Chapter 15: Common Chemical Industries in Pakistan – Chemistry 2nd Year Notes

This chapter covers Common Chemical Industries in Pakistan from the 2nd Year (FSc Part-II) Chemistry syllabus of the Punjab Curriculum and Textbook Board (PTB/PCTB). Chemical industries turn raw materials into the products a country needs. This chapter looks at three of the most important chemical industries in Pakistan: the fertilizer industry, the cement industry and the paper industry.

Because Pakistan is an agricultural country, the fertilizer industry is especially important; it supplies the nutrients that keep our soils fertile and our crops productive.

Learning Objectives

• Explain the importance of the fertilizer industry for Pakistan.
• Name the three main plant nutrients and the fertilizers that supply them.
• Describe the manufacture of important fertilizers such as urea.
• Describe the raw materials and manufacture of cement.
• Describe the raw materials and manufacture of paper.
• Appreciate the role of these industries in the national economy.

Key Concepts

The Fertilizer Industry

Fertilizers supply the nutrients that plants need. The three most important are nitrogen, phosphorus and potassium (NPK). Nitrogen promotes leafy green growth, phosphorus helps the roots, flowers and seeds, and potassium improves disease resistance and fruit quality. Urea and ammonium sulphate supply nitrogen, superphosphate supplies phosphorus, and diammonium phosphate (DAP) supplies both nitrogen and phosphorus.

Manufacture of Urea

Urea is the most widely used nitrogen fertilizer in Pakistan because it has the highest nitrogen content, about 46 percent. It is made from ammonia (from the Haber process) and carbon dioxide: the two gases first form ammonium carbamate, which is then decomposed by heat to give urea and water. The overall reaction is 2NH3 + CO2 gives urea plus water. Pakistan has several large urea plants that use natural gas as the source of hydrogen for the ammonia.

The Cement Industry

Cement sets into concrete, the basis of nearly all modern building. Its main raw materials are limestone (which provides calcium) and clay (which provides silica, alumina and iron). The manufacture has four steps: the raw materials are crushed and mixed, the mixture is heated in a rotary kiln at about 1450 to 1500 degrees Celsius to form small lumps called clinker, the clinker is ground to a fine powder, and a small amount of gypsum (about 2 to 5 percent) is added to control the setting time.

The Paper Industry

Paper is made mainly from cellulose fibres from wood or, in Pakistan, from bagasse (the fibrous residue left after crushing sugar cane). The raw material is digested (pulped) with chemicals to free the cellulose fibres, the pulp is bleached and beaten, and it is then spread out, pressed and dried into thin sheets of paper. The paper industry is closely linked to Pakistan large sugar industry, which supplies the bagasse. Together these industries support agriculture, construction and education and add to the national economy.

Important Definitions

Formulas & Rules

Item	Fact
NPK roles	N leaves, P roots and flowers, K disease resistance
Urea	2NH3 + CO2 gives urea plus water; about 46 percent nitrogen
Cement raw materials	limestone plus clay; kiln gives clinker; add gypsum
Gypsum in cement	controls the setting time
Paper	cellulose from wood or bagasse, pulped and bleached

Diagrams & Illustrations

The NPK nutrients: a chart showing nitrogen for leafy growth, phosphorus for roots, flowers and seeds, and potassium for disease resistance and fruit.

Cement manufacture: a flow chart from limestone and clay through crushing and mixing, the rotary kiln (clinker), grinding with gypsum, to finished cement.

Paper manufacture: a flow chart from wood or bagasse through pulping, bleaching and beating, to sheet forming and drying.

Solved Examples & Numericals

Example 1: Choosing a fertilizer

A crop has pale, poor leafy growth. Which nutrient is deficient and which fertilizer would help? A nitrogen deficiency; a nitrogen fertilizer such as urea would help.

Example 2: Cement

Why is gypsum added to cement? A small amount of gypsum is added to slow down and control the setting time so the cement can be worked before it hardens.

Example 3: Paper

Which by-product of the sugar industry is used to make paper? Bagasse, the fibrous residue left after the juice is crushed out of sugar cane.

Short Questions & Answers

Long Questions & Answers

Q1: Describe the fertilizer industry and the manufacture of urea.

Because Pakistan economy depends heavily on agriculture, the fertilizer industry is one of its most important chemical industries. Fertilizers replace the nutrients that crops take from the soil, the three most important being nitrogen, phosphorus and potassium: nitrogen encourages green leafy growth, phosphorus develops the roots, flowers and seeds, and potassium improves disease resistance and fruit quality. Different fertilizers supply these nutrients, for example urea and ammonium sulphate for nitrogen and diammonium phosphate for both nitrogen and phosphorus. Urea is the most widely used because it has the highest nitrogen content, about 46 percent. It is manufactured from ammonia (made by the Haber process using hydrogen from natural gas) and carbon dioxide: the two gases form ammonium carbamate, which is then decomposed by heat to give urea and water. Pakistan has several large urea plants that help the country grow enough food and reduce imports.

Q2: Describe the raw materials and manufacture of cement.

Cement is the essential building material that sets hard with water to bind sand and gravel into concrete. Its two main raw materials are limestone, which provides calcium oxide, and clay, which provides silica, alumina and iron oxide; a small amount of gypsum is also needed. The manufacture takes place in four steps. First, the limestone and clay are crushed and mixed in the correct proportions, sometimes with water to make a slurry. Second, the mixture is fed into a large sloping rotary kiln and heated to about 1450 to 1500 degrees Celsius, where it becomes hard lumps called clinker. Third, the cooled clinker is ground to a fine grey powder. Fourth, a small amount of gypsum, about 2 to 5 percent, is ground in with the clinker to control the setting time. The finished cement is then packed and sold. Pakistan has a large cement industry supporting its construction sector.

Q3: Describe how paper is manufactured, and its link with the sugar industry.

Paper is made from cellulose fibres, which come from wood and, in Pakistan especially, from bagasse, the fibrous material left after the juice has been pressed from sugar cane. First the raw material is cut up and digested with chemicals, which free the cellulose as a soft pulp. The pulp is then bleached to make it white and beaten to the right texture. Next the watery pulp is spread evenly on a moving wire screen, where the water drains and the fibres mat into a thin wet sheet. Finally the sheet is pressed and dried over heated rollers to give finished paper. Because bagasse is a by-product of sugar making, the paper industry is closely linked to Pakistan large sugar industry, turning waste into a valuable raw material. The paper industry supports education, printing, newspapers and packaging.

MCQs with Answers

Quick Revision Summary

• Fertilizers supply NPK: nitrogen for leaves, phosphorus for roots and flowers, potassium for disease resistance.
• Urea has the highest nitrogen (about 46 percent); made from ammonia and carbon dioxide.
• Cement: limestone plus clay, heated in a kiln to clinker, ground with gypsum.
• Gypsum controls the setting time of cement.
• Paper: cellulose from wood or bagasse, pulped, bleached and dried into sheets.
• These industries are vital to Pakistan agriculture, construction and economy.

Exam Tips

• Learn the NPK roles and match each nutrient to its fertilizer.
• Remember urea has the highest nitrogen content and its manufacturing equation.
• Know the four steps of cement manufacture and why gypsum is added.
• Link bagasse to the sugar industry for the paper question.
• Mention the economic importance for Pakistan in long answers.