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Chapter 30 Detergents 30.1 Introducing detergents

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1 Chapter 30 Detergents 30.1 Introducing detergents
30.2 Structure of detergents 30.3 Properties of detergents 30.4 Making detergents 30.5 Washing powder 30.6 Comparing soaps and soapless detergents 30.7 Problems associated with use of detergents CONTENTS OF CHAPTER 30

2 30.1 INTRODUCING DETERGENTS
We use detergents every day, in one form or another. Like plastics and alkanols, most detergents are made from petroleum products. INTRODUCING DETERGENTS

3 toothpaste shampoo soap body lotion face cleaning lotion
washing powder dish-washing liquid car wash Figure Detergents for different cleaning jobs. INTRODUCING DETERGENTS

4 WHAT IS A DETERGENT? TYPES OF DETERGENTS
A DETERGENT is a substance which helps water to clean things better. TYPES OF DETERGENTS There are two types of detergents:  Soapless detergents (or synthetic detergents)  Soapy detergents (or soaps) INTRODUCING DETERGENTS

5 Soapy detergents include bath soaps, laundry soaps and liquid soaps.
Figure 30.2 Soapless detergents include washing powders, washing-up liquids, shampoos and hair conditioners. They are called ‘soapless’ because they contain no soap. Figure 30.3 Soapy detergents include bath soaps, laundry soaps and liquid soaps. INTRODUCING DETERGENTS

6 30.2 STRUCTURE OF DETERGENTS
GENERAL STRUCTURE OF DETERGENT PARTICLES Detergents are usually sodium (or potassium) salts of long-chain organic acids. The detergent anion consists of two parts: (1) An ionic group (the ‘head’) (2) A hydrocarbon chain (the ‘tail’) STRUCTURE OF DETERGENTS

7 Figure 30.4 General structure of a detergent anion.
Detergent anions therefore attract to both water and oil. This dual nature explains two important properties of detergents — the wetting property and the emulsifying property. STRUCTURE OF DETERGENTS

8 Structure of soapless detergent particles
Two common soapless detergents are:  Sodium alkylbenzene sulphonate STRUCTURE OF DETERGENTS

9  Sodium alkyl sulphate
STRUCTURE OF DETERGENTS

10 Structure of soap particles
Soaps are sodium (or potassium) salts of long-chain alkanoic acids. The ionic head of soaps is always a carboxylate group (–COO-). A common soap is sodium stearate: STRUCTURE OF DETERGENTS

11 A30.1 STRUCTURE OF DETERGENTS

12 30.3 PROPERTIES OF DETERGENTS
AS A WETTING AGENT Water has a high surface tension. Figure 30.6 A pond skater. It can ‘walk’ on water, which has a high surface tension. PROPERTIES OF DETERGENTS

13 A detergent reduces the surface tension of water
A detergent reduces the surface tension of water. As a result of this, water spreads over the surface and wets it more easily. A detergent thus acts as a wetting agent. PROPERTIES OF DETERGENTS

14 detergent solution tap water Figure 30.7
A detergent increases the wetting power of water. Tap water does not wet this piece of cloth easily, but a detergent solution does. PROPERTIES OF DETERGENTS

15 AS AN EMULSIFYING AGENT
Oil and water do not mix. An oil-water emulsion is unstable. On standing, the tiny oil droplets rapidly join together and grow larger to form a separate oily layer again. PROPERTIES OF DETERGENTS

16 oil water Figure 30.8 Oil and water do not mix.
PROPERTIES OF DETERGENTS

17 Shaking a mixture of water and oil and allowing it to stand.
Figure 30.9 Shaking a mixture of water and oil and allowing it to stand. PROPERTIES OF DETERGENTS

18 An oil/water emulsion is unstable.
PROPERTIES OF DETERGENTS

19 Figure 30.10 Shaking a mixture of water and oil (with a little detergent added) and allowing it to stand. PROPERTIES OF DETERGENTS

20 An oil-water emulsion is stabilized by a detergent.
Figure 30.11 How detergent anions arrange themselves in an oil-water mixture: (b) after shaking (c) negatively charged oil droplets repel each other. (a) before the mixture is shaken PROPERTIES OF DETERGENTS

21 An oil/water emulsion is stabilized by a detergent.
PROPERTIES OF DETERGENTS

22 To test properties of a detergent.
PROPERTIES OF DETERGENTS

23 CLEANSING ACTION OF DETERGENTS
foam oil/water emulsion stabilized by detergent Figure 30.12 A detergent solution stabilizes an oil/water emulsion. PROPERTIES OF DETERGENTS

24 30.3 PROPERTIES OF DETERGENTS

25 DETERGENTS are cleansing agents
DETERGENTS are cleansing agents. They are surfactants (surface active agents). They work by reducing the surface tension of water, enabling it to wet things more effectively, and by emulsifying grease. In general, ionic groups joined to hydrocarbon chains having 12 to 20 carbon atoms have good detergent properties. PROPERTIES OF DETERGENTS

