Chapter 30Detergents

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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
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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.
30.1 INTRODUCING DETERGENTS
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Figure 30.1 Detergents for different
cleaning jobs.
30.1 INTRODUCING DETERGENTS
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WHAT IS A DETERGENT?
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)
30.1 INTRODUCING DETERGENTS
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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.
30.1 INTRODUCING DETERGENTS
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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)
30.2 STRUCTURE OF DETERGENTS
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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.
30.2 STRUCTURE OF DETERGENTS
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Structure of soapless detergent particles Two
common soapless detergents are ? Sodium
alkylbenzene sulphonate
30.2 STRUCTURE OF DETERGENTS
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? Sodium alkyl sulphate
30.2 STRUCTURE OF DETERGENTS
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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
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A30.1
30.2 STRUCTURE OF DETERGENTS
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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.
30.3 PROPERTIES OF DETERGENTS
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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.
30.3 PROPERTIES OF DETERGENTS
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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.
30.3 PROPERTIES OF DETERGENTS
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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.
30.3 PROPERTIES OF DETERGENTS
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Figure 30.8 Oil and water do not mix.
30.3 PROPERTIES OF DETERGENTS
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Figure 30.9 Shaking a mixture of water and oil
and allowing it to stand.
30.3 PROPERTIES OF DETERGENTS
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An oil/water emulsion is unstable.
30.3 PROPERTIES OF DETERGENTS
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Figure 30.10 Shaking a mixture of water and oil
(with a little detergent added) and allowing it
to stand.
30.3 PROPERTIES OF DETERGENTS
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An oil-water emulsion is stabilized by a
detergent.
30.3 PROPERTIES OF DETERGENTS
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An oil/water emulsion is stabilized by a
detergent.
30.3 PROPERTIES OF DETERGENTS
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To test properties of a detergent.
30.3 PROPERTIES OF DETERGENTS
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CLEANSING ACTION OF DETERGENTS
Figure 30.12 A detergent solution stabilizes an
oil/water emulsion.
30.3 PROPERTIES OF DETERGENTS
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30.3 PROPERTIES OF DETERGENTS
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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.
30.3 PROPERTIES OF DETERGENTS
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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-).
30.3 PROPERTIES OF DETERGENTS
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30.4 MAKING DETERGENTS MAKING SOAPLESS
DETERGENTS Soapless detergents are manufactured
from hydrocarbons obtained from petroleum.
30.4 MAKING DETERGENTS
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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.
30.4 MAKING DETERGENTS
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Fats and oils are naturally occurring triesters.
In general, the formula of fats and oils can be
represented as
30.4 MAKING DETERGENTS
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Figure 30.15 (a) General formula of fats and
oils. (b) Model of a fat/oil molecule.
30.4 MAKING DETERGENTS
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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
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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
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To prepare a soap.
30.4 MAKING DETERGENTS
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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.
30.4 MAKING DETERGENTS
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30.6 COMPARING SOAPS AND SOAPLESS DETERGENTS C
OMPARING 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.
30.6 COMPARING SOAPS AND SOAPLESS
DETERGENTS
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To compare action of soap and soapless detergent
in soft water and hard water.
30.6 COMPARING SOAPS AND SOAPLESS
DETERGENTS
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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.
30.6 COMPARING SOAPS AND SOAPLESS
DETERGENTS
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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.
30.6 COMPARING SOAPS AND SOAPLESS
DETERGENTS
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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)
30.6 COMPARING SOAPS AND SOAPLESS
DETERGENTS
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Figure 30.19 (a) Soap in soft water lather is
formed.
(b) Soap in hard water no lather is formed.
Note the scum formed.
30.6 COMPARING SOAPS AND SOAPLESS
DETERGENTS
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(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)
30.6 COMPARING SOAPS AND SOAPLESS
DETERGENTS
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Figure 30.20 Soap in strongly acidic
solution insoluble alkanoic acid is
precipitated out.
30.6 COMPARING SOAPS AND SOAPLESS
DETERGENTS
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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 (Na2CO3 10H2O).
30.6 COMPARING SOAPS AND SOAPLESS
DETERGENTS
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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.
30.6 COMPARING SOAPS AND SOAPLESS
DETERGENTS
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Figure 30.22 Specially designed soapless
detergents each suited for a particular purpose.
30.6 COMPARING SOAPS AND SOAPLESS
DETERGENTS
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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.
30.7 PROBLEMS ASSOCIATED WITH USE OF
DETERGENTS
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Figure 30.23 The structure of an early
soapless detergent.
30.7 PROBLEMS ASSOCIATED WITH USE OF
DETERGENTS
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Figure 30.24 This river had a persistent thick
foam caused by non-biodegradable detergents.
30.7 PROBLEMS ASSOCIATED WITH USE OF
DETERGENTS
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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.)
30.7 PROBLEMS ASSOCIATED WITH USE OF
DETERGENTS
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A30.7
Hydrocarbon chains in soaps are straight (i.e.
unbranched).
30.7 PROBLEMS ASSOCIATED WITH USE OF
DETERGENTS
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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.
30.7 PROBLEMS ASSOCIATED WITH USE OF
DETERGENTS
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Figure 30.26 Detergents may not be harmful to the
environment, but the additives may.
30.7 PROBLEMS ASSOCIATED WITH USE OF
DETERGENTS
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Figure 30.27 Rapid growth of algae due to
rich phosphates in water.
30.7 PROBLEMS ASSOCIATED WITH USE OF
DETERGENTS
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Figure 30.29 Fish killed by red tides.
30.7 PROBLEMS ASSOCIATED WITH USE OF
DETERGENTS
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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.
30.7 PROBLEMS ASSOCIATED WITH USE OF
DETERGENTS
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Figure 30.31 Detergents with too high or
too low a pH are harmful to the skin.
30.7 PROBLEMS ASSOCIATED WITH USE OF
DETERGENTS
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A30.8
30.7 PROBLEMS ASSOCIATED WITH USE OF
DETERGENTS
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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
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4. (a) General structure of a detergent anion
(b) General structure of a soapless detergent
anion
SUMMARY
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(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
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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
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? Many detergents contain phosphate additives.
The phosphates are nutrients for algae. This may
lead to red tides and death of water life.
SUMMARY