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Soaps

A soap is a water soluble substance made of sodium salts of fatty acids orpotassium salts of fatty acids. It is made by the reaction of an alkali(sodium or potassium) and fatty acids (RCOOH) in a hydrolysis process.

This process must be conducted in a alkaline medium. The functionalgroup that is involved in the production of the soap is ester RCOO - (R isthe alkyl group of the carbon chain) and the ionic forms of alkali which aresodium and potassium ions. The general formula for soap making isRCOO-Na+ (sodium salt fatty acids) or RCOO -K+ (potassium salt fattyacids).

The hydrolysis process of the salt production is called saponification. Inthe saponification process, fatty acids (esters) are hydrolysed by an alkali(Na or K). The equation for the reaction is:

The Preparation Of Soaps

Saponification, or the process of soap preparation, involves heating thefats or oils together with an alkali (concentrated sodium hydroxide orconcentrated potassium hydroxide solutions). The fats and oils are largeand long-chained natural ester molecules made of fatty acids and glycerol

joined together. The presence of the ester molecules gives the flavour andsmell of soap. These characteristics of the soap can be modified byexploiting the ester group chain of reactions.

The oils used in the production of soap are usually natural vegetable-based oils such as palm oil, olive oil and coconut oil. Fats, such as cowand goat fats, can also be used. The preparation of soap involves twostages as follows:


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Stage 1

The oils or fats are heated with water and a concentrated alkaline solutionto obtain fatty acids and glycerol through the hydrolysis process. Thepresence of the alkali is used as the catalyst of the reaction.

Hydrolysis Of Fat

Stage 2

The fatty acids produced in stage 1 react with the alkali to form sodiumsalt of fatty acids or soap. Apart from soap, water is also produced.


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Reaction of fatty acids with an alkaly to form soap

Taking stage 1 and stage 2 together, the overall chemical equation for thepreparation of soap is:

The overall equation for the preparation of soap is:

Formation of soap

The ester group has a long hydrocarbon chain. Different lengths of thechain give different properties of soaps. The type of soap formed willdepend on the number of carbons on the fatty acid chain.


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The Cleaning Action Of Soaps

Oil and grease found on cloth cannot be removed by water alone. This isbecause oil and grease form a covalent bond which is insoluble in water.Soap is needed to undertake the cleaning action.

The cleaning action is action involving the lowering of the surface tensionof water, emulsifying the oil and grease and holding them in suspension inwater. This ability is due to the structure of the soap itself when it isdissolved in water, the soap produces soap anions that have two parts.One part dissolves in water while the other part dissolves in oil andgrease.

To see how the cleaning action works, let us consider sodium palmitate(soap). We know now that the molecule of soap consists of salt (sodium)and fatty acids (hydrocarbon chain). So, when this soap is added to water,

it dissociates into salt ions (Na+) and soap ions (soap anions). Theequation is:

Detergent

Soap anions have a long hydrocarbon chain and can be divided into twoparts. The first part is the head which is the ionic part (negatively charged)forming the hydrophilic region which dissolves in water. The second part isthe tail (neutral) which is the hydrocarbon chain forming the hydrophobicregion which is insoluble in water but are soluble in oil and grease. Inother words, the soap anions RCOO- have two parts: the COO- which isthe head that dissolves in water and the R chain which is the tail part thatdissolves in oil and grease.


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The hydrophilic and hydrophobic parts of soap anions

The process of cleaning involves two steps, namely:

Lifting the oil or grease from the surface

Emulsifying the oil and grease in the water into droplets

Lifting the oil or grease from surfaces


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When soap is added to water, the water surface tension is reduced andthe entire surface is wet. The hydrophilic region of the soap ions dissolvesin the water while the hydrophobic region dissolves in oil or grease.

Emulsifying the oil and grease in water into droplets


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Emulsification of oil or grease into droplet

The attachment of the soap anions on the grease results in theemulsification of the grease into droplets. This is due to the negativelycharged hydrophilic part of the soap anions on the surface of the greasewhich repel each other, preventing bonding from taking place.

