2.5 soaps detergents and emulsions

Question 1

how are soaps produced?

Answer 1

-the alkaline hydrolysis of edible fats and edible oils
produces:
-3 fatty acid molecules
-1 glycerol molecule
the fatty acid molecules are neutralised by the alkali, forming water soluble ionic salts (soap)

Question 2

What can soaps be used for?

Answer 2

to remove non-polar substances such as oil and grease.

Question 3

describe the structure of a soap ion

Answer 3

• non-polar hydrocarbon covalent hydrophobic oil and grease soluble tail
• negatively charged polar hydrophilic ionic water soluble head

Question 4

Describe the action of soap removing oil or grease from a surface

Answer 4

• the hydrophobic tails dissolve in the oil or grease
• the negatively-charged hydrophilic head remains in the surrounding water
• agitation causes ball like structures to form
• the negatively charged ball like structures repel each other and the oil or grease is kept suspended in the water

Question 5

What is hard water?

Answer 5

water containing high levels of dissolved metal ions

Question 6

What happens when soap is used in hard water?

Answer 6

• scum, an insoluble precipitate, is formed

- scum reduces the cleaning action of soap

Question 7

What is a soapless detergent and what do they do?

Answer 7

• substances with non-polar hydrophobic tails and ionic hydrophilic heads
• these remove oil and grease the same was as soap
• soapless detergents do not form scum with hard water

Question 8

What is an emulsifier?

Answer 8

a substance that can be used to prevent non-polar and polar liquids separating into layers

Question 9

What is an emulsion?

Answer 9

small droplets of one liquid dispersed in another liquid

Question 10

How can you make emulsifiers for use in food?

Answer 10

by reacting edible oils with glycerol

Question 11

describe the structure of an emulsifier

Answer 11

• only one or two fatty acid groups are linked to each glycerol backbone
• the hydroxyl groups are hydrophilic (polar)
• fatty acid chains are hydrophobic (non-polar)

Question 12

What does hydrophilic mean?

Answer 12

dissolves in water

Question 13

What does hydrophobic mean?

Answer 13

doesn’t dissolve in water

Question 14

What does the hydrophilic head of soap dissolve in?

Answer 14

water

Question 15

What does the hydrophobic tail of soap dissolve in?

Answer 15

oil or grease

Question 16

What is soap a salt of?

Answer 16

a carboxylic acid

Question 17

Why do the head and tail of a soap molecule dissolve in their respective substances?

Answer 17

• head is polar, water is polar, like dissolves like

- tail is non-polar, oil and grease is made from fats and oils which are non-polar, like dissolves like

Question 18

What is the difference between soap and detergent?

Answer 18

• detergents have a similar structure to soaps

- detergents will not form precipitates when used in hard water

Question 19

Give 2 examples of emulsions

Answer 19

• milk

- mayonnaise

Question 20

name 2 types of emulsifiers and why they are called this

Answer 20

-monoglyceride - contains one ester group
-diglyceride - contains two ester groups
emulsifiers will have at least one hydroxyl group

Question 21

Explain the use of the hydroxyl group in emulsifiers

Answer 21

-OH is the polar part of the molecule, which can attract water where the long hydrocarbon chains will attract non-polar molecules

Question 22

the alkaline hydrolysis of fats and oils produce what and what can they also be known as?

Answer 22

soaps

• salts of fatty acids
• carboxylate salts