CLASS 10th CHEMISTRY NOTES CHAPTER 15 ENVIRONMENTAL CHEMISTRY II: WATER

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CLASS 10th CHEMISTRY NOTES CHAPTER 15 ENVIRONMENTAL CHEMISTRY II: WATER

CLASS 10th CHEMISTRY NOTES CHAPTER 15 ENVIRONMENTAL CHEMISTRY II: WATER. Environmental chemistry is the study of chemical processes that occur in water, air, terrestrial and living environments, and the effects of human activity on them. Includes topics such as astrochemistry, atmospheric chemistry, environmental modeling, geochemistry, marine chemistry, and pollution remediation.CLASS 10th CHEMISTRY NOTES CHAPTER 15 ENVIRONMENTAL CHEMISTRY II: WATER.

CLASS 10th CHEMISTRY NOTES CHAPTER 15 ENVIRONMENTAL CHEMISTRY II: WATER
CLASS 10th CHEMISTRY NOTES CHAPTER 15 ENVIRONMENTAL CHEMISTRY II: WATER

CLASS 10th CHEMISTRY NOTES CHAPTER 15 ENVIRONMENTAL CHEMISTRY II: WATER

CLASS 10th CHEMISTRY NOTES CHAPTER 15 ENVIRONMENTAL CHEMISTRY II: WATER INTRODUCTION:

CLASS 10th CHEMISTRY NOTES CHAPTER 15 ENVIRONMENTAL CHEMISTRY II: WATER. This is the first of the remaining chapters in this book dealing with environmental chemistry. In discussing this topic, the environment will look like consisting of five spheres: the hydrosphere, the atmosphere, the geosphere, the biosphere and anthrosphere. Although it is often not recognized as one of the spheres, the anthrosphere, which consists of the things that humans build, use, and make in the environment, it is very important to consider it as one of these five spheres. CLASS 10th CHEMISTRY NOTES CHAPTER 15 ENVIRONMENTAL CHEMISTRY II: WATER .

CLASS 10th CHEMISTRY NOTES CHAPTER 15 ENVIRONMENTAL CHEMISTRY II: WATER

CLASS 10th CHEMISTRY NOTES CHAPTER 15 ENVIRONMENTAL CHEMISTRY II: WATER . For this By doing, we can begin the essential process of using our human activities to preserve and improving the terrestrial environment on which we and all living organisms depend. Water is one of the five “spheres” in which environmental chemistry develops. discussed. This chapter introduces the environmental chemistry of water.CLASS 10th CHEMISTRY NOTES CHAPTER 15 ENVIRONMENTAL CHEMISTRY II: WATER.

CLASS 10th CHEMISTRY NOTES CHAPTER 15 ENVIRONMENTAL CHEMISTRY II: WATER

CLASS 10th CHEMISTRY NOTES CHAPTER 15 ENVIRONMENTAL CHEMISTRY II: WATER
CLASS 10th CHEMISTRY NOTES CHAPTER 15 ENVIRONMENTAL CHEMISTRY II: WATER

Chapter No.15

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Q. 1. Describe the occurrence/sources of water

Ans. Occurrence of water:

Water is one of the most abundant natural resources present on earth. It has been estimated’ that the total volume of water present on earth is about 1.33billion cubic kilometers. It covers nearly 70 percent of earth surface.

The major reservoirs of water on earth surface are oceans, ice caps, glaciers, underground water, inland water and atmospheric water.

The oceans contain more than 97percent of the total water. The rest of water is in the form of glaciers, ice caps, underground water, inland water and atmospheric water.

The inland water includes rivers, lakes, streams, canals and soil moisture.

 

Water reservoirs

Amount of water

1

Oceans

97.5%

2

Glaciers and ice

caps

2.14%

3

Underground water

0.6%

4

Inland water

0.2%

5

Atmospheric water

0.001%

Although enormous amount of water is present on earth but the fresh water needed for humans is only 0.2% of the total.

Q.2. Describe the importance of water?

Ans. Importance of water:

Water is very important for us and for the whole world. After air, water is second important agent for the survival of life. Without water, life is impossible. In the holy Quran the importance of water has been revealed as mentioned in the following verse:

Translation: And we made every living thing from water.

