FORMS OF WATER

HARD WATER:

Is water which does not form lather readily with soap. This is because the water contains (II) and magnesium (II) ions which react with soap to form scum.

Scum is calcium or magnesium stearate

 SOFT WATER:

Is water which will form lather readily with soap

 Types of hardness of water – 2 types

1. Temporary hardness
2. Permanent hardness
3. Temporary hardness:

Is caused by presence of dissolved calcium or magnesium hydrogen carbonates.  CaHCO₃ and MgHCO₃.

This types of hardness is termed “temporary” because it can be removed by boiling the water. This is because hydrogen carbonates of calcium and magnesium are decomposed by heating.

4. Permanent hardness: is due to presence of dissolved calcium or magnesium sulphates, CaSO₄(aq), MgSO₄. This type of hardness is termed “permanent” because I can not be removed by boiling.

Note:

Whether the water hs temporary or permanent hardness, cause is presence of calcium  (II), or magnesium  (II) ions..

 How does water acquired temporary hardness

Rain water dissolves carbon dioxide gas. Some dcarbon dioxide reacts with the water to form carbonic acid

Some of this acidic water percolates into the soil and it dissolves calcium carbonate from rocks containing, cahlk, marble, limestone

How does water acquire permanent

If waters passes through rocks containing calcium or magnesium sulpahtes some of its dissolves.

Removal of hardness

1. Physical methods
2. Distillation

Soft water is collected as a distillate. Impurities remain in the distillation can. This methods is not suitable for large plants. (cost of living is high). This method removes temporary and permanent hardness.

2. Boiling

– it removes only temporary hardness. Because calcium and magnesium sulphates don’t decompose of heat.

When temperature hard wwater is boiling calcium and magnesium carbonates decompose to give CO2 and water and dilute precipitate of calcium or magnesium carbonate which is filtered.

It is unsutable for large water works because heating is expensive.

Chemical methods

1. Adding of a calculated quantity of calcium hydroxide. (excess calcium hydroxide would cause hardness).

This method only removes temporary hardness

2. Addition of sodium carbonate (washing soda)

This method removes temporary and permanent hardness

This method is economical for large water works because washing soda is a cheap chemical.

 Disadvantages of this method

Addition of sodium carbonate to the water makes the water alkaline due to hydrolysis

3. Permutit method (ion exchange method):

This method removes temporary and permanent hardness. It works on the principle of ion exchange.

The calcium (II) and Mg²⁺ ions are removed from hard water and are replaced by sodium ions which don’t cause hardness.

The ion exchange substance is complex for simplicity you can regard it as Na₂Y or Na₂ perm. (Sodium permits). When hard water passes over sodium permuted ion exchange occurs.

The compound is renewed by running concentrated sodium chloride over it and washing away the soluble calcium or magnesium chloride formed.

 Disadvantages of hard water

1. It wastes soap
2. Soap and hard water react to form scu, which leaves dirty marks on clothes and can also damage nylon and silk.
3. Causes wrong colors in dying skill
4. 1. Poor finish in leather turning
   2. Calcium and magnesium carbonates from “fur” in kettles in which hard water is boild. “fur” is a bad conducor of heat therefore it wastes fuel

Boiler scale

Calcium and magnesium carbonates and sulphates from inside boiler. This solid “boiler scale”. It wastes fuel because it’s a bad conductor. The scale may block narror boiler tubes causing steam pressure to raise and possibility damage ofr burst the pipes.

 Advantages

1. Calcium compounds in hard water can be used to form strong teeth and bone
2. It is good for brewing
3. Shells of gets of animals contain calcium carbonate some of which comes from water.
4. Hard water cn be safely conducted using lead pipes because it doesn’t dissolve poisonous lead metal. On the contrary soft water dissolves poisonous lead metal therefore, it can not safely conducted by lead pipes.

Soap:

Soap is a metallic salt of long chain fatty acids.

Give an example of soap

Sodium stearate, nast

Soap is prepared by boiling a mixture of sodium hydroxide solution and a lipid like castor oil. The reaction is termed saponification because it involves preparation of soap. The aqueous soap prepared is precipitated from mixture by cooling concentrated sodium chloride solution.

Manufacture of soap

Soap is manufactured by boiling a mixture of a lipid e.g palm oil and sodium or potassium hydroxide (saponification)

Concentrated sodium chloride is added to a mixture of precipitate (saltout) soap.

Action of soap

For soap to work, it has to e dissolved in water

Structure of soap

Hydrocarbon tails are soluble in organic dirt and fat globules. During cleansing the nonpolar hydrocarbon tails penetrate organic dirt, fat globules or oils. But the heads remain in contact with water. The lipid / fat / oil if broken into fragments which are suspended into water farming an emulsion.

 Reaction of soap with hard water

Soap reacts with hard water to form insoluble scum. Scum is calcium or magnesium stearate.

Scum is a white precipitate. Therefore hard water wastes soap and leaves dirty marks on cloth.

Detergents

Soapless detergents

They are manufactured from petroeleum products, sulphur acid and sodium hydroxide.

Structure of detergents

It is a similar to that soap. They consists of non – polar hydro carbon tail and a polar (ionic) head.

Action of detergents

Detergents work in the same way as soap but unlike soap they don’t form scum in hard water because there calcium and magnesium salts are soluble in water.

They don’t form scumm in acidic water

Detergents dissolve more easily in water than soap.

Some detergents contain added enzymes to remove biological stains e.g blood, plant sap.

Some contain inorganic phosphates to improve their efficiency. Unfortunately this inorganic phosphates enter water bodies via sewage and pollute it easily faster growth water plants.

Some detergents contain florescent materials to act as whitners.

Disadvantages of detergents

1. Contain inorganic phosphates which pollute water bodies .
2. Some are non-biodegradable therefore, accumulate in water bodies causing pollution.
3. Foaming in a river is evident that the water contains detergents

Detergents are more expensive

Advantages

1. Dissolve more easily in water compared to soap.
2. More efficient than soap
3. Work well with soft and hard water.
4. Unlike soap they work well with acid waste

Detergents with straight hydrocarbon tails / chains can be biodegrable