Transcript
Page 1: Qualitative organic analysis

Qualitative organic analysis

Page 2: Qualitative organic analysis

Reactions of alkanes with bromine.

Alkanes decolourise

bromine in the light.

Alkane layer

Water

But not in the dark!

Page 3: Qualitative organic analysis

Reactions of alkenes with

bromine

Alkenes decolourise bromine in both the dark and the light.

Page 4: Qualitative organic analysis

Reactions of alkenes with potassium manganate (vii)

Alkenes decolourise acidified manganate (vii)

Manganese is reduced from purple +7

To colourless +2

Page 5: Qualitative organic analysis

If there is insufficient alkene…

the intermediate brown Manganese (iv) is formed.

Page 6: Qualitative organic analysis

Reactions of alkanes with manganate (vii)

Alkanes do not decolourise

acidified manganate (vii) as they are saturated.

Page 7: Qualitative organic analysis

Reactions of haloalkanes with silver nitrate

Silver nitrate is colourless

Chloroalkanes give a white ppt, which darkens to purple on exposure to bright light.

Page 8: Qualitative organic analysis

Reactions with silver nitrate

Silver nitrate is colourless

Bromoalkanes give a buff ppt, which darkens on exposure to bright

light.

Page 9: Qualitative organic analysis

Reactions with silver nitrate

Silver nitrate is colourless

Iodoalkanes give a light yellow ppt,

which is not photo sensitive.

Page 10: Qualitative organic analysis

Alcohols give effervescence with sodium

This is because they are extremely weak acids.

Hydrogen gives a “pop” with a lighted splint.

Page 11: Qualitative organic analysis

But as alcohols are extremely weak acids they are unable to neutralise bases.

Page 12: Qualitative organic analysis

Reactions with sodium dichromate.Sodium dichromate is an oxidising agent, ie it oxidises other chemicals, being reduced in the process.

Orange chromium (vi) is

reduced togreen chromium (iii) when heated

with acid.

Page 13: Qualitative organic analysis

Oxidation of primary alcohols.

Primary alcohols are oxidised as

orange chromium (vi) is

reduced togreen chromium (iii) when heated

with acid.

Two organic products are possible; Aldehydes or Carboxylic Acids.

Page 14: Qualitative organic analysis

Oxidation of aldehydes.

Aldehydes are oxidised as

orange chromium (vi) is

reduced togreen chromium (iii) when heated

with acid.

Only one organic product is possible; a Carboxylic Acids.

Page 15: Qualitative organic analysis

Oxidation of secondary alcohols.

Secondary alcohols are also

oxidised as orange

chromium (vi) is reduced to

green chromium (iii) when heated

with acid.

Only one organic product is possible; a Ketone.

Page 16: Qualitative organic analysis

Oxidation of tertiary alcohols

Tertiary alcohols cannot be oxidised

by acidified potassium

dichromate.

To oxidise them a much stronger oxidising agent is needed that can break C/C bonds.

Page 17: Qualitative organic analysis

Testing for carbonyl compounds.

Both aldehydes and ketones give an orange/red

precipitate with 2,4 dinitro phenyl hydrazine.

Page 18: Qualitative organic analysis

Distinguishing between aldehydes and ketones.

Aldehydes are oxidised as

orange chromium (vi) is

reduced togreen chromium (iii) when heated

with acid.

Only one organic product is possible; a Carboxylic Acids.

Page 19: Qualitative organic analysis

Distinguishing between aldehydes and Ketones

Ketones cannot be oxidised by acidified

potassium dichromate.

To oxidise them a much stronger oxidising agent is needed that can break C/C bonds.

Page 20: Qualitative organic analysis

Reaction with Fehling’s Solution

Aldehydes change the colour of

Fehling’s Reagent upon heating from

blue to red.

Blue copper (ii) ions are reduced to red

copper (i).

Cu 2+ + e- → Cu+

Page 21: Qualitative organic analysis

Ketones do not react with Fehling’s

Solution as they are not oxidised by mild

oxidising agents.

Page 22: Qualitative organic analysis

Reaction with Tollen’s ReagentAldehydes react with Tollen’s Reagent (ammonical silver solution), depositing a silver mirror on the side of the tube.

Silver ions are reduced to metallic silver.

Ag+(aq) + e- → Ag(s)

Page 23: Qualitative organic analysis

But Ketones do not react with Tollen’s reagent as they are not oxidised by mild oxidising agents.

Page 24: Qualitative organic analysis

Reactions of carboxylic acids

Acids react with metals giving hydrogen.

Carboxylic acids react with sodium, producing effervescence.

Hydrogen gives a “pop” with a lighted splint.

Page 25: Qualitative organic analysis

Reaction of carboxylic acids with sodium carbonate.

Effervescence (CO2)

Phenols and alcohols are weaker acids and will not react.

Acids react with

carbonates to give a salt,

water and carbon dioxide.

Page 26: Qualitative organic analysis

Reactions with Universal Indicator

Alcohols, carbonyl compounds and esters

are neutral so turn Universal Indicator

green.

Page 27: Qualitative organic analysis

Alcohols might react with sodium like acids, but…

they are unable to neutralise bases.

Page 28: Qualitative organic analysis

Carboxylic Acids are acidic, so turn Universal

Indicator red.

Page 29: Qualitative organic analysis

Carboxylic acids neutralise bases.

Page 30: Qualitative organic analysis

Amines are basic so turn Universal Indicator blue.

Page 31: Qualitative organic analysis

Amines neutralise acids.


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