Some importance of water is given below:

i. Importance for life survival:

Humans can live without food for more than two months but without water they cannot live for more than a week. ii. Importance for body of humans and plants:

Human body contains about 65-70 percent of water while plants contain from 50 to 80 percent water.

iii. Importance for biological processes:

Water maintains various biological processes. The main function of protoplasm is due to the presence of constant amount of water in it. Th; various reactions which occur in out body, for our existence, are due to water.

iv. Medicinal Importance:

A large number of medicines are prepared in water.

v. Importance in transport:

Water is a good medium of transportation as ships and boats move on water.

vi. Importance as universal solvent:

Water is a universal solvent as it can dissolve many substances in it. Due to this property water is used for various purposes like cleaning, making medicines etc.

vi. Cooking and washing:

Cooking and washing is done in water.

Vii. As coolant:

It is used as coolant in radiators of automobiles engines. It is also used as coolant in nuclear power plants, iron and steel industries and other heavy industries.

viii. Agricultural importance:

Large amount of water is needed to cultivate fruits, vegetables and Other crops.

ix. Industrial importance:

Various industries requires water for various purposes like textile industries, paint industries, fertilizer industries Thus in short it can rightly be said that without water life is impossible.

Q.3. Write a note on maintaining water quality.

Ans. Maintaining water quality:

It is explained under the following headings:

Good quality water:

Water which supports living organisms and protects their health is good quality water.

Basis of water quality:

The quality of water is determined on the basis of its physical, chemical, biological and radiological characteristics.

Ways to maintain good quality water:

A wide range of human activities are affecting the quality of water. If this is not controlled, riot only the environment will suffer but we will face numerous problems shortage of drinking water, irrigation problems etc. Following are the some ways to maintain good quality water.

i. Awareness campaign:

As humans are responsible for affecting the good quality of water. Therefore, its quality can be maintained by promoting awareness among the people about water quality.

ii. Process waste materials:

Waste material must be properly processed and must not be added to water reservoirs.

iii. Process sewage water:

Sewage water must not be added to water reservoirs and must be processed properly.

iv. Avoid wasting water:

As only 0.2 percent of water is available of human use. Therefore, wastage of water must avoid. We must use the water whenever needed.

Q.4. Describe the composition of water.

Ans. Composition of water:

Water is a compound of hydrogen and oxygen. However, it was considered as an element before 1776 AD. In 1776 AD, Henry Cavendish, experimentally proved that water is not an element but a compound of hydrogen and oxygen. The composition of water is given below:

Composition by volume:

Water contains two parts of hydrogen and one part of oxygen by volume. This ratio can be determined experimentally by the electrolysis of water in Hoffman’s voltmeter in the presence of an electrolyte. When electric current is passed through acidified water it gives two parts of hydrogen and one part of oxygen.

Composition by mass:

Water contains one part of hydrogen to eight parts of oxygen by mass. It was experimentally determined by Joseph Proust in 1799. Since the atomic mass of hydrogen is one while that of oxygen is sixteen, so,

According to the formula H2O the ratio between masses of hydrogen oxygen is 1:8.

Percentage composition:

The percentage of hydrogen and oxygen in water by mass is given below:

2(aRniiic mass ().f)

% of H – x100

Binocular mass of H20

Putting the values we get: ,

% of H = -(1) 100

18

% of H = 11.11

Now % of 0 – 1(ammic macs of O)

X100

Molecular mass of H,0 Putting the values we get:

6)

% of 0 = 1(1x 100

18′

% o f = 88.88

Ratio between hydrogen arh, oxygen is:

H 0

11.11 : 88.88

1 : 8

Q.S. Describe the physical properties of water.

Ans. Physical properties of water:

Physical properties of water are given below:

1. Physical state:

Water exists in nature in all the three states i.e. solid gas(vapours)

2. Taste, odor and colour:

Pure water is colorless, odorless and tasteless. The water is due to the presence of dissolved substances in it.

3. Melting point and boiling point:

Under normal atmospheric pressure the melting point of water is 0 °C while the boiling point is 100 00.

4. Density:

The density of water is 1g/cm3 at 4t.

5. Heat capacity:

The specific heat capacity of water is 4.18J/g°C which is higher than any other common substances.

6. Latent heat of fusion:

The latent heat of fusion of water is 6KJ/mol (334KJ/Kg)

7. Latent heat of vaporization:

The latent heat of vaporization of water is 41 KJ/mol (2277KJ/kg)

8. Surface tension:

Water has high surface tension.

9. Polarity:

Water is a polar molecule.

10. Electrical conductivity:

Pure water is bad conductor of electricity.

