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.

Water Science for std 8 to 12 CBSE, GSEB

WATER

Hard and soft water – experiments with hard water – removal of hardness – conservation of water.

REVIEW

You have studied many aspects of water in your previous classes. Water is a wonderful substance. It is one of our invaluable resources. Without it life can neither exist on earth nor can the bio-chemical reactions take place. Let us once again recall some of the important points that you have already studied about water.

Water is a compound made of hydrogen and oxygen.

Most of the land on earth is Covered with water.

Water exists on earth in all the three states – solid, liquid, and vapor.

Water can dissolve the highest number of substances in it.

Most of the substances that dissolve in water are inorganic ionic compounds.

The ionic compounds dissociate into positive and negative ions when dissolved in water.

Seawater is saline and hence not potable. Distillation is a method of obtaining pure water from seawater.

Even distilled water is not potable.

Water gets cycled continually through the biosphere and this movement is called water cycle.

Water sources are being polluted due to human activities.

Indian philosophers regarded water as one of the five elements that constitute the universe. Even the westerners had similar views. A British chemist, Sir Henry Cavendish showed for the first time in 1781, that water is produced when hydrogen burns is air. Lavosier, a Frech chemist proposed that water is not an element but a compound made of hydrogen and oxygen.

INTRODUCTION

The water obtained from natural sources have several salts dissolved in it. Salts such as nitrates, sulphates, chlorides, and bicarbonates might have been dissolved in water. Pure water has neither color and taste nor smell.

Water gets colour, teste, and smell due to impurities. Water acquires certain properties other than colour, taste and smell, when certain salts are dissolved in it. The change in the way it interacts with soap is one such property. Based on the way in which it acts with soap, water is classified as soft water and hard water.

Note

Rainwater dissolves small amount of atmospheric carbon dioxide in it to form a weak acid called carbonic acid. The other chemicals that are let into the atmosphere may also e dissolved in it. Hence even rainwater is not pure.

SOFT WATER AND HARD WATER

Water that gives lather with soap easily and readily is called soft water. Pure water is always soft. Water may be soft even when some salts are dissolved in it.

Experiment 1 : 

Collect samples of water from different sources – tap, bore well, pond or lake etc. Take equal quantity of the samples collected in different test tubes. Add about 1 gram of soap powder to each of them. Shake well. Which of them gave lather easily and spontaneously ? Which sample does not give lather readily ?

Experiment Soap formation in different water

Experiment of soap formation in different water

Experiment 2 : 

Collect samples of water from various sources as mentioned in the experiment cited above. Add 1 gram of soap powder to each of them and stir until the soap dissolves in water. Now blow the contents of each of the test tubes using a straw few times. Which of them gives lather profusely ?

Experiment of soap by air in different water sample

Experiment of soap by air in different water sample

Experiment 3 : 

Does the water you use at home give lather readily with soap ? Test and find out.

Experiment 4 : 

Take equal quantities of water in two beakers. Add about 1 gram of calcium chloride to one of them and stir well. Now add about 1 gram of soap powder to each beaker. Blow the contents of the beakers using a straw. Which of them give lather well ? Repeat the experiment by using sodium chloride, sodium bicarbonate, magnesium chloride, calcium sulphate, and magnesium sulphate instead of calcium chloride. Which of them give lather ? Which of them does not give lather ? Examine.

Test of water with different substance like Calcium Chloride

Test of water with different substance like Calcium Chloride

Test of water with different substance like Calcium Chloride

It is not practically possible to obtain calcium bicarbonate and magnesium bicarbonate in solid form. This is because these salts chemically dissociate much before the evaporation is complete and form their respective carbonates.

Therefore, it is only possible to have solutions of calcium bicarbonate and magnesium bicarbonate.

Certain salts dissolved in water from a scum with soap. Water that forms an insoluble scum with soap before giving lather is called hard water. Hard water does not readily give lather with soap. The dissolved salts such as calcium bicarbonate, calcium sulphate, calcium chloride, magnesium bicarbonate, magnesium sulphate and magnesium chloride are the chief salts that cause hardness of water. Let us consider how these salts render water hard.

Note that the salt that cause hardness are ionic compounds. These salts ionize to give positive ions and negative ions when dissolved in water. For example, magnesium sulphate when dissolved in water, dissociates into Mg++ ions and SO4- ions. Similarly calcium sulphate (CaSO4) dissociates into Ca++ and SO4-. The equations showing the process of ionization of salts causing hardness of water, are given below.

The salts that cause hardness in water include calcium fluoride and salts of iron. Ions of iron and manganese will also cause hardness of water.

MgSo4                -         Mg++         +       SO4 --

CaSO4                -         Ca++          +       So4--

CaCL2                -         ca++           +       So4--

MgCL2               -         Mg++         +       2CL-

Ca(HCO3)2        -        Ca++          +       2(HCO3)-

Mg(HCO3)2       -        Mg++         +       2(HCO3)-

Of the ions mentioned above, only Mg++ and Ca++ ions cause hardness. These ions form an insoluble scum with soap. How does hard water form scum with soap ? Soap (you will know more about it later) is a sodium salt or potassium salt (Ex: sodium stearate or potassium stearate repectively). These salts react with Mg++ and Ca++ ions present in water to form magnesium stearte and calcium stearate respectively. These insoluble precipitates, from a scum on the surface of contact. Soap begins to give lather only after all the Mg++ and Ca++ ions present in this water samples are precipitated.