12th Class Chemistry Chapter 15 Common Chemical Industries in Pakistan Short Question Answers

The people of a country need resources for their livings. Natural resources are exhausting every moment. This is due to growing population. High standard of living also needs the industrial products.

Fertilizers are the substances which contain elements essential for growth of plants. Fertilizers stimulate the process of metabolism in plant cells. They help the growth of plants and give additional supply of the food. They also maintain the PH of the soil between 7-8.

Those elements which are required in very small amount for the growth of plants are called micronutrients. These elements are B, Cu, Fe, Mn, Zn, Mo, and CI₂.

Nutrients which are required in large amounts for the growth of plants are called macronutrients. The elements are carbon hydrogen oxygen nitrogen phosphorus, Potassium calcium magnesium and sulphur.

The derived elements of fertilizers should be water soluble. Fertilizers should be stable in the soil. It should be cheap to manufacture and should not be injurious to plants. Moreover they should be stable enough to stand for a long time.

Important nitrogen fertilizers are:
(NH₄)₂SO₄, NH₄NO₃, NH₄CI, Ca(NO₃)₂ CaCN, NH₃, NH₂CO NH₂.

Nitrogen is essential for the rapid growth of plants. It is the main constituent of proteins. It gives green color to the leaves and increases the yield and quality of plants. Urea NH4NO3 (NH4)2SO4 are important nitrogenous fertilizers.

Ammonia contains 82% nitrogen. It is gas at ordinary temperature and is directly injected 6-8 inches in the form of liquid under the surface of the soil so that it may not seep out.

Urea is prepared in six steps:
i) Preparation of hydrogen.            ii) Preparation of NH₃.
iii) Preparation of ammonium carbamate.
iv) Preparation of urea.         V) Concentration of urea.
vi) Prilling.

Molten urea is sprayed at the prilling tower. It is done by means of prilling buckets. The molten urea is cooled by air which rises upwards. The molten droplets of urea solidify in the form of prills.

i) It is used as a fertilizer for many crops except peddy rice. ii) It is also used in the combined form with limestone. iii) It is hydroscopic in nature.

There are two important water soluble phosphorus fertilizers:
i) Calcium superphosphate CaH₂PO₄.
ii) Di-ammonium hydrogen phosphate (NH₄)₂ HPO₄.

i) Phosphorus stimulates the early growth of plants. ii) It accelerates the seed and fruit formation. iii) It increases the resistance to diseases and frosts.

It is prepared by the reaction of ammonia with H₃PO₃. It contains 16% nitrogen and 48% P₂O₅. This product contains 75% of the plant nutrients.

i) Potassium is needed for the formation of starch sugar and fibrous material of plants. ii) It increases the resistance to diseases. iii) It gives healthy root development. iv) It helps in the ripening of seeds fruits and cereals.

KNO₃ is prepared on the industrial scale by double decomposition reaction of KCI and NaNO₃. It contains 13% nitrogen and 44% Potash.

There are approximately 14 plants in private as well public sector. The total production of urea in Pakistan upto 2002 is 56, 30100 metric tones per annum.

An English mason joseph aspdin heated a mixture of limestone and clay with water and allowed to stand. The matter was hardered like a stone. This hardened mass resembled with Portland rock.

The cement is a material which is obtained by burning an intimate mixture of calcareous and argillaceous material at sufficiently high temperature to produce clinker. This clinker is consequently ground to a fine powder. The essentiall constituents of cement are lime silica and alumina.

The important raw materials used for the manufacture of cement are: i) Calcareous material. ii) Argargillaceous material. iii) Another raw material like gypsum water and fuel.

Dry process needs excessive find grinding so this process is employed. Then the material is hard. Wet process is free from dust grinding is easier and the composition of the cement can be easily controlled.

i) Curshing and grinding ii) Mixing in correct proportion. iii) Heating the rotary kiln. iv) Grinding the clinker. v) Mixing and grinding of clinker with gypsum.

Rotary kiln heats the material to high temperature to produce the cement clinker. This clinker is crushed to fine powder to get cement.

In preheating zone the temperature is 500ᵒC. In the decomposition zone the temperature goes up 800ᵒC. In the burning zone temperature rises upto 1500ᵒC.

It is the final product from the rotary kiln. These are small greenish black or grey colored balls. Their sizes very from small nuts to pease.

Clinker are cooled by air. Gypsum is ground to fine powder and mixed with clinker upto 5%. This mixture is ground to fine powder.

The reaction of cement with water with the passage of time is called setting of cement and setting time is noted.
Reactions taking place in first 24 hours:
i) After  a short time of the paste formation tri-calcium aluminate absorbs water. This is called hydration. It forms a colloidal gel of composition.
3Ca. AI₂O₃. 6H₂O
ii) This gel starts crystallizing slowly. Its reacts with gypsum having the formula CaSO₄. 2H₂O. It given the crystals of calcium sulpho-alminate. Its formula is as follows:
3Ca. AI₂O₃ 3CaSO₄. 2H₂O

There are 22 cement factories in private as well as public sector. Some of them work on the basis of wet process and other on the dry process.

: Paper is a sort of material made up of a network of natural celluloic fibre which have been deposited from aqueous structure. The raw material is of two types: i) Woody raw material. ii) Non-woody raw material.

It is neutral sulphite semi chemical process and following four physical operations are performed: i) Dry cleaning. ii) Washing iii) Heat treatment iv) Physical process for dewatering.

The air is blown into the raw material. It removes unwanted particles. Wheat grains are separated in the primary dry cleaners. In the secondary dry cleaning, we remove the lumps dust and sand particles.

Na₂SO₃ is buffered with Na₂CO₃ and soda ash to have a pH of 7-9. The  digester is closed carefully and it revolves at 2.5 rotation per minute. The temperature maintained is 160-180ᵒC.

It is an aromatic polymer and it causes the paper to become brittle. It is consisted of 17-33% of dry weight of wood.

i) Oxygen               ii) NaCIO
iii) H₂O₂                          iv) Ozone
v) Chlorine                   vi) CIO^–

Enough chlorine is required for this purpose. The residence time for chlorine is 45-60 minutes and the temperature should be maintained at 45ᵒC. After chlorination the pulp is washed with hard water at 60ᵒC.

It is consisted of:
i) Flow spreader                  ii) Head box.
iii) Fourdrinier table.          iv) Press section.
v) Drier section.

There are than 30 paper and pulp industries in private as well as in the public sector.