11. Neutral nature:

Pure water is neutral i.e. It has a pH value of 7

Q.6. Describe the chemical properties of water.

Ans. Chemical properties of water;

The chemical properties of water are given below:

1. Thermal stability:

Water is thermally stable and only one percent of its molecules decomposes to hydrogen and oxygen at about 2000 °C.

2H20(g) 2H2 (g) + 02(g)

2. Reaction with metals:

Water reacts with metals in different ways. The reactivity of metals depends on their position in reactivity series. Some reactions of various metals with water are given below:

i. Reaction with alkali metals:

Alkali metals like sodium, potassium reacts vigorously with cold water, forming metal hydroxides and hydrogen gas. These are exothermic reactions and due to the heat produced the liberated hydrogen catches fire.

2Na(s) + 2H20(1)–♦ 2NaOH (aq) + H2 (g)

2K(s) + 2H20(1) ♦ 2KOH (aq) + H2 (g)

ii. Reaction with alkaline earth metals:

Calcium reacts with water on heating to produce calcium hydroxide and hydrogen gas.

Ca(s) + H20 (g) Ca (OH)2(s) + H2(g)

Magnesium reacts with steam to form magnesium oxide and hydrogen gas.

Mg(s) + H20 (g) Mg0(s) + H2 (g)

iii. Reaction with transition metals:

Zinc reacts with steam to form zinc oxide and hydrogen gas Zn(s) + H20 (g) ZnO(s) + H2 (g)

Steam reacts with red hot iron to form magnetic oxide and H2 gas¬3Fe(s) + 4H20(g) –*Fe304(s) + 4H2 (g)

3. Reaction with non-metals:

Water reacts with non-metals under different conditions to form different compounds.

a. Reaction with chlorine:

Water reacts, with chlorine to hydrochloric acid (HCI) and Hypochlorus acid (HOCI). Hypochlorus acid is unstable and decomposes to hydrochloric acid and atomic oxygen which decolorizes the dye molecule and also kill the germs. So chlorine can be used as bleaching agent and germicide in water.

H20 (1) + Cl2 (g) HCI (aq) + HOCI (aq)

HOCI (aq) HCI (aq) + [0]

Dye + [0] craterless dye

b. Reaction with carbon:

Water in the form of steam reacts with red hot coke to form a fixture carbon monoxide and hydrogen which is called water gas. Water .gas is used as fuel.

H20 (g) + C(s) CO (g) + H2(g)

(Water gas)

c. Reaction with silicon:

• Steam reacts with silicon to form silica and hydrogen gas. H20(g) + Si (s) Si02(s) + H2(g)

d. Reaction with sulphur:

Steam reacts with sulphur to form sulphur dioxide and hydrogen sulphide.

2H20(g) + 3S (s) ► S02(s) + 2H2S(g)

4. Reaction with metal oxide:

Water reacts with metal oxides to form metal hydroxides (bases). H20(1) + Na20 (s)—-2Na0H(aq)

H20 (1) + CaO (s) 0 Ca (OH) 2(aq)

H20 (1) + ZnO (s) Zn (OH) 2(aq)

5. Reaction with non-metal oxide:

Water reacts with non-metal oxides to produce acids.

H20 (I) + CO2 (g) —1-12003(aq)

H20 (1) + 2NO2 (g)_ HNO3(aq) + HNO2(aq)

H20 (1) + SO3 (g) H2SO4 (aq)

6. Hydrolysis reaction:

“The reaction of salt of weak acid or weak base with H2O in such a way by breaking H— OH bond to form basic or acidic solution is called hydrolysis.”

Hydro means water and lysis mean breaking. In hydrolysis reaction the water molecules splits up into H. and OH- ions by the reaction of salt of weak acid or base. It is the reverse of neutralization reaction.

NH4CI(s) + H20 (1) 0 NH4OH (aq) + HCI (aq)

CH3COONa(s) + H20 (1) 0 CH3COOH (aq) + NaOH (aq)

Q.7. Explain water as a universal solvent.

Ans.Water as universal solvent:

Water can dissolved a large number of solutes in it due to which it is called universal solvent. This property of water is due to the following three reasons:

1. Polarity

2. Hydrogen bonding

3. Dielectric constant

The detail is given below:

1. Polarity:

Consider the structure of water molecule which is polar due to high electronegativity, oxygen end of water is partial negatively charged while hydrogen end is partial positively charged. Due to this fact majority of ionic and polar solutes dissolve in water.e.g. Mineral acids, salts. Base, alcohols, sugar etc.

