Role of lime in agriculture

ROLE OF LIME IN AGRICULTURE AND INDUSTRY

Lime, (CaO) is a soft, white compound which is obtained by the thermal decomposition of CaCO2. Role of Lime in Agriculture Large quantities of calcium oxide are used in agriculture for neutralizing acidic soils has been found that application of time to acidic soils increases the amount of readily soluble phosphorus.

 Calcium oxide is also used in large amounts for making lime-sulphur sprays which have a strong fungicidal action. The hydroxide of calcium is obtained when the oxide of the calcium is allowed to react with water. The process is called slaking of lime and it is an exothermic reaction.

Functions of Calcium in Plant-Growth

The presence of calcium is essential for the normal development of plants. The quantity of calcium required by different plants varies considerably. An adequate supply of calcium appears to stimulate the development of root hairs and, in fact, the entire root system.

Calcium is also necessary for normal leave development and tends to accumulate in leaves as well as in bark. An adequate supply of calcium is also essential for the optimum activity of microorganisms that produce nitrates.

The effect of calcium on the supply of available phosphorus in the soil is of special significance. Soils containing suff

icient calcium are slightly alkaline in nature. When a deficiency of calcium exists various substances such as aluminium and manganese may accumulate in plants in harmful concentrations.

Role of Lime in Industries

1. Large quantities of lime are used in the extraction and refining of metals.

2. Lime is also used in paper, cement and leather industries.

3. The ability of lime to react with sand at high temperature forming calcium silicate (CaSiO,) serves as an important basis for glass manufacture.

4. Lime is used in ceramic industry for producing different types of sanitary materials.

5. Ordinary mortar, also called lime mortar, is prepared by mixing freshly prepared slaked lime (one volume) with sand (three or four volumes) and water to form a thick paste. This material when placed between the stones and bricks hardens or sets, thus binding the blocks firmly together. The equations for the chemical reactions which take place when mortar hardens are:

6. Lime is also used in refining of sugar and other food products.

7. Lime is used in the manufacturing of bleaching powder, which is used for the bleaching of the fabric and paper pulp.

8. A suspension of the calcium hydroxide is called milk of lime and is used as a whitewash.

9. When lime is heated with coke at about 2800°C in an electric furnace, calcium carbide is produced, which on hydrolysis yields acetylene .

10. Lime is often employed as a dehydrating agent, for example, in the preparation ofa alcohol and the drying of ammonia gas. A mixture of sodium hydroxide and calcium hydroxide (soda lime) is often employed to remove both water and carbon dioxide from certain gases.

KEY POINTS

• The elements of group IA except hydrogen are called 'alkali metals' while those of group IIA are named as alkaline earth metals.

• Alkali metals have only one electron in s-orbital of their valence shell. They lose one electron of the valence shell forming monovalent positive ions.

• Alkaline earth metals have two electrons in s-orbital of their valence shell. They lose two electrons forming dipositive ions M².

• Spodumene, Chile saltpetre, trona, borax, carnallite, sylvite, alunite, halite, natron, are the common minerals of alkali metals.

• Beryl, magnesite, dolomite, epsom salt, asbestos, calcite, gypsum, strontionite and barite are the important minerals of alkaline earth metals.

• Lithium behaves different from the other alkali metals.

• Lithium forms only normal oxide, whereas the others form higher oxides like peroxides and superoxides.

• Beryllium is the only member of group II, which reacts with alkalies to give hydrogen.

• The other members do not react with alkalies.

• Nitrates of lithium, magnesium and barium on heating give oxygen, nitrogen peroxide and the corresponding metallic oxides.

• When gypsum is heated above 100°C, it loses three quarters of its water of crystallization, giving white powder of CaSO, 1/2H,O which is called Plaster of Paris.

• Sodium is prepared by the electrolysis of molten sodium chloride in Downs' cell.

• Calcium is necessary for development of leaves and it tends to accumulate in leaves and bark. An adequate quantity of calcium is essential for the optimum activity of microorganisms that produce nitrates.

• Lime is used in paper and glass industries. It is also used for refining sugar and other food products.

EXERCISE

Fill in the blanks:

o Alkali metals are............reactive than alkaline earth metals.

o Alkali metals decompose water vigorously producing............and oxygen.

o When heated in a current of dry hydrogen, alkaline earth metals form white crystals of the type MH₂.

o The beryllium oxide, like the oxide of aluminium is amphoteric, while the hydroxides of the other members of the group II-A are_........

o The elements of the group I-A are termed as alkali metals, because their ......... are alkaline.

o Spodumene is an ore of...........metal.

o Alkali metal nitrates on heating give the corresponding ............reactive than and oxygen.

o Na,CO,.H₂O is the chemical formula of a mineral of sodium which is known as_........

o Metallic bicarbonates are decomposed on heating into their carbonates, alongwith........and........

o Metal nitrates other than the alkali metals on heating decompose into the corresponding metal.............along with the evolution of nitrogen peroxide and oxygen.

Indicate True or False.

1. Group I-A elements are called alkali metals because their chlorides are alkaline in nature Alkali metals are very good conductors of electricity.

2. The hydroxides of alkali metals and alkaline earth metals are soluble in water.

3. Plaster of Paris is a hemihydrate.

4. Alkali metals have low melting and boiling points as compared to those of alkaline earth metals.

5. Lithium carbonate is decomposed to its oxide, but the carbonates of the other alkali

6. metals are stable towards heat.

7. All alkali metal sulphates are insoluble in water.

8. Lithium combines with nitrogen to form lithium nitride but other alkali metals do not react with nitrogen.

9. Trona is a mineral of lithium.

10. Alkaline earth metals are stronger reducing agents than alkali metals.

11. Discuss the trends in chemical properties of compounds like oxides, hydroxides carbonates, nitrates and sulphates of IA and IIA group elements.

12. Give the names, electronic configurations and occurrence of s-block elements.

13. Discuss the peculiar behaviour of lithium with respect to the other members of alkali metals.

14. Compare the chemical behaviour of lithium with magnesium.

15. Mention the properties of beryllium in which it does not resemble with its own family.

16. Why is the aqueous solution of Na CO, alkaline in nature?

17. Describe with diagram the manufacture of sodium by Downs' cell.

18. Point out the three advantages of this process.

19. Compare the physical and chemical properties of alkali metals with those of alkaline earth metals.