Chemistry SSC II

Chemistry Solved Exercise Class 10

 

Chapter 9 Chemical Equilibrium

Q.2 Give Short answers.

1. Differentiate between forward and reverse reactions. 

Forward Reaction	Reverse Reaction
It is written from left to right.	It is written from right to left.
Reactant produce products	Products produce reactants.
Initially rate is fastest and gradually slows down.	Initially rate is zero and gradually speeds up.

1. What is chemical equilibrium? 
   It is a state of a chemical reaction in which forward and reverse reactions take place at the same rate. 
2. State the law of Mass Action. 
   Two chemists C.M Guldberg and P. Waage in 1864 proposed this law. This law states that the rate at which a substance reacts is directly proportional to its active mass and the reaction proceed is directly proportional to the product of the active masses of the reactants.

1. State the conditions for equilibrium. 

Conditions for equilibrium are:

• Concentration of none of the reactants or products is changed. 
• Temperature of the system is kept constant 
• Pressure or volume of the system is kept constant. 

1. What is the importance of equilibrium constant for a chemical reaction? 

Importance of equilibrium constant:

• It is used to determine the equilibrium concentration of equilibrium mixture. 
• It is used to predict the direction of a chemical reaction. 
• It is used to predict the extent of a chemical reaction. 
• It is used to predict the effect of change in conditions of the chemical reaction on equilibrium state. 

Q.3 Following reaction can occur during lightning storms. 

3O₂ 2O₃ 

For this reaction write 
i. Equilibrium Constant Expression. 

 

ii. Determine the units of equilibrium constant. 

 

 

 

iii. Forward and reverse reactions. 

Forward Reaction = 3O₂  2O₃ 
Reverse Reaction = 2O₃  3O₂ 

Q.4 Coal reacts with hot steam to form CO and H2. These substances react further in the presence of a catalyst to give methane and water vapour. 

CO + 3H₂  CH₄ + H₂O 

i. Write forward and reverse reactions for it. 

Forward Reaction = CO + 3H₂  CH₄ + H₂O 
Reverse Reaction = CH₄ + H₂O CO + 3H₂ 

ii. Derive K_c expression for the reaction. 

iii. Determine units for Kc. 

 

 

 

Q.5 Write equilibrium constant expression for each of the following reactions. 
i. H₂O H2 + ½O₂

ii. CO + 2H₂  CH₃OH 

iii. COCl₂  CO + Cl₂ 
iv. 4HCl + O₂  2Cl₂ + 2H₂O

Q.6 Determine the units of equilibrium constants for the following reactions. 
i. COCl₂  CO + Cl₂ 

=

 

ii. H₂ + I₂  2HI 

=

iii. 2H₂ + O₂ 2H₂O 

=

iv. N₂ + 2O₂  2NO₂ 

=

Q.7 State the ways that equilibrium can be recognized?

• It can be determined by determining concentration of reactants and products at regular intervals.
• When constant concentration of products and reactants are observed, the reaction is at equilibrium.
• This can be done by both physical methods as well as chemical methods such as titration, spectroscopy etc.

Q.8 Describe the macroscopic characteristics of an equilibrium reaction. 

Forward Reaction	Reverse Reaction
It is written from left to right.	It is written from right to left.
Reactant produce products	Products produce reactants.
Initially rate is fastest and gradually slows down.	Initially rate is zero and gradually speeds up.

Q.9 Bromine chloride (BrCl) decomposes to form chlorine and bromine. For this reaction write

i. Chemical Equation: 

2BrCl Br₂ + Cl₂ 

ii. Kc Expression: 

 

iii. Units of K_c: 

=

Q.10 K_c expression for a reaction is given below. Write chemical equation for this reaction and derive the units of K_c. 

a. Chemical Equation: 

N₂O₄  2NO₂ 

b. Unit of K_c: 

=

Q.11 For which of the following reactions are both reactants and products likely to be found when the reaction appears to be complete? Justify

i. C + O₂ CO₂

ii. 2HF H₂ + F₂

In reversible reactions both reactants and products likely to be found when the reaction appears to be complete. So in reaction (ii) arrow shows that is a reversible reaction. So reaction (ii) appears to be complete.

Q.12 Cobalt chloride forms pink crystals (CoCl3.6H2O). When they are heated water is evolved and they turn blue (CoCl3). Explain how you could use Cobalt chloride as a test for water, argue. 

COCl₃.6H₂O COCl₃ + 6H₂O 

Cobalt chloride paper is blue. But in water or any sort of moisture it starts to turn pink. So if we are using it keep out of air and don’t touch it with our hands because the moisture on our fingers would change the outcome of our cobalt chloride paper. 

Chapter 10 Acids, Bases and Salts

2. Give short answers.

i. Write the equation for self-ionization of water? 
The reaction in which two water molecules produce ions is called as the self-ionization or auto ionization of water. Simple ionization of water can be written as: 

H₂O H⁺ + OH^– 

A water molecule that loses a proton becomes a negatively charged hydroxide ion (OH-). The other water molecule which gains the proton becomes positively charged hydronium ion (H3O+). This can be written as: 

2H₂O H₃O⁺ + OH^– 

ii. Define and give examples of Arrhenius acids. 

Arrhenius Acids:
An acid is a substance that ionizes in water to produce H⁺ ions. For example: 

HCl H⁺ + Cl^– 

H₂O 

HNO₃  H⁺ + NO3^-1 

Since HCl and HNO₃ produce H⁺ ions, therefore HCl and HNO₃ are acids.

iii. Why H⁺ ion acts as a Lewis acid? 
A Lewis acid is a lone pair acceptor, the H⁺ ion has no electrons, so can easily accept a lone pair from another atom. That is why H⁺ ion acts as a Lewis acid. 

iv. Why NH₃ acts as Bronsted-Lowry base? 

• According to Bronsted-Lowry theory an acid is a proton donor and a base is a proton acceptor.
• Ammonia is a gas at room temperature. When it is dissolved in water, the following reaction takes place.

• Water is proton donor and ammonia is proton accepter. Therefore water acts as an acid and ammonia as a base. 

1. Why BF₃ acts as Lewis acid? 

Boron in BF₃ has incomplete octet. It has six electrons. So it needs an electron pair to complete its octet. Hence BF₃ is an electron pair accepter or Lewis acid. 

3. Ammonium hydroxide and nitric acid react and product ammonium nitrate and water. Write balanced chemical equation for this neutralization reaction. 

NH₄OH + HNO₃  NH₄NO₃ + H₂O 

4. Write balanced chemical equations for the following neutralization reactions. 

a. Sulphuric acid + Magnesium hydroxide Magnesium sulphate + water 

H₂SO₄ + Mg(OH)₂ MgSO₄ + 2H₂O 

b. Sulphuric acid + Sodium hydroxide Sodium sulphate + water 

H₂SO₄ + 2NaOH Na₂SO₄ + 2H₂O 

c. Hydrochloric acid + Calcium Hydroxide Calcium Chloride + water 

2HCl + Ca(OH)₂  CaCl₂ + 2H₂O 

5. Identify Bronsted-Lowry acids or bases in the following reactions. 

a. HNO₃ + H₂O H₃O⁺ + NO^–₃ 

Since HNO₃ is converted to NO^–₃ by donating proton therefore HNO₃ is an acid.

Since H₂O accepts the proton that HNO₃ donates and forms H₃O⁺, water is a base.

b. NH₃ + HNO₃  NH₄NO₃ 

Since HNO₃ is converted to NO₃^– by donating proton therefore HNO₃ is an acid.

Since NH₃ accepts the proton and forms NH₄⁺ so it is a base.

6. Identify Lewis acid and Lewis base in the following reactions. 

a. F^– + BF₃  [BF₄]^– 

F^– has a lone pair on F – atom. So it is electron pair donor. F^– is a Lewis base.

Boron in BF₃ has incomplete octet. It has six electrons, so it needs an electron pair to complete its octet. Hence BF₃ is an electron pair accepter or Lewis acid.

b. H⁺ + NH₃  [NH₄]^– 

A Lewis acid is a lone pair acceptor, the H⁺ ion has no electrons, so can easily accept a lone pair from another atom. Therefore H ⁺ ion acts as a Lewis acid.

NH₃ has a lone pair on N-atom. So it is electron pair donor. So, NH₃ is a Lewis base.

c. NH₃ + AlCl₃  [H₃N – AlCl₃] 

In AlCl₃, Al is deficient of two electrons. Therefore it will be called Lewis acid.

NH₃ contains a lone pair and can be donated to AlCl₃ and hence it will act as Lewis base.

7. Classify the following solutions as acidic, basic or neutral. 
i. A solution that has hydrogen ion concentration 1.0 x 10^-3 M. 

[H⁺] = 1.0 x 10^-3 M > 1.0 x 10^-7 M

So, solution is acidic. 
ii. A solution that has hydrogen ion concentration 1.0 x 10^-10 M. 

[H⁺] = 1.0 x 10^-10 M < 1.0 x 10^-7 M

So, solution is basic. 

iii. A solution that has hydroxyl ion concentration 1.0 x 10^-3 M. 
[H⁺] = ? 

