topic 12 soaps and detergents

7/29/2019 TOPIC 12 Soaps and Detergents

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Topic 12: Manufactured Materials - Soaps and Detergents

Learning Outcomes:

1. Describe the preparation of soaps and detergents by saponification.

2. State the properties of soaps and detergernts.3. Explain the cleansing effect of soaps and detergent.

4. Prepare soap using the process of saponification (Practical Activity)

Introduction

Soaps are sodium or potassium salts of higher fatty acids like stearic, palmitic and oleicacids. Fatty acids are organic acids that have more than sixteen carbon atoms in their molecularstructure. The sodium soaps are called hard soaps and the potassium soaps are known as softsoaps. Soaps are obtained from oils and fats. For e.g., tristearin is got from beef and mutton

tallow, tripalmitin from palm oil and triolein from lard (pig fat), olive oil and cotton seed oil. InIndia, soap is commonly got from coconut, groundnut, til and mahua oils.

Saponification of Triglycerides

One of the organic chemical reactions known to ancient man was the preparation of soapsthrough a reaction calledsaponification. Saponificationis a process by which triglycerides arereacted with sodium or potassium hydroxide to produce glycerol and a fatty acid salt, called'soap'.

Natural soaps are sodium or potassium salts of fatty acids, originally made by boiling lard orother animal fat together with lye or potash (potassium hydroxide). Hydrolysis of the fats andoils occurs, yielding glycerol and crude soap.

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Lipids that contain fatty acid ester linkages can undergo hydrolysis. This reaction is catalyzed bya strong acid or base. Saponification is the alkaline hydrolysis of the fatty acid esters.

In the industrial manufacture of soap, tallow (fat from animals such as cattle and sheep) orvegetable fat is heated with sodium hydroxide. Once the saponification reaction is complete,sodium chloride is added to precipitate the soap. The water layer is drawn off the top of themixture and the glycerol is recovered using vacuum distillation.

Manufacture of Soap Saponification

Saponification is the process where oil or fat (tristearin) is treated with sodium hydroxidesolution called lye, to form soap and glycerine.

Soap can be manufactured by:

a) The hot processb) The cold processc) The modern process

The Hot Process

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Manufacture of soap by the hot process involves the following steps:

Saponification

Oil or fat is taken in a huge iron-pan called soap kettle and heated with open steam. 10%

sodium hydroxide solution (lye) is added in a thin stream. The steam keeps the mass boilingand ensures thorough mixing as well. Saponification is complete after several hours to give afrothy mixture of sodium salts and glycerine.

Salting out of Soap

Saponfication is complete when we see a slight excess of the alkali in the transparent reactionmixture. Common salt or brine is then added to precipitate soap and heating is continued. Soapforms in the upper layer as a thick mass. This is known as salting out of soap.The unused alkali solution in the lower layer is called spent lye or sweet lye. This along with

glycerol and salts is drawn from below the reaction vessel. Glycerol can be recovered from this .

Finishing

The soap obtained after salting out is boiled again with sodium hydroxide for completesaponificaiton. This converts all the unsaponified fat. The spent lye is then drawn off. The solidsoap is then boiled with water to dissolve excess of alkali. It is then allowed to settle when theimpure soap called nigre forms the lower layer. The pure soap in the upper layer is transferredthrough a swing pipe to a steam-jacketed tank called crutcher.It is then shredded into small chips, dried to the requisite amount of moisture content and mixedwith colouring substances and perfumes. Some fillers like rosin, sodium silicate, borax andsodium carbonate are added to laundry soaps. They have detergent value and are less

expensive than soap.In the next step, the soap is allowed to run into moulds and permitted to solidify. The biggerblocks are then cut with steel wires into smaller slabs, which are then cut into smaller cakes andstamped.

The Cold Process

Oil or molten fat is taken in an iron pan fitted with a stirrer. It is then treated with lye (any strongalkaline solution, like potassium hydroxide used for washing or cleansing). Stirring is continuedtill the soap begins to set. After solidification in frames, it is cut into slabs and further into cakes.

All the glycerine remains in the soap. Starch or other fillers are thoroughly mixed with the oilbefore lye is added. This process is not so economical as the hot process and the soapobtained is also not pure.

Proportions of Ingredients

Alkali 1 part ; Water 7 parts; Starch 1 part

Preparation of Soaps

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Soap can be made by boiling the beef tallow (means a triglyceride) combined with lye animpure sodium hydroxide. The top layer can be solidified and cooled; the yellow soap (meanssodium stearate) can be made by cutting the above into cubes. It may be very hard on handsand clothes. But it should be good cleaning action with soft water.

Preparation of Soap:The molecular mass of fats and oils (esters) with high amount are said to betriglycerides can be saponified (means hydrolyzed) in basic solution, it will give soap andglycerol.

