Organic chem 4

Question 1

Draw the funtional group of aldehydes. (L.C)

Answer 1

In notes - check!

Question 2

Draw the functional group of carboxylic acids. (L.C)

Answer 2

In notes - check!

Question 3

What is an ester? (L.C)

Answer 3

A compound formed when the hydrogen of the functional group of a carboxylic acid is replaced by an alkyl radical of an alcohol.

Question 4

Give the two functions of using concentrated sulfuric acid in an esterification reaction. (L.C)

Answer 4

• As a catalyst

- As a dehydrating agent

Question 5

Name the following molecule, CH₃CHBrCHO. (L.C)

Answer 5

No idea tbh help!

Question 6

What is meant by a condensation reaction? (L.C)

Answer 6

Occurs when two different moleculescombine to form a more complex molecule with the production of a smaller molecule such as H₂0.

Question 7

A sample of ethanoic acid (CH₃COOH) was prepared by the oxidation of ethanol. Describe and explain the colour change observed in the reaction flask as the ethanol was oxidised. (L.C)

Answer 7

• Orange to green

- dicromate reduced to chromium

Question 8

Reflux is a widely used technique in organic chemistry. Identify an experiment from your course where you refluxed a mixture. Draw a fully labeled diagram of the reflux apparatus used in this experiment. (L.C)

Answer 8

- Preparation of soap
Draw : Flask with contents shown or labeled
- Anti-bumping granules
- condenser in correct position
- Labelled source of heat.

Question 9

Reflux is a widely used technique in organic chemistry. Identify an experiment from your course where you refluxed a mixture. What happened to the liquid in the flask during reflux? (L.C)

Answer 9

• Liquid evaporated / hot vapour rose

Question 10

Reflux is a widely used technique in organic chemistry. Identify an experiment from your course where you refluxed a mixture. How did refluxing this mixture help bring the reaction to completion? (L.C)

Answer 10

Allowed enough time to bring reaction to completion

Question 11

A sample of ethanoic acid (CH₃COOH) was prepared by the oxidation of ethanol. Describe your observations when a small quantity of solid sodium carbonate was added to a sample of the ethanoic acid produced. Write a balanced chemical equation for the reaction which occured. (L.C)

Answer 11

• Effervescence / gas given off

- Na₂CO₃ + 2CH₃COOH → 2CH₃COONa + H₂0 + CO₂

Question 12

Alcohol X ⇋ Aldehyde Y ⇋ Carboxylic acid Z

Name X,Y and Z (L.C)

Answer 12

X = Ethanol
Y = Ethanal
Z = Ethanoic acid

Question 13

Give a major use for ethanoic acid. (L.C)

Answer 13

As a flavouring agent

Question 14

Draw the structure of ethanal, showing the boding between the atoms. (L.C)

Answer 14

In notes check :)

Question 15

What ester is formed from ethanol and ethanal? (L.C)

Answer 15

Ethylethanoate

Question 16

Give two reasons why alcohols have a higher boiling point than corresponding alkanes. (L.C)

Answer 16

• Alcohols have higher relative molecular mass

- Intermolecular hydrogen bonds

Question 17

Explain why the difference in boiling points between methane and methanol is 226.5K while the difference in boiling points between butane and butanol is only 119K. (L.C)

Answer 17

Due to a longer carbon chain / hydrogen bonding is weaker in butanol.

Question 18

Describe in general terms, the solubilities of methane and methanol, butane and butanol in water. (L.C)

Answer 18

Methane - virtually insoluble
Methanol - compleatly soluble
Butane - virtually insoluble
Butanol - slightly soluble

Question 19

A group of students prepared ethanal by slowly adding an aqueous solution of ethanol and sodium dichromate to a hot aqueous solution of sulfuric acid. Why was the receiving vessel cooled in ice-water? (L.C)

Answer 19

• Volatile product / ethanal has low boiling points

Question 20

A group of students prepared ethanal by slowly adding an aqueous solution of ethanol and sodium dichromate to a hot aquous solution of sulfuric acid. State 2 features of the preparation that are necessary to maximise the yield of ethanal and for each feature, explain. (L.C)

Answer 20

1. Excess ethanol - so it doesn’t go to ethanoic acid

2. Dichromate in funnel - small amount of oxidising agent in flask

Question 21

A group of students prepared ethanal by slowly adding an aqueous solution of ethanol and sodium dichromate to a hot aquous solution of sulfuric acid. Describe how you would carry out Fehling’s test on a sample of ethanal. What observation would you expect to make in this test? (L.C)

Answer 21

Test - Mix equal amounts of Fehling’s 1 and Fehling’s 2 and add ethanal and warm
Observe - Brick-red → precipitate produced