Esters, triglycerides and fats

Question 1

What are two ways you can make esters?

Answer 1

• reacting a carboxylic acid with an alcohol in the presence of an acid catalyst
• gently heating an acid anhydride with an alcohol

Question 2

Describe the esterification of carboxylic acids with alcohols

Answer 2

concentrated sulfuric acid is used as the catalyst

OH from acid and the H from alcohol adds together to form H20

Question 3

Describe the esterification of acid anhydrides with alcohols

Answer 3

• gives a better yield

- anhydride + alcohol -> ester + carboxylic acid

Question 4

Describe the acid hydrolysis of esters

Answer 4

• ester is heated under reflux with either dilute sulphuric acid or dilute hydrochloric acid
• ester is broken down by water, acid acts as the catalyst

Question 5

Describe the alkaline hydrolysis of esters

Answer 5

• aq sodium/potassium hydroxide is refluxed with the ester
• non reversible
• forms sodium salt of the carboxylic acid (carboxylate salt)

Question 6

State the uses of esters

Answer 6

Perfumes, flavourings

Question 7

Define “triglyceride”

Answer 7

a triester of glycerol (propane-1,2,3-triol) and fatty acids

Question 8

Compare the structures of saturated fats, unsaturated fats and fatty acids.

Answer 8

fatty acids are long chain carboxylic acids
saturated fats have no double bonds
unsaturated fats have double bonds

Question 9

Explain the shorthand naming of fatty acids

Answer 9

Two numbers separated by a colon

• first number indicates number of carbons
• second number indicates number of double bonds
• number in brackets indicates position of double bond(s)

Question 10

Compare the structure of cis and trans unsaturated fats.

Answer 10

in cis form, molecules cannot pack closely to each other -> liquids at room temp
trans form, fats can pack closely together -> higher melting point than cis unsaturated fats

Question 11

Which fat is said to increase the risk of coronary heart disease

Answer 11

saturated fats and trans unsaturated fats are though to increase the risk of coronary heart disease beause they raise LDL levels and increase the risk of heart disease.

Question 12

Describe and explain the increased use of esters of fatty acids as biodisesal

Answer 12

-biodiesel is considered carbon neutral because it absorbs the same amount of carbon dioxide as it releases