A mixture of carboxylate anions and univalent cation of salt contained in soap. Eachtriglyceride molecules can be a variety of fatty acids residues formed by mixture of anions. Amixture of molecules can be named as fat or oil.

Sodium soaps can be very hard to soluble in water as compared to potassium soaps.The liquid soap and shaving cream can be made from the potassium soaps. From the highlysaturated, solid fats, such as lard or, tallow are very hard in the soap. Unsaturated oil such asolive oil gives soft soap by the saponification process.

Soap Preparation Using Fat

Soap Solution with Hydrochloric Acid:

It produces a mixture of fatty acids. A long chain of carboxylic acids (C10 to C8) can besaturated or unsaturated called fatty acids.

Procedure for the Preparation of Soap:

A solid fat with mass of 1.5 g (means lard, tallow, or shortening) taken in a large testtube. The fat will automatically melt and fall down in a test tube when it is heated for the

preparation of soap. In 95% percentage of ethyl alcohol, 10mL of a 10% solution of KOH can beadded.

Heating Process for the Preparation of Soap

1. A 250 mL beaker can be filled with half of the water and it can be boiled. Then place thetest tube inside the boiling beaker. Alcohol can be evaporated with ethyl alcohol, it can bereplaced and it should be flammable.

2. Heating the test tube in a beaker for 15 minutes can be done.

3. After that, saponification can be done by adding a few drops of the reaction mixture towater. There is a droplets of fat can be presented in it. If there are no drops of fat present,

then the saponification is not completed.4. Then saponification can be over, the contents presented in a test tube can be pouredinto 100 mL beaker.

5. Evaporate the alcohol up to the residue becomes tacky and viscous. Dont do over heat,otherwise the soap will become darken.

6. Then it can be heated by adding 30 mL of distilled water with the mixture. Stir it well untilthe solution is obtained.

7. The product is a solution of potassium soap.

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(Please refer to Practical 6)

Special Varieties of Soap

Floating SoapsMade by beating large quantities of air into soap in a crutcher when the soap is in a creamystate

Transparent SoapsContains glycerol or alcohol. Obtained by dissolving soap in alcohol and evaporating thesolvent alcohol.

Medicated SoapsMedicinal substances added. Examples are neem soap and carbolic soap.

Shaving SoapsPotassium sodium stearates (produces lasting lather) containing gum and glycerine to

prevent lather drying.

Difference between Toilet Soap and Laundry Soap

Cleansing Action of Soap

Unimolecular film of soap molecules on water surface

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A soap has two dissimilar ends. At one end is the hydrocarbon chain that is non-polarand hydrophobic (oil soluble). At the other end there is the carboxylate ion that is polarand hydrophilic (water soluble).

When soap is added to water, its molecules make a unimolecular film on the surface ofwater with their carboxyl groups dissolved in water and the hydrocarbon chains standingon end to form a hydrocarbon layer as shown in the figure below.

Figure 1

Cleansing action of a soap

Each soap molecule has a long hydrocarbon chain, sometimes called its 'tail', with acarboxylate 'head'. In water, the sodium or potassium ions float free, leaving a negatively-charged head.

When a soiled cloth is soaked in soap solution, soap dissolves dirt (fat or oil with dustabsorbed in it) by micelle formation. Micelles are an aggregate of molecules in a colloidalsolution.

The oil or fat is at the centre of the sphere with fat-soluble hydrocarbon chains of soapdissolved in it. The water soluble carboxylate ions make a hydrophilic surface around thissphere and render the miscelles of oil or fat water-soluble. Thus the micelles are dissolved

in water and are washed away (Figure 1).

Soap tends to concentrate on the solution surface and therefore lowers its surface tension,causing foaming. This helps it to penetrate the fabric. It emulsifies fat in dirt to form micellesand renders all the micelles water-soluble. Thus the water washes the dirt away.

Soap is an excellent cleanser because of its ability to act as an emulsifying agent. Anemulsifier is capable of dispersing one liquid into another immiscible liquid. This means that

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while oil (which attracts dirt) doesn't naturally mix with water, soap can suspend oil/dirt insuch a way that it can be removed.

Figure2

A soap micelle has ahydrophilic head that isin contact with thewater and a center ofhydrophobic tails,which can be used toisolate grime.

Mariana Ruiz Villarreal

The organic part of a natural soap is a negatively-charged, polar molecule. Its hydrophilic*(water-loving) carboxylate group (-CO2) interacts with water molecules via ion-dipoleinteractions and hydrogen bonding.

The hydrophobic** (water-fearing) part of a soap molecule, its long, nonpolar hydrocarbonchain, does not interact with water molecules. The hydrocarbon chains are attracted toeach other by dispersion forces and cluster together, forming structures called micelles(Figure 2). In these micelles, the carboxylate groups form a negatively-charged sphericalsurface, with the hydrocarbon chains inside the sphere.

