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LC Chemistry Experiments > Reactions of Ethanal > Flashcards

Reactions of Ethanal Flashcards

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1
Q

what are the 3 reactions of ethanal

A

reaction with acidified potassium permanganate
tollens reagent
fehlings reagent

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2
Q

what is added to the test tube at the start of reaction with APP

A

dilute potassium permanganate
equal amount of sulphuric acid

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3
Q

why is sulphuric acid added to the test tube in the reaction with APP

A

acidifying is needed to ensure complete reduction of Mn +7 to Mn+2 without forming the Mn+4 intermediate

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4
Q

what does Mn+4 look like

A

brown ppt

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5
Q

what is added to the acidified potassium permanganate

A

5 drops of ethanal + put in water bath for 5 min

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6
Q

what is the control for the reaction with APP

A

propanone

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7
Q

why is propanone used as a control in the reaction with APP

A

it is a ketone so it does not oxidise so there is no colour change

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8
Q

what colour change is noted in the test tube in the reaction with APP

A

purple to colourless

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9
Q

why is there a colour change from purple to colourless in the reaction with APP

A

ethanal is oxidised to ethanoic acid by the acidified potassium permanganate oxidising agent

Mn+7 (purple) reduced to Mn + 2(colouress)

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10
Q

explain the colour change with reference to the ions in the reaction with APP

A

Mn+7 (purple) reduced to Mn + 2(colouress)

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11
Q

why does the propanone (control) stay colourless in the reaction with app

A

ketones are not easily oxidised by potassium permanganate

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12
Q

what is ethanal oxidised into in the reaction with APP

A

ethanoic acid

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13
Q

write the balanced equation for the reaction with APP

A

MnO4- + 8H+ + 5e- ——> Mn+2 + 4H20

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14
Q

why does tollens reagent (TR) have to be freshly prepared and never stored?

A

it forms explosive products

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15
Q

how do you make tollens reagent

A

add 1cm3 o silver nitrate to a test tube + add one drop of sodium hydroxide solution, brown ppt forms
add dilute ammonia solution drop by drop until brown ppt dissolves

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16
Q

what is the brown ppt that forms when making tollen reagent

A

silver oxide

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17
Q

how do we ensure we thoroughly clean the test tube in the reaction with tollens reagent

A

rinse with detergent, water, and propanone

18
Q

why do we rinse the test tube with propanone

A

so it dries faster

19
Q

what is the reaction with tollens reagent also known as

A

the silver mirror test

20
Q

how do we form the silver mirror

A

pour tollens reagent into clean test tube
add 3 drops of ethanal
place into hot water bath or 5 min
note silver mirror forms on inside of the test tube

21
Q

control for reaction with tollens reagent

A

propanone

22
Q

why is no change observed when experiment is repeated with propanone (TR)

A

ketones are not easily oxidised by tollens reagent

23
Q

is tollens reagent a strong or weak oxidising agent

A

weak

24
Q

what oxidising agent will oxidise ketones

A

strong oxidising agents such as nitric acid

25
Q

what is happening in side the test tube in the silver mirror test

A

ethanal is oxidised to ethanoic acid
ag+ is reduced to a silver ppt which coats the inside of the test tube

26
Q

write a balanced equation which shows what happens in the silver mirror test

A

Ag+ + e- —-> Ag(downward arrow)

ethanal—-> ethanoic acid

27
Q

what is fehlings reagent?

A

equal amounts of Fehlings A and B

28
Q

what colour is Fehlings reagent

A

royal blue

29
Q

what is Fehling’s A

A

solution of copper sulphate in water

30
Q

what colour is fehlings A

A

blue

31
Q

what is fehlings B

A

potassium sodium tartrate and sodium hydroxide in water

32
Q

what colour is fehlings B

A

colourless

33
Q

what is fehlings reagent used for

A

it is an oxidising agent used to differentiate between aldehydes and ketones

34
Q

how does fehlings reagent help us to distinguish between aldehydes and ketones

A

aldehydes are oxidised by Fehling’s reagent but ketones are not

35
Q

procedure for reaction with fehlings reagent

A

add 5 drops of ethanal into fehlings reagent and put in a hot water bath for a few min

36
Q

what colour ppt is formed from the reaction of ethanal with fehlings reagent

A

brick red ppt

37
Q

what is the colour change observed in the reaction with fehlings reagent

A

royal blue to brick red

38
Q

why is a brick red ppt formed when ethanal reacts with fehlings reagent

A

ethanal is oxidised to ethanoic acid
Cu+2 ions (blue) have been reduced to Cu+ ions (red)

39
Q

why is there no colour change when propanone reacts with fehlings reagent (control)

A

ketones are not oxidised by fehlings reagent

40
Q

writes the balanced equation of the reaction with fehlings reagent

A

Cu+2 + e- —–> Cu+

LC Chemistry Experiments (11 decks)

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