26 A30.2 (a) C, F and G. Detergents are sodium or potassium salts of long-chain organic acids (usually with number of carbon atoms between 12 and 20). A is an ester. B is an alkanoic acid. D has too few carbon atoms, while E has too many, H is a magnesium salt of alkanoic acid, so they do not possess good detergent properties. (b) C and F. (G is a soapless detergent as its anionic group is — OSO3, not — COO-). PROPERTIES OF DETERGENTS

27 30.4 MAKING DETERGENTS MAKING SOAPLESS DETERGENTS
Soapless detergents are manufactured from hydrocarbons obtained from petroleum. MAKING DETERGENTS

28 MAKING SOAPS Soaps are made from animal fats (e.g. beef and mutton fat) or vegetable oils (e.g. palm oil and coconut oil). Figure 30.14 The palm oil from these palm trees can be used to make soap. MAKING DETERGENTS

29 Fats and oils are naturally occurring triesters
Fats and oils are naturally occurring triesters. In general, the formula of fats and oils can be represented as: MAKING DETERGENTS

30 (a) General formula of fats and oils. (b) Model of a fat/oil molecule.
Figure 30.15 (a) General formula of fats and oils. (b) Model of a fat/oil molecule. MAKING DETERGENTS

31 Saponification There are two basic processes in making soaps:
 Salting-out of soap Saponification Fat is hydrolysed (broken down by water) in alkaline solution to give a soap. The process is called saponification. fat / oil + sodium hydroxide  glycerol + soap MAKING DETERGENTS

32 A30.3 (a) No. Paraffin oil is a mixture of hydrocarbons, not esters. (b) No. Only alkalis can saponify fats and oils. Salting-out of soap After saponification is complete, much of the soap dissolves in the solution. To get the soap out , add a concentrated sodium chloride solution. This process is called salting-out of soap: conc. NaCl(aq) Soap(aq) soap(s) MAKING DETERGENTS

33 To prepare a soap. MAKING DETERGENTS

34 (1) Wear safety spectacles.
(2) Cover the beaker with a watch glass (to prevent solution from spurting out of the beaker). (3) Heat the beaker gently. MAKING DETERGENTS

35 30.6 COMPARING SOAPS AND SOAPLESS DETERGENTS
COMPARING CLEANING ABILITIES IN SOFT WATER AND HARD WATER Water may be soft or hard. Soft water contains no or only very small concentrations of dissolved calcium and/or magnesium ions. Hard water contains appreciable concentrations of calcium and/or magnesium ions. COMPARING SOAPS AND SOAPLESS DETERGENTS

36 To compare action of soap and soapless detergent in soft water and hard water.
COMPARING SOAPS AND SOAPLESS DETERGENTS

37 Experiment results show that soaps form a lather easily in soft water; they hardly form any lather in hard water. Instead, they give a sticky insoluble substance called scum. On the other hand, soapless detergents form a lather easily in both soft water and hard water. A30.5 (a) (i) Yes (ii) No. (b) (i) Yes (ii) Yes. COMPARING SOAPS AND SOAPLESS DETERGENTS

38 ADVANTAGES AND LIMITATIONS OF SOAPS Advantages
Soap has several advantages as a detergent: (1) It cleans very well in soft water. (2) It is non-toxic to water life. (3) It is biodegradable (i.e. can be broken down by bacteria). Therefore it will not cause foaming in sewage works and rivers. (4) It is only mildly alkaline (with pH between 8 and 9). Thus it seldom causes skin allergy. COMPARING SOAPS AND SOAPLESS DETERGENTS

39 Limitations Soap has the following limitations:
(1) Soap is only slightly soluble in water. Thus it is seldom used in washing machines. (2) It does not work well in hard water. Taking sodium stearate as an example of soap, Ca2+(aq) + 2CH3(CH2)16COO–(aq)  (CH3(CH2)16COO)2Ca(s) Mg2+(aq) + 2CH3(CH2)16COO–(aq)  (CH3(CH2)16COO)2Mg(s) stearate ion (scum) COMPARING SOAPS AND SOAPLESS DETERGENTS

40 (a) (b) Figure 30.19 (a) Soap in soft water — lather is formed.
(b) Soap in hard water — no lather is formed. Note the scum formed. COMPARING SOAPS AND SOAPLESS DETERGENTS

41 CH3(CH2)16COO–(aq) + H+(aq)  CH3(CH2)16COOH(s)
(3) Soap cannot be used in strongly acidic solutions. Taking sodium stearate as example, CH3(CH2)16COO–(aq) + H+(aq)  CH3(CH2)16COOH(s) stearate ion (from acid) stearic acid (with no detergent properties) COMPARING SOAPS AND SOAPLESS DETERGENTS

42 Figure 30.20 Soap in strongly acidic solution — insoluble alkanoic acid is precipitated out. COMPARING SOAPS AND SOAPLESS DETERGENTS

