2B Soaps, detergents & emulsions Flashcards
How are soaps formed?
Soaps formed from alkaline hydrolysis of fats/oils by sodium or potassium hydroxide under reflux conditions.
What is formed when an ester is hydrolysed?
1 mole of glycerol and 3 moles of fatty acids.
What sort of salts are soaps?
Sodium or potassium salts of fatty acids.
E.g. sodium stearate
C17H35COO- Na+
(Sodium or potassium carboxylate salts)
Which part of the soap is ionic?
Head.
Carboxylate group (-) and Na or K ion (+)
Which part of the soap is covalent?
Tail.
Hydrocarbon chain.
Which part of the soap molecule is soluble in water?
Ionic head.
Which part of the soap molecule is soluble in non-polar oily substances?
Hydrocarbon tail.
Define the term “hydrophobic”.
“Water hating”
Define the term “hydrophilic”
“water loving”
Which part of the soap molecule is hydrophobic?
Tail
Which part of the soap molecule is hydrophilic?
Head.
Explain with diagrams how soaps work.
Hydrophilic head dissolves in water. Hydrophobic tail dissolves in oily droplets.
Agitation of oil/water mixtures produces oil droplets surrounded by negatively charged “heads”.
These “heads” repel similar charges on other oil droplets and then cannot rejoin and so are dispersed.
(Page 6 of notes for diagram)
What is soap scum?
Calcium or magnesium carboxylate salts that are insoluble in water.
When is soap scum formed?
When soaps are used in hard water areas a white precipitate is formed. This is soap scum.
True of false?
“Detergents form soap scum”.
False.
Detergents do not form soap scum as they have a sulfonate group at the end of their chain (soaps have a carboxylate group).
Ca and Mg salts of sulfonates are soluble in water. No soap scum!