When the water is slightly agitated, the grease droplets are lifted off thesurface. The droplets do not coagulate because the force of repulsion


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between them prevents them from doing so. The droplets remainsuspended in water and can be removed by rinsing with excess water.

A detergent is a cleaning agent that can be used other than soap. It issynthesised from synthetic resources obtained from the petroleum

industry. As such, these detergents are also known as syntheticdetergents.

Detergents are sodium salts of sulphonic acid. The functional group ofdetergents is different compared to that of soaps. The ester functionalgroup of soaps is replaced by the sulphonic acid group. The two commondetergents are sodium alkyl sulphate and sodium alkylbenzenesulphonate. Their structures are as follows:

The General Structure Of Detergent

Here, R is the long alkyl carbon chain containing 12 to 18 carbon atomsper molecules. The properties of the detergents can be modified bychanging the alkyl carbon chain or the ionic head to meet specificrequirements.

The Preparation Of Detergents

We shall look at the preparation of two common detergents:

Sodium alkyl sulphate

Sodium alkylbenzene sulphonate


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Preparation of sodium alkyl sulphate

The preparation of sodium alkyl sulphate involves two steps.

Step 1: Sulphonation

In this process, the long chain hydrocarbons (alkenes) which are by-products of petroleum fractions are first hydrated to produce a long chainalcohol. The alcohol then reacts with concentrated sulphuric acid to formalkyl sulphonic acid and water.

Sulphonation

Step 2: Neutralisation

The alkyl sulphonc acid is then neutralised. This is done by adding sodium

hydroxide to the alkyl sulphonic acid. The reactions form sodium alkylsulphate (detergent) and water.

Neutralisation

Preparation of sodium alkylbenze sulphonate

The preparation of sodium alkylbenzene sulphonate involves three steps.


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Step1: Alkylation

The long alkene carbon chain obtained from the petroleum fractions isallowed to react with benzene to form alkylbenzene.

Alkylation

Step 2: Sulphonation

The alkylbenzene is then allowed to react with sulphuric acid to formalkylbenzene sulphonic acid.

Sulphonation

Step 3: Neutralisation

The alkylbenzene sulphonc acid is then neutralised. This is done byadding sodium hydroxide to the alkylbenzene sulphonic acid. The reactionresults in sodium alkylbenzebe sulphonate (detergent) and water.


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Neutralisation

The Cleaning Action Of Detergents

When detergent is mixed with water, the detergent dissociates to form

sodium ions and detergent anions. For example, the reaction of sodiumalkyl sulphate with water results in alkyl sulphate ions (detergent ions) andsodium ions.

Dissociation of detergent

Similarly with soaps, the detergent ions have hydrophobic and hydrophilicparts.


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The hydrophobic and hydrophilic part of detergent ions

The process of cleaning by a detergent is similar to that done by soap.The tail (hydrophobic neutral part) penetrates into the grease while thehead (hydrophilic negatively charged part) sticks out at the surface of thegrease. The repulsive forces between the heads turn the grease intodroplets which do not coagulate and remain suspended in water. They canbe removed by rinsing.

Effectiveness Of The Cleaning Action Of Soaps And

Detergents

The type of water determines the effectiveness of both soaps anddetergents as cleaning agents.There are two types of water influencingthe effectiveness. They are:

i. Hard water/soft water

ii. Acidic/ non-acidic water

Hard water/soft water

Hard water is water with a high concentration of calcium and magnesiumions. Conversely, soft water contains very small or no calcium andmagnesium ions. Calcium and magnesium ions react with soap to formscum (insoluble precipitate), thus reducing the effectiveness of the soap


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as a cleaning agent. As such, soap is an effective cleaning agent in softwater but not so in hard water.

On the other hand, detergents do not form scum in hard water. So,detergents are equally effective both in hard and soft water.