Dissolution of an ionic compound in water:

When an ionic compound like NaCI is added to water, the water splits its crystal to Na+ and Cl- ions. These ions will be surrounded by the water molecules. The Na’ ions are surrounded by water molecules in such a way that its negative end is directed towards positive end of water (H+) while the Cl- ions are surrounded by water molecules in such a way that its positive end is directed towards negative end of water. This process is called hydration, Majority of ionic solutes are dissolved in water by this process

2. Hydrogen bonding:

In water partial positive hydrogen end of one water molecule make bond with partial negative oxygen atom of another molecule. This is hydrogen bonding. As one water molecule has two partial positive hydrogen atoms and two lone pairs on oxygen atom. Therefore. a water molecule forms four hydrogen bonds with other water molecules in tetrahedral manner.

Due to hydrogen bonding, polar molecules like sugar, glucose, alcohols are dissolved in water. On the other hand non-polar molecules like alkanes, alkenes, alkynes, benzene etc. are not dissolved in water.

Dielectric constant:

“The measure of the ability of a substance to reduce the forces of attraction between the oppositely charged ions is called dielectric constant.”

Explanation:

According to Coulomb’s law the force of attraction between two oppositely charged bodies is directly proportional to the product of their charges and inversely proportional to the square of the distance between them. Mathematically:

FO: -1– F-

Where 01 and Q2 are oppositely charged bodies, r is the distance between them and D is constant of proportionality called dielectric constant of the medium in which the charged particles are present. Relation of dielectric constant with the solubility:

Dielectric constant is directly proportional to solubility. Greater the dielectric constant lower will be the force of attraction between the solute ions. Thus they can easily be separated and dissolved. Thus it will be easy to separate ions of an ionic or polar solute in a solvent having high dielectric constant value.

Water has a high dielectric constant value i.e. 80 at 18 ‘C due to which the ionic and polar solutes particles have less force of attraction and remain soluble in it. The dielectric constant value of other solvents are extremely small therefore, they are not good solvents.

Q: What is soft water and hard water?

Ans. Soft water:

“Water which produces lather easily with soap is called soft water hard water:

“Water which produces scum or curd with soap and affects the cleaning effect of soap is called hard water.” OR

“Water which does not produce lather easily with soap is called hard water.”

Hard water wastes soap because it does not produce lather easily. Causes of hardness of water:

Hardness of water is due to the presence of dissolved bicarbonates, sulphates and chlorides of calcium and magnesium. e.g.

• Calcium bicarbonate [Ca (HCO3)2]

• Magnesium bicarbonate [Mg (HCO3)2]

• Calcium sulphates (CaSO4)

• Magnesium sulphates (Mg SO4)

• Calcium chloride (CaCl2)

• Magnesium chloride (Mg 012)

Q.9. Describe the types of hard water.

Ans. Types of hard water:

There are two types of hard water which are as follows:

i. Temporary hard water

ii. Permanent hard water

Their detail is given below:

i. Temporary hard water:

“The water which contains dissolved calcium bicarbonate or magnesium bicarbonate is called temporary hard water.”

It is called temporary hard water because it can be removed simply by boiling.

Mechanism of formation of temporary hard water:

Rain .water dissolves CO2 of air forming carbonic acid, H2CO3, which reacts with insoluble calcium carbonate or magnesium carbonate of rocks forming dissolved calcium bicarbonate or magnesium bicarbonate.

H20 (1) + CO2 (9) ► H2CO3 (a4)

H2CO3 (aq) + CaCO3 (s) ►Ca (HCO3)2

H2003 (aq) + MgCO3 (s) ►Mg (HCO3)2

These salts exist in the form ions in water i.e.

Ca (HCO3)2(aq) ► Ca+2(aq) + 2 HCO; (aq)

Mg (HCO3)2(aq) ► Mg+2(aq) + 2 HCCX, (a

ii. Permanent hard water:

“The water which contains dissolved sulphates and chloride of calcium and magnesium is called permanent hard water.”

It cannot be removed by boiling therefore, it is called permanent hard water. These salts are dissolved by water from the earth. They are present in water in ionic form e.g.

