Carboxylic acids and esters

Question 1

What are the conditions for the reduction of aldehydes and ketones using hydrogen? What is the product?

Answer 1

reagent: H2

Catalyst: Nickel (finely- divided)

Equation: CH3CHO + H2 → CH3CH2OH

Product: ethanol

Question 2

What type of bond can NaBH4 only reduce?

Answer 2

C=O

Question 3

Draw the equation for when carboxylic acids partly dissociate in water?

Answer 3

Question 4

What are the two ways carboxylic acids can be formed?

Answer 4

• Hydrolysis of nitrile
• oxidation of a primary alcohol

Question 5

Write the equations for the hydrolysis of propanenitrile to form a carboxylic acid. Name the conditions and the reagents

Hint : two different ways

Answer 5

Question 6

What’s the general equation for carboxylic acid + base? Write the word equation for ethanoic acid reaction with NaOH

Answer 6

Acid + base = salt + water

ethanoic acid + sodium hydroxide → Sodium Ethanoate + Water

Question 7

What’s the general equation for carboxylic acid + metal? Write the word equation for propanoic acid reaction with magnesium?

Answer 7

Acid + metal → salt + hydrogen

propanoic acid + Magnesium → Magnesium Propanoate + hydrogen

Question 8

What’s the general equation for carboxylic acid + metal carbonate/ hydrogen carbonate? Write the word equation for butanoic acid reaction with sodium carbonate?

Answer 8

Acid + metal carbonate → salt + Water + CO2

Butanoic acid + Sodium carbonate → sodium butanoate + water + carbon dioxide

Question 9

How are esters formed? (Name the two types of methods and what they entail)

Answer 9

Esterification (reversible reaction)

alcohol +carboxylic acid in the presence of a concentrated sulphuric acid catalyst.

Acylation (Nucleophilic addition elimination)

acid chloride + alcohol = esters

acid anhydride + carboxylic acid = esters

Question 10

Draw the esterification of ethanoic acid + ethanol

Answer 10

Question 11

Draw the hydrolysis of methyl propanoate

Answer 11

Question 12

What can the hydrolysis of esters be used to make?

Answer 12

soaps

Question 13

Why is soap not an ester?

Answer 13

Because it doesn’t have R groups on both sides of the C=O

Question 14

What is the IUPAC name for glycerol?

Answer 14

propane-1,2,3- triol

Question 15

What is the difference between acid hydrolysis of ester vs alkali hydrolysis?

Answer 15

Acidic hydrolysis of an ester gives a carboxylic acid and an alcohol.

Basic hydrolysis of an ester gives a carboxylate salt and an alcohol.

Acidic hydrolysis is revisible and uses an acidic catalyst

Badic hydrolysis is not reversible and normally uses NaOH or KOH

Question 16

Draw the alkaline hydrolysis for triesters

Answer 16

Question 17

What are the conditions of acid hydrolysis and alkali hydrolysis?

Answer 17

heated under reflux with a dilute acid like dilute hydrochloric acid or dilute sulphuric acid, or a dilute alkali like dilute sodium hydroxide solution.

Question 18

Draw the acid hydrolysis for ethyl propanoate

Answer 18

Question 19

What is transesterification?

Answer 19

It is a reversible reaction

When an alcohol molecule and an ester molecule react in either the presence of an acid or base to form a new ester and a new alcohol

Question 20

What is Biodiesel and how is it made?

Answer 20

it is a renewable, non-petroleum based fuel obtained mainly from vegetable oils by acid-catalysed or by base- catalysed transesterification

Made from methanol only: it is a methyl ester

Question 21

Draw the transesterification of triglycerides with methanol (general equation)

Answer 21

Question 22

What are the pros and cons of biodiesel compared with petrol/diesel?

Answer 22

Pros:

• non toxic
• burns more cleanly

cons:

• non-biodegradable
• some farmers may stop planting staple food crops = food shortage