Chemistry For HSC Part 2 - Chapter No.10 - Questions And Answers

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Chapter No.10
CHEMISTRY OF LIFE
Questions And Answers

By Sir Asif Izhar (Anees Hussain)

CONTENT

1. Biochemistry
2. Food and Nutrition
3. Carbohydrates
4. Amino Acid
5. Proteins
6. Lipids
7. Enzymes
8. Vitamins
9. Digestion of Food
10. Absorption or Assimilation

Q.1: Define biochemistry?
Ans: BIOCHEMISTRY:
Chemistry of life, in short written as Biochemistry (Bio = Life + Chemistry). It is a branch of Chemistry which deals with the study of chemical and physical processes, by means of which the chemical compounds such as vitamins, lipids, carbohydrates proteins and nucleic acids are transformed into one another by the cell itself (occur in living things) in order to maintain its organized structure and activities.

OR 

"The branch of chemistry which deals with the study of chemicals and physical processes taking place in the body during food intake is called Biochemistry or the Chemistry of Life".

Q.2: What do you know about Food and Nutrition? Explain the balanced and unbalanced diet. Illustrate the effects of unbalanced diet.
Ans: FOOD AND NUTRITION:
Food and Nutrition is a field of biochemistry which deals with the Nutrient and caloric requirement of the living body. It deals with the effect on growth and metabolism of the living system arising from the imbalanced diet.

PURPOSE OF FOOD:
The food is required by the body to achieve three purposes:

1. Energy in the form of calories
2. Growth and maintenance of tissues
3. Regulation of body processes

CLASSIFICATION OF FOOD:
Food and nutrients are classified into six groups, as:

1. Carbohydrates
2. Lipids and fats
3. Proteins
4. Vitamins
5. Minerals
6. Water

BALANCED DIET:
For healthy performance, each day the diet must supply the body with:

1. Adequate calories
2. Vitamins
3. Mineral salts
4. Water

Such foodstuff in a diet can cover all the above needs of the living system and such diet is known as a balanced diet.

MALNUTRITION OR BAD NUTRITION OR UNBALANCED DIET:
A malnutrition or bad nutrition is a state in which body is poorly nourished due to long use of a diet which lacks in essential elements and becomes subject to deficiency diseases and other disorders. Such diet is also known as unbalanced diet.

EFFECT OF UNBALANCED DIET:
The statistical survey data of food and nutrition showed that 30% of population was suffering from the diseases of malnutrition (Faulty nutrition).

• Diseases like decayed and crocked teeth
• Bone deformation
• Lack of mental alertness and
• Under weight

were real outcome of the unbalanced food and diet.

Q.3: Illustrate of elements of nutrition.
Ans: ELEMENTS OF NUTRITION:
The essential elements of nutrition are:

• Adequate calories
• Vitamins
• Mineral salts
• Water

Our body needs these elements in our diet, daily for healthy performance. Such diet is known as a balanced diet.

(A) CALORIES:
The energy and the fuel value of foods is measured in calories and is define as:

"The amount of heat required to raise the temperature of 1 Kg of water by 1°C."

It is denoted by capital C or kilo calories (kcal).

Main Source Of Calories:
Almost all the physiological activities of the body are energy dependent and this comes from the break down of carbohydrates, fats and proteins, the three major nutrients. Carbohydrates and to lesser extent fats are the cheaper sources of the calories than the proteins.
The quantity of food needed to provide required calories for an individual could be calculated as follows:

Carbohydrates give 4 calories per gram

Fats give 9 calories per gram

Proteins give 4 calories per gram

(i) Carbohydrate intake:

• Carbohydrates are the cheap and an efficient source of energy for animals.
• Carbohydrates furnish 60-80% of the total calories intake.

Daily requirement:

• A minimum quantity of 5g of carbohydrate per 100 K cal of the total diet is necessary to prevent the development of ill-effects of fasting or of high fat and protein diet.

Main sources: of carbohydrates are:

• cereals or grains-wheat, maize, rice, oats, barley, sorghum and millet.
• roots and tubers-Potatoes, sweet potatoes.
• sugar, honey, beat roots, fruits and sugar-cane.

(ii) Fat Intake:

• Fats also provide energy double than that of proteins or carbohydrates and therefore they serve an effective source of energy store in both animals and plants (seeds).
• The available fat sources also provide the fat soluble vitamins.

Daily requirement:

• The minimum daily requirement of appropriate fats varies from 15-25 g per day depending upon the intake of calories from other sources of diet.
• The level of recommended fat can go up to 100 g/day, for calorific purposes.
• 35% of the total calories required per day, are acquired from fats containing 10% poly unsaturated fatty acids and 10% saturated fatty acids.

Main sources of Fats are:

• Animal sources -Tallow, butter
• vegetable source - Oils from seeds of all kinds of sunflower, cotton seed, coconuts, soybean and mustard.

(iii) Protein Intake:

• When the required calories per daily an energy supplying diet are not adequately met by the carbohydrates or fats, the proteins do furnish energy.
• Protein as nutrient,is important for the maintenance of body than to supply calories.
• Proteins can also supply some amino-acids which like glucose function as an energy donor, that fat can not do so. The energy deficiency is always accompanied by the symptoms of proteins deficiency and results in certain ailment.

Daily requirement:

• It varies from body to body

 Main sources of protein are:

• Meat
• Milk and eggs
• Pulses, beans, peas, lentil
• Edible seeds, nuts and oil containing fruits.

(B)VITAMIN INTAKE:

• Vitamins are necessary food factors which act as stimulant 
• Chemically vitamins are organic in nature and are classified according to their solubility as:
  (a) fat soluble vitamins such as A, D, E, K
  (b) water soluble vitamins such as B-Complex and C.

Daily requirement:

• They are required only in small amounts in the range of milligrams per day.
• Water soluble vitamins are more readily absorbed than the fat soluble and are not stored in the body thus taken in excessive amounts than the body requirements and are excreted.
• Fat soluble vitamins are stored in large amounts, mainly in the liver hence need not be taken daily.

Main Sources: of vitamins are:

• Milk, egg
• green vegetables
• cereal grains and wheat grains

Side Effects Of Excess Vitamin Intake:

• Repeated intake in excess amounts of fat soluble vitamins causes severe toxic effects.
  For instance vitamin A is required for normal growth, for vision in dim light and for keeping skin and the mucous linings of the body healthy. If it is taken as little as 7.5 mg per day over a period of 20-30 days.
  The excess of vitamin A will cause an increase in cerebral spinal fluid pressure, headaches and irritability.
• To prevent wasting of many vitamins, the rigorous treatment of washing or refinement of cereal grains or cooking should be avoided.

