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What is Soap ?

SOAP AND DETERGENT

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What is Soap?

• Soaps are sodium or potassium salts of long-chain fatty acids. The general formula of a soap can be written as:

RCOO-K+ or RCOO-Na+.

• Where R is alkyl group, can be saturated or unsaturated which is consist of 12 to 18 carbons atom.

Example:Sodium palmitate, CH3(CH2)14 COO-Na+

Potassium stearate,CH3(CH2)16COO-K+

Note: State several types of alkyl group

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Soap Preparation Process

• Soap can be made from animal fats and vegetable oils. They are prepared

by hydrolysing fats or oils under alkaline condition. The reaction is called saponification.

• Saponification process involves boiling fats or oils with concentrated sodium hydroxide, NaOH solution to produce gylcerol and soaps.

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General Equation Oil/ fats + alkali Soaps + water + glycerol

• The three alkyl group can be the same or different groups.

• When concentrated potassium hydroxide, KOH solution is used instead of concentration sodium hydroxide, NaOH solution, a potassium soap, potassium palmitate, CH3(CH2)14COO-K+ is formed.

Note: Show the chemical reaction of making soap

GlycerolOil/fats

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What is Detergent

• Any cleaning agent that is

not a soap is a detergent.

• Detergent are usually made

from synthetic resources such

as petroleum fractions.

• Detergents are usually sodium salts of sulphonic acid.

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Preparation of detergent

• During the preparation of detergents, long-chain hydrocarbon obtained from petroleum fractions is converted into an organic aid through a series of steps.

• The organic acid is then neutralized with sodium hydroxide, NaOH solution to produce a detergent.

• The summarizes steps involved in the preparation of sodium alkyl sulphate and sodium alkylbenzene sulphonate as follows:

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Preparation of sodium alkyl sulphate

Long-chain alcohol

CH3(CH2)nCH2OH Sulphonation Alkyl sulphonic

acid+

Concentrated

Sulphuric acid

STEP 1: Formation of an organic acid

STEP 2: Neuralization

Alkyl sulphonic acid + NaOH

Neutralization Sodium alkyl sulphate

H2O+

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Preparation of sodium akylbenzene sulphonate

Long-chain

alkene+ Benzene Alkylbenzene

Alkylation

+

Concentrated sulphuric acid

SulphonationAlkylbenzene sulphonic

acid

Neutralization

Sodium alkylbenzene sulphonate

+NaOH

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HOW THIS HAPPENED- Cleansing Action

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STEP 1

• When soap or detergent is added to water, it reduces the surface tension of water. This increases the wetting ability of water. Therefore, the surface of the cloth is wetted thoroughly.

• The hydrophobic part of the soap or detergent anion is soluble in the grease. The hydrophilic part is soluble in water.

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STEP 2

• Mechanical agitation during scrubbing helps pull the grease free.

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STEP 3

• The droplets do not coagulate and redeposit on the surface of the cloth due to the repulsion between the negative charges on their surface.

• These droplets are suspended in water, forming an emulsion. Rinsing washers away these droplets and leaves the surface clean.

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How Water Hardness Affects Cleaning Action

• Although soap is a good cleaning agent, its effectiveness is reduced when used in hard water. Hardness in water is caused by the presence of mineral salts - mostly those of calcium (Ca) and magnesium (Mg), but sometimes also iron (Fe) and manganese (Mn).

• The mineral salts react with soap to form an insoluble precipitate known as scum.

• 2Na+(R-COO)- (aq) + Ca2+(HCO3-)2(aq) →

2Na+(HCO3)-(aq) + Ca(R-COO)2(scum)

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Comparison between a soap and detergent

Cleaning agent Soap Detergent

Effectiveness

Effective cleaners in soft water

Effective cleaners in both hard and soft water

Formation of Scum

Form scum in hard water

Do not form scum in hard water

Formation of precipitate

Form precipitate in acidic water

Do not form precipitate in acidic water

Sources Natural resources Synthetic resources

Effect to environment

Biodegradable Non- biodegradable