► Ca (aq) + 2C1 (aq)

► Mg+2(aq) + (aq)

* Ca+2(aq) so42 (aq)

MgSO4 (aq) —•Mg+2(aq) SO4 (aq)

k (a

10. How temporary hardness of water can remove? OR

Describe the methods to remove temporary hardness of water.

Ans. Methods for removal of temporary hardness of water:

There are two methods for removal of temporary hardness of water which are given below:

i. Boiling method:

In this method temporary hard water, containing dissolved bicarbonates of calcium and magnesium are converted to insoluble carbonates by boiling. The carbonates of calcium and magnesium settle down and thus water becomes soft which will produce lather easily.

Ca (HCO3)2(aq) Boiling >CaCO3(s) + CO2 (g) + H20 (1)

Mg (HCO3)2(aq) Bulling >MgCO3(s) + CO2 (g) + H20 (1)

ii. Clark’s method:

This method is used to remove temporary hardness of water on large scale. In this method a calculated amount of slaked lime, Ca (OH)2, is added to the reservoirs containing temporary hard water. The slacked lime converts the soluble bicarbonates of calcium and magnesium to insoluble carbonates which settle down. Thus water becomes soft which is removed from the top.

Ca (HCO3)2(aq) + Ca (OH) 2(aq) –•2CaCO3(s) + 2H20(I) Mg (HCO3)2(aq)+Ca(OH)2(aq) –•MgCO3(s)+CaCO3(s)+ 2H20(1)

11. How permanent hardness of water can remove? Or describe the methods to remove permanent hardness of water.

Ans. Methods to remove permanent hardness of water:

There are two methods to remove permanent hardness of water which are given below:

i. Reaction with washing soda:

In this method washing soda (Na2CO3) is added to permanent hard water. The dissolved Ca+2and Mg+2 ions of sulphates and chlorides are converted into insoluble calcium carbonate and magnesium carbonate and thus the water becomes soft.

Na2CO3 (aq) + CaSO4 (aq) ♦ CaCO3(s) + Na2SO4 (aq)

Na2CO3 (aq) + MgSO4 (aq) MgCO3(s) + Na2SO4 (aq)

Na2CO3 (aq) + CaCl2 (aq) CaCO3(s) + 2NaCI (aq)

Na2CO3 (aq) + MgCl2 (aq) ♦ MgCO3(s) + 2NaCI (aq)

ii. Ion exchange method:

In this method hard water is passed through sodium zeolite (Na2Al2Si208). The sodium ion of sodium zeolite is changed with soluble calcium or magnesium ion of permanent hard water forming calcium zeolite or magnesium zeolite. Thus the water becomes soft. The reactions are given below:

Na2-zeolite + CaSO4 (aq) •Ca-zeolite + Na2SO4 (aq)

Na2-zeolite + MgSO4 (aq) -*Mg-zeolite + Na2SO4 (aq)

Sodium zeolite can be obtained naturally or it may be prepared artificially. It becomes inactive after some days and it can be made active. By reacting it with the concentrated solution of sodium chloride. Ca-zeolite + 2NaCI (aq) .Na2-Zeolite + CaCl2

Q.12. Describe the disadvantages of hard water

Ans. Disadvantages of hard water:

The disadvantages of hard water are given below:

I. Wastage of soap:

Due to hard water a large quantity of soap is wasted in the formation of scum or curd and more soap will be needed for actual washing.

ii. Wastage of fuel:

The hard water produces insulating scales in steam engines or turbines. As a result more fuel is used in producing steam.

iii. Damage to the boiler:

As hard water produces insulating scales in boiler therefore, It damages the material of boiler due to overheating. It may also cause explosion.

iv. Cause of diseases:

Drinking hard water causes various diseases of stomach and intestine.

Q.13. what is wear pollution? Describe the major sources of water pollutant

Ans: 1. Water pollution:

“When harmful biological or chemical substances called pollutants are added with water, then it is called water pollution,”

2, Water pollutants:

Harmful substances causing water pollution are called water pollutants. Common water pollutants include human or animal wastes, disease producing organisms, radioactive material, toxic metals such as mercury or lead, pesticides and acid rain. Besides these heated water discharged from power plants cause thermal pollution.

  1. Major sources of water pollutants:

The major sources of water pollutants are:

i. Industrial wastes

ii. Household wastes

iii. Agricultural wastes

iv. Animal wastes

Their detail is given below:

i. Industrial wastes:

Many industries discharge their wastes directly to streams, rivers and canals which are highly toxic and harmful to life. The industrial wastes contain highly toxic compounds of mercury, arsenic, cadmium, chromium, lead and antimony. In addition to these it also contains acids, bases, dyes, oils and grease.

