SOAPS AND DETERGENTS std 8 to 10 GSEB CBSE

Preparation of soap

SOAPS AND DETERGENTS

Soaps – preparation of soaps – 

Detergents – 

advantages and disadvantages.

REVIEW

You have learnt the reasons for hardness of water.

Let us recall some of them.

·       Water which readily produces lather with soap is called soft water and that which does not readily produce lather is called hard water.

·       Hard water contains dissolved sulphates, chlorides and bicarbonates of calcium and magnesium.

·       The natural water is generally impure.

·       The polar nature of water makes it an excellent solvent.

  INTRODUCTION

When water is used for washing, it dissolves dirt; but some dirt will not dissolve in water. Soaps and detergents help water to remove dirt. The rod detergent means something which cleans. Soapnut powder has been inuse for about 3,000 years. In India even now some still use soapnut powder as a natural soap to remove oily substance. People have been using soap for a long time.

 SOAPS

Metallic salts prepared from natural fats are called soaps. Soap is a sodium salt or potassium salt of long chain fatty acide that has clensing action in water. Sodium stearate, sodium oliate and sodium plamitate are some examples of soaps.

Stearic acid is a long chain fatty acid. Its formula is C₁₇H₃₅COOH. This reacts with sodium hydroxide to give a compound called sodium stearate, which has properties of soap.

Similarly, sodium hydroxide reacts with oleic acid and plamitic acid forming sodium oleate (C₁₇H₃₃COONa) and sodium palmitate C₁₇H₃₁ COONa) respectively.

Please note !

Fatty acids are organic compounds. The molecules of these compounds contain a carboxyl group (-COOH). These molecules react with a trihydric alcohol called glycerol to form a class of compounds called esters. Groundnut oil, coconut oil, palm oil, caster oil, ginegely oil, animal fat etc are all esters of fatty acids. Fats and fatty oils are called glyceryl esters or glycerides.

While writing the formulae of inorganic csalts. It is the convention to write cation first However cation js written at end in the case of organic salts. Consider the following examples

Sodium chloride -        NaCL

Sodium acetate   -        Ch₃COONa

PRPARATION OF SOAP

Experiment : Take  about 30 ml of a vegetable oil in a beaker. Add about 60 ml of 20% sodium hydroxide solution to it. Heat slowly until the mixture boils. After 5-10 mimutes of boiling, add about 5g of sodium chloride to separate soap from the solution. Cool the solution. Observe the creamy layer of soap floating on the solution.

When a mixture of a oil/fat and a strong solution of sodium hydroxide is boiled in an iron tank, a sodium salt of the fatty acid and glycerol ane formed. The sodium salt of the fatty acid thus formed is nothing but soap.

Preparation of soap Experiment.

Video  how to make soap by cold process in Laboratory

A Swedish chemist, Carl Wihelm Scheel, discovered accidentally the process of preparation of soap in 1783. He boiled olive oil with lead oxide and obtained a substance which was sweet to taste. This substance is now known as glycerine.

Oil/fat + Sodium hydroxide – soap + glycerol

Glycerol

Glycerol is a sweet viscous liquid soluble in water. It is a byproduct of saponification process. It is commonly called glycerine. Its formula is CH₂OH.CHOH.CH₂OH. It is used in the manufacture of explosives, plastics. And pharmaceuticals. It is also used to prevent freezing.

Soap thus formed is separated with the help of sodium chloride. Addition of sodium chloride reduces the solubility of soap considerable. Soap, being lighter, flots like a cream on the solution. It is separated from the solution, suitable chemicals of suitable colour and odour are added to it and cast into moulds. When soap cools and solidifies, it is cut into desired shapes and packed. Glycerol exists in dissolved state in the solution. It is separated by distillation.

How does soap clean ?

Soap cleans process

Soap dissolves in water. This is due to the contrasting properties of the ends of the soap molecules. A soap molecule has a long hydrocarbon end (Ex:CH₃(CH₂)₁₆) and  a short ionic end containing COONA₊. The non-ionic hydrocarbon end attaches to the dirt or grease to form structures called ‘micelles’.

1.    water 2. soap molecule 3. Dirt

In micelles soap molecules are arranged radially. The end attached to water pulls out the dirt from the fabric. This can be washed off with water.

DETERGENTS

The term detergent is derived from a Latin word which means surface active. Synthetic detergents are commonly known as detergents. Detergents are also called soapless soaps. Detergents do not from insoluble ‘scum’ with magnesium and calcium ions present in hard water. Therefore, detergents clean better than soap even in hard water.

Detergents are sodium salts of long chain benzene sulphonic acid or sodium salts of long chain alkyl hydrogen sulphate. A detergent molecule consists of a large hydrocarbon group that is non-ionic and a sulphonate (SO₃- Na⁺) or a sulphate (SO₄-Na⁺) group that is ionic. Sodium n-dodecyl benzene sulphonate and sodium dodecyl sulphate are two well-known detergents.

Let us now consider a method of making detergents. Long chain hydrocarbons obtained from petroleum are treated with concentrated sulphuric acid. The organic acids produced during this process are neutralized with sodium hydroxide. The sodium salt obtained is a detergent.