K_w = [H⁺][OH^–] 

1.0 x 10^-14 = [H⁺]1.0 x 10^-3 

[H⁺] = 1.0 x 10^-11 M < 1.0 x 10^-7 M

So, solution is basic. 
iv. A solution that has hydroxyl ion concentration 1.0 x 10^-10 M. 

[H⁺] = ? 

K_w = [H⁺][OH^–] 

1.0 x 10^-14 = [H⁺]1.0 x 10^-10 

[H⁺] = 1.0 x 10^-4 M > 1.0 x 10^-7 M

So, solution is acid.

8. Classify following substance as Lewis acid and bases. NH₃, F ^– , H₂O, BF₃ 
a. Since NH₃ accepts the proton and forms NH₄⁺ so it is a base. 
b. F^– has a lone pair on F-atom. So it is electron pair donor. F^– is a Lewis base. 
c. Since H₂O donate a proton therefore H₂O is an acid. 
d. Boron in BF₃ has incomplete octet. It has six electrons. So it needs an electron pair to complete its octet. Hence BF₃ is an electron pair accepter or Lewis acid.

9. Give the Bronsted-Lowry definition of an acid. Write an equation that illustrates the definition. 
In 1923 J.N Bronsted and T.M Lowery independently proposed another theory to overcome the shortcomings of Arrhenius theory. According to Bronsted-Lowry theory an acid is a proton donor. For example: 

In the above reaction HCl donates proton. So HCl is an acid.

10. Identify Bronsted acids and Bronsted bases in the following. 

i. CH₃COOH + H₂O CH₃COO^– + H₃O⁺ 

• CH₃COOH donate proton and become CH₃COO^–, therefore CH₃COOH is an acid. 
• H₂O accepts proton and become H₃O⁺, therefore H₂O is a base.

ii. HCO₃^– + H₂O CO₃^-2 + H₃O⁺  (H⁺ and proton is same)

• HCO₃^– donates proton, so it is the Bronsted-Lowry acid.
• H₂O accepts proton, so it is the Bronsted-Lowry base. 

iii. NH₃ + H₂O NH₄⁺ + OH^– 

• H₂O donate proton and become OH^– , so H₂O is an acid.
• NH₃ accepts the proton and become NH₄⁺ so it is a base. 

iv. HCl + HCO₃^–  H₂CO₃ + Cl^– 

• HCL donates proton, so it is the Bronsted-Lowry acid.
• HCO₃^– accepts proton, so it is the Bronsted-Lowry base. 

v. HS^– + H₂O S^-2 + H₃O⁺ 

• HS^– donates proton, so it is the Bronsted-Lowry acid.
• H₂O accepts proton, so it is the Bronsted –Lowry base. 

vi. H₂S + NH₃  NH₄⁺ + HS^– 

• H₂S donate a proton, so H₂S is an acid.
• NH₃ accepts the proton and become NH₄⁺ so NH₃ is a base. 

11. Identify the Lewis acids and the Lewis bases in the following reactions. 

i. Ag⁺ + 2CN^–  Ag(CN₂) 

• Cation Ag⁺ is Lewis acid since it is able to accept electrons.
• Anion CN^– is Lewis base since it is able to donate electrons. 

ii. B(OH)₃ + OH^–  B(OH)₄^– 

• B(OH)3 is Lewis acid since it is able to accept electrons.
• Anion OH- is Lewis base since it is able to donate electrons. 

iii. Cu⁺² + 4NH₃  [Cu(NH₃)₄]⁺² 

• Cation Cu⁺² is Lewis acid since it is able to accept electrons.
• NH₃ has a lone pair on N-atom. So it is electron pair donor. NH₃ is Lewis base since it is able to donate electrons. 

iv. OH^– + Al(OH)₃  Al(OH)₄^– 

• Al(OH)₃ is Lewis acid since it is able to accept electrons.
• Anion OH^– is Lewis base since it is able to donate electrons. 

12. Identify Lewis acids and bases from the following. 

AlCl3	AlCl3 is Lewis acid since it is able to accept electrons.
Ag+	Ag+ is Lewis acid since it is able to accept electrons.
	Is a Lewis base since it is able to donate electrons.
	Is a Lewis base since it is able to donate electrons.
CN–	Anion CN– is Lewis base since it is able to donate electrons.
OH–	Anion OH– is Lewis base since it is able to donate electrons.
FeCl3	FeCl3 is Lewis acid since it is able to accept electrons.

13. Classify water as proton donor and proton acceptor.

Water is amphoteric in nature. It behave as acid as well as bese. For example,

In this reaction water accepts proton. So water is a base.

In this reaction water donates proton. So water is an acid.

14. Write equations showing the ionization of following as Arrhenius acids. 
a. HI

HI H⁺ + I^– 

b. HNO₂ 

HNO₂  H⁺ + NO₂^-1 

According to Arrhenius theory an acid is a substance that ionizes in water to produce H⁺. So HI and HNO₂ are acids.

15. Write equations showing the ionization of the following as Bronsted-Lowry acids. 

a. HNO₂ 

HNO₂ + H₂O H₃O⁺ + NO^– 

• HNO₂ donate proton and converted to NO^– therefore HNO₂ is an acid.
• H₂O accepts the proton and form H₃O⁺, so water is a base.

b. HCN 

HCN + H₂O H₃O⁺ + CN^– 

• HCN donate proton and converted to CN^– therefore HCN is an acid.
• H₂O accepts the proton and form H₃O⁺, so water is base.

16. Compare the relative concentrations of hydrogen ions and hydroxide ions in each kind of solution?

a. acidic

[OH^–] < [H⁺] 

b. basic

[OH^–] > [H⁺]

c. neutral  

[OH^–] = [H⁺] 

17. Codeine, C18H21NO3 is commonly prescribed as pain killer. It dissolves in water by following reaction. 
C₁₈H₂₁NO₃ + H₂O  [C₁₈H₂₁HNO₃]⁺ + OH^–

Differentiate Codeine and water as Bronsted-Lowry acid and base.

Codeine is Lewis acid because it is able to accept electrons and water is Lewis base.

18. Examine some ways in which you might determine whether a particular water solution contains an acid or a base.

Three acid-base indicators are:

• Litmus paper
• pH meter
• phenolphthalein indicator

19. The table below shows the colours of two indicators in acidic and alkaline solutions.

Indicator	Colour in acidic solution	Colour in alkaline solution
A	Red	Blue
B	Colourless	Red

1. Predict the colour of the indicator A?
2. In a solution of pH 3

The solution of pH 3 is acidic, so the colour of indicator A will be red.

1. In a solution of pH 10

The solution of pH 10 is alkaline, so the colour of indicator A will be blue.

1. Predict the colour of the indicator B in a solution of pH 5?

The solution of pH 5 is acidic, so the colour of indicator B will be blue.

1. When a few drops of indicator B are placed in a solution X, it turns red immediately. Evaluate the properties of solution X?

Solution X is alkaline and is basic in nature.

20. Bacteria in our mouth feed on small particles of food stuck to our teeth and change it into acid. Explain how using toothpaste of pH 10 can help to prevent the acid from damaging our teeth? 
Toothpaste of pH 10 mildly alkaline. The alkaline pH of toothpaste helps to neutralize the plaque acids which cause tooth decay. 

21. Can a substance be a Lewis acid without being a Bronsted – Lowery acid? Argue

Yes, a substance can be a Lewis acid without being a Bronsted – Lowery acid. According to Bronsted-Lowry theory an acid is a proton donor. BF₃ behave as acid but it does not have ability to donate proton. Nature of such substances cannot be explained by Bronsted-Lowry theory. It can be explained by Lewis theory, which states that:

“A Lewis acid is substance that can accept a pair of electrons to form a coordinate covalent bond.”

Boron in BF₃ has incomplete octet. It has six electrons. So it needs an electron pair to complete its octet. Hence BF₃ is an electron pair accepter or Lewis acid. 

Chapter 11 Organic Chemistry

2. Give short answers.

i. What is catenation? 
The self-linking ability of carbon atoms is called catenation. This ability of carbon results in enormous range of compounds of carbon. 

ii. Define isomerism. 
Compounds having same molecular formula but different structural formula is called isomers and this process is called isomerism. 

iii. Give three examples of alkyle groups. 
Examples of alkyle groups:

i. Methyle = CH₃ – 
ii. Ethyle = CH₃CH₂ – 
iii. Propyle = CH₃ – CH₂ – CH₂ – 

iv. Define Functional Group. 
An atom or groups of atoms that give a family of organic compounds its characteristics (chemical and physical properties) is called a functional group. For example Carboxyl group, Carbonyl group etc. 

1. What is difference between an alkane and an alkyle radical? 

• Alkane is a hydrocarbon containing only single bonds and have general formula C_nH_2n+2.
• Alkyle radical is a group of atoms obtained by removing one hydrogen atom from an alkane. Alkyle radicals are represented by symbol R. Their general formula is C _nH_2n+1.

3. What do you mean by term destructive distillation? 
When coal is heated in the absence of air at high temperature, it is converted into coal gas, coal tar and coke. This process is called destructive distillation. 

4. List some general properties of organic compounds. 

Occurrence: 
Most of them come from living things or from the things that were once living. 

Covalent nature: 
They are generally covalent in nature. They may have polar and non-polar bonds. 

Composition: 
Carbon is main part of organic compounds. Hydrogen is also frequently present. 