(C) MINERAL INTAKE:

• Inorganic elements present in diet do not supply any energy / calories. Their role in the diet is equally important for maintenance, building and rebuilding of tissues.
• Only 23 elements have been observed to be essential for life.
  Out of these, eleven are non metals (C,H, 0, N, S, P, Cl, F, 1, B, Si) and
  The rest are metals (Ca, Na, K, Mg, Fe, Cu, Zn, Co, Al, Ni, Mo, Se).

Daily requirement:

• Every element has own range.
• Requirement of the minerals varies from 100 mg or more, to a few micro grams per day. The elements required in microgram, are Cu²⁺, Co²⁺, Ni²⁺, Al³⁺ etc.

Main sources: of minerals are:

• Eggs, meat, and cereals are common acid forming foods.
•  Fruits, vegetables and milk are common base forming food.
•  Sugar and fats are among neutral foods.
• Many of these elements are usually found as ions, such as Fe²⁺, Na⁺, K⁺, Mg²⁺, SO₄^2-, Ca²⁺, CO₃^2-, N0_-3^-.

Side effect:
The concentration of these ions present in body are maintained within narrow limits and small variations result in many abnormal biological functions.

Uses:
Among all H, C, N, 0, Na, K, Mg, Ca, S, P are of universal importance, as:

• The minerals are useful to maintain pH, osmotic pressure and act as ion antagonists.
• Bones and teeth require calcium and phosphorus.
• Iron is picked up for the production of hemoglobin and cytochrome system of body.
• Iodine is needed in thyroxine, the hormone of thyroid gland.
• Mineral salts control acid-base balance of the body, and as co-factors of the many enzymes and thus activate the metabolic system. 

(D) WATER INTAKE:

• About 70% of the body weight is water, which remains constant. The total water lost per day from the body is being balanced by the water intake per day.

Daily requirement:

• The water requirement of the body per day is about 2.5 to 3 litres which is gained from three different sources mainly fluids, food, and the same amount is being lost through urine, skin (perspiration), lungs (expiration) and faeces.

Main sources: of water are

• Ground water
• rivers
• springs

Uses:

• The daily intake of water is the most important item of the diet. Because an individual without food may survive for a month, but without water one can not live more than 15 to 16 days.
• Transportation of different material inside body.
• Regulate body temperature.

Chemistry For HSC Part 2 - Chapter No.11 - MCQs and Fill In The Blanks

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Chapter No.11
Chemical Industries In Pakistan
Multiple Choice Questions - [MCQs]

1. Fertilizers maintain the pH of soil:
a) From pH 7 to 8 ✓
b) Above pH 10
c) Below pH 3
d) None of the these

2. Urea, Ammonia nitrate and ammonium sulphate are examples of:
a) Nitrogenous Fertilizers ✓
b) Potassic Fertilizers
c) Phosphatic Fertilizers
d) None of these

3. Urea is an excellent nitrogenous direr which contains nitrogen about:
a) 36%
b) 47% ✓
c) 80 %
d) 60%

4. The most commonly and widely used nitrogenous fertilizer in Pakistan is:
a) Nitrolin
b) Urea ✓
c) Ammonium Sulphate
d) Ammonium Nitrate

5. The phosphatic fertilizer obtained by mixing phosphorite with sulphuric acid in special chamber is called
a) Super Phosphate ✓
c) Di ammonium Phosphate
b) Triple Phosphate
d) None of these

6. Fertilizers that are derived from plants and animals are called:
a) Artificial Fertilizers
b) Natural Fertilizers ✓
c) Synthetic Fertilizers
d) None of the above

7. Artificial or Mineral fertilizers generally contain:
a) N, P or K ✓
b) C, H or 0
c) C, H or N
d) None of the these

8. Formula of Triple phosphate is:
a) Ca₃(PO₄)₂
b) Na(H₂PO₄)₂
c) 3Ca(H₂PO₄)₂✓
d) None of these

9. Which can be used in hard water effectively without any wastage in the form of scum:
a) Soap
b) Detergent ✓
c) None of these
d) Both of these

10. A transparent amorphous substance obtained by the fusion of various metallic silicates is called:
a) Plastic
b) Rayon
c) Glass✓
d) None of these

11. A glass which is a mixture of sodium silicate and calcium silicate is called:
a) Soda glass ✓
b) Pyrex glass
c) Lime glass
d) Coloured glass

12. The glass apparatus used in chemistry laboratory is made up of:
a) Soft glass
b) Lime glass
c) Flint glass
d) Pyrex glass ✓

13. Blue colour glass are made by adding:
a) Fe⁺⁺
b) Fe⁺⁺⁺
c) Co ✓
d) Ni

14. The best phosphatic fertilizer containing high % of assimilable P₂O₃ is:
a) Super Phosphate
b) Triple Phosphate ✓
c) Phosporite
d) None of these

15. Which is the better cleaning agent:
a) Soap
b) Detergent ✓
c) None of these
d) Both of these

16. The fibers obtained from cotton, jute, silk wool are called:
a) Artificial fibers
b) Synthetic fibers
c) Natural fibers ✓
d) Semi-synthetic fibers

17. Which is the naturally occurring polymer:
a) Polythene
b) PVC
c) Proteins ✓
d) Propylene

18. Which is not a natural polymer:
a) Silk
b) Wool
c) Leather
d) Nylon ✓

19. Which of the following is not a polymer:
a) Rubber
b) Cellulose
c) Fructose ✓
d) Protein

20. The monomer of PVC is:
a) Succinic acid
b) Vinyl chloride ✓
c) Propylene
d) Glycol

21. Teflon is a polymer of:
a) Polytetra fluoro ethylene ✓
c) Polytetra fluoro butylenes
b) Polytetra fluoro propylene
d) None of the these

22. The natural polymer among the following is:
a) Polyethylene
b) PVC
c) Teflon
d) Cellulose ✓

23. The substances added to soil to provide one or more nutrient elements essential for plant growth are called.
a) Fertilizers ✓
b) Salts
c) Minerals
d) Detergents

24. The percentage of Nitrogen in Ammonia is:
a) 18%
b) 45%
c) 65%
d) 82% ✓

25. Which are Sodium or Potassium salts of long chain fatty acids?
a) Fertilizers
b) Soap ✓
c) Detergents
d) Nylon

26. Boron oxide and Silica are the main constituents of:
a) Pyrex glass ✓
b) Soda-lime glass
c) Hard glass
d) Flint glass

27. Fertilizers maintain the pH of Soil at:
a) 7.0 - 8.0 ✓
b) 4.0 - 6.00
c) 1.2 - 42
d)12.0 - 14.0

28. Bakelite is formed by the combination of:
a) Phenol and Formaldehyde ✓
b) Phenol and Acetaldehyde
c) Benzene and Phenol
d) Benzene and Alcohol

29. The materials, which increase the mechanical strength of plastics and their resistance to fire, are celled:
a) Fillers ✓
b) Plasticizers
c) Pigments
d) Stabilizers.

