Soaps, Detergents and Emulsions

Question 1

process which turns fats into soaps

Answer 1

saponification

Question 2

what happens during saponification?

Answer 2

fats undergo an alkaline hydrolysis which breaks the ester linkage between glycerol and the three fatty acids. The carboxylic acid group then reacts with NaOH to produce the sodium salt of the fatty acid. This is soap. (3x soap ions)

Question 3

structure of a soap

Answer 3

soaps have an ionic carboxylic head which is negatively charged and water soluble. They have a covalent hydrocarbon tail which is soluble in non-polar substances like oil and grease.

Question 4

hydrophobic meaning

Answer 4

‘water-fearing’ will not dissolve in water

Question 5

hydrophilic meaning

Answer 5

‘water-loving’ will dissolve in water

Question 6

Lipophilic

Answer 6

loves fat dissolves in non-polar

Question 7

Lipophobic

Answer 7

hates fat does not dissolve in non-polar

Question 8

how to soaps work/lift stains etc?

Answer 8

• the hydrophobic, non-polar tails dissolve in the non-polar grease stain. The hydrophilic heads are in the polar water region.
• the negatively charged oxygen ions repel one another which causes the grease to form a droplet with O- ions now as far apart as possible.
• the micelles are suspended in water. This emulsion can be washed away and you are left with a clean surface.

ALWAYS DRAW DIAGRAMS FOR THIS QUESTION

Question 9

what is ‘hard water’?

Answer 9

water which contains magnesium and calcium ions

Question 10

what does soap form in places with ‘hard water’?

Answer 10

a precipitate known as scum

Question 11

structure of scum

Answer 11

/\/\/\/\/\/\/C=O-O- Ca2+ -O-C=O\/\/\/\/\/\/\

Question 12

what must be used instead of soaps in places with hard water

Answer 12

detergents

Question 13

structure of detergents

Answer 13

hydrophilic head and a hydrophobic tail

they have a different ionic head that will not react with calcium or magnesium ions to form a precipitate

Question 14

ionic head in detergents

Answer 14

sulfonate ion

does not form a precipitate with water (no scum)

Question 15

what is an emulsion?

Answer 15

an emulsion is a liquid which contains small droplets of another liquid

Question 16

everyday uses of emulsions

Answer 16

food such a ice-cream and mayonaise

Question 17

how are emulsifiers made?

Answer 17

similar structure to fats and oils however usually only one or two fatty acid chains are added to leave at least one OH group in tact.
made by reacting glycerol with edible oils (free fatty acids)

Question 18

examples of emulsifiers

Answer 18

• E471

- Lecithin

Question 19

how do emulsifiers work?

Answer 19

• hydrophilic polar heads exposed to water region

- hydrophobic tails dissolve in non-polar fat droplets

Question 20

during hydrolysis how many molecules of soap are made per molecule of glycerol?

Answer 20

3

3:1 ratio of fatty acid:glycerol