Some industries and power stations use water for cooling purposes. The water become hot after use and when this hot water discharged to rivers, it destroys aquatic life especially when the temperature is above 30°C.

ii. Household wastes:

Household waste is the waste which is produced daily by cleaning of houses. It contains many things like plastics, cans, glasses, paper, burnout light bulbs etc. Household wastes can broadly be classified into three categories:

Waste water or grey water untreated sewage or black water Solid wastes

a. Waste water or grey water:

It includes the water we use in kitchens, washrooms and cleaning floors etc. This waste water is discharged directly to water bodies. It contains harmful chemicals because in most washing detergents and powder are used which contain phosphates to soften water. Besides these it may also contains acids, medicines, bleaches, dyes, insecticides, rodent killer, waxes, .hair color etc. which badly affect aquatic life.

b. Untreated sewage or black water:

Untreated sewage is the major source of water pollution because it contains pathogens such as bacteria, viruses and protozoans.

The drinking water supply pipes and open sewage water go side by side and due to leakage the sewage water pollute the drinking water. The sewage water also seeps into ground and thus pollutes the underground water.

Solid wastes:

It is also called domestic waste or urban waste. It is either in solid or semisolid form. It contains newspapers, glasses, glass bottles. cans, metals, plastics etc.

In cities these wastes are collected by municipality and are placed in open fields without proper disposal. Chemicals from these wastes dissolve in rain water which is called leaching and the resulting mixture is called leachate. It contains decomposed organic matter, newspaper ink, pesticides, fertilizer and other dangerous chemicals. The leachate either seeps into the ground or pollutes underground water or it finds its way to stream and rivers through rain water.

iii. Agricultural wastes:

Agricultural wastes are produced as a -esult of various agricultural activities. It includes manure, waste rom poultry forms and slaughterhouses, harvest waste, fertilizer run off from fields, pesticides and insecticides etc.

Non-natural or synthetic waste includes packaging, agrochemicals, used syringes, oils, tyres, batteries and building wastes like asbestos sheeting. These pollutants are very dangerous and harmful.

iv. Animal wastes:

They also pollute the water. The animal’s excreta are usually discharged into the canals and rivers which pollutes the water with micro-organisms.

Q.14: Explain water borne diseases.

Ans: Waterborne diseases:

The diseases spread by water or by the substances made by using polluted water, are called waterborne diseases.

These diseases are very dangerous and can cause death. For example, according to WHO 1.8 million people die every year by a water born disease diarrhea.

Some examples of waterborne diseases are given below:

1. Bacterial infections:

i.Dysentry:

It is one the most common waterborne diseases. It is an intestinal disease which causes abdominal cramps, anal pain and bloody stool.

ii. Cholera:

It is also water born disease which affects the intestine. Its symptoms are watery diarrhea and vomiting. Due to this, dehydration Occurs.

iii. Typhoid fever:

This is also a waterborne disease which is caused by a bacterium. It enters the blood stream, making the person infected with typhoid fever. The main symptoms of typhoid fever are high temperature and headache. Viral infections:

i. Polio:

Polio is a viral disease which usually enters the environment through the feces of infected person. This virus easily spread through air, water etc. It destroys CNS and cause paralysis.

ii. Hepatitis A and E:

These two types of hepatitis spread through contaminated water or food. These viruses attack liver and cause jaundice and even liver failure.

3. Protozoa infections:

These include Amoeboid in which amoeba enters contaminated water. The people face gastrointestinal illness.

4. Parasitic infections:

Guinea worm and pinworm infections are common parasitic infections. It is mainly loud in children. They spread by eating the eggs of these worms through contaminated water or food. They cause ulcer, fever, vomiting, nausea etc.

5. Arsenicosis:

It is a disease caused by drinking water with high levels of arsenic. It is also called arsenic poisoning. The symptoms of arsenic poisoning are excess of saliva, vomiting, nausea, blood in urine etc. The WHO recommends limit of arsenic in drinking water as 0.01nig/m3.

6. Fluorosis:

It is a disease caused by drinking water with excess of fluorine. It damages bones and teeth.

Q.15: What are the effects of water pollutants?

Ans: Effects of water pollutants:

The effects of water pollutants are not only dangerous for humans but also for other living organisms. Polluted water is unsuitable for drinking, recreation, agriculture and industry. Polluted water destroys aquatic life and reduces its reproductive ability.