Melting and Boiling points: 
Generally organic compounds are volatile, so they have low melting and boiling points. 

Solubility: 
They are non-polar in nature, therefore most of them are soluble in organic solvents like ether, benzene etc. Polar organic compounds are soluble in alcohols such as methyl alcohol. 

Homology: 
There exist a close relationship between different organic compounds. This similarity in behaviour has made the study of millions of organic compounds easier. They can be classified into few families. A series of related compounds in which any two adjacent molecules differ by -CH₂– group is called homologous series.

Reaction rates: 
Organic compounds are generally less stable than inorganic compounds. Due to covalent bonding in them, their reaction rates are often slow. 

5. List major commercial sources of alkanes.

The major commercial sources of alkanes are coal, natural gas, petroleum and living organism.

Coal:

• Coal is a source of many organic compounds.
• When coal is heated in the absence of air at high temperature, it is converted into coal gas, coal tar and coke. This process is called destructive distillation.
• Coal gas contains methane, hydrogen and carbon dioxide.
• Coal tar is source of many organic compound such as benzene and its derivatives.

Natural Gas:

• Natural gas is a mixture of low boiling hydrocarbons.
• It is mostly methane.
• It also contain ethane, propane and butane.

Petroleum:

• Petroleum contain wide variety of alkanes.
• On fractional distillation petroleum separate into various hydrocarbon components.

Living organisms:

Plants and animals are sources of organic compounds such as proteins, fats, carbohydrates, vitamins, drugs and medicines.

Synthesis in Laboratory:

More than ten million organic compounds have been prepared in the laboratories.

6. Identify the following compounds on the basis of functional groups they contain.

7. What is the name of alkane having seven carbon atoms in the chain? 
Heptane (C₇H₁₆) 

8. What is the name of the alkyl group obtained by removing an end hydrogen atom from:

1. Propane:

Propyl

1. Ethane:

Ethyl

9. Give the structural formula of two simple alkanes and one alkyne.

Alkanes:

Alkyne:

10. What is meant by term Functional Group? 
An atom or groups of atoms that give a family of organic compounds its characteristics (chemical and physical properties) is called a functional group. For example Carboxyl group, Carbonyl group etc. 

11. Identify following as an alcohol, aldehyde or ketone. 

i. HCHO, which is used to manufacture polymers, such as urotropine which is used to treat urinary tract infection.

Aldehyde because of CHO- group is attached 

ii. CH₃COCH₃, which is used in nail polish remover.

Ketone because of CO- group is attached.

iii. CH₃CH₂OH, which is used in the preparation of many organic substance such as plastics, cosmetics, tinctures etc.

Alcohol because of OH group is attached to alkyl group. 

11. Given a molecular formula of a compound containing C, H and O and single bonds. List all possible functional groups this compound can have?

Functional group containing Carbon, Hydrogen and Oxygen:

Alcohols:

Alcohols are characterized by the presence of the hydroxyl group(-OH) attached to a carbon chain.

General Formula:

Example:

Ethers:

Organic compounds that have two alkyl groups attached to the same oxygen atom are called ethers. These compounds have C – O – H linkage in their molecules.

General Formula:

Example:

12. Give the condensed structural formulas of the following compounds and classify each on the basis of functional group.

Condensed Structural Formula	CH3 CH2 CH2OH (1-Propanonol)	CH3O CH3 (Dimethyl ether)
Functional Group	Alcohol	Ether

13. The diagram represents an organic compound that contains three different elements.

Select the possible compound from the following.

a. Ethanoic acid b. Propene c. Ethanol d. Propane

The compound is Ethanol.

15. Polyvinyl chloride (PVC) is a polymer. It is used for making vinyl sheets, drainage pipes, wire insulation etc. It is obtained from vinyl chloride.

Classify Vinyl chloride as saturated or unsaturated compound.

Vinyl chloride contain double bond between two carbon atoms, so it is unsaturated hydrocarbon.

16. For each of the following, sketch the structural formulas of a two – carbon compound containing the indicated functional group.

Alcohol
Aldehyde
Carboxylic acid
Alkene

17. Aspirin is a mild pain killer and fever reducer. It is manufactured from salicylic acid.

Select functional groups present in it and encircle them. Justify your selection.

Functional groups:

• Carboxyl group because two oxygen atoms are attached with a carbon atom.
• Carbonyl group because one oxygen atom is attached with carbon atom.

18. General formula for alkane is C_nH_{2n + 2}. Construct the general formula for alkyl radical?

General formula for alkyl radical is C_nH_{2n + 1}.

19. Water adds to ethane according to the following reaction.

Compare the functional groups in the reactant and product molecules.

In reactants:

Functional group in the reactant is alkene.

In product:

Functional group in the product is alcohol.

Bonding of carbon atom to heteroatoms increases the number of organic compounds. Justify it.

Unit 12. Hydrocarbons

2. Give short answers.

i. Give three examples of unsaturated hydrocarbons? 

Hydrocarbons containing carbon-carbon multiple bonds are called unsaturated.

Ethene	1-Pentene	1-Butyne

1. Draw electron dot and cross structure for ethene. 

1. Draw structural formula of an alkane, an alkene and an alkyne containing five carbon atoms.

Alkane (Pentane)	Alkene (Pentene)	Alkyne (Pentyne)

 

1. How can you differentiate between ethane from ethene? 

• Add a small amount of bromine water to each jar. 
• Shake the jar containing ethane will de-colour the bromine water. 
• The jar containing the ethane the bromine water will remain brown. 
• This is because the Br₂ will add on across the double bond of the unsaturated ethane to produce dibromoethane. 
• The Br₂ is removed from the water which becomes clear.
• In the case of ethane this is already saturated, so no reaction occurs – Bromine water remains brown. 

1. What do you mean by dehydration reaction? Give one example 
   Dehydration means a chemical reaction that involves the loss of a water molecule from the reacting molecule.
   Example: 
   Alcohols dehydrate when their vapour are passed over heated alumina. 

3. How can you convert? 
i. Ethene into ethane: 

diffused 

ii. Methane into Carbon tetrachloride: 

CH₄ + Cl₂  CH₃Cl + HCl 

CH₃ – Cl + Cl₂  CH₂Cl₂ + HCl  

CH₂ – Cl₂ + Cl₂ CHCl₃ + HCl 

CHCl₃ + Cl₂  CCl₄ + HCl 

Sunlight

Sunlight

Sunlight

Sunlight

diffused 

diffused 

diffused 

iii. Ethene into glycol: 

1. Ethyl Chloride into ethane: 

v. Ethyl bromide into ethene: 

4. Write a chemical equation to show the preparation of an alkane from an alkene and an alkyne.

5. Write a chemical equation to show the preparation of ethane from dehydration of an alcohol and dehydrohalogenation of alkyl halides. 

a. By Dehydration of Alcohols: 

b. By dehydrohalogenation of alkyl halides: 

6. Write a chemical equation to show the preparation of ethyne from dehalogenation of 1, 2 – dihalide and a tetrahalide. 

a. By dehydrohalogenations of 1,2 – dihalide:

b. By Dehalogenation of Tetrahalides: 

7. Write chemical equation showing reactions of KMnO4 with ethene and ethyne. 

a. Reaction with Ethene: 

b. Reaction with Ethyne: 

8. List some industrial uses of ethene and ethyne. 

Uses of Ethene: 

• Ethene is used for artifical ripening of fruits.
• It is used in the manufacture of plastics, such as packing films, wire coatings, and squeeze bottles.
• It is used as antifreeze in automobile radiators.

Uses of Ethyne: 

• In oxy-acetylene torch for welding and cutting metals.
• For ripening of fruits.
• For the manufacture of polyvinyl acetate (PVA), polyvinyl chloride (PVC), polyvinyl ethers and rubbers.

9. Explain why a systematic method of naming chemical compounds is necessary. 
There are millions of organic compounds. It is impossible to study individual compound. To understand, recognize and classify these compounds, systematic naming of organic compounds is necessary. Organic chemists devise a system naming organic compounds depend on their structure. An international body, the International Union of Pure and Applied chemistry (IUPAC) constantly reviews the rules for naming organic compounds. IUPAC system of naming organic compounds is based on the following principle. 

“Each different organic compound should have a different name.”

10. Draw electron dot and cross structure for:

Propane	Propyne	Propene

11. Write chemical equations for the preparation of propene from:

CH₃ – CH₂ – CH₂ – OH CH₃–CH = CH₂ + H₂O 

 170^oC 

 CH₃ – C = CH + 2H₂  CH₃ – CH = CH₂ 

200 – 300^oC  

Ni 

12. Write down structural formulas for the products which are formed when 1-butene is reacted with:

1. H₂ / Ni

1. Dilute alkaline aqueous KMnO₄ solution

1. Bromine water

1. Chlorine

13. Identify A, B, C and D in the following reactions.

Solution:

14. How can you convert ethene into ethane?

Ethene is converted into ethane by the process of hydrogenation. Hydrogenation takes place in presence of finally divided nickel at 200 – 300⁰C and high pressure.

15. You are given two flammable liquid hydrocarbons. One of them is an alkene and other is an alkane. How would you find out which is which?