Acidic/non-acidic water

Acidic water is water that contains hydrogen ions such as rain water. Soapreacts with hydrogen ions to form insoluble carboxylic molecules. Thisreduces the amount of soap available for cleaning. As such, soap is onlyeffective in non-acidic water.

Additives In Detergents

Additives are added in detergents to enhance their cleaning properties

and to undertake specific purposes. The table below shows the additivesadded to detergents together with their functions.

Example Questions Resource
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We have seen in the previous section how chemicals are being used in cleaningprocesses to remove dirt and grease from cloth and fibres, thus improving thequality of our life tremendously. Chemicals are also being used in our food forfood preservation, improving the taste and texture as well as adding the nutrientsneeded by our body. In this section, we look at types of food additives, theirfunctions as well as the advantages and disadvantages of using them.

Learning Objectives Resource

WHAT ARE FOOD ADDITIVES?

Food additives are natural or synthetic ingredients which are added in theprocess of food preparation. The functions of the food additives are topreserve the food, slow down food spoilage, make food more attractive inappearance, improve the taste and increase the essential nutrients in thefood.

Usually, food additives are added to food in very small amounts. The useof food additives must conform to various acts such as the Food Act(1985). This is to ensure that additives used are safe for consumption.

Additives can be classified into six main types. They are:
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Preservatives

The functions of preservatives are to reduce, prevent or inhibit the growthof microorganisms, such as bacteria, yeast and fungi, in food thus slowingdown food spoilage and increasing the shelf life of the food. Preservativeswork by drawing out the water from food and providing an environmentunconducive for the growth of microorganisms.

Chemicals used as food preservatives

Many types of chemicals can be used as preservatives. Examples aresalt, vinegar, benzoic acid, sulphuric acid, and sodium benzoic, sodiumnitrate, sulphur dioxide, etc.

Examples of food using preservatives

Types of food that contain preservatives are salted fish, canned productssuch as jams, sardines, burgers, sausages, chilli sauces, fruit juices, etc.


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Antioxidants

Oils and fats can undergo an oxidation process when exposed to air. The

oxidation deteriorates the food and can give them a rancid odour and anunpleasant taste after a short period of time of exposure. Examples of theoxidation process on food include the browning of apples and potatoes assoon as they have been cut.

Antioxidants are chemicals that are added to food to inhibit or slow downthe oxidation process thus extending the quality of the food for a longerperiod of time.

Chemicals used as antioxidants

The chemicals used as antioxidants are ascorbic acids, citric acids andascorbic palmitate. Vitamins C and E are also antioxidant agents. Theyare safe antioxidants for human beings to consume as they help theimmune system and reduce the risk of heart diseases.

Examples of food using antioxidants

Examples of food using antioxidants are cakes, biscuits, margarine,vegetable oils, etc.

Flavourings


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The function of flavourings is to make food taste better or resemble naturalflavours such as the fruity flavours of durians, bananas, strawberries, etc.They are also used to restore the natural sweetness of food some ofwhich might have been lost or destroyed during the preparation process.

Chemicals used in chemical flavourings

The most popular chemical used for flavouring is MSG (monosodiumglutamate) added to food to enhance the taste. Esters such as pentylethonate, ethyl butanoate, aspartame and pentyl ethanoate also functionas flavourings.

Examples of food using flavourings

Esters are used to produce a taste which is the same as the original taste.For example, some resins have been used to produce the fruity flavours inice creams and flavoured canned drinks.

Stabilisers

Stabilisers are additives used in emulsions. Emulsions are mixturescontaining droplets of oil in water or droplets of water in oil. The function ofa stabiliser is to prevent the emulsion from separating and forming a layer


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of oil and water. This will thus ensure a smooth taste and a finer texture ofthe mixture.

Chemical used as stabilisers

Examples of stabilisers are gelatine, lecithin and acacia gum.

Examples of food using stabilisers

Stabilisers are used in food containing water and oils. Examples of foodusing stabilisers are mayonnaise, chocolate, butter, ice creams,homogenised milks, creamy soaps and salad creams.