Because they are negatively charged, soap micelles repel each other and remain dispersedin water.

Introduction to action of soap:

We are using water for the washing purpose, it dissolves dirt. But some dirt may notdissolve in water. Soap can be used for removing dirt. Soap contains sodium or potassium fattyacids of long chain that can be used for cleansing purpose of action in water. Organiccompounds are otherwise called as fatty acids. The organic compounds can contain carboxylgroup (COOH).

Chemically, a soap is a sodium salt of a long chain carboxylic acid (fatty acid) which has

cleaning properties in water. A soap has a large non-ionic hydrocarbon group and an ionicgroup, COO-Na+. E.g. Sodium stearate (C17H35COO-Na+), Sodium oleate (C17H33COO-Na+),Sodium palmitate (C15H31COO

-Na+) etc.

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Examples of Soap:

Examples of Soaps are sodium oilate, sodium stearate, sodium palmitate.

Cleansing Action of Soap

A soap molecule can be classified into two dissimilar parts: Figure 3

Figure 3

1. Hydrophilic action of soap:

The polar end consists of short ionic part comprising the carboxylate salt, - COO Na+.

It should be soluble in water (that is water attracting or hydrophilic) and the remainingattached to water.

2. Hydrophobic action of soap:

In non-polar end, there is along hydrocarbon chain. The end is said to be hydrophobicand it is water repelling and it should be soluble in oil and grease.

Action of Mono Layer of Soap on Water

A colloidal suspension can be formed by dissolving soap in water. The soap molecules canbe clustered together to form a micelles and it should be remains radially and suspended inwater with ionic end directed outwards and hydrocarbon end towards the centre.

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Figure 4

The ionic salt end of the molecule is attracted towards water and can be dissolvedtogether. The hydrocarbon end of the molecule in a non-polar end can be repelled by water. Atwo or more drop of soap in a water formed as a monolayer on the water surface. The soap canbe polar carboxyl salt attracted towards the ends of the polar water.

Soap - Familiar Cleansing Action

Action takes place when dirty gent cloth is dipped in soap solution :

Figure 5

The oily or greasy layer when the dirt particles presented in the skin or clothes. In asoap solution, dirty cloth can be dipped; the non-polar end of the hydrocarbon micelles attachedto the grease or oil to be presented in the dirt and the polar end can be remained in water layer.Rubbing the cloth dislodges the oily layer form the surface, it can forms small globules.

Therefore, the stable emulsion of oil in water is formed. The action of emulsified greaseor oil globules bearing the dirt and it can be readily washed with water.

Synthetic Detergents

Synthetic detergents possess the desirable properties of ordinary soaps and can beused with hard water and in acidic solutions as well. Synthetic detergents are sodium salts oflong chain benzene sulphonic acids or sodium salt of long chain alkyl hydrogen sulphates. Theircalcium or magnesium salts are soluble in water.

The hydrophobic part is the hydrocarbon chain and the water soluble part can be:

An anionic group like sulphate or sulphonate

A cationic group like amine salt or quaternary ammonium compound

A non-ionic group like alcohol or ether

Some examples of detergents are as follows:

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Alkyl Sulphates (Anionic)

CH3(CH2)10CH2OSO3-Na+ - sodium lauryl sulphate

CH3(CH2)16CH2OSO3-Na+ - sodium stearyl sulphate

Alkyl benzene sulphonates (Anionic)

Properties Some of the synthetic detergents with a branched hydrocarbon chain have very lowbiodegradability.

They are resistant to bacterial attack and are not fully degraded in sewage treatmentunits. Therefore, they cause water pollution when they are discharged into a river or anyother water body.

Phosphate salts present in synthetic detergents cause rapid growth of algae that depletethe oxygen content in the water. (A condition known as eutrophication). Due to this aquaticanimals die resulting in the imbalance of the ecosystem as well.

These detergents lower the surface tension of water and act as cleansing agents(wetting agents).

They can be used for delicate fabrics because they do not hydrolyze to give hydroxylions.

They have equal action in both hard and soft water.

Composition of a Common Detergent

Sodium alkylbenzene sulphonate 18%

Dedusting agent 3%

Foam booster 3%

Sodium tripolyphosphate, builder 50%

Anti-corrosion agent 6%

Optical brightener 0.3%

Water and inorganic filler 19.7%

Tripolyphosphate can produce hydroxyl ions by reacting with water. It keeps the wash waterslightly alkaline, to emulsify grease particles. They can also tie up calcium and magnesium ionsthat cause hardness of water.

Introduction to cleansing action of detergents :

Chemically, a synthetic detergentis the sodium salt of a long chain benzene sulphonic acid orthe sodium salt of a long chain alkyl hydrogen sulphate which has cleaning properties in water.It has a large non-ionic hydrocarbon group and anionic group like sulphonate group, SO3

-,Na+ or sulphate group SO4

-, Na+. E.g: Sodium n-dodecyle benzene sulphonate, Sodium n-dodecyle sulphate etc.