Bromine water is a dilute solution of bromine, which is a brownish red liquid. This becomes a colourless solution when mixed with an alkene or unsaturated fats.

But when mixed with alkanes or saturated fats, the colour remains the same.

16. How many possible products are there when chlorine reacts with ethane? Draw them all.

The reaction of ethane and chlorine in diffused sunlight occurs as follows.

1. Chloroethane:

1. Dichloroethane:

1. Trichloroethane:

1. Tetrachloroethane:

1. Pentachloroethane:

1. Hexachloroethane:

17. Differentiate between ethene and ethyne.

Ethene	Ethyne
Ethene have double bond between carbon atoms.	Ethyne have triple bond between carbon atoms.
Formula: C2H4	Formula: C2H2
Structure:	Structure:

 

Unit 13. Biochemistry

2. Give short answers.

i. Decide whether sucrose is a disaccharide or monosaccharide. Give reason? 
Since Sucrose consists of two monomers, therefore sucrose is a disaccharide. Common names are table sugar, cane sugar or sugar. Sucrose is a disaccharide of glucose and fructose. 

ii. What is a dextrose sugar? 
Some monosaccharide molecules can rotate the plane of plane polarized light to right (clockwise). They are called dextro-rotatory or dextrose sugars. Glucose, manose, galactose are dextrose sugars. 

1. Write the formula of an amino acid and identify functional groups in it. 
   An amino acid has two functional groups. All amino acids have a carboxyl and amino group in order for them to form long continuous chains of proteins. Structure of amino acid is as follows:
   
2. What is peptide bond? 

Molecules of amino acids join together through amino (-NH₂) group of one molecule and carboxyl

(-COOH) group of another molecule by eliminating a molecule of water.

O 
|| 
The linkage – C – NH – which joins two amino acids units is called a peptide bond. The resulting molecule is called dipeptide. 

1. Which compounds are included in lipids? 

• Fats and oils
• Cholesterol
• Reproductive hormones
• Components of cell membrane called phospholipids.
• Some vitamins (A, D, E and K)

1. What is the function of DNA? 
   DNA can store and transmit all the genetic information needed to build organisms. For instance, in human beings the single fertilized egg cell carry the information for making legs, hands, head, liver, heart, kidneys etc. DNA is found primarily in the cell nucleus. 

3. Distinguish between mono, di-, and tri-saccharides. 

Monosaccharide: 
Monosaccharide is simple sugar consists of only one unit. They serve as building blocks for more complex carbohydrate forms. For example Glucose, Fructose, Galactose, Lyxose and Xylose. 

Disaccharides: 
Disaccharides are group of sugars composed of two monosaccharide groups linked together through the loss of sugar. For example 
Maltose = Glucose + Glucose 
Sucrose = Glucose + Fructose 
Lactose = Glucose + Galactose 

Trisaccharides: 
Trisaccharides are sugars containing three hexoses. For example Raffinose, found in molasses contain the three hexoses. Nigerotriose, Maltotriose and Melezitose. 

4. Describe bonding in a protein molecule.

Proteins are high molecular weight polymers. The building blocks of all proteins are amino acids. An amino acid has two functional groups. These are carboxylic acid and amino group. Twenty different amino acids are involved in protein synthesis. Out of twenty amino acids, our bodies can synthesize only ten amino acids. Such amino acids are called non-essential amino acids. The remaining ten molecules are called essential amino acids.

Molecules of amino acids join together through amino (-NH₂) group of one molecule and carboxyl (-COOH) group of another molecule by eliminating a molecule of water.

O 
|| 
The linkage – C – NH – which joins two amino acids units is called a peptide bond. The resulting molecule is called dipeptide. There is still an amino group on left and a carboxyl group on right. Each of these groups can further to join more amino acid units. In this way thousands of amino acids units join to form a giant molecule of protein.

5. Explain sources and uses of lipids.

Sources:

• Animals, plants, and marine organisms such as salmon and whales are rich source of lipids.
• Milk is an important source of animal fat from which butter, ghee, ground nut, coconut, olive etc. are good source of vegetable oils.
• Cod liver oil is obtained from salmon and whales.

Uses:

• Butter, ghee and vegetable oils are used for cooking and frying of food, preparing bakery products and sweets.
• In mammals a layer of fat is present under the skin. This layer acts as a thermal insulator.
• Fats protect delicate organs from shocks. A layer of fat around our heart and kidneys protect these organs from injury.
• Lipids provide some vitamins such as A, D and E which are essential for health. These vitamins are insoluble in water and soluble in lipids.
• Fats and oils are important food stores in living organisms. They provide about twice, as much energy per gram as do carbohydrates.
• Vegetable oils are converted into vegetable ghee or margarine by catalytic hydrogenation.
• Fats and oils are also used for the manufacture of materials like soaps and detergents, cosmetic, polishes, paints and varnishes
• In our bodies cholesterol is essential for the synthesis of several hormones, vitamin D and bile acids.

6. Give sources and uses of proteins.

Sources of proteins: 

Meat, fish, eggs, milk and cheese are important sources of proteins. Plants also provide us proteins. For example, pulses, beans, meat, egg, fish etc. are rich in proteins. 

Uses of Proteins: 

• We require proteins in our diet, to provide amino acids to make muscles, hair, enzymes and repair of body tissues.
• Proteins are essential for the formation of protoplasm and components of cells.
• Proteins are essential for both physical and mental growth especially in children.
• A protein called gelatin is obtained by heating bones and tendons in water.
• It is used in bakery goods.
• Enzymes are proteins that catalyse specific biological reactions, without which life would be impossible.
• The antibodies that help us to fight against disease are large protein molecules.

7. Give sources and uses of carbohydrates.

Sources:

• Monosaccharides such as glucose, fructose and galactose are obtained from fruits, vegetables and cerals. They are also present in honey.
• Cellulose is obtained from plants.
• Starch is present in wheat, rice and potato.
• Disacchraide such as sucrose is obtained in sugarcane, sugar beet and fruits.

Uses:

• Carbohydrates store and transport energy in both plants and animals. 1g of glucose provides us 15.6 KJ of energy.
• Starch is used to make rectified spirit by fermentation process.
• Starch is converted to dextrin which is used as an adhesive for stamps and as wallpaper glue.
• Cows, cattle, goats, deer, sheep and termites derive nutrition from cellulose.
• We use cellulose in the form of wood for heat, housing and furniture.
• Wood is also used to make paper and wood pulp.
• Sucrose in used as common table sugar.

8. Differentiate between fats and oils.

Fats	Oils
A lipid is called fat if it is solid at room temperature.	A lipid is called oil if it is liquid at room temperature.
Mostly derived from animals.	Mostly derived from plants.
Fats contain larger proportion of saturated fatty acid units.	Oils contain larger proportion of unsaturated fatty acid units.
Example: Butter fat and beef fat.	Example: Coconut oil and sunflower oil.

9. Define and explain vitamins. 
Vitamins are specific organic compounds which are required by our bodies to prevent specific diseases but cannot be produced by our bodies. They must be present in our diet in addition to proteins, fats, carbohydrates and minerals. Vitamin D deficiency causes softening of bones. Vitamin B3 deficiency causes inflammation and abnormal pigmentation. 

Importance of vitamins: 
Vitamins are substances that are essential for our bodies. 

Vitamin A: 
Vitamin A is important in vision. It helps in the chemical transmission of images from the eye to the brain. It also keeps the cornea moist. 

Vitamin C: 
Vitamin C is required for the formation of blood and boosting the immune system that protects against illnesses ranging from common cold to cancer. 

Vitamin B: 
Vitamin B helps to regulate nerve impulse transmissions, in the formation of haemoglobin and activates more than 100 different enzymes. 

Vitamin D: 
Vitamin D regulates blood calcium. It is necessary for proper bone and tooth growth. 

10. Why are vitamins important for us?

Importance of vitamins: 
Vitamins are substances that are essential for our bodies. 

Vitamin A: 
Vitamin A is important in vision. It helps in the chemical transmission of images from the eye to the brain. It also keeps the cornea moist. 

Vitamin C: 
Vitamin C is required for the formation of blood and boosting the immune system that protects against illnesses ranging from common cold to cancer. 

Vitamin B: 
Vitamin B helps to regulate nerve impulse transmissions, in the formation of haemoglobin and activates more than 100 different enzymes. 

Vitamin D: 
Vitamin D regulates blood calcium. It is necessary for proper bone and tooth growth. 

11. Describe the importance of nucleic acids.

Nucleic acids are vital components of all life. They are found in every living cell. They serve as the information and control centers of the cell.

12. Explain why agricultural and nutritional sciences are vital.

Protein deficiency leads to physical and mental retardation. Excess lipids or fats may lead to heart diseases or a stroke, cancer, diabetes and other health problems. The nutritional chemists recommend that no more than 30 % of your daily caloric intake come from fat. So, healthy diet is necessary for human growth.

13. Explain hydrogenation of vegetable oil. 
Addition of hydrogen to an alkenes is called hydrogenation. This reaction takes place in the presence of Ni, Pd or Pt as catalyst. 

This reaction is used to make margarine or vegetable ghee. Fatty acid component of vegetable oil contains carbon-carbon double bonds. When hydrogen is added to these oils, they become saturated and harder.