 ADVANTAGES OF DETERGENTS OVER SOAPS

Detergents have more advantages that soap. Therefore. Detergents are more widely used that soap. Let as now turn our focus towards the advantages of detergents.

·       Detergents cleanse well even in hard water. Soap is not so good for washing when water is hard.

·       Detergents are made from hydrocarbons obtained from petroleum. Soap is prepared from vegetable oil or animals, fat that are usually edible. Detergents are not bio-degradable. Soaps are biodegradable.

·       Detergents cleanse well evening acidic medium. Soap does not cleanse well in such a medium.

Detergents have their disadvantages.

·       Detergents are non bio-degradable. They pollute water and soil.

Points to remember :

·       Metallic salts prepared from natural fats are called soaps.

·       Sodium hydroxide, fatty acid and sodium chloride are the raw materials used in the preparation of soap.

·       Sodium oleate and sodium palmitate are example for soap.

·       Detergents are also called soapless soap.

·       Detergents cleanse well even in hard water.

·       Detergents cleanse well in acid medium.

·       Detergents pollute water and soil.

·       The process of preparing soap using sodium hydroxide or potassium hydroxide is called saponification.

METHODS OF SOFTENING HARD WATER, std 8 to 10 CBSE

Methods of removal of temporary hardness.

Boiling : You already know that temporary hardness is causes due to dissolved bicarbonates of calcium and magnesium.
Boiling is a method of removal of temporary hardness.
When water is boiled, the bicarbonates that cause temporary hardness are converted into insoluble carbonates, leading to the removal of Ca++ and Mg++ from water.

Calcium and Magnesium carbonate reaction with water

The precipitates that are formed are removed by filtering.
Boiling is the easiest method of softening a small quantity of water.
Softening a large quantity of water by boiling is highly expensive.
The Process is also time consuming.
Temporary hardness is rare.
Boiling removes the bicarbonate component only.
Therefore, we need to consider other methods of softening.

Do if yourself
It the water you use at home is hard, can it be softened by boiling ? Boil and examine. 

Methods of removal of permanent hardness.

1. Distillation : 

Water obtained from any source. However hard it may be, can be softened by distillation. Distilled water is both soft and pure. The condensation of water vapours produced on heating is the principle involved in this process. This method removes both temporary and permanent hardness. 

Think it over
Why is the process purification of seawater through distillation not so feasible ?

2. Soda process : 

Both temporary hardness and permanent hardness of water can be removed by adding sodium carbonate.
This method is called Soda process.
Sodium carbonate reacts with salts that causes hardness to give their respective carbonates.
The following chemical equations clarify these reactions. 

Different Chemical  reacts with salt equation.

The insoluble carbonates present in the softened water are removed by filtration.
The water softened by this method.
However, contains salts such as sodium sulphate, sodium chloride and so on.
The presence of these salts does not pose serious problems.
These salts do not come in the way of formation of lather with soap.

3. Permutit process : 

Permutit is used in softening hard water.
Naturally occurring sodium aluminium silicate is called zeolite.
This compound can also be prepared artificially. Artificially prepared sodium aluminium silicate is called permutit.
Permutit is prepared by heating quartz, sand, china clay and sodium carbonate.
Fusing sodium silicate and sodium aluminates is another method of preparing permutit.
Permutit is in the from of a porous gel.
The principle involved in this process is to convert the dissolved salts of calcium and magnesium into insoluble calcium and magnesium permutits, respectively.
This is done by exchanging the base ion radicals such as Ca++ and Mg++ with the base ion Na+ of sodium aluminium silicate.
Hence this process is also known as ‘base exchange process’.

This is carried out by passing hard water through the layers of zeolite or permutit. This method removes both temporary hardness and permanent hardness.

Permutit process removes temp. as well as permanent hardness.

In the permutit process, there will be a column in which gravel, sand and permutit are placed in alternate layers.
Hard water is made to rise up through the various layers.
As water passes through the permutit, the ions of calcium (Ca++) and magnesium (Mg++) which causes hardness are exchanged with the sodium ions of the permutit.
Permutit is changed eventually into calcium aluminium silicate and magnesium aluminium silicate.
These are called calcium permutit and magnesium permutit respectively. We shall discuss two examples to understand how this happens.

Sodium permutit + Calcium chloride " Calcium permutit + Sodium chloride

Sodium permutit + Magnesium sulphate " Magnesium permutit + Sodium sulphate

Water that comes out of the permutit column contains neither calcium ions nor magnesium ions.
However, the water softened by this method contains sodium ions.
The presence of these ions, however, will not make water hard.
Permutit process is an economical way of softening water.
The hardness is more or less completely removed by this method.
This method is not so appropriate if the hard water contains sodium salts or suspended matter in large quantities.
Lead, if present in water, is not removed in this method.
The permutit process is useless if the water contains iron or manganese impurities.
What we get through permutit process is only soft water and not pore water.

Justify 
Pure water is soft However, soft water need not be pure. It this possible ? How ?