing it to decolourise - If the organic compound is unsaturated (contains double or triple bonds), it will react with the bromine water, causing it to turn from light brown/orange to colourless
- This is due to the formation of a colourless dibromoalkane compound
- It is important to note that this test is specific for unsaturation and does not provide
information about the type or location of the unsaturated bonds
3
Q
potassium permanganate test
A
- The reaction between KMnO4 and an unsaturated compound involves the reduction of the purple-coloured KMnO4 solution to a colourless solution
- If the organic compound is unsaturated, such as an alkene or alkyne, the purple KMnO4 will be gradually decolourised and/or turned into a brown precipitate. The brown precipitate formed in alkaline conditions is manganese dioxide, MnO2
- It only indicates the presence of double or triple
bonds in the organic compound.
4
Q
tests for hydroxyl groups
A
- Acidified potassium dichromate test and silver mirror test
- lucas test
- esterification test
- sodium metal test
5
Q
acetified potassium dichromate test
A
- Adding acidified potassium dichromate (K2Cr2O7(aq)/H+(aq)) can be used to
qualitatively determine whether a primary or secondary alcohol is present in a solution. When Cr6+(aq) ions are reduced to form Cr3+(aq) ions, the solution turns from orange to green (figure 5) in the presence of a primary or secondary alcohol. - primary alcohols will oxidise to an aldehyde and then to a carboxylic acid (green)
- secondary alcohols will oxidise to a ketone (green)
- tertiary alcohols will not react
6
Q
silver mirror test
A
- to distinguish between a primary and a secondary alcohol, the silver mirror test can be used
- The silver mirror test (Tollens’ test) involves mixing the suspected oxidised primary alcohol with Tollens’ reagent (ammoniacal silver nitrate solution)
- If an aldehyde is present, then a reduction reaction occurs and a silver mirror-like
substance is formed - The silver mirror test will show a positive result with aldehydes (which are produced from the partial oxidation of primary alcohols) but not ketones (which are produced from the oxidation of secondary alcohols).
7
Q
lucas test
A
- The Lucas test can be used to qualitatively determine whether a primary, secondary
or tertiary alcohol is present. When the suspected alcohol has been mixed with Lucas reagent (a mixture of concentrated hydrochloric acid and zinc chloride), if an alcohol is present, it will produce a cloudy liquid
8
Q
esterification test
A
- The sample to be tested, a carboxylic acid and a concentrated sulfuric acid catalyst are added to a tube and heated.
- The production of an ester can be detected by a fruity smell, confirming that the test substance is an
alcohol.
9
Q
tests for carboxyl groups
A
- pH test
- reaction with metal carbonates or metal bicarbonates
- esterification test
10
Q
pH test
A
- Adding an acid-base indicator, such as phenolphthalein, to the unknown compound
can help in identifying the carboxyl group. The indicator changes colour from its basic form to its acidic form in the presence of carboxyl groups
11
Q
metal carbonates or bicarbonates
A
- Carboxylic acids can react with carbonates or bicarbonates to produce carbon dioxide gas, which can be observed as effervescence or bubbling
- bubbling and gas in limewater indicated carbon dioxide
12
Q
esterification test
A
- Treating the unknown compound with an alcohol and a strong acid, such as concentrated sulfuric acid, can lead to the formation of an ester. The sweet, aromatic smell of the ester can imply the presence of a carboxyl group.
