Unit 4.4 - Aldehydes and Ketones (physicsandmathstutor)

Question 1

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

Answer 1

oxidation

Question 1

what does oxidising a 1° alcohol produce

Answer 1

aldehyde

Question 2

what does oxidising a 2° alcohol produce

Answer 2

ketone

Question 3

what is needed for the oxidation of an alcohol to aldehyde

Answer 3

distillation

Question 4

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

Answer 4

otherwise will undergo further oxidation = carboxylic acid

Question 5

what is the oxidising agent used in the oxidation of alcohols

Answer 5

acidified potassium dichromate

Question 6

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

Answer 6

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

Question 7

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

Answer 7

solution will remain orange
(tertiary alcohols cannot be oxidised)

Question 8

what does the oxidation of propan-2-ol produce

Answer 8

propanone + water

Question 9

what does the oxidation of ethanol produce

Answer 9

ethanal + water

Question 10

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

Answer 10

• tollens’ reagent
• fehling’s reagent

Question 11

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

Answer 11

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

Question 12

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

Answer 12

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

Question 13

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

Answer 13

reduction

Question 14

what type of alcohol will an aldehyde be reduced to

Answer 14

1° alcohol

Question 15

what type of alcohol will an ketone be reduced to

Answer 15

2° alcohol

Question 16

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

Answer 16

NaBH₄ dissolved in water with methanol

Question 17

what does the reduction of butanone produce

Answer 17

butan-2-ol

Question 18

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

Answer 18

nucleophilic substitution

Question 19

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

Answer 19

potassium/sodium cyanide + sulfuric acid = hydrogen cyanide

temp = 20°c

Question 20

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

Answer 20

hydrogen cyanide = very poisonous gas, hard to store

Question 21

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

Answer 21

nucleophilic addition

Question 22

why are hydroxynitriles important

Answer 22

can be hydrolysed to form hydroxy acids
useful in cosmetic industry

Question 23

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

Answer 23

nucleophilic addition-elimination reaction
(condensation)

Question 24

how can 2,4-dinitrophenylhydrazine be used to test for aldehydes + ketones

Answer 24

when reacted with aldehyde/ketone, orange-yellow precipitate is formed

Question 25

how can 2,4-dinitrophenylhydrazine be used to identify specific aldehydes/ketones

Answer 25

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

Question 26

what reagents can be used for the triiodomethane (iodoform) test

Answer 26

iodine and sodium hydroxide solution
or
potassium iodide and sodium chlorate(I) solutions

Question 27

describe the method and results of the iodoform test (using iodine and sodium hydroxide)

Answer 27

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

Question 28

what is the iodoform test used to identify

Answer 28

aldehydes/ketones