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*Chemistry: Experiments > Q2. * Properties Of Ethanal > Flashcards

Q2. * Properties Of Ethanal Flashcards

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1
Q

What three chemicals will you study the reactions of with ethanal?

A

Acidified potassium manganate (VII) solution

Fehling’s reagent

Ammoniacal silver nitrate

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2
Q

What are these tests repeated with?

A

Propanone (acetone)

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3
Q

Why are these tests repeated with propanone (acetone)?

A

To show that ketones are not easily oxidised

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4
Q

What is the main use of Fehling’s solution?

A

It can be used to distinguish between aldehydes and ketones

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5
Q

List the steps to the reaction of ethanal with acidified potassium permanganate.
(3)

A

Add about one-tenth of very dilute potassium permanganate solution to a test-tube

Add about five drops of ethanal to the test-tube

Place the tube in a beaker of hot water for a few minutes

Note the colour change from purple to colourless

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6
Q

How much acidified dilute potassium permanganate is needed?

A

About one-tenth of a test tube

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7
Q

How much ethanal should be added to the potassium permanganate?

A

About five drops

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8
Q

What should be done after the ethanal is added to the test tube of potassium permanganate?

A

It should be placed in hot water for five minutes

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9
Q

What colour change takes place when ethanal is heated with potassium permanganate?

A

purple to colourless

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10
Q

Why does the potassium permanganate and ethanal solution change from purple to colourless?
(2)

A

This is because the ethanal has been oxidised to ethanoic acid

The Mn(VII) ions have been reduced to Mn2+ ions

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11
Q

What happens when the potassium permanganate reaction is carried out with propanone?

A

There is no colour change

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12
Q

Why is there no colour change when the potassium permanganate reaction is carried out with propanone?

A

This is because the ketones are not oxidised by potassium permanganate

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13
Q

Describe the steps to the Fehling’s reagent reaction with ethanal.
(4)

A

Make up some Fehling’s reagent by mixing about one-tenth of a test-tube of Fehling’s A with Fehling’s B (should be royal blue)

Add about five drops of ethanal to the test tube

Stand the test-tube in a beaker of hot water for a few minutes

Note the brick-red colour

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14
Q

How do you make up some Fehling’s reagent?

A

Mix about one-tenth of a test-tube of Fehling’s A with the same amount of Fehling’s B (should be royal blue)

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15
Q

What colour is Fehling’s reagent?

A

A royal blue colour

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16
Q

What colour change takes place when ethanal is heated with Fehling’s reagent?

A

Royal - blue to brick red

17
Q

Explain what has happened when the ethanal and Fehling’s reagent solution turns brick red.
(2)

A

Ethanal has been oxidised by Fehling’s reagent

The Cu2+ ions (blue) have been reduced to Cu+ ions (red) by the ethanal

18
Q

What is the silver mirror test also called?

A

Ammoniacal silver nitrate test

19
Q

Describe the steps to forming Tollens’ reagent.

3

A

Add one drop of dilute sodium hydroxide solution to 1 cm cubed of a silver nitrate solution

A brown precipitate of silver oxide is formed

Add dilute ammonia solution, drop by drop, until the brown precipitate dissolves

20
Q

How much dilute sodium hydroxide solution is needed to form Tollens’ reagent?

A

One drop

21
Q

What should the dilute sodium hydroxide be added to to form Tollens’ reagent?

A

1 cm cubed of a silver nitrate solution

22
Q

How much silver nitrate solution do you need to make Tollens’ reagent?

A

1 cm cubed

23
Q

What is formed when one drop of dilute sodium hydroxide solution is added to 1 cm cubed of a silver nitrate solution ?

A

A brown precipitate of silver oxide

24
Q

What should be added once the silver oxide is formed when making Tollens’ reagent?

A

Dilute ammonia solution

25
Q

Describe the steps to carrying out the silver mirror test.

5

A

Wash out a test-tube with detergent, then water then propanone to remove any droplets of water and allow to dry

Pour the Tollens’ reagent into the clean test-tube

Add about three drops of ethanal

Stand the test-tube in a beaker of boiling eater for a few minutes

A silver mirror is formed

26
Q

What needs to be done to the test tube before the Tollens’ reagent is added?
(4)

A

Washed with detergent

Washed with ordinary water

Washed with propanone to remove any droplets of water

Allow to dry

27
Q

How much ethanal is needed in the silver mirror test?

A

Three drops

28
Q

What is formed when ethanal is heated with Tollens’ reagent?

A

A silver mirror

29
Q

What happens when propanone is used in the Fehling’s reagent test?

A

No red precipitate is observed

30
Q

What happens when propanone is used in the silver mirror test?

A

No change is observed

31
Q

Why is no silver mirror formed with propanone?

A

This is because ketones are not oxidised by Tollens’ reagent as it is not a strong enough oxidising agent

*Chemistry: Experiments (15 decks)

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