Types of Hardness in Water for std 8 to 10 GSEB CBSE Course.

TYPES OF HARDNESS

Depending on the kind of negative ions present along with Mg⁺⁺  and Ca⁺⁺ ions, hard water is classified into two types namely temporary hard water and permanent hard water.

The water that contains bicarbonate ions along with Mg⁺⁺  and Ca⁺⁺ ions could be softened by mere boiling. Hence, such water is called temporary hard water.

The water that contains chloride or sulphate ions along with Mg⁺⁺ and Ca⁺⁺ ions is called permanent hard water.

This means the hardness causes by dissolved magnesium bicarbonate and calcium bicarbonate is temporary hardness.

The hardness caused by dissolved magnesium chloride, calcium chloride, magnesium sulphate or calcium sulphate is called permanent hardness.

Water samples may contain more that one salt that causes hardness.

DISADVANTAGES OF HARD WATER

We use water daily for a number of activities such as washing clothes, cleaning utensils, bathing, drinking, cooking and so on.

Hard water is not so suitable for these activities.

Pulses and vegetables are not cooked properly in hard water.

Hard water used for bathing makes the skin dry and leaves a whitish residue on the skin.

The utensils lose shine and get stained when washed with hard water.

Hard water is not suitable even for washing. Clothes are not cleaned in hard water.

Soap is also wasted.

The salts present in hard water from a yellow stain on clothes.

The salts accumulated on the inner walls of the cooking utensils makes their cleaning difficult.

It also wastes fuel energy.

Hard water poses many problems in industries such as paper, dye, printing, textiles, sugar etc.

Hard water forms a scale on the inner walls of industrial boilers.

Why does hard water causes scales on the walls of boilers ?

Hard water usually contains dissolved bicarbonates.

The dissolved bicarbonates, on boiling, dissociate to form insoluble carbonates which go on depositing on the inner walls of the boiler.

Hard water contains bicarbonates.

This results in scaling.

The scale not only corrodes the boiler but wastes fuel as well.

Hard water sometimes causes foaming and explosions of the boiler.

The scales formed inside the pipes reduce the size of the pipes and corrode them (fig).

Therefore hard water is not suitable for use in boilers.

Hence we need to soften water and then use it.

There are many methods of softening water.

Some methods remove only temporary hardness while others remove both types of hardness.

Activity

Take some amount of hard water in a glass beaker and boil it. Allow the water to cool. Observe the walls of the beaker closely. Repeat the experiment with soft water. What difference do you notice ? Why ? Explain.

Soaps and detergents for std 8 to 10 Science

SOAPS AND DETERGENTS 

Soaps 
– preparation of soaps 
– Detergents 
– advantages and disadvantages.

REVIEW
· 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.

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 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. 

Preparation of Soap

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.