14. List commercial uses of enzymes. 
Enzymes are large protein molecules. They are biological catalysts. They catalyze chemical reactions in living organisms. Enzymes are also commercially important. They are used in the production of sweeteners, chocolate syrup, bakery products, infant foods, detergents to remove food stains, in cheese making, in paper and pulp industries to remove sticky matter, to prepare fabrics for clothes, furniture and other household items. 

15. What is the use of dextrose in drips? 
5% m/v aqueous solution of dextrose is used in drips. 5% m/v aqueous solution means 5 grams of dextrose dissolved in water to form 100cm³ of solution. It is intravenously given to patient who is severely dehydrated or is unable to eat or is not allowed to eat. 

16. Separate water soluble vitamins from the following. Vitamin A, Vitamin C, Vitamin E, Vitamin B.

Water soluble vitamins are: Vitamin A, Vitamin C and Vitamin B.

17. What three elements are important in both proteins and carbohydrates?

Three elements important in both proteins and carbohydrates are Carbon, Hydrogen and Oxygen.

18. What is the name of the bond that forms between two amino acids in building a protein?

Peptide bond is formed between two amino acids in building a protein.

19. How many molecules of water are needed to allow a disaccharide to form monosaccharaides?

One molecule of water is needed to allow a disaccharide to form monosaccharaides.

20. Draw the structure of each of the following molecules.

1. An amino acid having –CH₃ as R group.

1. A protein containing two amino acids.

21. What five elements are primarily responsible for the makeup of DNA and RNA?

Elements are primarily responsible for the makeup of DNA and RNA are:

• Carbon
• Oxygen
• Hydrogen
• Nitrogen
• Phosphorus

22. Write structural formula of an amino acid containing four carbon atoms.

21. Distinguish between DNA and RNA.

DNA	RNA
DNA stands for Deoxyribonucleic Acid.	RNA stands for Ribonucleic Acid.
DNA exists in the form of two strands.	RNA exists in the form of single strands.
It is made of a deoxyribose sugar, phosphorus unit and nitrogen base.	It is made of a ribose sugar, phosphorus unit and nitrogen base.
Storing genetic information.	Transferring genetic information from the DNA to proteins.
For a particular species, the DNA number remains constant for every cell.	The number of RNA may differ from cell to cell.

22. Hydrogenation is an important reaction in food industry. Interpret this statement.

The process of hydrogenation involves the addition of hydrogen (H₂) to produce a chemical reaction with organic compounds (hydrocarbons). It is hugely important and widely used in the food industry. Hydrogenation is used to convert margarine or vegetable oil into margarine and vegetable ghee in the presence of Ni, Pd or Pt as catalyst. 

Unit 14: Atmosphere

2. Give short answer

i. List two main sources of acid rain.

Acid rain is caused mainly by the burning of fossil fuels such as coal and gasoline. Oxides of nitrogen and sulphur are released into the air when fossil fuels are burnt and when they mix with the precipitation in clouds acid rain is formed

ii. List four human activities which contribute to air pollution.

1. Burning fossil fuel.
2. Cutting trees.
3. Use of Freon gas.
4. Production of methane from dead plant material decay

iii. What is the importance of stratospheric ozone?

Importance of stratospheric ozone:

Ozone saves us from harmful effects of incoming ultraviolet radiations from the sun. When ozone absorbs energy from the sun, the energy’s converted into heat, warming the air. The ozone layer protects the living things on the Earth from dangerous ultraviolet radiation from the sun

iv. What is the role of automobile in air pollution?

Exhaust fumes of automobiles including dangerous gases such as carbon monoxide, oxides of nitrogen, hydrocarbons and particulates. These exhaust fumes of automobile are responsible for air pollution.

v. Define atmosphere.

Atmosphere:

The envelope of gases and water vapour surrounding the planet earth is called atmosphere

3. Explain temperature variation in stratosphere and troposphere.

Temperature variation in stratosphere:

In the stratosphere temperature varies from -55°C to -5°C.

Temperature variation in troposphere:

As altitude increases in the troposphere, the temperature decreases from 17°C to about -55⁰C. On average for every 1 km increase in altitude, the air gets about 6.5°C cooler

4. List components of stratosphere and troposphere.

Component of stratosphere:

This layer contains little water vapours. Interesting information about this layer is that it contains maximum amount of ozone (about 1Oppm/parts per million). The presence of ozone is responsible for the rise in temperature in stratosphere.

Components of troposphere:

Nearly all the dust particles and water vapours are in the troposphere. Weather occurs in this layer. Most of the clouds are formed in the troposphere. Aircrafts fly in this region.

5. Describe sources of air pollutants.

Sources of Air Pollution:

1. Natural Sources:

Many natural processes such as forest fires and dust storms release smoke and dust particles into the air. Volcanoes emit clouds of dust and poisonous gases along with ash. Termites and cows also release large amount of methane in the air. Considerable electrical discharges in the atmosphere produce nitrogen oxides.

1. Human Activities:

Most of the air pollution is the result of burning fossil fuels, such as coal, petroleum and natural gas. Nearly half of the air pollution comes from cars and other motor vehicles. Factories and power plants that burn coal or oil release poisonous gases in the air. Burning fossil fuels and incineration release carbon monoxide (CO), nitrogen oxides (NO. NO₂) and sulphur oxides (SO₂, SO₃).

C + 0₂ (limited) CO

S + 0₂ SO₂

N₂ + 0₂ 2NO

2NO + 0₂ 2NO₂

Chlorofluorocarbons:

Chlorofluorocarbons have been widely used as solvents for cleaning electronic circuit boards, as refrigerant in fridges and air-conditioning units and as propellants in aerosol sprays (air fresheners, hairsprays, deodorants, spray paints). Such products are not “Environment friendly”. During manufacture, in use and after disposal, these compounds escape into the air.

Lead particles:

Lead particles in the air come mainly due to the combustion of leaded petrol or fuel used in motor vehicles or from lead based paints.

Ozone:

Ozone is produced when electrical discharges pass through oxygen in the air. You can feel its presence near photocopier, television set, microwave oven and other electrical equipment.

 

Electrical

30₂ 2O₃

discharge

 

6. Describe acid rain and its effects.

Acid Rain:

Acid rain is defined as rain having pH less than 5.6. Normal rain water is saturated with carbon dioxide. It has pH of 5.6 however; the acidity of rain greatly increases in polluted areas during thunderstorm.

Sulphur dioxide from power plants using fossil fuels and nitrogen oxides from exhaust fumes of automobiles dissolve in rain water producing acids.

2S0₂ + 0₂ 2S0₃

SO₃ + H₂O H₂SO₄

2NO₂ + 30₂ + 2H₂0 4HNO₃

Therefore, during thunderstorm the pH of rain water can be much lower because of sulphuric acid and nitric acids formed by lightening. This rain may have pH as low as 2.1. This value is lower than the pH of vinegar or lemon juice.

Effect of acid rain:

Acid rain may often fall hundreds .of kilometer away from their sources. Acid rain corrodes metals, stone buildings and statues. Marble statues are slowly eroded by acid rain.

Sulphuric acid eats away metals to form water soluble salts and hydrogen.

Fe + H₂S0₄ FeSO₄ + H₂

Marble buildings and statues:

Marble buildings and statues are disintegrated by acid rain.

CaC0₃ + H₂SO₄ CaS0₄ + H₂O + CO₂

CaCO₃ + 2HNO₃ Ca(NO₃)₂ + H₂O + C0₂

Acid rain also kills fish, and destroys trees. Lakes and river may become too acidic for living things to survive. Trees destroyed by acid rain. Fish are killed by acid rain.

7. Describe ozone depletion and its effects.

Ozone Depletion and Its Effects:

Over recent years, scientists have discovered a reduction in the amount of ozone in the stratosphere.

Ozone hole:

The region in which the amount of ozone has been reduced is called as ozone hole.

Ozone hole was first observed in October, 1980 over Antarctica.

Chlorofluorocarbons:

Chlorofluorocarbons (from aerosol cans, air conditioning systems, refrigerators etc) escape into the atmosphere. CFCs are gases or low boiling liquids. They are so inert that they do not react with any other chemicals in the troposphere. They slowly diffuse into the ozone layer. UV radiation break CFCs molecule producing chlorine free radicals.

CCI₃F CCl₂F + CI

Chlorine free radical reacts with ozone to form chlorine monoxide (CIO) and molecular oxygen. CIO reacts with atomic oxygen produced by the decomposition of ozone by UV radiations.

.

The chlorine free radical that reacts in step 1 is regenerated in step 2. One Cl can destroy thousands of ozone molecules.

8. Describe global warming.

Global warming: The warming of the atmosphere which is due to our influence on the greenhouse effect is known as global warming.

Global warming as a greenhouse effect:

Global warming is due to an upset in the natural balance of the concentration of greenhouse gases in the atmosphere. If global warming continues, then:

• Temperature of the earth will gradually increase.
• The earth climate may change, affecting both where there is rainfall and how much there is of it. This could cause both increased risks of flooding in some regions and drought in others.
• Polar ice may melt and cause significant increase in sea levels.
• So the atmosphere becomes hotter.

