26.2 identifying aldehydes and ketones Flashcards

1
Q

what is 2,4-dinitrophenylhydrazine also called?

A

Brady’s reagent

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2
Q

what is 2,4- DNP used to detect?

A

presence of a carbonyl group

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3
Q

what coloured precipitate forms in the presence of a carbonyl group?

A

orange

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4
Q

describe the procedure for the detection of a carbonyl group

A
  1. add 5cm of 2,4-DNP
  2. add 3 drops of unknown compound
  3. if no crystals form, add a few drops of sulphuric acid
  4. orange precipitate forms if positive
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5
Q

what is Tollen’s reagent used to detect?

A

presence of an aldehyde group

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6
Q

describe the procedure for making Tollen’s reagent

A
  1. add 3cm of AgNO3(aq)
  2. add NaOH(aq) until a brown precipitate is formed
  3. add dilute NH3 until a clear colourless solution is formed
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7
Q

describe the procedure for testing for aldehydes

A
  1. add 2cm to unknown solution to test tube
  2. add an equal volume of Tollen’s reagent
  3. leave in a warm water bath for 10-15 minutes
  4. if silver mirror forms, positive result
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8
Q

what happens to the aldehyde in Tollen’s reagent test

A

aldehyde is reduced to carboxylic acid as Ag+ is reduced to Ag

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9
Q

what symbol is used to show a oxidising agent?

A

[O]

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