30. The glass used in making electric bulbs is called:
a) Soda glass
b) Lime glass
c) Pyrex gloss
d) Flint glass. ✓

31. Which of the following is Thermosetting plastic?
a) Bakelite ✓
b) Polyethylene
c) Polystyrene
d) None of these.

Fill in the blanks:

1. The soil having pH above 10 or below 3 is sterile.
2. Phosphatic fertilizers accelerate fruit formation, gowth and development and increase resistance to diseases.
3. In water-based paints, solvent is water which carries a pigment or emulsion.
4. Fillers are inert, solid substances like China clay, talc, which are added to the paint to increase its durability.
5. Detergents are soapless cleaning agents.
6. Glass is a super-cooled liquid of artificial silicates.
7. Serious disadvantage of synthetic detergents is that they're not Biodegradable.
8. A type of plastic which softens on heating and becomes hard on cooling is thermoplastic.
9. PVC is manufactured by polymerization of vinyl chliride.
10. Terylene is mainly used in clothing and fishing lines.

True or False:

1. Thermosetting plastics become hard on heating. True
2. The widely used thinner for paints is Turpentine oil. True
3. Polyvinylchloride is a polymer, which is used in the manufacture" of chewing gum. False
4. The mixture of Sodium and Calcium silicates is called Nylon. False
5. Such substances which are not soaps by nature possess cleaning properties, are called detergents. True
6. Nylon is made by treating Hexamethylene diamine with Adipic acid. True
7. Plasticizers are the chemicals added to synthetic plastics to make them soft and flexible. True
8. Detergents cannot work in hard water.False
9. Soft glass is ordinary soda-lime silicate. True
10. Triple phosphate contains phosphorus nearly three time phosphate that of super phosphate. True

Chemistry For HSC Part 2 - Chapter No.11 - Questions And Answers

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Chapter No.11
Chemical Industries In Pakistan
Questions And Answers

By Sir Asif Izhar (Anees Hussain)

Content

• Fertilizers
• Detergents
• Glass
• Rayon (Fibre)
• Plastic
• Paints

Q.1: What is a fertilizer? Give names and uses of some of the fertilizers.

FERTILIZER:

"Fertilizers are the substances which contain elements essential for the plant growth and which are introduced into the soil to obtain increased amount of crop regularity."
Nitrogen, phosphorus and potassium containing salts are specially important for the plants.

OR

"Fertilizers are commonly inorganic salts and containing elements such as nitrogen, phosphorus, potassium etc, which are very essential for the growth and development of plants. The yield of agricultural crops can be increased by introducing fertilizers to the soil."

NEED OR USES OF FERTILIZERS:
Fertilizers stimulate the process of metabolism is the plant cells. The need of fertilizers are due to three reasons.

• To make up the deficiency of elements (like N, P, K) and become fertile again.
• To give an additional supply of food.
• To maintain pH of the soil near neutrality or slightly alkalinity i.e from pH 7 to 8. The soil having pH above 10 or below 3 is sterile.

CLASSIFICATION OF FERTILIZERS:
There are two types of fertilizers, depending upon the source and chemical nature:

1. Natural or Organic Fertilizers
2. Synthetic or Mineral Fertilizers

NATURAL OR ORGANIC FERTILIZERS:
These are derived from Plant and animals and may be organic or inorganic. They includes manures and peats for e.g

• Plant matter like oil cakes of cotton seed meal.
• Animal manure and peats like cow dung, sheep dung, and human excretion.
• Animal matter like ground fish and other animal products.
• Example of inorganic natural fertilizers are rock phosphate and Chillie salt peter etc.

Uses: Natural fertilizers provide more nutrient than synthetic fertilizers.

SYNTHETIC OR MINERAL FERTILIZERS:
Mineral fertilizers are obtained from mineral raw materials. These are preferred on natural fertilizers because they contain exact percentage of elements (e.g. Nitrogen and Phosphorus) as required for an specific crop. They are also called artificial fertilizers.
The important mineral fertilizers are:

a) Nitrogen Fertilizers:
Fertilizers containing nitrogen as essential elements are called "Nitrogenous Fertilizers". These fertilizers are Water soluble. Important nitrogen fertilizers are given below:

1. Urea (NH₂ - CO - NH₂): It contains 46% nitrogen.
2. Ammonia NH₃: It has 82 % nitrogen.
3. Ammonium Nitrates (NH₄NO₃): It has 33 % nitrogen and is an ideal nitrogen fertilizer.
4. Ammonium Sulphate {(NH₄)₂SO₄}: It is a favored fertilizer because it is less hydroscopic and can be handled safely. It contain only 21% nitrogen.

Importance or Uses of Nitrogen:

1. It is necessary in the early stage for the rapid growth of plants.
2. It is main constituent of proteins.
3. It imparts green color to the leaves.
4. It increase the yield and quality of plants.
5. These help in the developments of root leaves and stem.

b) Potassic Fertilizers:
Fertilizers containing potassium as essential element are called "Potassic Fertilizers", such as:

1. Chile saltpeter or Potassium Nitrate, KNO₃.
2. Potassium Sulphate K₂SO₄.

Importance or Uses of Potassium:

1. It provides potassium to the plant or soil.
2. It is required in the formation of starch, sugar and fibrous material.
3. It resist plant diseases.
4. It makes plant strong by making root healthy.
5. It helps in ripening of seeds, fruits and cereals.

c) Phosphatic Fertilizers:
Fertilizers containing phosphorous as essential element are called "Phosphatic Fertilizers." The raw material for these fertilizers is phosphate rock or phosphorite, [Ca₃(PO₄)₂]₃CaF₃, which being water insoluble can not be assimilated directly by the plants. Therefore it should he converted into soluble form before it can be taken in through the roots. The important phosphorus fertilizers are given below:

1. Super Phosphates:
   The mixture of calcium hydrogen phosphate Ca(H₂.PO₄)₂ and gypsum or calcium sulphate (CaSO₄) is called super phosphate. It contain 18-20% phosphorous in the form of assimilable P₂O₅, and also called phosphate of lime.
   It is obtained by mixing phosphorite with sulphuric acid in special chambers. Following reaction takes place:
   
   
   
   
   
2. Triple phosphate:
   It is also a good phosphorus fertilizer and prepared by the reaction of phosphorite rock with phosphoric acid.
   

