1. Detergents and Surfactants
National 6 Higher Chemistry

2. What is a Detergent? Detergents for different cleaning purposes.
A detergent is a substance which helps water clean better

3. Types of detergents There are two types of detergents:
1. Soapy detergents (or soaps — made from fats or oils like butter or palm oil).
2. Soapless detergents (or synthetic detergents — made from petroleum).

4. Soapless detergents include washing powder, washing-up liquids and shampoos. They are called ‘soapless’ because they contain no soap.

5. Structures of soaps and soapless detergents
Detergents are usually sodium (or potassium) salts of long-chain organic acids.
hydrogen atom
carbon atom
oxygen atom
sodium ion + -

6. (with the sodium ion detached)
A detergent anion:
(with the sodium ion detached)
hydrophobic tail (oil-soluble part)
hydrophilic head (water-soluble part) -

7. Properties of detergents
Wetting property of detergents
Water has a surface tension, the result
of H-Bonding between adjacent water molecules

8. A water skater. It can ‘walk’ on water, which has a high surface tension.

9. tap water
detergent solution
A detergent increases the wetting power of water. Tap water does not wet this piece of cloth easily, but a detergent does.

10. Emulsifying property of detergents
We all know that oil and water do not mix. An oil-water emulsion is unstable.
oil
water
tiny oil droplets
emulsion
oil
water
allow it to stand
shake

11. allow it to stand shake oil
emulsion
foam
tiny oil droplets
water + a little detergent
oil
tiny oil droplets
emulsion
foam
allow it to stand
shake
Shaking a mixture of water and oil (with a little detergent added) and allowing it to stand.

12. (a) Before the mixture is shaken. (b) After shaking.
detergent
anion
hydrophobic
hydrocarbon
tail in oil
hydrophilic
ionic head in
water
oil
oil droplet
(a) Before the mixture is shaken.
(b) After shaking.
How detergent anions arrange themselves in an oil-water mixture.

13. repulsion between oil droplets
(c) Negatively charged oil droplets repel each other.
How detergent anions arrange themselves in an oil-water mixture.

14. foam
oil/water emulsion
stabilized by
detergent
A detergent solution stabilizes an oil/water emulsion.

15. How detergent removes grease and dirt from a surface.
The hydrophobic tails of detergent anions dissolve in grease.
A detergent enables water to wet the object thoroughly.
detergent
anion
water
grease
dirt
particles
surface
(a)
(b)
How detergent removes grease and dirt from a surface.

16. How detergent removes grease and dirt from a surface.
Water molecules attract the hydrophilic heads of detergent anions, lifting up the grease from the surface.
By stirring, the grease forms tiny droplets, forming an emulsion.
tiny grease
particles
(negatively
charged)
(c)
(d)
How detergent removes grease and dirt from a surface.

17. Structure of soap particles
Soaps are sodium (or potassium) salts of long-chain carboxylic acids. The ionic head of soaps is always a carboxylate group (COO).
CH3(CH2)16  COO Na+
hydrocarbon tail
ionic head

18. hydrogen atom
carbon atom
oxygen atom
sodium atom
Soap is made by the alkaline hydrolysis (saponification) of animal fats and vegetable oils (e.g. beef fat, palm oil and coconut oil).

19. The palm oil from these palm trees can be used to make soap.

20. glyceryl tristearate (an animal fat)
sodium hydroxide
glycerol
sodium stearate (a soap)
Soapy detergents (or soaps) are made from _________ or _________ . They are sodium (or potassium) salts of long-chain __________ acids.
fats
oils
carboxylic

21. Cleaning abilities of soaps in hard water
containing considerable concentrations of calcium and/or magnesium ions
Soft water
contains no or only very small concentrations of dissolved calcium and/or magnesium ions

22. Experimental results show that soaps do not work properly in hard water.
This is because soap anions form insoluble substance (called scum) with calcium and/ or magnesium ions.

23. Ca2+(aq) + 2CH3(CH2)16COO(aq)  (CH3(CH2)16COO)2Ca(s)
calcium stearate
(scum)
stearate ion
Mg2+(aq) + 2CH3(CH2)16COO(aq) 
(CH3(CH2)16COO)2Mg(s)
stearate ion
magnesium stearate
(scum)

24. Soap cannot be used in strongly acidic solutions.
 CH3(CH2)16COO–(aq) + H+(aq) CH3(CH2)16COOH(s)
(from acid)
stearic acid
stearate ion

25. The above reactions make soaps useless.
Besides, the scum formed sticks to the materials being washed.
This problem can be solved by using soapless detergents. This is because the ionic head (SO3) of soapless detergent particles does not form precipitate with either calcium or magnesium ions.

26. Soapless detergent 1. Sodium alkylbenzenesulphonate oxygen atom
carbon atom
oxygen atom
hydrogen atom
sulphur atom
sodium ion

27. 2. Sodium alkylsulphate sodium ion oxygen atom carbon atom
hydrogen atom
sulphur atom

28. Soapless detergents are made from chemicals obtained from petroleum.
The ionic head of a common soapless detergent anion is usually a sulphonate group (SO3) or a sulphate group (OSO3).
Soapless detergents are made from chemicals obtained from petroleum.
conc. H2SO4
NaOH
from petroleum industry

29. Soapless detergents are derived from ____________
Soapless detergents are derived from ____________ . They are usually sodium salts of long-chain alkylbenzenesulphonate or ___________________.
petroleum
alkylsulphate
The ionic head (SO3) of soapless detergent particles does not form precipitate with either calcium or magnesium ions in hard water.

30. Effect of length of hydrocarbon tail on detergent properties
In general, detergent particles with hydrocarbon chains having 12 to 20 carbon atoms have good detergent properties.

31. Problems Associated with Non-Biodegradable Detergents
Detergents used in the early 1950s were non-biodegradable. This is because the early detergent particles contained branched hydrocarbon chains.
Micro-organisms can only digest straight hydrocarbon chain.

32. CH 3 2 SO Na
(non-biodegradable) SO 3 Na
side chains

33. This river had a persistent thick foam caused by non-biodegradable detergents.  

34. Soapless detergents nowadays are biodegradable
Soapless detergents nowadays are biodegradable. They contain straight (unbranched) hydrocarbon chains.
biodegradable
The structure of a biodegradable soapless detergent. (Note the straight hydrocarbon chain.)

35. Biodegradable detergents Use up dissolved oxygen in water
Problems Associated with Bio-Degradeable Detergents
Biodegradable detergents
Broken down by bacteria in water
Use up dissolved oxygen in water
Water life will die

36. Figure 37.26 Rapid growth of algae due to rich phosphates in water.

37. Fish killed by red tides.

38. Effect of Detergents on Skin
Most detergent solutions have pH values between 5 and 9. Detergents with pH values outside this range may cause skin allergy.

39. It is advisable to wear gloves whenever working with detergents.