9. Differentiate between stratosphere and troposphere.

Troposphere	Stratosphere
Tropo- means “turning” or “changing”.	Strato- means “layer” or “spread out”.
It is the first layer of atmosphere.	It is the second layer of atmosphere.
Height: 0 – 12 km	Height: 12 – 50 km
Temperature: 170C to -550C	Temperature: -550C to -50C
It contains dust particles, water vapours and clouds.	It contains ozone.

10. Explain ozone formation.

Formation of ozone:

Ozone is an allotropic form of oxygen comprising there oxygen atoms. 0₃ Ozone is an important gas in the stratosphere.

Most of the ultraviolet (UV) radiations coming from sun are filtered or screened out by the ozone layer Otherwise, sunlight would be much more hazardous for human beings, animals and plants. On absorbing UV radiation, ozone molecule breaks up to form an oxygen molecule and atomic oxygen.

Atomic oxygen is very reactive. Atomic oxygen reacts readily with an oxygen molecule to form ozone, thereby releasing heat.

These reactions maintain level of ozone in the stratosphere. Both the destruction and the reformation of ozone are powered by UV radiation. In the absence of outside intervention, the rates of ozone destruction and formation are equal. However, human activities disturb this natural balance.

11. Why is global warming often referred to as the greenhouse effect?

The enhanced greenhouse effect (or accelerated greenhouse effect) is the warming effect caused by all the extra carbon dioxide greenhouse gas that man has put into the atmosphere in the past 100 years by burning fossil fuels (coal, oil and natural gas). Global warming is the warming of the earth because of this enhanced greenhouse effect.

12. There is scientific evidence that CFCs contribute to the depletion of ozone. Why?

Ozone hole:

The region in which the amount of ozone has been reduced is called as ozone hole.

Ozone hole was first observed in October, 1980 over Antarctica. The CFCs are so stable that only exposure to strong UV radiation breaks them down. When that happens, the CFC molecule releases atomic chlorine. One chlorine atom can destroy over 100,000 ozone molecules.

13. Sulphur dioxide is a common pollutant from burning coal. State two effects caused by this pollutant.

Sulphur Oxides (SOx):

In the air sulphur dioxide is converted into sulphur trioxide, which is responsible for acid rain. Sulphur dioxide is readily absorbed in the respiratory system. Being powerful irritant, it aggravates the symptoms of people who suffer from asthma, bronchitis, emphysema and other hung diseases.

14. Dibenzothiophene (C₁₂H₈S) is a common sulphur containing compound of coal. It is responsible for acid rain. How?

Dibenzothiophene (C₁₂H₈S) is a sulphur containing compound of coal on burning it produces sulphur dioxide. In the air sulphur dioxide is converted into sulphur trioxide, which is responsible for acid rain.

15. There have been various attempts to remove sulphur from coal before it is burned. Suggest reason.

Sulphur containing compound of coal on burning produces sulphur dioxide. In the air sulphur dioxide is converted into sulphur trioxide, which is responsible for acid rain. Therefore various attempts to remove sulphur from coal before it is burned have been done.

16. Examine the option there are some ways to reduce pollution caused by cars?

Catalytic converter:

A catalytic converter transforms CO into CO₂, NO into N₂ and 0₂, and unburned hydrocarbons to CO₂ and H₂O. Metals like platinum, palladium and rhodium are used as catalyst in the converter. Government of Pakistan should direct car manufacturers to install catalytic converters in car exhaust system. Government should make strict laws in this regards.

Similar to scrubbers on power plants, catalytic converters reduce NO_x emissions from cars.

17. Certain human activities are responsible for a significant increase in green house effect, argue.

Human activities increase the amount of greenhouse gases. These gasses play important role in global warming. Following human activities are responsible for greenhouse effect:

• Cutting forests (deforestation).
• Burning of fossil fuels such as coal, oil and gas.
• Household, industrial and livestock waste.
• Use of leaded paints.

18. As a global citizen, how can you play a part to reduce air pollution at a personal level? Argue.

As a global citizen, we take following steps to reduce air pollution at a personal level.

• Walk short distances or ride cycles instead of using vehicles.
• Use Catalytic Converters in vehicles.
• By growing more plants.
• Dispose house hold waste at proper places.
• Use public transport.

19. Compare and contrast between stratosphere and troposphere.

Troposphere	Stratosphere
Tropo- means “turning” or “changing”.	Strato- means “layer” or “spread out”.
It is the first layer of atmosphere.	It is the second layer of atmosphere.
Height: 0 – 12 km	Height: 12 – 50 km
Temperature: 170C to -550C	Temperature: -550C to -50C
It contains dust particles, water vapours and clouds.	It contains ozone.

Unit 15. Water

2. Give short answers.

1. List the impurities present in rain water. 
   Rainwater contains pollutants, soil, plant parts, insect parts, bacteria, algae, and sometimes radioactive materials that the rain/snow has washed out of the air. 
2. List toxic substances present in household wastes. 
   Household wastes include, human wastes, livestock wastes, soaps and detergents, paints and oil, food and vegetable wastes, garbage etc. 
3. In what ways, industrial wastes pollute water. 
   Manufacturing of industrial products are always accompanied by some by-products and waste effluents. These wastes may contain highly toxic compounds and heavy metals such as Pd, Cd, Cr, Hg, As, Sb etc. Water from leather tanneries contains large quantities of chromium (VI) salts. Chromium (VI) ions are highly toxic and known to cause cancer. 
4. What is water pollution? 
   Water pollution is the contamination of water bodies (e.g. lakes, rivers, oceans, aquifers and groundwater). Water pollution occurs when pollutants are discharged directly or indirectly into water bodies without adequate treatment to remove harmful compounds. 
5. List some waterborne diseases. 

• Cholera
• Dysentery
• Jaundice
• Typhoid
• Hepatitis

1. What are pathogenic microorganisms? 
   An organism of microscopic size, usually a bacteria or virus, that causes disease. These organisms are transmitted through food, water and direct contact. These organism may cause typhoid fever, dysentery and hepatitis. 

3. What is hard water? Why is it sometimes undesirable? 
Water that gives little lather or forms scum with soap is called hard water. 

Hard water is undesirable: 

• Hard water wastes a lot of soap, when used for washing.
• The soap forms scum with hard water, which adhere to the clothes being washed. Scum can spoil the finish of some fabrics.
• Cause kettles to fur.
• Can cause hot water pipes, boilers and car radiators to block due to the formation of insoluble calcium and magnesium salts, causing great damage

4. List two ways in which lakes and streams become polluted. 
Industrial units generally discharge their wastes either to open land or into water bodies, lakes, ponds, rivers or oceans.

• Water from leather tanneries contains large quantities of chromium (VI) salts. Chromium (VI) ions are highly toxic and known to cause cancer.
• Industrial wastes cause irreversible degeneration of the environment causing serious health problems for public and marine life.

5. Give chemical equations for the: 

a. Reaction of slaked lime with alum: 

3Ca (OH)₂ + Al₂ (SO₄)₃  2Al (OH)₃ + 3CaSO₄ 
b. Carbonated rain water with lime stone: 

CaCO₃ + H₂CO₃ Ca(HCO₃)₂ 
c. Reaction that occurs when temporary hard water is boiled: 

Ca(HCO₃)₂  2CaCO₃ + CO₂ + 2H₂O 
Mg (HCO₃)₂  2MgCO₃ + CO₂ + 2H₂O 

d. Ca⁺² ions interact with sodium zeolite: 

Ca⁺² + Na₂Z 2Na+ + CaZ 

6. How can buildings made of limestone be affected by acid rain? 

• Acid rain has a corrosive effect on limestone or marble buildings or sculptures. It is well established that either wet or dry deposition of sulphur dioxide significantly increases the rate of corrosion on limestone, sandstone, and marble.
• Sulphur trioxide plus water makes sulphuric acid. Marble buildings and statues are disintegrated by this acid.

CaCo₃ (s) + H₂SO₄ (aq) CaSO₄ (aq) + H₂O (aq) + CO₂ (g)

Therefore buildings made of limestone are affected by acid rain.

• The acid reacts with carbonates in the lime stone. The lime stone dissolves and the marble buildings gradually crumbles away.

7. Make a list of main methods of softening hard water. In each case write a chemical equation to summarize the chemical reactions involved.

Methods to remove temporary hardness:

a. By Boiling: 
Hardness of water can be removed simply by boiling. During boiling the soluble calcium and magnesium hydrogen carbonates are decomposed forming insoluble carbonates. Since Ca⁺² and Mg⁺² ions are removed as insoluble carbonates, water becomes soft. 

Ca (HCO₃)₂  CaCO₃ + CO₂ + H₂O 

Mg (HCO₃)₂  MgCO₃ + CO₂ + H₂O 

b. By adding slaked lime (Clark’s method): 
Temporary hardness in water on the large scale can be removed by adding an estimated amount of slaked lime in it. The slaked lime reacts with the hydrogen carbonates to form insoluble carbonates. 

Ca (HCO₃)₂ + Ca (OH)₂  2CaCO₃ + 2H₂O 
Mg (HCO₃)₂ + Ca (OH)₂ CaCO₃ + MgCO₃ + 2H₂O 

Methods to remove permanent hardness:

a. By adding washing soda: 

On the large scale permanent hardness in water can be removed by adding washing soda (Na₂CO₃.1OH₂O). Ca⁺² and Mg⁺² ions are removed as their insoluble carbonates. 