   Ca₃(PO₄)₂ + 4H₃PO₄ ⟶ 3Ca(H₂PO₄)₂

   
   

It contain about 48% phosphorus in the assimilable form of P₂O₅ which is nearly three time that of ordinary super phosphate.

Importance or Uses of Phosphorus:

1. It provides phosphorous to the plant soil.
2. It stimulates the early growth and development of plants.
3. It accelerates the seed and fruit formation processes.
4. It also resist plant against diseases and frost.

SCOPE OF FERTILIZERS IN PAKISTAN:
Pakistan is an agricultural country It does not only prepare fertilizers of its own demand but also exports in a bulk.

INDUSTRIES IN PAKISTAN:
The important fertilizer factories of Pakistan are enlisted below:-

1. TSF Plant and urea fertilizer plant, Hazara.
2. Faisalabad Fertilizer Ltd.
3. Pak American Fertilizer Ltd. at Daud Khel.
4. Single Super Phosphate Plant at Jaran Wala.
5. Natural Gas Fertilizer Factory, Multan.
6. Dawood Urea Plant, Lahore.
7. Dhariala Potash Fertilizer Project, Dhariala.
8. Fauji Urea Complex, Sadiqabad.
9. Exxon Fertilizer Co. Dahrki.
10. Urea Plant, Mirpur Mathelo.

Q.2: What is a detergent? Describe the cleaning action of detergent.

DETERGENTS:

"Detergents are complex organic salts with a long carbon chain and defined as Sodium or potassium salt of alkyl or aryl sulphonated acid."
Detergents are soapless cleansing agents. They react with the ions of the salts that cause hard water, thereby producing soluble compounds in which dirt and grease are readily carried away.

Structure:

All the detergents have the same basic structure. They are made up of two parts:

1. Hydrophobic (Water repelling group):
   Hydrophobic part is the long hydro carbon chain which is covalently bonded. Being nonpolar in nature, it attracts oil and grease which are also nonpolar.
2. Hydrophilic (Water loving or attracting group):
   Hydrophilic part is small ionic group like sulphonate (SO₃^-1 ), sulphate (-O-SO₃^-2 ), quaternary ammonium groups (NR₄⁺¹ ) or hydroxyl groups (-OH^-1 ). 

Difference between Soap and Detergent

S.NO.	SOAPS	DETERGENTS
1.	Calcium and magnesium salts are insoluble in water.	Calcium and magnesium salts are soluble in water.
2.	Hydrophilic part contains long chain of carboxyl group (C00-).	Hydrophilic part contains sulphonate (SO3-1 ), sulphate (-O-SO3-2 ), quaternary ammonium groups (NR4+1 ) or hydroxyl groups (-OH-1 ) etc.
3.	Hydrocarbon chain of hydrophobic part can be broken down by bacteria.	Hydrocarbon chain of hydrophobic part cannot be broken down by bacteria.
4.	It can be obtained by the natural resources	They are the synthetic materials.
5.	They produces scum in hard water	Hard water do not effect its cleansing.
6.	Examples are Lux, Palmolive, Capri etc.	Examples are Surf, Arial, Lquid handwash etc.

Cleansing Action Of Detergents:

Remove Oil Or Grease stains:
A detergent removes dirt very easily. The presence of two groups (hydrophobic and hydrophilic) allows the mixing of water with non-polar substances such as oil and grease. Grease is an organic covalent compound. The hydrophobic part of the detergents readily dissolves in grease (both being non-polar). The hydrophilic part of the detergent dissolves in water (both being polar) so that slight agitation removes the grease and it is carried away with the water along with dirt.

Merits Of Detergents:

The calcium and magnesium salts of detergent are soluble in hard water whereas corresponding salts of soaps are insoluble and reduces the foaming and cleansing action. This means that a detergent can be used in hard water and resulting products are soluble. Therefore, there is no wastage in the shape of scum (Precipitate).

Demerits Of Detergents:

One disadvantage of detergent over soap is that hydrocarbon chain, unlike those of soaps which are derived from food substances (fats and oils) cannot be broken down by bacteria and dispersed. Therefore, bacteria remains in water.

Scope In Pakistan:

Pakistan has developed a large detergent industry. These detergent are used as washing powder and washing liquids and sold under various brand names.
Examples: Brite, Surf etc.

Q.3: What do you know about glass ? Describe in detail.

GLASS

"Glass is one of the most important artificial silicates. Glass is a super cooled liquid i.e. a solid solution without crystallization. The molecules are arranged in random position that's why a glass does not show sharp melting point."

Preparation:

Ordinary soft glass or soda glass is a mixture of sodium silicate (Na₂SiO₃) and calcium silicate (CaSiO₃). It is produced by heating sand, soda (Na₂CO₃) or sodium sulphate and lime stone (CaCO₃) in a furnace at 1400°C.

Na₂CO_{3 (s)} + SiO_{2 (s)} ⟶ Na₂SiO_{3 (s)} + CO_{2 (g)}

CaCO_{3 (s)} + Si0_{2 (s)} ⟶ CaSiO_{3 (s)} + CO_{2 (g)}

OR

Na₂CO₃ + CaCO₃ + 6SiO₂ ⟶ 2CO₂ + Na₂O.Ca0.6SiO₂

Where Na₂O.Ca0.6SiO₂ is glass.

Properties:

1. Glass is not a true solid because molecules are not arranged in a definite pattern.
2. It is a super cooled liquid i.e a solid solution without crystallization.
3. The molecules of glass are arranged in random position as in case of liquids that's why a glass does not have sharp melting point.
4. On heating it gradually becomes more and more plastic in nature.
5. Glass is attacked by hydrofluoric acid. This acid is used to make designs on glass. This process is called etching.

Types of Glass:

There are several types of glass:

•  Ordinary window glass:
  is a mixture of sodium and calcium silicates. It is manufactured from sand, soda and lime-stone. It is further classified as:
  a. Common Glass: It is used in making bottles.
  b. Soda Glass: It is fusible and also called soft glass. It is expensive type of glass. We can use these type of glasses in bottles, windows and glass sheets.
  c. Water Glass: It is a thick liquid and used as adhesive in paper as fire proofing.
  d. Quartz Glass: It is used in making dishes, tubes etc. It resist heat upto 1000 °C.
  
  
• Refractory potassium glass:
  is obtained by using potash K₂CO₃ instead of soda. This is used for making chemical glass ware.
  