Cleansing Action of Detergents : Types of Detergents

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There are 3 types of detergents:

1. Anionic detergents: These detergent molecules have a negative ionic group. Alkysulphates and alkyl benzene sulphonates are considered to be the anionic type ofdetergents.

2. Cationic detergents: These detergent molecules have a positive ionic charge on them.It is generally found in a shampoo or clothes "rinse". The purpose of these detergents isto neutralize the static electrical charges from residual anionic detergent molecules.

3. Non-ionic detergents: These detergents are used in dish washing liquids. Since thesedetergents do not have any ionic groups, they do not react with hard water ions. Inaddition, nonionic detergents produce less foam than ionic detergents.

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Cleansing Action of Detergents : Cleansing Action (Figure 1)

Since a detergent is a made up of two parts: a long hydrocarbon part and a short ionicpart containing COONa+ group.

The long hydrocarbon chain is hydrophobic, so the hydrocarbon part of detergentmolecule is insoluble in water but soluble in oil and grease.

The ionic part of detergent molecule is hydrophilic so it is soluble in water but insolublein oil and grease.

When the detergent added to dirty clothes, which contains grease and oily substances,the greasy and oily dirt particles attach themselves to the hydrocarbon part and ionic partremains attached to the water.

When the dirty clothes are agitated in a detergent solution, the dirt particles attached to

the hydrocarbon part molecule get washed away in water and the clothes get cleaned.

Cleansing Action of Detergents : Detergents in Hard Water

Synthetic detergents can lather well even in hard water because they do not forminsoluble calcium or magnesium salts on reacting with the calcium and magnesium ionspresent in the hard water.

Whereas when we talk about soaps, they are not suitable in hard water as they forminsoluble calcium or magnesium salts (scum) on reacting with the calcium and magnesiumions present in the hard water.

Advantages of detergents over soaps:

Detergents and soaps are used as the cleansing agents instead they differ in someproperties. Detergents perform well in removing stains comparing soaps. Detergents are madeof synthetic chemicals where soaps are made of natural oils and fatty acids. We can see theadvantages of detergents over soap in the rest of the following.

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Soap:

Soaps are the salts of sodium that composed of long chain of higher fatty acids. Soapsare Eco- friendly they are bio-degradable. They do not form foams in hard water and left scumafter washing. They have weak cleansing property than detergents.

Detergents:

Synthetic detergents are the salts of sodium which is composed of long chain ofbenzene sulphonic acids. Detergents are non bio-degradable. They form foams in hard waterand thus forms no scum after washing. They have strong cleansing property than soaps. Theyare effective in hard and salt water.

Advantages of Detergents over Soaps:

The following are the advantages of detergents over soaps,

Detergents can produce better performance in hard water while the soaps cannotsuitable for use in hard water.

Detergents are made of synthetic petrochemicals while the soap is made of vegetableoils and fatty acids, so that consumption of natural resources is high in soaps whereas indetergents only chemicals is needed, so no consumption of natural resources highly.

Production of soap is costlier than the detergents production and detergents have moreadvantages over soap.

A detergent doesnt produce any scum or residue during washing of clothes and so it isbetter to wash clothes with detergents earlier. But soap will produce scum or residue duringwashing of clothes and this requires repeated washing of clothes with water until the scum isremoved from the clothes completely.

Detergents can perform well even in acidic water but the soaps cannot fit for use in

acidic water because the fatty acids settled down in the form of precipitate in acidic water. Soap is less soluble in water comparing detergents.

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.References

http://www.tutorvista.com/content/chemistry/chemistry-iv/chemistry-in-life/soaps-and-

detergents.php.Retrieved 26/09/10

http://www.tutorvista.com/chemistry/preparation-of-soap . Retrieved 26/09/10

http://www.tutorvista.com/chemistry/action-of-soap. Retrieved26/1010

http://www.tutorvista.com/content/chemistry/chemistry-iv/chemistry-in-life/synthetic-

detergents.php. Retrieved 26/09/10

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Soaps Detergents

Soaps are sodium salts of higher fatty acids

Detergents are sodium salts of long chain benzenesulphonic acid or the sodium salts of a long chain

alkyl hydrogen sulphateCalcium and magnesium salts of soaps arein soluble in water. Therefore cleansingaction of soap reduces in hard water

Calcium and magnesium salts of detergents aresoluble in water. Therefore cleansing action ofdetergents remain unaffected in hard water

Soaps are prepared from natural oils andfats

Synthetic detergents are prepared fromhydrocarbons of petroleum

Soaps cannot be used in acidic medium Detergents can be used in acidic medium

Soaps are biodegradable Most of the detergents are non-biodegradable
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