Ca⁺² + CO₃^-2  CaCO₃ 

Mg⁺² + CO₃^-2  MgCO₃ 

b. By ion Exchange Resins: 

The hard water is passed through a container filled with a suitable resin containing sodium ions. Zeolite is one of the natural ion exchanger. Chemically it is sodium aluminium silicate. It is usually written as Na₂Z. The Ca⁺² or Mg⁺² ions causing the hardness are exchanged with Na⁺ ions in the resin. 

Ca⁺² + Na₂Z 2Na⁺ + CaZ 

Mg⁺² + Na₂Z 2Na⁺ + MgZ 

The used up zeolite can be regenerated by heating with concentrated solution of NaCl. This makes the process economical.

CaZ + 2NaCl Na₂Z + CaCl₂ 

8. List some disadvantages of water hardness. 

• Hard water wastes a lot of soap, when used for washing.
• The soap forms scum with hard water, which adhere to the clothes being washed. Scum can spoil the finish of some fabrics.
• Cause kettles to fur.
• Can cause hot water pipes, boilers and car radiators to block due to the formation of insoluble calcium and magnesium salts, causing great damage.

9. What are the Earth’s four main water sources?

Earth main water sources are:

• Atmospheric Water
• Rivers and Lakes
• Groundwater
• Glaciers and icecaps

10. How does hard water differ from soft water? 

Soft Water	Hard Water
Water that easily gives lather with soap and does not form scum is called soft water.	Water that gives little lather or forms scum with soap is called hard water.
Does not contain dissolved salt.	It contain dissolved salt, i.e Ca and Mg.
It does not waste soap when used for washing.	It waste lot of soap when used for washing.

11. What is the purpose of coagulation in water treatment? 
Coagulation is the process in which water is treated with slaked lime and alum. These materials react to form a gelatinous mass of aluminum hydroxide. 

3Ca (OH)₂ + Al₂ (SO₄)₃  2Al (OH)₃ + 3CaSO₄ 

The aluminium hydroxide carries down dirt particles and bacteria. 

12. Explain how hard water hampers the cleansing action of soap. 

Hardness in a water is due to the presence of dissolved salts for example Ca and Mg. Soap is good cleaning agent, but Ca and Mg reacts with soap and form scum. Which hampers cleansing action of soap.

13. Why are municipal water supplies treated with aluminum sulphate and slaked lime?

Municipal water supplies treated with aluminum sulphate and slaked lime, these materials react to form a gelatinous mass of aluminum hydroxide. 

3Ca (OH)₂ + Al₂ (SO₄)₃  2Al (OH)₃ + 3CaSO₄ 

The aluminium hydroxide carries down dirt particles and bacteria. In this way water become purified.

14. What are some health effects of biological contamination of water?

Human wastes are dumped on the ground or into the nearest stream. Human waste contains pathogenic microorganisms. These organisms may cause typhoid fever, dysentery and hepatitis. Hepatitis is a viral disease occasionally spread through drinking water. Some waterborne diseases are cholera, dysentery and jaundice.

15. Write a word and balanced chemical equation to show the effect of heat on magnesium hydrogen carbonate in an aqueous solution.

Heat 

Magnesium hydrogen carbonate Magnesium carbonate + Carbon dioxide + Water

Heat 

Mg (HCO₃)₂  MgCO₃ + CO₂ + H₂O 

16. Why is it cooler near a lake than inland during summer?

Water has a high heat of vaporization. So large amount of heat is required to evaporate small amount of water. This property accounts for climate-modifying property of lakes and oceans. Thus in summer it is cooler near a lake than in interior land areas.

17. Evaluate the option, ion exchange resins can be used to remove temporary hardness.

In ion exchange method the hard water is passed through a container filled with a suitable resin containing sodium ions. Zeolite is one of the natural ion exchanger. Chemically it is sodium aluminium silicate. It is usually written as Na₂Z. The Ca⁺² or Mg⁺² ions causing the hardness are exchanged with Na⁺ ions in the resin. 

Ca⁺² + Na₂Z 2Na⁺ + CaZ 

Mg⁺² + Na₂Z 2Na⁺ + MgZ 

The used up zeolite can be regenerated by heating with concentrated solution of NaCl. This makes the process economical.

CaZ + 2NaCl Na₂Z + CaCl₂ 

18. Public health depends on water quality. Give arguments.

Unclean water supplies, poor sanitation and poor hygiene kill 2, 668, 000 people worldwide each year. Water is crucial for sustaining the reactions that keep us alive. For instance digestion, distribution of food through blood, removal of waste matter from the body. We also need water for drinking, cooking and cleaning. Clean water is very important for public health.

19. Hard water causes kettles to fur. This fur can be removed by using an acid. Justify.

Temporary hardness is caused by the presence of soluble bicarbonates of calcium and magnesium. Boiling will decompose these bicarbonates into carbonates, which are insoluble. Calcium and magnesium carbonate make up the fur on kettles. Carbonates are soluble in acids, so adding some acid will decompose the carbonate salts and the fur is removed from kettles.

20. The following chemical equation is about a calcium compound.

Comp A + 3Ca (OH)₂   Comp B + H₂O

Comp B + H₂CO₃ Comp C

1. Name and give the formula of.
2. Compound A

Ca (HCO₃)₂ + Ca (OH)₂  2CaCO₃ + 2H₂O 

Compound A is Ca (HCO₃)₂ which is calcium hydrogen carbonate.

1. Compound C

CaCO₃ + H₂CO₃ Ca (HCO₃)₂ 

Compound C is Ca (HCO₃)₂ which is calcium hydrogen carbonate.

1. Describe with the aid of balanced chemical equation. What happens when compound C is heated?

Heat 

Ca (HCO₃)₂  CaCO₃ + CO₂ + H₂O 

When calcium hydrogen carbonate is heated it changes into calcium carbonate, carbon dioxide and water.

1. Compound C is soluble in water. Write a balanced chemical equation to show what happens when its aqueous solution is treated with washing soda?

Ca (HCO₃)₂  + Na₂CO₃ CaCO₃ + NaHCO₃

21. How chemistry helps maintain a dean swimming pool? Explain
Water in swimming pools is purified from pathogenic organisms by aeration and chlorination. Chlorination is a probably the best and the cheapest method of sterilization of water and it is the most effective in destroying pathogenic bacteria. For chlorination, liquid chlorine may be added directly in the swimming pool water. 

22. Why it is advisable to wash hands well with soap after using bathrooms? 
If your hands are not clean and you touch your face or public surfaces, you may be infecting yourself and others by spreading germs and disease. Colds, flus, and infectious diarrhea are all known to be spread by hand-to-hand contact. Washing your hands regularly can help keep you and those around you healthy by controlling the spread of germs (bacteria and viruses). 

23. Differentiate between raw water treatment and sewage treatment process.

Raw water treatment:

The raw water is treated in a municipal water purification plant, to make it fit for drinking and domestic purposes. Various stages in this treatment are; 

Sedimentation: 

It is the process in which water is allowed to stand in a reservoir. The suspended matter sinks to the bottom. 

Coagulation: 

It is the process in which water is treated with slaked lime and alum. These materials react to form a gelatinous mass of aluminum hydroxide. 

3Ca(OH)₂ + Al₂(SO₄)₃  2Al(OH)₃ + 3CaSO₄ 

The aluminum hydroxide carries down dirt particles and bacteria. 

Filtration: 

The water is then filtered through sand and gravel. Sometimes it is filtered through charcoal to remove coloured and odorous compounds. 

Chlorination: 

In the final step, chlorine is added to kill any remaining bacteria. Chlorine reacts with water to form hypochlorous acid HClO which kills bacteria. 

Cl₂ + H₂O HClO + H⁺ + Cl^– 

Sewage Water Treatment:

In many countries, sewage water is passed through certain treatment stages before it is discharged into a lake, stream, river or ocean. This treatment involves following steps.

Primary Sewage Treatment:

Primary treatment removes some of the solids as sludge. For this purpose waste water is allowed to stand in a large sedimentation tank to remove suspended particles.

Secondary Sewage Treatment:

Effluent from the primary treatment is passed through sand and gravel filters. There is some aeration in this step, and aerobic bacteria convert most of the organic matter to stable inorganic materials.

Activated Sludge Treatment:

The sewage is then placed in tanks and aerated with large blowers. This results in the formation of large, porous clumps, which absorbs contaminants. The aerobic bacteria further convert the organic material to sludge. This sludge is stored on land or sometimes used as fertilizer.

Chlorination:

The effluent from sewage plant is treated with chlorine to kill any remaining pathogenic microorganism.

24. Evaluate the advantages of waste water treatments.

Water treatment is essential for many reasons.

• Through water purification, we can avoid drinking impure and containimated water, which causes many epidemic diseases and unsafe for healthy life.
• It removes bacteria, viruses and parasites which may cause serious health problems.
• It also removes heavy metals like As, Bs, Cr and Pb which can cause long term neurological problems, kidney diseases and cancer.
• It also improves the flavour and appearance.