  
• Pyrex glass:
  is a borosilicate mixture which is produced by using boron oxide place of some of silica; this glass can withstand sudden changes of temperature. Pyrex glass is used in manufacturing of apparatus in laboratory. In fact pyrex glass has a very low coefficient of expansion i.e it expands greatly when heated. Pyrex glass is not manufactured in Pakistan.
  
  
• Crystal Glass:
  It is prepared by silica, lead oxide (PbO), Potassium carbonate and CaCO₃. It is very expensive and a heavy glass. It is used in decorative show pieces.
  
  
• Coloured glass:
  is manufactured by adding certain transition metal oxides in ordinary glass. For example CuO gives light blue, CoO dark blue and Cr₂0₃ green. Addition of selenium oxide and zinc oxide gives red coloured glass.

Position Of Glass Industries In Pakistan:

In Pakistan there are about 25 glass Industries which arc producing about 75.000 tons of glass per year. Now a days, there Is definite improvement in the quality of glass.
The names of some of the glass producing factories are:

• Indus Glass Work. Hyderabad.
• Toyo Nasik Glass Factory, Lahore.
• Khawaja Glass Works, KPK.

Q.4: Write short note on synthetic fibers.

FIBRE:

There are two types of fibres:
1. Natural Fibre:
Silk is a natural fibre obtained by silk worm.

Synthetic Or Artificial Fibre:
Synthetic fibres are the man made polymers which consist of macro-molecules (Poly = many; macros = parts).
Preparation:
The polymers are built by linking together of many smaller units called monomers. This process is called polymerization. Synthetic fibres are usually prepared by condensation polymerization in which linking of two different substances occurs with the elimination of water. The resulting polymers are known as copolymers.
Examples:
The examples of important synthetic or artificial or man-made fibres are Nylon, Rayon, Dacron,Terylene etc.
Advantages:
Among the advantages of synthetic fibers are:

1. Lightness of weight
2. Ease of ironing
3. Softness and
4. Heat retention or heat conductivity.

Position Of Synthetic Fibre Industries in Pakistan:
The manufacture of synthetic fibers is one of the branches of the chemical industry that has been developing at a very fast rate in our country.
Govt. of Pakistan is taking all the measures to increase the production of all kinds of artificial and synthetic fibers in the coming years. A number of industries have been established to manufacture synthetic fibers.

1. RAYON (FIBRE):

"Rayon is synthetic cellulose fibre and is considered as the man-made fibre. It has soft silky appearance and commonly use as silk apparels."
A French scientist "Chardonnet". discovered it in 1884, while he was investigating the silk worm disease.
Preparation:
Rayon is a fibre obtained mechanically from silk worms. The starting material is cellulose. The silk worm on mulberry tree eats cellulose, digests it and changes it into silk which comes out in a viscous form and solidifies on contact with air and becomes silk thread. Man does the same with cellulose, when preparing silk mechanically.
Preparation Of Viscose Rayon:
is manufactured from cellulose when it is digested with sodium hydroxide solution. When carbon disulphide is passed through the solution, a mixture of sodium cellulose xanthate is formed which is soluble in NaOH.

Due to very high viscosity, the silk thus obtained is called viscose rayon. The solution is forced through a spinneret into H₂SO₄ bath where cellulose is precipitated as fine threads. This artificial silk is cheaper than cellulose acetate silk or nitrocellulose silk. It is produced in the largest quantity.

Q.5: How nylon is prepared and state its characteristics?

2. NYLON:

(The name come from New York and London)
"It is a synthetic fibre and developed for the production of stackings and other wearing apparel. It was introduced to public at New York worlds fair 1939."
Nylon is the type of polymer in which amide linkages (-CONH-) hold the chain together. Chemical structure of nylon is not similar to that of material silk but resembles it to certain extent.
Preparation:
Nylon is made of diamines and dibasic acids which can be synthesized from the common raw materials i.e coal, water and air.
Adipic acid (hexan dioic acid) when heated with hexamethylene diamine under nitrogen at 200 °C. a polymerization process occurs to give hexamethylene di-ammonium adipore commonly known as Nylon-6,6. The name Nylon-6,6 is also derived from the fact that both the components consist of six carbon atoms each.

Elimination of water forms the amide linkage. This is the same type of linkage found in proteins.

Merits:
1. It is stronger than other natural fiber.
2. It has good flexible tenacity

Uses:
It is mostly used:

• for stacking and other wearing apparel.
• to make fibre for clothing and carpeting.
• to make filaments for fishing lines and ropes.
• to make bristles for brushes tires.
• to make parachute fabrics.
• to make moulded objects such as gear and bearings.

TERYLENE:

Terylene is the most important polyester fabric which is formed from many ester molecules. It is a synthetic fibre.
Preparation:
It is obtained by heating ethylene glycol and tereph-thalic acid at 300 °C in the presence of metal oxide. During condensation polymerization, water molecule is eliminated giving rise to ester linkage.

It is commonly called Dacron or Polyester.

Uses:
Terylene is mainly used:

• in making bottles and sheets.
• in making clothing and fishing lines.
• in water tanks.

Q.6: What do you know about plastics?

PLASTICS:

These are synthetic polymers and physically solid material which contract on heat and then cast into moulds.
Physical State: These are macromolecules, formed by addition or the condensation polymerization of simple, organic molecules. In other words, plastics are also polymers formed from monomers.
For example: polyethylene or polypropylene

Common Plastics:
1. Polyethylene Or Polyethene:
Ethylene is an unsaturated hydrocarbon polymerized in presence of suitable catalysts at 200 °C and 1000 atmospheric pressure. The extra bond opens, forming an unstable molecule which joins with many others of its own kind to form macro molecules called polyethylene or Polyethene.

n = degree of polymerization. (here n= 600 to 1000)
Uses:
Polyethylene is the most common plastic used:

• to form polythene bags and to package foods.
• in making bottles and pots.

2. Poly propylene:
It is superior to polyethylene in its resistance to breakage and to temperature. Polypropylene is prepared by addition polymerization of propene at 200 °C and 1000 atmospheric pressure.
Uses:
Polypropylene is the most common plastic used:

• to form polythene bags and to package foods.
• in making bottles and pots.

3. Perspex Or Transparent Plastic:
It is a polymer of (or prepared by addition polymerization) of methyl methacrylate, an ester of an unsaturated acid.

Glass like transparency and resistance to weathering make it useful as a glass substitute.
Uses:
The transparent plastic or perspex is used to make:

• combs and hair brushes
• in aircraft windows
• reflectors on auto vehicles
• T.V guard screens and
• Street light fittings.