Thickeners

Thickeners are food additives used so that the mixtures of food arethickened, preventing them from becoming watery. Thickeners allow foodto have fine, smooth, uniform, consistent textures with gel-likeappearances. This is achieved as the thickening agents absorb water fromthe food.

Chemicals used as thickeners

Chemicals used as thickeners are modified starch, pectin, acacia gum,

gelatine, xanthan gum, etc.

Examples of food using thickeners

Examples of food using thickeners are jams, jellies, wines, yogurt andpuddings.


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Colourings

Colourings are food additives which give colour to food so that the foodlooks more attractive, appealing and fresh looking. There are natural andartificial colourings. Natural colourings are derived from plants as mostplants have their own colour pigments such as chlorophyll and carotene.Artificial colourings are dyes consisting mostly of the azo and triphenylcompounds which can give various colours to food.

Chemicals used as colourings

Examples of chemicals used as colourings are azo compounds, triphenylcompounds (blue, purple and green) and tartrazine (yellow).

Examples of food using colourings

Beverages, jellies, confectionery and syrups use colourings.

Advantages And Disadvantages Of Usage Of FoodAdditives


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Example Questions Resource

We have seen in the previous two sections the use of chemicals in everyday life.They are the cleaning properties of soaps and detergents and are food additives.There is another important use of chemicals in everyday life which is as
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medicine. In this section, we shall focus first on traditional medicine andsubsequently look at modern medicine. We shall look at each facet of modernmedicine and its side effects including drug abuse.

Medicine is a natural or synthetic chemical which is used in medical treatment in

order to overcome illness. The functions of medicine are to cure diseases andrelieve pains by restoring the body functions disrupted by the diseases. Thereare two classes of medicine. They are traditional medicine and modern medicine.

Learning Objectives Resource

TRADITIONAL MEDICINE

Traditional medicine is medicine which is not chemically synthesised. Thedifferent types of traditional medicine are used in their original form. Theyare obtained naturally from animals, plants (herbs) and minerals.Knowledge of traditional medicine is inherited from generation to

generation and its effectiveness is not scientifically established but isbased on experiences and beliefs. Each community has its own traditionalmedicine which is different from that of other communities.

Side Effects In Using Traditional Medicine

Some types of traditional medicine are toxic or poisonous and are harmfulto human health. Extreme care must be taken so that only reliabletraditional medicine that is safe to human health is consumed. Someexamples of reliable traditional medicine are listed below:

Aloevera

This plant is also known as lidah buaya. The juice obtained from its leavesis used traditionally to treat skin diseases such as itches, wounds or burntskin.

Eurycoma longifolia (Tongkat Ali)
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The Tongkat Ali juice is obtained from the root of this plant and it is usedas an energy or tonic drink. It is also often used as an aphrodisiac. It canalso be used to relieve headaches, to cool down body temperatures andstomach aches and by women who have just given birth.

Ginger

The rhizome of ginger is used to treat stomach aches. By keeping thebody warm, it is also used to prevent colds during winter.

Garlic

Garlic is used traditionally to treat colds, asthma, influenza and to preventcancer. It can also be used to reduce high blood pressure. Garlic hasantibiotic properties

Ginseng


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The root of the ginseng is used to keep the body healthy and to enhancethe immunity against infectious diseases.

MODERN MEDICINE

Modern medicine is the medicine that is processed chemically. It is the

synthesised medicine that is used to treat specific diseases and has beenclinically tested and approved by relevant government agencies beforebeing administered to patients. Modern medicine may come in the form oftablets, liquids, powder and capsules. There are three main classes ofmodern medicine. They are:

Analgesics

Antibiotics

Psychotherapeutic medicine

Analgesics

An analgesic is a pain killer. It is used to reduce pains for a short timebefore further treatment is obtained. It does not cure diseases. There arethree types of analgesic medicine: aspirin, paracetamol and codeine.

