Unit 4.4 - Aldehydes and Ketones (physicsandmathstutor) Flashcards

1
Q

what is the type of reaction alcohols undergo to form aldehydes and ketones

A

oxidation

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1
Q

what does oxidising a 1° alcohol produce

A

aldehyde

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2
Q

what does oxidising a 2° alcohol produce

A

ketone

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3
Q

what is needed for the oxidation of an alcohol to aldehyde

A

distillation

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4
Q

why is immediate distillation required for the oxidation of an alcohol –> aldehyde

A

otherwise will undergo further oxidation = carboxylic acid

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5
Q

what is the oxidising agent used in the oxidation of alcohols

A

acidified potassium dichromate

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6
Q

what is observed when an alcohol undergoes oxidation by acidified potassium dichromate

A

orange (dichromate) is reduced to green (chromium ion)

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7
Q

what is observed when acidified potassium dichromate is added to a tertiary alcohol

A

solution will remain orange
(tertiary alcohols cannot be oxidised)

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8
Q

what does the oxidation of propan-2-ol produce

A

propanone + water

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9
Q

what does the oxidation of ethanol produce

A

ethanal + water

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10
Q

what 2 reagents can be used to distinguish between aldehydes and ketones

A
  • tollens’ reagent
  • fehling’s reagent
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11
Q

how can tollen’s reagent be used to determine whether you have an aldehyde or a ketone

A

when warmed with aldehyde, it forms a silver mirror on test tube

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12
Q

how can fehling’s reagent be used to determine whether you have an aldehyde or a ketone

A

reagent = blue
reagent + aldehyde = brick red ppt
reagent + ketone = no reaction

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13
Q

what type of reaction do aldehydes and ketones undergo to form alcohols

A

reduction

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14
Q

what type of alcohol will an aldehyde be reduced to

A

1° alcohol

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15
Q

what type of alcohol will an ketone be reduced to

A

2° alcohol

16
Q

what is a common reducing agent used in the reduction of aldehydes and ketones to alcohols

A

NaBH₄ dissolved in water with methanol

17
Q

what does the reduction of butanone produce

A

butan-2-ol

18
Q

what is the mechanism for the reduction of propanal to propan-1-ol called

A

nucleophilic substitution

19
Q

what are the conditions required for the formation of an hydroxynitrile from an aldehyde/ketone

A

potassium/sodium cyanide + sulfuric acid = hydrogen cyanide

temp = 20°c

20
Q

why is hydrogen cyanide not added directly to an aldehyde/ketone for a nucleophilic addition reaction

A

hydrogen cyanide = very poisonous gas, hard to store

21
Q

what mechanism is used for the formation of 2-hydroxypropanenitrile from ethanal and hydrogen cyanide

A

nucleophilic addition

22
Q

why are hydroxynitriles important

A

can be hydrolysed to form hydroxy acids
useful in cosmetic industry

23
Q

what type of reaction occurs when aldehydes/ketones react with 2,4-dinitrophenylhydrazine

A

nucleophilic addition-elimination reaction
(condensation)

24
how can 2,4-dinitrophenylhydrazine be used to test for aldehydes + ketones
when reacted with aldehyde/ketone, orange-yellow precipitate is formed
25
how can 2,4-dinitrophenylhydrazine be used to identify specific aldehydes/ketones
1. add 2,4-DNP so that ppt forms 2. purify solid by recrystallisation compare M.P of pure crystals formed with M.P of 2,4-DNP of all common aldehydes/ketones
26
what reagents can be used for the triiodomethane (iodoform) test
iodine and sodium hydroxide solution or potassium iodide and sodium chlorate(I) solutions
27
describe the method and results of the iodoform test (using iodine and sodium hydroxide)
1. iodine added to small amount if ketone/aldehyde 2. sodium hydroxide added to remove iodine colour Pale yellow ppt will be formed if aldehyde/ketone is present
28
what is the iodoform test used to identify
aldehydes/ketones
29