4. PVC or Poly vinyl chloride:
It is the polymer of vinyl chloride (CH₂ = CHCl).
Preparation:
In the presence of catalyst hydrogen peroxide at the temperature of 80°C, vinyl chloride polymerizes to poly vinyl chloride.

Uses:
PVC is used:

• for the insulating., covering for electrical cables
• for the manufacture of gramophone records, suit-case coverings etc.
• for making imitation leather.
• for making floor covering
• for making rubber like texture

5. PVA or (Poly vinyl acetate):
It is the polymer of vinyl acetate (CH₂ = CHO.CO.CH₃).

Uses:
It is used:

• as an adhesive material
• as a binder for emulsion paints
• in the manufacture of chewing gum
• in the water proofing industries and in the textiles industries.

6. Bakelite:
It is a polymer of phenol and formaldehyde.

Uses:
Bakelite is used to make:

• buttons, switches, electrical boards
• cameras, radio and
• telephone components.

Components Of Plastics:
Plastics entirely consist of high molecular compounds (polymers).To produce specific properties, various compositions are used by mixing the polymer with the following substances.
1. Plasticizers:
Addition of plasticizer reduces the brittleness and improve the elasticity of plastics. They are organic substances in nature. One disadvantage of artificial plasticization is an increase in the rigidity and loss of elasticity when solvent evaporates.

2. Fillers: Usually increase the mechanical strength of plastics and resistance to fire. It also make the savings of the more costly polymer. Various fillers which are used are wood flour, saw dust.

3. Stabilizers:
It is antioxidant and prevent the chemical degradation of plastic.

4. Pigments:
These are used to color the plastic.

Properties Of Plastic:

• Plastics are generally tough, resistant to the action of acids and alkalis and not very much affected by the change of temperature.
• The plastics have a fair range of deformability and mouldability due to which articles of any desired shape and form can be manufactured.

Plastic Industry in Pakistan:
Plastic industry in Pakistan essentially consists of moulding of plastic powders into various articles of daily use. Modern plastics are assuming an ever increasing importance in our economy.

Types Of Plastic:
Plastics are of two types:

1. Thermoplastic
2. Thermosetting

(i) A Thermo plastic or thermosoftening plastic:
is a material which softens on heating and hardens on cooling. This process of heating, softening, moulding and cooling can be repeated and it does not affect the properties of plastics. Such plastics are easily moulded into shapes but are not very heat resistant.
Examples:
The examples are:

• nitro cellulose
• cellulose acetate and
• vinyl polymers.

(ii) Thermosetting plastics:
are those materials which can be heated only once before they set i.e they can not be reworked. In other words, thermosetting plastics do not soften on reheating.
Examples:
The examples are:

• phenol formaldehyde or Bakelite
• urea formaldehyde
• silicones etc.

Q.7: Write short notes on:
(i) Paints
(ii) Varnishes

PAINTS:

Paints may be defined as liquid products which held in suspension solid colouring matter known as pigments, so blended that such mixture can be applied evenly to a surface for protective and decorative purposes.

OR

The material used to coat over metals (iron articles) to prevent them from corrosion or rusting, and the walls, doors, windows, etc. for the decorative and protective purposes are called "paints".

Components Of Paint:
Paints can be formulated with fantastic variety of colours, textures and resistances. A paint is usually composed of three components:-

1. BINDER (Drying Oil):
   i) A binder which hardens to form a continuous film on a surface.
   ii) It suspends or adhere coloring particles (pigments) in paints.
   iii) It is also known as vehicle.
   iv) In an oil-based paint, linseed oil is often used as a binder.
   
   
2. PIGMENT:
   i) A pigment which supplies the desired colour and opacity to the paint.. 
   ii) These are finely powdered materials and insoluble in organic solvents.
   iii) They protect against weather and provide impermeability to moisture.
   iv) The pigment may be Titanium dioxide, TiO₂ (White), Carbon black (C), Chrome yellow (PbCr0₂), oxides of iron (brown or red) or organic dyes of various colours.
   
   
3. VOLATILE SOLVENT (Thinner):
   i) A volatile solvent which evaporates after application.
   ii) It decreases the viscosity of paints.
   iii) The solvent is usually turpentine, a mixture of hydrocarbons obtained from pine trees.
   
   
4. DRIERS:
   They accelerate the drying of film and make it hard.
   
   
5. EXTENDER:
   i) These are low refractive index inorganic material.
   ii) They are used to reduce the cost of paint.
   
   
6. STABILIZER:
   They stabilize the film and prevent its composition.

Classification Or Types Of Paints:
1. Oil - based Paints:
In an Oil - based paint, Linseed oil is often used as a binder. The solvent is volatile with some pigments as dispersed medium.

2. Water Based Paints:
In Water based paint (Emulsions) a synthetic polymer with rubber like properties is used as the binder. These "Latex" paints are emulsified in water to give a variety of spreading characteristics.
e.g: resin in water, distempers are water - based paints which are consists of pigments compounded with water and adhesive Zinc oxide casein.

3. Latex Paints:
Among the plastics used in latex paints are polyvinyl acetate, polymethyl methacrylate, polystyrene, styrene - butadiene copolymers and polytetrafluoro ethylene (Teflon).

4. Varnish:

Varnish is a mixture of resins, a volatile organic solvent such as ether, and a drying oil such as linseed oil. when it is applied on a surface, forms tough, solid, durable and a glossy film

Paint industry in Pakistan:-

A number of multinational companies are involved in the preparation of paints of various kinds.

Names of some of industries in Pakistan are given below:

1. Berger Robbialac, Karachi.
2. I.C.I. Dulux, Lahore.
3. Buxly's paints, Karachi.
4. Nelson paints, Karachi

VARNISH:

Varnish is a mixture of resins, a volatile organic solvent such as ether, and a drying oil such as linseed oil. when it is applied on a surface, forms tough, solid, durable and a glossy film.
Preparation:
Resin is dissolved in a volatile organic solvent and then a drying oil is added when varnish is obtained.
Method OF Varnish Making And Applying:

• A varnish contains a mixture of resins, a volatile organic solvent drying oils.
• The drying oils (linseed oil) consist of esters of highly unsaturated acids containing two or more double bonds.
• When it is applied on a surface, It exposed to air and absorbs oxygen.
• The volatile organic solvent evaporates quickly.
• It dried up forming tough solid water insoluble film on the surface.
• The glossy appearance is due to the presence of resin.

Q.8: Why white lead has been banned as pigment for paints. Give reason?
White lead having approximate composition [Pb(OH)₂ . 2PbCO₃] was once extensively used, but it has now been banned for interior use due to high toxicity of lead. Infant illnesses have been attributed to the ingestion of chips of old lead paint.

