Q2 - Organic Experiments

Question 1

Why is the first test tube of ethyne gas collected discarded?

Answer 1

It is less pure as it only contains displaced air

Question 2

What is observed when dilute bromine solution is added to ethyne

Answer 2

Colour change from red to colourless

Question 3

What is observed when dilute bromine solution is added to ethene

Answer 3

Colour change from red to colourless

→ unsaturated

Question 4

What is observed when dilute acidified potassium manganate (VII) solution is added to ethyne

Answer 4

Colour change from purple to colourless

Question 5

What is observed when dilute acidified potassium manganate (VII) solution is added to ethene

Answer 5

Colour change from purple to colourless
→ unsaturated

Question 6

How would you test to see if ethyne gas is flammable

Answer 6

Hold a lighted taper at arms length above the mouth of the gas jar in a fume cupboard.
Burns with a luminous smoky flame

Question 7

Describe the flame observed when ethyne gas is burned in air

Answer 7

Burns with a luminous smoky flame

Question 8

How to prevent suck-back when preparing ethene

Answer 8

Remove delivery tube

Question 9

How to prevent a fire when preparing ethene gas

Answer 9

Do not allow flame of Bunsen burner near the end of the delivery tube as the gas is flammable

Question 10

What type of organic reaction occurs when bromine water is added to ethene gas

Answer 10

Addition reaction

Question 11

Identify an organic product of the reaction between ethene and the bromine solution

Answer 11

2 - bromoethanol

Question 12

Draw ethene apparatus

Question 13

Draw ethyne apparatus

Question 14

Describe the appearance of phenylmethanol at room temperature

Answer 14

Colourless liquid

Question 15

Name a suitable piece of apparatus to measure accurately 1.5cm^3 of phenylmethanol

Answer 15

Graduated dropper

Question 16

When preparing soap, why was the reaction mixture refluxed?

Answer 16

To bring the reaction to completion

Question 17

When preparing soap, suggest a suitable method for refluxing the reaction mixture and then distilling of the ethanol
Justify the suitability of your heating method

Answer 17

Hot water bath, ethanol distills off at 78°C

Mixture boils gently

Question 18

When preparing soap, why is it desirable to remove all the ethanol?

Answer 18

Makes it easier to isolate soap

Question 19

What colour change is observed when ethanal is oxidised to ethanoic acid using acidified potassium permanganate

Answer 19

Purple to colourless

Question 20

What colour change is observed when ethanal is oxidised to ethanoic acid using Fehling’s reagent

Answer 20

Royal blue to brick red

Question 21

What colour change is observed when ethanal is oxidised to ethanoic acid using the silver mirror test

Answer 21

A silver mirror is formed inside the test tube

Question 22

What colour change is observed when ethanal is oxidised to ethanoic acid using ammoniacal silver nitrate

Answer 22

A silver mirror is formed inside the test tube

Question 23

What can be concluded from the reactions of ethanal with acidified potassium permanganate, Fehling’s reagent and ammoniacal silver nitrate

*when compared to ketones, e.g. propanone

Answer 23

Aldehydes can be oxidised to carboxylic acids but ketones cannot

Question 24

What type of reaction is involved in the preparation of soap?

Answer 24

Saponification

Substitution

Question 25

What is the function of brine when preparing soap?

Answer 25

Precipitate soap

Question 26

Why is the ethanol i) added and ii) removed when preparing soap?

Answer 26

i) acts as a solvent

ii) to increase yield of soap

Question 27

When preparing benzoic acid, state and explain the colour change in the flask during the initial heating

Answer 27

Purple to brown

Mn +7 to Mn +4

Question 28

When preparing benzoic acid, name the organic compound that gave rise to the smell of almonds during the heating phase

Answer 28

Benzaldehyde

Question 29

When preparing benzoic acid, why was the solution acidified with concentrated hydrochloric acid

Answer 29

• Convert sodium benzoate to benzoic acid
• Neutralise any alkali (base) remaining in solution
• Provide acidic medium to enable Mn +4 to be reduced to Mn +2

Question 30

When preparing benzoic acid, how do you test to ensure enough acid has been added?

Answer 30

Dip a rod in solution and touch it off moist blue litmus paper. The colour should go red

Question 31

When preparing benzoic acid, what was the purpose of adding the sodium sulphite solution ?

Answer 31

Reduces Mn +4 to Mn +2

Question 32

When preparing benzoic acid, why was the flask placed in ice before filtration

Answer 32

To ensure all benzoic acid crystallises out of solution

Question 33

Test for saturation example

Answer 33

Addition of bromine
If saturated - no colour change
If unsaturated - red to colourless

Question 34

Why is it preferable to use whole cloves instead of ground cloves?

Answer 34

Whole cloves contain more clove oil

Question 35

Describe the appearance of the product of steam distillation of clove oil and give the name of this type of mixture

Answer 35

Milky liquid

Emulsion

Question 36

How did you separate clove oil from cyclohexane

Answer 36

• lower aqueous layer collected in beaker
• drying agent (anhydrous MgSO4) added
• solvent allowed to evaporate by placing beaker in water bath

Question 37

Draw eugenol