Some Useful Chemicals

In this chapter, we discuss about water, hard and soft water, removal of hardness of water, some useful chemicals in Grade 8 Science.

Water

Water is the most common substance on the earth. Rain is produced by the condensation of the water vapour present in the air.  The natural sources of water are rain, rivers, lakes, springs, sea, wells, etc. Rainwater is regarded as one of the purest forms of naturally occurring water.

Nearly one-third of the rainwater sweeps into the ground through soft and loose strata of sand, gravel and chalk and then reaches some impermeable stratum of clay and slate. It remains trapped in this layer and tries to escape out through the small cracks of rocks which we call spring. The water in the well is one example of trapped water below the ground. Water from wells has been used from time immemorial for drinking and irrigational purposes.

Physical properties of water:

• Pure water is colourless, tasteless and has no smell.
• Water can be found in three state solid, liquid and gas.
• Water is transparent.
• Melting and boiling point of water is 0 degree C and 100 degree C respectively.
• Water has no definite shape.
• Water retains heat, so its temperature falls slowly.

Chemical properties of water

• Water is formed from two atoms of hydrogen and one atom of oxygen (H2O).
• Water is neutral. It has neither basic or nor acidic properties.
• Temperatures of 212°F (or 100°C) are required to break the hydrogen bonds and convert liquid water into water vapor.

Hard and Soft Water:

Soft water is the one which can produce lather with soap easily. But the hard water cannot produce lather easily as soft water.

The hardness of water is due to the presence of soluble salts of magnesium and calcium. The salts of magnesium such as magnesium bicarbonate (Mg(HCO3)2), magnesium chloride (MgCl2) or the salts of calcium such as calcium bicarbonate (Ca(HCO3)2), calcium sulphate (CaSO4), when dissolved in water, brings hardness in water.

The hardness of water may be temporary or permanent. Permanent hardness is due to the presence of salts such as magnesium chloride (MgCl2), magnesium sulphate (MgSO4), calcium sulphate (CaSO4), and calcium chloride (CaCl2) in water. Temporary hardness is due to the presence of salts such as calcium bicarbonate (Ca(HCO3)2) or magnesium bicarbonate (Mg(HCO3)2). Temporary hardness can be removed easily.

Advantages of Hard Water are as follows:

• It contains calcium salt dissolved in it which helps to strengthen the bones and teeth.
• It is used in beer industries.
• Water is somewhat tasty due to dissolved salts of calcium and magnesium.

Disadvantages of Hard Water are as follows:

It leads to the consumption of more soap while washing clothes.
A bright white cloth becomes dull due to the salts dissolved in water.
In industries, due to hard water, the life of boilers decreases. This is due to the calcium salt deposited during boiling.

Drinking water

The water that contains micro-organisms, contaminated water, should not be used for drinking. Contaminated water carries many diseases such as cholera, typhoid, and many more. To be healthy, we must drink safe and clean water. The drinking water must be boiled. After boiling, the micro-organisms in water gets killed. So, it is advised to everyone to drink boiled water in order to stay from diseases that transmit through water.

Removal of Hardness of Water

a. Removal of Temporary Hardness of water:

Temporary hardness present in the water can be removed by using the following methods: -

By heating: Salts like calcium bicarbonate and magnesium bicarbonate, when dissolved in water causes temporary hardness. While heating, soluble salts of calcium and magnesium (bicarbonates) change into insoluble salts.

The chemical equations are as follows:

Calcium bicarbonate → Calcium carbonate + Carbon dioxide + Water
Ca(HCO3)2 → CaCO3 + CO2 + H2O

Magnesium bicarbonate → Magnesium carbonate + Carbon dioxide + Water
Mg(HCO3)2 → MgCO3 + CO2 + H2O

Treating with lime water: The temporary hardness of water can be removed by treating it with lime water. The chemical equations are as follows:

Calcium Bicarbonate + Calcium Hydroxide → Calcium Carbonate + Water
Ca(HCO3)2 + Ca(OH)2 → 2CaCO3 + 2H2O

Magnesium Bicarbonate + Calcium Hydroxide → Calcium Carbonate + Magnesium Carbonate + Water
Mg(HCO3)2 + Ca(OH)2 → CaCO3 + MgCO3 + 2H2O

b. Removal of Permanent Hardness of water:

Permanent hardness cannot be removed by heating only. Soluble salts of calcium and magnesium are turned to insoluble salts by the following methods.

Treatment with washing soda: Soluble salts of calcium and magnesium change into insoluble salts due to the treatment with sodium carbonate (washing soda).

Calcium Chloride + Sodium Carbonate → Calcium Carbonate + Sodium Chloride
CaCl2 + Na2CO3 → CaCO3 + 2NaCl

Magnesium Sulphate + Sodium Carbonate → Magnesium Carbonate + Sodium Sulphate
MgSO4 + Na2CO3 → MgCO3 + Na2SO4

Permutit Process: Permutit is the trade name for an artificially prepared sodium zeolite or sodium aluminium orthosilicate obtained by fusing together sodium carbonate silica and alumina. Its composition resembles Na2Al2SiO8 or Na2Z, where, Z stands for Zeolite = Al2SiO8. It possesses the higher quality of reactivity with calcium and magnesium ions forming insoluble calcium or magnesium zeolites.

2Na2Z + Ca++ → CaZ2 +4Na

Thus by passing hard water through a cylinder packed with permutit, all the ions of soluble salts of calcium and magnesium responsible for the hardness of water are retained and replaced by sodium ions. In due course, however, the permutit is exhausted or losses its capacity of reacting with these salts by having given up all its sodium ions. This can be regenerated by soaking in a 10% solution of common salt when the reverse change takes place and calcium and magnesium ions pass into solution and sodium zeolite is formed again.

CaZ2 + 2NaCl → Na2Z + CaCl2
MgZ2 + 2NaCl → Na2Z + MgCl2

The resulting calcium and magnesium chlorides are washed out and the regenerated permutit is used over again.

Sodium Carbonate, Sodium Bicarbonate and Glycerol

Sodium Carbonate, Sodium Bicarbonate and Glycerol are some useful chemicals used in our daily life. Sodium carbonate is used to make soaps and detergents whereas sodium bicarbonate is used to make baking powder and glycerol is mostly used as sweetener.

Sodium Carbonate

Sodium Carbonate is a multi-use chemical. This is also called washing soda. Its molecular formula is Na2CO3. It is white in colour.

Uses

• It is used to make soaps and detergents.
• It is used to manufacture paper.
• It is used to manufacture different types of glasses.
• It is used to remove hardness of water.
• It used to make caustic soda in the lab.
• It is used for the various purpose in the lab.

Sodium Bicarbonate

Sodium Bicarbonate is the useful chemical made from sodium. It is also called baking soda. Its molecular formula is NaHCO3. It is white solid which is soluble in water. Baking soda, or sodium bicarbonate, is a base (alkaline in nature) that is formed when sodium carbonate (purified form of a mineral mined in Wyoming) is mixed with a solution of carbonic acid.

Uses of sodium bicarbonate:

• It is used to make baking powder.
• It is used as medicine to produce carbon dioxide gas in the stomach to remove the acid.
• It is used to make soft drinks.
• It is used to make fire extinguishers.

Glycerol

Glycerol is also called glycerine. Glycerol is a simple polyol compound. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. Its molecular formula is C3H5(OH)3. It is soluble in water.

Uses of glycerol:

• It makes the skin soft.
• It is used to make sweets.
• It is used to make medicine and printing ink.