SOAP AND DETERGENT

 

Week:                   TEN                                        Date:                                                    

Period:                                 Duration: 1 HR 20 MIN.                                                  Average age of learners: 17YEARS

Subject:                               CHEMISTRY                                                                         Class: SS 3

Topic:                                    SOAP AND DETERGENTS

Sub topic:

Reference materials:

(1) ESSENTIAL CHEMISTRY, TONALD PUBLISHERS, I. O ODESINA

(2) NEW SCHOOL CHEMISTRY, AFRICAN FIRST PUBLISHERS, OSEI YAW ABABIO

(3) INTERNET

Instructional materials: soap and detergent

Entry behavior: The students have been familiar with soaps and detergents.

Behavioural objective: At the end of the lesson the students should be able to:

1.       Explain soap and detergent.

2.       Explain saponification

3.       State the advantages of soap over detergent vis-a –vis

4.       Differentiate between soap and detergent

5.       Explain the cleansing action of soaps

CONTENT

SOAP AND DETERGENTS

Soaps or detergents are cleansing agents that are capable of reacting with water to dislodge these foreign particles from a solid surface (e.g. cloth or skin). Soaps have their origin in oils and fats present in the animal and plant kingdom and synthetic detergents find their source in mineral oils (hydrocarbon compounds of petroleum or coal).

Soaps are produced by the alkaline hydrolysis of fats and oils. Fats and oils are esters. The hydrolysis of a fat and oils produces fatty acids and glycerol (propane 1,2,3 - trial)in the ratio of three moles of fatty acid to one mole of glycerol. Can also be produced by  the neutralisation of carboxylic acids

Soap is the sodium salt of long chain fatty acids that has cleansing property in water.

·         Types of soaps:

                      i.        Hard soap is a sodium salt of fatty acids. Hard soaps are used for washing clothes.

                     ii.        Soft soap is a potassium salt of fatty acids. It does not cause skin irritation and is hence used for bathing.

·         The formula for soap is C17H35COONa or sodium stearate.

Saponification:

The process by which soap is prepared by the reaction of animal or plant fat with sodium hydroxide solution is saponification.

Process of formation of soap

Soap is prepared by boiling animal fats or vegetables oil with sodium hydroxide . The fats or oils react with alkali or sodium hydroxide to form soap and glycerol. Glycerol is the trihydric alcohol.

Fat or Oil + Sodium hydroxide→ Soap + Glycerol

Detergents:

Detergents are the sodium salts of long chain benzene sulphonic acid or long chain alkyl benzene sulphate which has more cleansing property in water.

 

Advantages of detergents over soap:

i.                     They can be used even in hard water.

ii.                   They give stronger cleansing property than soap.

iii.                  They are more soluble in water than soap.

Advantages of soap over detergents:

I.                    Soap is biodegradable.

II.                  They do not pollute water bodies like ponds, lakes, etc.

Differences between soap and detergent

Soap

Detergent

They are sodium salts of higher fatty acids.

They are sodium salts of long chain benzene sulphonic acid.

They have relatively weaker cleansing action

They have relatively strong cleansing action

It is biodegradable

It is non biodegradable

It is not suitable for washing in hard water.For example: Sodium state

It is suitable for washing in hard water. For example: Sodium lauryl sulphate

Cleansing action of soap

Soaps and detergents do the same job due to the structure of the molecules:

The Soap molecule has two ends with different properties. They are hydrophillic end and hydrophobic end.
Hydrophillic end : Hydrophillic end dissolves in water (a polar ionic carboxylate "head").

 Hydrophobic end:Hydrophobic which dissolves in hydrocarbons (long non-polar hydrocarbon chain which is readily soluble in non polar).

During cleaning, the hydrophobic tails dissolve the droplet of grease, whilst the hydrophilic heads face out into the surrounding water, resulting in ball-like globules of grease dispersed in water. When a soap or detergent is added to water that contains oil or other water-insoluble materials, the soap or detergent molecules surround the oil droplets. The oil or grease is “dissolved” in the alkyl groups of the soap molecules while the ionic end allows the micelle to dissolve in water. As a result, the oil droplets are dispersed throughout the water (this is referred to as emulsification ) and can be rinsed away.

 PRESENTATION

I.                    The teacher explains soap and detergent.

II.                  The teacher explains the advantages of soap and detergent

III.                The teacher explains the cleansing action of soaps

EVALUATION

 The teacher evaluates the lessons by asking the following questions:-

1.       Explain soap and detergent.

2.       Explain saponification

3.       State the advantages of soap over detergent vis-a –vis

4.       Differentiate between soap and detergent

5.       Explain the cleansing action of soaps

ASSIGNMENT

1a.           What is meant by saponification?

b.            List the raw materials needed for the manufacture of soap.

c.             Name the main by-product obtained from the manufacture of soap.

       d.             State the reason why sodium chloride is used during the manufacture of soap.

 

 

 

 

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