25. Water borne diseases are no longer common in developed countries. Defend this statement.

Human wastes are dumped on the ground or into the nearest stream. Human waste contains pathogenic microorganisms. These organisms may cause typhoid fever, dysentery and hepatitis. In developed countries raw water is treated in a municipal water purification plant, to make it fit for drinking and domestic purposes.

Unit 16. Chemical Industries

2. Give short answers.

i. How are urea prills produced? 
The urea solution is concentrated in vacuum evaporators, which is then rapidly cooled and sent to the prilling tower. Urea prills thus produced are packed and then marketed. 

ii. What is slaked lime? How is it produced? 
Slaked lime (Ca(OH)₂ ) a white caustic alkaline substance consisting of calcium oxide, obtained by heating limestone.

Preparation of slaked lime: 
Carbon dioxide is produced by heating limestone in a kiln. 

Heat

CaCO3  CaO + CO2 

Carbon dioxide is fed into the carbonating tower from the top. Equal amounts of lime (CaO) and water are mixed to produce slaked lime, Ca(OH)₂. 

CaO + H2O Ca(OH)₂ 

1. Write chemical reactions that take place during carbonation in Solvay process. 

Carbonation: 
In the carbonating tower, carbon dioxide is passed through ammonical brine. Following reaction takes place in it. 

CO₂ + NH₃ + H2O NH₄HCO₃ 

NH₄HCO₃ + NaCl NaHCO₃ + NH₄Cl 

15°C 

In the lower compartments of carbonating tower, the temperature of the mixture is lowered to 15°C. At this temperature, NaHC0₃ precipitates out. 

1. Explain the process “Roasting” with two examples. 
   Some minerals are converted to oxide by heating in the air at temperature below their melting point. This process is called roasting. For example, the roasting for zinc blende (ZnS) is: 

Heat

2ZnS + 3O2  2ZnO + 2SO2 

Roasting reaction for cinnabar (HgS) is:

Heat

HgS + O2  Hg + SO2 

Roasting reaction of copper pyrite ore is: 

Heat

2CuFeS2 + O2  Cu2S + 2FeS + SO2 

1. Write chemical reactions that take place during urea formation. 

Raw materials for the manufacture of urea: 
i. Ammonia (NH₃) 
ii. Carbon dioxide (CO₂) 

Manufacturing of urea consists of following steps. 

a. Reaction between NH3 and CO2 to form ammonium carbonate. 

NH₃ + CO₂  NH₂CONH₄ + H₂O 

b. Distillation of ammonium carbonate. 
NH₂CONH₄

c. Evaporation of liquid urea and its granulation. 
The urea solution is concentrated in vacuum evaporators, which is then rapidly cooled and sent to the prilling tower. Urea prills thus produced are packed and then marketed. 

3. Describe following with an example.

a. Roasting:
Some minerals are converted to oxide by heating in the air at temperature below their melting point. This process is called roasting. For example, the roasting for zinc blende (ZnS) is. 

2ZnS + 3O₂  2ZnO + 2SO₂ 

b. Smelting:

The method to reduce metal ions to free metal is called smelting.

The most common reducing agents are coke, carbon monoxide and hydrogen.

Example:

Fe₂O₃ + CO 2Fe + 3CO₂ 

1. Flotation:

• Pulverized ore is fed into a tank containing water and an oil-detergent mixture. 
• The mixture is agitated with air. 
• Detergents wet the mineral particles but not the silicate gangue. 
• The mineral particles rise to the top of the mixture as a forth, from where they are skimmed off. 
• Particles of the gangue fall down to the bottom. 
• The copper ore is concentrated generally by flotation process. 

4. Make a list of metallurgical operations. 

Metallurgy: 
The process of separating a metal from its ore and preparing it for use is known as metallurgy. 

Basic Metallurgical Operations: 

• Crushing, grinding or pulverizing of the ore 
• Concentration of the ore 
• Extraction of metal 
• Refining of metal. 

5. How was crude oil formed? 

Origin/formation of Petroleum or crude oil: 

• It is believed that petroleum was formed from organisms that lived hundreds of millions of years ago. 
• Plants and animals in the seas died. Their remains piled up. Layers of sand, rock and mud buried the dead organisms. 
• Over time, in the absence of air, heat and pressure of sediments and bacterial effect changed the material into dark brownish viscous liquid called petroleum. It is also called crude oil. 
• The gaseous products accumulated over the petroleum, is called as natural gas. 

6. State five specific products made from crude oil. 
Natural gas, Butane, Propane, Gasoline, Home heating oil, Plastics, Kerosene and jet fuel, Diesel. 

7. Outline basic reactions of Solvay process. 

i. Preparation of ammonical brine: 
Ammonical brine is prepared by dissolving ammonia gas in brine. Ammonical brine is fed into the carbonating tower. 

ii. Carbonation: 
In the carbonating tower, carbon dioxide is passed through ammonical brine. Following reaction takes place in it. 

CO₂ + NH₃ + H₂O NH₄HC0₃ 

NH₄HCO₃ + NaCI NaHC0₃ + NH₄Cl 

15°C 

In the lower compartments of carbonating tower, the temperature of the mixture is lowered to 15°C. At this temperature, NaHCO₃ precipitates out. 

iii. Filtration: 
Precipitates of NaHCO₃ are separated from the milky solution by filtration. It is used as baking soda. 

iv. Calcinations: 
Sodium hydrogen carbonate is heated to get sodium carbonate 

Heat

2NaHCO₃  Na₂CO₃ + CO₂ + H₂O 

Carbon dioxide released is re-cycled in the process. 

v. Preparation of carbon dioxide and slaked lime:
Carbon dioxide is produced by heating limestone in a kiln.  

CaCO₃  CaO + CO₂ 

Carbon dioxide is fed into the carbonating tower from the top. Equal amounts of lime (CaO) and water are mixed to produce slaked lime, Ca(OH)₂ 

CaO + H₂O Ca (OH)₂ 

Slaked lime is pumped to the ammonia recovery tower. 

vi. Recovery of ammonia: 
Solution congaing ammonium chloride produced in the carbonation tower is heated with slaked lime. 

Heat

2NH₄Cl + Ca(OH)₂  2NH₃ + CaCl₂ + 2H₂O 

Almost all the ammonia is recovered in this process. It is reused in the process. 

8. Draw flow sheet diagram of Solvay process. 

9. Describe the composition of petroleum. 
Petroleum is essentially a mixture of hydrocarbons particularly alkanes, cycloalkanes and aromatic hydrocarbons. Apart from hydrocarbons it may also contain compounds containing oxygen and nitrogen. 

10. Make a list of raw materials for Solvay process. 

Raw Materials: 

• Ammonia 
• Brine (concentrated sodium chloride solution) 
• Lime stone as a source of carbon dioxide and slaked lime, Ca(OH)₂ 

11. Describe the composition of petroleum. 
Petroleum is essentially a mixture of hydrocarbons particularly alkanes, cycloalkanes and aromatic hydrocarbons. Apart from hydrocarbons it may also contain compounds containing oxygen and nitrogen. 

12. Relate the study of chemistry to careers in industry. 

• Chemists have opportunities in all the field of chemistry. For instance, organic chemists have good opportunities to work in industries like petroleum, petrochemical and pharmaceutical. 
• They can research on new products, more effective medicines, new pesticides for better crops, new ways to help people reduce environmental pollution etc. 
• As a food chemist; you can work in food processing industry. 
• We can discover new methods to store, improve texture and flavour of foods. 
• In hospitals, chemists analyse blood, urine and stood samples to detect any disease, disease causing bacteria, virus, or other microorganisms. 

13. Draw flow sheet diagram of manufacture of urea.

14. Petroleum is a mixture of several compounds, which are separated in a refinery.

a) What is the name of the apparatus used for this purpose?

Fractionating tower.

b) What is the name of the process used in separating crude oil?

Fractional distillation.

1. Write name of the fraction that represents gases.

Liquefied petroleum gas (LPG)

1. Which fractions represent liquids with the lowest boiling points?

Petrol (35⁰C – 70⁰C)

15. Petroleum is a source of fuels. Name two fuels which are not obtain from petroleum. 
There are several types, such as hydrogen fuel (for automotive uses), ethanol, and biodiesel, which are also categorized as a liquid fuel. 

16. What has to be done to crude oil before it is useful? 
Crude oil is a mixture of hydrocarbons. These are separated into useful products, such as fuels, using a process called fractional distillation in fractionating tower. 

17. The table below lists some petroleum fractions with their approximate boiling points.

Fraction	Approximate Boiling Point/0C
P	Below 20
Q	35 – 70
R	170 – 250
S	350 – 500

1. Name the process by which the fractions are obtained from petroleum?

Refining

1. Which fraction will contain the shortest chain molecules?

Fraction P, Liquefied petroleum gas (LPG)

1. Which fraction will contain the longest chain molecules?

Fraction S, lubricating oil.

1. In what state will fraction P be at room temperature and pressure?

Gas

18. Should fossil fuels be burned to provide energy, or should they be used to make useful products like drugs, plastics and chemicals? 
Hemp oil or hemp-seed oil is obtained by pressing hemp seeds can be used to create biofuels to replace gasoline for diesel engines. Unlike fossil fuels, biofuels are renewable and produce less of the greenhouse gas carbon monoxide. Therefore fossil fuels should be used to make useful products like drugs, plastics and chemicals.