43 SOLVING THE SOAP PROBLEM
(a) Hard water. Sea water contains magnesium salts in addition to sodium chloride. (b) No. Sea water is hard water. The calcium and/or magnesium ions present would react with soaps to form scum. SOLVING THE SOAP PROBLEM (1) Remove the hardness and acidity of water. An effective water softener is washing soda, sodium carbonate-10-water (Na2CO3 •10H2O). COMPARING SOAPS AND SOAPLESS DETERGENTS

44 ADVANTAGES OF SOAPLESS DETERGENTS
Ca2+(aq) + CO32–(aq)  CaCO3(s) Mg2+(aq) + CO32–(aq)  MgCO3(s) Phosphates are also used as softeners. (2) Use soapless detergents instead of soaps. ADVANTAGES OF SOAPLESS DETERGENTS (1) Soapless detergents do not have the limitations of soaps. They do not form scum with hard water. (2) Soapless detergents are made from petroleum products, not from fats and oils. (3) Soapless detergents can be ‘tailor-made’ to suit a particular cleaning problem. COMPARING SOAPS AND SOAPLESS DETERGENTS

45 Figure 30.22 Specially designed soapless detergents each suited for a particular purpose. COMPARING SOAPS AND SOAPLESS DETERGENTS

46 30.7 PROBLEMS ASSOCIATED WITH USE OF DETERGENTS
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. PROBLEMS ASSOCIATED WITH USE OF DETERGENTS

47 Figure 30.23 The structure of an early soapless detergent.
PROBLEMS ASSOCIATED WITH USE OF DETERGENTS

48 Figure 30.24 This river had a persistent thick foam caused by non-biodegradable detergents. PROBLEMS ASSOCIATED WITH USE OF DETERGENTS

49 Soapless detergents nowadays are biodegradable
Soapless detergents nowadays are biodegradable. They contain straight (unbranched) hydrocarbon chains. Figure 30.25 The structure of a biodegradable soapless detergent (Note the straight hydrocarbon chain.) PROBLEMS ASSOCIATED WITH USE OF DETERGENTS

50 Hydrocarbon chains in soaps are straight (i.e. unbranched).
PROBLEMS ASSOCIATED WITH USE OF DETERGENTS

51 PROBLEMS ASSOCIATED WITH BIODEGRADABLE DETERGENTS
Even biodegradable detergents affect rivers and lakes. Firstly, because they are biodegradable, bacteria would use up dissolved oxygen in water. Secondly, commercial detergents usually contain phosphate additives. Phosphates are plant nutrients, causing rapid growth of algae in rivers and seas. This is believed to be one of the causes for ‘red tides’ in Hong Kong waters. PROBLEMS ASSOCIATED WITH USE OF DETERGENTS

52 Figure 30.26 Detergents may not be harmful to the environment, but the additives may. PROBLEMS ASSOCIATED WITH USE OF DETERGENTS

53 Figure 30.27 Rapid growth of algae due to rich phosphates in water.
PROBLEMS ASSOCIATED WITH USE OF DETERGENTS

54 Fish killed by red tides.
Figure 30.29 Fish killed by red tides. PROBLEMS ASSOCIATED WITH USE OF DETERGENTS

55 EEFECT 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. PROBLEMS ASSOCIATED WITH USE OF DETERGENTS

56 Figure 30.31 Detergents with too high or too low a pH are harmful to the skin.
PROBLEMS ASSOCIATED WITH USE OF DETERGENTS

57 A30.8 PROBLEMS ASSOCIATED WITH USE OF DETERGENTS

58 SUMMARY 1. A detergent is a substance which helps water to clean things better. A detergent has cleaning properties because it can act as a wetting agent and an emulsifying agent. 2. There are two types of detergents:  Soapless detergents — made from petroleum products  Soaps — made from animal fats or plant oils 3. Detergents are usually sodium (or potassium) salts of long-chain organic acids. SUMMARY

59 4. (a) General structure of a detergent anion:
(b) General structure of a soapless detergent anion: SUMMARY

60 (c) General structure of a soap anion:
5. Soaps can be made by reacting animal fats or plant oils with sodium hydroxide. Two processes are involved:  Saponification fat / oil + sodium hydroxide  glycerol + soap  Salting-out of soap SUMMARY

61 8. Problems associated with the use of detergents:
6. Soft water contains no or only very low concentrations of dissolved calcium and/or magnesium ions. Hard water contains appreciable concentrations of calcium and/or magnesium ions. 7. Soaps work well in soft water but not in hard water. Soapless detergents work well in both soft water and hard water. 8. Problems associated with the use of detergents:  Detergents may cause skin allergy.  Detergents go down the drain into the sewage system and eventually to rivers or seas. Bacteria in water use up oxygen during the decomposition of these detergents. This would kill water life. SUMMARY

62 . Many detergents contain phosphate additives
 Many detergents contain phosphate additives. The phosphates are nutrients for algae. This may lead to ‘red tides’ and death of water life. SUMMARY


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