Aspirin (acetyl salicylic acid)


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Aspirin is taken to reduce body pains such as muscle pains, joint pains,headaches and toothaches. It also used to reduce swellings on the bodyand the body temperature during fever. It has anticoagulant properties andis taken to prevent the clotting of the blood thus reducing diseases suchas heart attacks or strokes. Aspirin is also used to treat inflammation of

the joints (arthritis). Aspirin is not safe for consumption by children.

Paracetamol

It is commonly known as Panadol. Paracetamol is used to reduce thebody temperature during fever as well as acts as a pain killer. The sideeffect of this medicine is that it can damage the kidneys and liver. Unlikeaspirin, paracetamol cannot be used to treat arthritis and it can be takenby children. Excess consumption of paracetamol damages the liver,causing blood disorders and inflammation.

Codeine

Codeine is used in headache tablets and cough medicine used to relieveminor to moderate headaches as well as to suppress coughing. It is morepowerful than aspirin and paracetamol as it is synthesised from morphine(a narcotic drug). Taken excessively, codeine causes sleepiness,drowsiness and the abuse of this medicine may lead to addiction.

Antibiotics

Some diseases are bought about by microorganisms such as bacteria andfungi. The growth of the bacteria causing a disease can be reduced usingantibiotics which can generate the growth of other bacteria that can inhibitthat of the bacteria causing the disease or kill them. Antibiotics are used totreat gonorrhoea and tuberculosis but they cannot treat diseases causedby viral infections such as small pox or measles. There are two types ofantibiotics: penicillin and streptomycin.

Penicillin

Penicillin is the most widely used antibiotic. It is extracted from the fungus

ofPenicillin notatum sp. Penicillin is used to threat pneumonia, anthrax-related diseases, syphilis, gonorrhoea and tuberculosis (TB).

Streptomycin

This antibiotic is produced by bacteria of the genus Streptomyces. It isused to treat tuberculosis (TB), pneumonia and coughs.


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Antibiotics have to be used as indicated by the pharmacist. Excessive useof antibiotics can cause side effects such as rashes, fever and damage tothe organs.

Psychotherapeutic medicine

Psychotherapeutic drugs are used to treat people with mental illness andwho are normally unstable about their feelings, thinking and behaviour.The uptake of these drugs affects the nervous system of the patients andreduces the symptoms of mental illness, enabling them to think normally.However, such drugs are unable to treat the illness permanently but onlyallow the patients to live their lives normally with the continuous intake ofthe medicine.

There are three major types of psychotherapeutic medicine. They includestimulants, antidepressants and antipsychotic drugs.

Stimulants

The function of stimulants is to increase the reaction of the nervoussystem; they affect the activities of the body and brain. They stimulate theheart, causing it to beat faster and increase the blood pressure thusincreasing alertness. In this way, patients become tireless, can increasetheir physical abilities and feel confident about what they are doing.

In addition, stimulants reduce depression. Examples of stimulants areamphetamines and caffeine. The excessive use of stimulants leads to

addiction and causes over- anxiety, hallucinations and the development ofa psychological dependence on the drugs.

Antidepressants

Antidepressants are used to control the depressed feelings of patients.Depression is a chronic mental illness due to a chemical imbalance in thebrain. The symptoms of depression include the feelings of panic, worry,anxiety, sleeplessness and loss of interest in life. With antidepressants,patients become less worried, feel calm and more confident and sleepwell. The most common antidepressants are barbiturates and

tranquillisers.

Antipsychotic drugs

These drugs are used to treat patients who have severe psychoticillnesses such as schizophrenia. Patients with schizophrenia hallucinateand see things which are not real as well as hold wrong beliefs regarding


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certain things (delusions). They also have severe mood swings andchange quickly from a normal to a depressed mood. The intake of themedicine makes the patient calm, stabilise their moods and reduceshallucinations. Examples of antipsychotic drugs are chlorpromazine,haloperidol and clozapine.

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