Q.9: What is the difference between a manure and a fertilizer?
Ans: Difference between a Manure and fertilizers:

S.NO.	Manure	Fertilizers
1.	Manure is a natural substances. They are also known as organic fertilizers.	Fertilizer is a human-made or natural substances. They are known as minerals fertilizers.
2.	It is obtained by decaying plant and animal waste	They are obtained from mineral raw materials
3.	Manures are not very rich in essential plant nutrients	Fertilizers are rich in plant nutrient like nitrogen, phosphorous or potassium.
4.	Manure provide a lot of humus to the soil.	Fertilizers does not provide any humus to the soil.
5.	They can be prepared in the fields	They are prepared in factories.
6.	Manure can applied to the soil to enhance its fertility	They can be applied to the soil to improve its fertility and increase the productivity.

Chemistry For HSC Part 2 - MCQs From All Chapters - By Adamjee Coaching Center

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Multiple Choice Questions
From All Chapters

By Adamjee Coaching Center

1. How many elements have been discovered so far?

• 100
• 110
• 120
• 150

2. Which of the following discovery resulted in a revision of the Mendeleev's periodic law?

• The nucleus of atom by Rutherford
• The elements polonium and radium by the curies
• Atomic numbers by Moseley
• X - Rays by Roentgen

3. Who classified the known elements into metals, nonmetals and their derivatives?

• Doberenier
• Al-Razi
• Newland's
• Mendeleev

4. In 1829, a German chemist,_____ made use of the idea of relationship between atomic weights and properties of elements for the classification of elements.

• Doberenier
• Al-Razi
• Newland's
• Mendeleev

5. The law of octaves was given by

• Doberenier
• Al-Razi
• Newland's
• None

6. "Physical and chemical properties of elements are periodic functions of their atomic weight". This is called

• Doberenier's law of Traids
• Newland's law of Octaves
• Mendeleev's Periodic law
• None

7. Lother Mayer arranged the elements in order of their increasing atomic weights and found that

• Physical properties of the elements were the periodic function of their atomic weights.
• Chemical properties of the elements were the periodic function of their atomic number
• Physical properties of the elements were the periodic function of their atomic number.
• Chemical properties of the elements were the periodic function of their atomic weights.

8. Modern classification of elements is based on

• Doberenier's law of Triads
• Newland's law of Octaves
• Mendeleev's Periodic law
• None

9. Which property is same in elements of same group of periodic table?

• Ionization potential
• Electronegativity
• Electron affinity
• Number of valance electrons

10. The valency, ionization energy, electron affinity and electronegativity of elements are related to its

• Atomic weight
• Properties
• Atomic size
• Family group

11. Which of the following is the set of most electronegative elements?

• Na, Mg, Al
• Ca, Sr, Ba
• N, 0, F
• Fe, Co, Ni

12. Which of the following elements has maximum ionization potential?

• Mg
• Al
• Na
• K

13. Each vertical column of the periodic table includes elements with chemical characteristics that are in general

• Non identical
• Similar
• Different
• Similar as well as different

14. Each horizontal row of the periodic table includes elements with chemical characteristics

• Identical
• Similar
• Different
• Similar and different

15. According to the Modern periodic law. the chemical properties of the elements are periodic functions of their

• Density
• Atomic number
• Atomic mass
• Mass number

16. The 3d transitional series contains elements having atomic numbers from

• 22 to 23
• 21 to 29
• 21 to 30
• 21 to 31

17. Elements in group IB, IIB through VIIB are known as

• Rare earth metals
• Transition elements
• Lanthanides
• Actinides

18. The fourteen elements following lanthanum are known as

• Lanthanones
• Lanthanides
• Rare earths
• All

19. Which of the following elements have the larger radius?

• F
• Cl
• Br
• I

20. Nitrogen is comparatively inert element because it has

• Stable electronic configuration
• Low atomic radius
• High electronegativity
• High dissociation energy

21. The trend of change in melting points and boiling points of elements in the period from left to right is graded

• Increase
• First increase then decrease
• decrease
• First decrease then increase

Chemistry For HSC Part 2 - Chapter No.7 - Shorts Answers, Scientific Reasons And Text Book Exercise

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Chapter No.6
Introduction To Organic Chemistry
Shorts Answers, Scientific Reasons And Text Book Exercise

Short Answers

Q.1: Draw and labelled the orbital Structure of Ethane, Ethene and Ethyne.

Q.2: Give the mechanism of the chlorination of methane in the presence of sunlight.

OR

Describe halogenation reaction in alkane.

OR

Describe free radical chain reaction of alkanes with halogen.

Scientific Reasons

Q.1: Why alkanes are called "Parafins"?
Ans: In alkanes all the four valencies of carbon atoms are fully satisfied, they can take up no more hydrogen or any other atom. Thus "fully saturated" in respect of chemical combination, these hydrocarbons are classed as "saturated hydrocarbons.
On account of their feeble chemical activity, they are also called "PARAFFINS" (Latin - Parum affinis = little affinity).

Q.2: Why alkenes or alkylene are called "OLEFINES"?
Ans: Alkenes are unsaturated hydrocarbons, containing a double bond. Since all the valencies of carbon of the carbon atom in alkenes are not fully satisfied, they can take up more hydrogen atoms are called unsaturated hydrocarbons.
The hydrocarbons of this class are frequently called olefines (olefiant = oil forming) as the first member of the class, ethylene reacted with chlorine to form an oily product.

Q.3: What is the qualitative test for unsaturation in ethene (alkene)?
Ans: The addition of Br₂ to ethene (alkene) is frequently used as a qualitative test for unsaturation.
Bromine itself is a dark red-brown liquid, where as both the ethene (alkene) and the addition product are colourless. Thus to test whether a substance is an alkene, we add to it a solution of bromine in CCl₄. If the substance is an alkene or an alkyne the bromine solution will be rapidly decolourized.

Text Book Exercise 

6. Describe simple chemical tests that would distinguish between:
(a) An alkene and an alkane
(b) An alkene and an alkyne
(c) An alkane and an alkyl — halide

Answer:
(a) Chemical tests which are used to distinguish the alkane and alkene
The presence of the double bond in alkenes makes them more reactive than alkanes. This higher reactivity of the alkenes over alkanes distinguish them by following simple tests:

1. WITH BAEYER’S REAGENT
2. WITH BROMINE WATER TEST

Experiment No.1: WITH BAEYER’S REAGENT (Hydroxylation):
Reaction with alkane: No reaction.
Reaction with alkene: In case of ALKENE, dilute and alkaline KMnO₄ solution on addition at room temperature gives a dihydroxy alcohol or glycol. The PINK color of KMnO₄ is changed to the brown precipitated MnO₂ which show the unsaturaion in the molecules of alkene.

