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1 Chapter 30Detergents 30.1Introducing detergents 30.2Structure of detergents 30.3Properties of detergents 30.4Making detergents 30.5Washing powder 30.6Comparing.

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Presentation on theme: "1 Chapter 30Detergents 30.1Introducing detergents 30.2Structure of detergents 30.3Properties of detergents 30.4Making detergents 30.5Washing powder 30.6Comparing."— Presentation transcript:

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

2 2 30.1INTRODUCING 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 3 toothpaste shampoo soapbody lotionface cleaning lotion washing powderdish-washing liquidcar wash Figure 30.1 Detergents for different cleaning jobs INTRODUCING DETERGENTS

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

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

6 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)

7 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 8 Structure of soapless detergent particles Two common soapless detergents are: Sodium alkylbenzene sulphonate 30.2 STRUCTURE OF DETERGENTS

9 9 Sodium alkyl sulphate 30.2 STRUCTURE OF DETERGENTS

10 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: 30.2 STRUCTURE OF DETERGENTS

11 11 A STRUCTURE OF DETERGENTS

12 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.

13 13 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 14 tap water detergent solution 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 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 16 water oil Figure 30.8 Oil and water do not mix PROPERTIES OF DETERGENTS

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

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

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

20 20 An oil-water emulsion is stabilized by a detergent PROPERTIES OF DETERGENTS Figure 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

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

22 PROPERTIES OF DETERGENTS To test properties of a detergent.

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

24 PROPERTIES OF DETERGENTS

25 25 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 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 OSO 3, not COO ) PROPERTIES OF DETERGENTS

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

28 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 The palm oil from these palm trees can be used to make soap MAKING DETERGENTS

29 29 Fats and oils are naturally occurring triesters. In general, the formula of fats and oils can be represented as: 30.4 MAKING DETERGENTS

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

31 31 There are two basic processes in making soaps: Saponification 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 30.4 MAKING DETERGENTS

32 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) 30.4 MAKING DETERGENTS

33 MAKING DETERGENTS To prepare a soap.

34 34 A30.4 (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 COMPARING SOAPS AND SOAPLESS DETERGENTS 30.6COMPARING 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.

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

37 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 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 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, Ca 2+ (aq) + 2CH 3 (CH 2 ) 16 COO – (aq) (CH 3 (CH 2 ) 16 COO) 2 Ca(s) Mg 2+ (aq) + 2CH 3 (CH 2 ) 16 COO – (aq) (CH 3 (CH 2 ) 16 COO) 2 Mg(s) stearate ion (scum) 30.6 COMPARING SOAPS AND SOAPLESS DETERGENTS

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

41 41 (3)Soap cannot be used in strongly acidic solutions. Taking sodium stearate as example, CH 3 (CH 2 ) 16 COO – (aq) + H + (aq) CH 3 (CH 2 ) 16 COOH(s) stearate ion (from acid) stearic acid (with no detergent properties) 30.6 COMPARING SOAPS AND SOAPLESS DETERGENTS

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

43 43 A30.6 (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 (Na 2 CO 3 10H 2 O) COMPARING SOAPS AND SOAPLESS DETERGENTS

44 44 Ca 2+ (aq) + CO 3 2– (aq) CaCO 3 (s) Mg 2+ (aq) + CO 3 2– (aq) MgCO 3 (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 45 Figure Specially designed soapless detergents each suited for a particular purpose COMPARING SOAPS AND SOAPLESS DETERGENTS

46 PROBLEMS ASSOCIATED WITH USE OF DETERGENTS 30.7PROBLEMS 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.

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

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

49 49 Soapless detergents nowadays are biodegradable. They contain straight (unbranched) hydrocarbon chains. Figure The structure of a biodegradable soapless detergent. (Note the straight hydrocarbon chain.) 30.7 PROBLEMS ASSOCIATED WITH USE OF DETERGENTS

50 50 A30.7 Hydrocarbon chains in soaps are straight (i.e. unbranched) PROBLEMS ASSOCIATED WITH USE OF DETERGENTS

51 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 52 Figure Detergents may not be harmful to the environment, but the additives may PROBLEMS ASSOCIATED WITH USE OF DETERGENTS

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

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

55 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 56 Figure Detergents with too high or too low a pH are harmful to the skin PROBLEMS ASSOCIATED WITH USE OF DETERGENTS

57 57 A PROBLEMS ASSOCIATED WITH USE OF DETERGENTS

58 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 59 SUMMARY 4.(a)General structure of a detergent anion: (b)General structure of a soapless detergent anion:

60 60 SUMMARY (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

61 61 SUMMARY 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.

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


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