This reaction is called the Baeyer's test for unsaturation.

Experiment No.2: WITH BROMINE WATER TEST:
Reaction with alkane: No reaction.
Reaction with alkene: When ethene is treated with a brown solution of bromine water in CCl₄ at room temperature, the bromine solution will be decolorized due to formation of vicinal dihalide (1,2-dibromoethane).

this reaction will occur for unsaturated compounds containing carbon-carbon double bonds.

(b) Chemical tests which are used to distinguish the alkene and alkyne
Terminal alkynes may be distinguished from other alkynes or alkenes because they react rapidly with:

1. Cuprous ions and
2. Silver ions

in alkaline solution to produce copper acetylide and silver acetylide respectively.

Experiment No.1: With Ammonical (Cu₂Cl₂)
Reaction with alkene: No Reaction.
Reaction with alkyne: When acetylene is passed through ammonical solution of Cuprous chloride, Reddish brown precipitate of copper acetylide are formed.

Experiment No.2: With Tollen's Reagent: (Ammonical AgNO₃)
Reaction with alkene: No Reaction.
Reaction with alkyne: When acetylene is passed through ammonical solution of Silver nitrate, a white insoluble silver acetylide are formed.

(c) Chemical tests which are used to distinguish the alkane and alky-halide
Alkyl halide may be distinguished from alkanes because they react rapidly with base.
Experiment: With warm NaOH and Silver Nitrate:
Reaction with alkane: No reaction.
Reaction with alkyl-halide (R-X): The reactivity of alkyl-halide is due to its nucleophilic nature. As Halogen group is highly electronegative and it develops partial positive charge on Carbon-halogen bond and become slightly acidic in nature. On reaction with base it forms salt.

R-X + NaOH → R-OH + NaX 

Add silver nitrate and a precipitate will form:

NaX + AgNO₃ → AgX ↓   + NaNO₃

If,
X= Cl - you get white ppt.
X= Br - pale tan color ppt.
X= I - pale yellow ppt. will formed

7. Which alkane may be obtained by the reduction of:
(a) 2 — bromo propane
(b) Sec — butyl bromide
(c) Isopropyl bromide

Answer:
(a) 2 — bromo propane

(b) Sec — butyl bromide

(c) Iso propyl bromide {same as (a)}

8. Write equations for the formation of hydrocarbon by the action of N a metal on:
(i) Ethyl chloride
(ii) 2 bromo butane
(iii) Methyl iodide

Answer:
(i) Ethyl chloride
When Ethyl chloride is treated with sodium matel butane is formed.

2CH₃-CH₂-I + 2Na ⟶ C₄H₁₀+ 2NaI

(ii) 2-bromo butane
When 2-bromo butane is treated with sodium matel 3,4-dimethyl hexane is formed.

2CH₃-CHBr-CH₂-CH₃ + 2Na → (CH₃)₂-(CH-CH₂-CH₃)₂ + 2 NaBr

OR

(iii) Methyl iodide
When Methyl iodide is treated with sodium matel ethane is formed.

2CH₃I + 2Na ⟶ C₂H₆+ 2NaI

9. A hydrocarbon, C₄H₆ absorbs two moles of hydrogen in the presence of platinum as a catalyst. The reduction product is inert towards bromine and potassium permanganate. Draw possible structures for C₄H₆. What further information is necessary in order to establish the identity of the hydrocarbon?
Answer: When 1 mole of C₄H₆ reacts with 2 moles of H₂ gas, 4 moles of H atoms are added and then the hydrocarbon becomes C₄H₁₀. C₄H₁₀is the molecular formula of a saturated straight-chained alkane, which is inert towards bromine and potassium permanganate. It can be deduced that C₄H₆ would have 2 C=C double bonds or 1 C≡C triple bond.
Hence, there are 4 possible structures for C₄H₆.

10. What are the principal sources of benzene and its homologous?
Answer: Besides aliphatic compounds, large number of compounds were obtained from natural sources e.g. resins, balsams and "aromatic' oils from plants, whose structures at that time were unknown but had one thing in common, a pleasant smell and were thus classified as aromatic (Greek aroma = pleasant smell). These compounds contained a much higher percentage of carbon content than corresponding aliphatic hydrocarbons and majority of simple aromatic compounds contained at least six carbon atoms.
It was also discovered that when these compounds were subjected to various treatment they often yielded benzene or its derivatives. It was thus concluded that aromatic compounds were related to benzene whose molecular formula was found to be C₆H₆.
Benzene was first isolated by Faraday, in 1825 and was found to be one of the constituents of coal tar by Hofmann in 1845. Thus Coal tar and petroleum are the two main or principal sources of obtaining benzene and its derivative on industrial and commercial scale.

11. Draw the structures, of the following compounds:
(i) Benzene
(ii) Toluene
(iii) Ethyl benzene
(iv) Nitrobenzene
(v) P-bromobenzoic acid
(vi) O-dichlorobenzene
Answer:

12. (a) What do you understand by the term "Aromaticity" and how will you explain the stability of benzene molecule?
(b) Draw resonance structures for benzene.
Answer: (a)

(b)

13. What would be the major monochloro product (or products) formed when each of the following compounds reacts with chlorine in presence of ferric chloride?
(i) Ethyl benzene, C₆H₅-CH₂CH₃
(ii) Trifluoromethyl benzene, C₆H₅-CF₃
(iii) Methyl benzoate, C₆H₅COOCH₃

Answer:
(i) Ethyl benzene, C₆H₅-CH₂CH₃

(ii) Trifluoromethyl benzene, C₆H₅-CF₃

(iii) Methyl benzoate, C₆H₅COOCH₃

Chemistry For HSC Part 2 - Chapter No.7 - Benzene (Reaction and Orientation)

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Chapter No.6
Introduction To Organic Chemistry
Benzene
(Reaction and Orientation)

Addition Reactions Of Benzene

Benzene behave like a saturated hydrocarbon towards addition reaction inspite of the fact it is highly unsaturated hydrocarbon. The reasons of stability of benzene towards addition reaction are given below:
1. The formation of pi - molecular orbital cause the stability of benzene and stabilization energy of pi molecular orbital in Benzene is 36 K cal/mole.
2. This stabilization energy due to the resonance is so great that pi bond of molecule will normally resist breaking. This explain the lack of reactivity of benzene towards the addition reaction.

Orientations Of Benzene