The major effects of water pollutants are as under:

a. Cause of infectious diseases:

Human infectious diseases are among the most serious effects of water pollutants especially in developing countries like Pakistan. These diseases occur when parasites or other disease causing micro-organisms are transmitted through contaminated water. The infectious diseases caused by water pollution include typhoid, dysentery, cholera, amoebiasis. ascariasis and hepatitis etc.

b. Nutrient pollution:

It is the most dangerous problem in coastal areas, rivers, streams and lakes. The discharge of nitrogen, phosphorus and other nutrients

Comes from agriculture. Waste disposal, coastal development and fossil fuels. This enrichment of nutrients (nitrogen, phosphorus etc.) in water bodies to enhance the harmful overgrowth of algae is called eutrophication.

Eutrophication causes nutrient pollution. Red and brown algae etc. are toxic and they have a direct effect to pollute water. Algae also pollute water when they die they are decomposed during which oxygen is used and shortage of oxygen occur in water in which fish species and other aquatic animal die. Algal growth also blocks the sunlight which is needed by sea grasses which serve as food and shelter for many fish species.

Effects of chemical contamination:

Some of the major effects of chemical contamination are given below:

i. Effects of pesticides:

Pesticides affect and damage nervous system, liver, endocrine system, glands and DNA. They also cause cancer and other dangerous disease that last for a long period of time.

ii. Effects of oils and petrochemicals:

Oil and petrochemical change the ecology of aquatic habitats and the psychology of marine animals. In humans it causes gastro intestinal irritation, liver and kidney damage nervous system effects.

iii. Effects of mercury and its compounds:

!n young children mercury and its compounds cause autism, brain damage, learning defects and incomplete mental development. In adults they cause Parkinson, Alzheimer’s diseases and heart diseases.

iv. Effect of persistent organic pollutants:

Persistent organic pollutant (POP) such as DDT (dichlorodiphenyltrichloroethane), dioxins and PCB(polychlorinated biphenyl) enter our body through food. POPs cause disruption of hormones in humans and animals, affect reproductive system and cause breast cancer in women.

d. Thermal water pollution:

The heated water is used in many industries which is directly thrown to rivers, streams etc. It affects the aquatic life in two ways:

i. The warmer water decreases the solubility of oxygen and many aquatic organisms die due to shortage of oxygen.

ii. Many aquatic animals’ especially young animals cannot survive above 30 °C and will die.

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A. Choose the correct Option.

1. Water has the ability to dissolve ionic-compounds due to

a. Ionic forces b. Dipole-dipole forces

c. Ionic-dipole forces d. Hydrogen bonding

2. All salts because the water become hard except

a. Calcium Chloride b. Calcium Bicarbonate

c. Magnesium sulphates d. Sodium chloride

3. The salt which causes temporary hardness in water is

a. Magnesium sulphates b. Calcium Chloride

c. Magnesium chloride d. Calcium ‘bicarbonate

4. Chlorine acts as bleaching agent in the presence of a. HCI b. H2O c. NaOH d. HNO3

5. Permanent hardness of water is removed by adding

a. Washing soda b. Soda lime

c. Caustic soda d. Baking Soda

6. Most of the aquatic animals cannot survive in water above,

a. 20°C b.25°C c. 30°C d. 35°C

7. The destiny of water maximum at

a. -40°C b. 40°C c. -4°C d. 4°C

8. The disease which cause liver infection

a. Hepatitis b. Cholera c. Typhoid d. dysentery

9. All are waterborne disease except

a. Hepatitis b. Malaria c. Typhoid d. dysentery

10. Water gas is a mixture of

a. CO and H2 b. C and H2 C. CO and H2O d. C and H2O

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1. Identify the factors which are responsible for dissolving polar substances in water?

Ans. Factors responsible for dissolving polar substances in water: The following two factors are responsible for dissolving polar substances in water:

i. Polarity of water

ii. Hydrogen bonding

The detail is given below.

1. Polarity:

Consider the structure of water which is polar. Due to high electronegativity, oxygen end of water is partial negatively charged while hydrogen end is partial positively charged. Due to this fact majority polar solutes dissolve in water. E.g. alcohols, sugar etc.

2. Hydrogen bonding:

In water partial positive hydrogen end of one water molecule make bond with partial negative oxygen atom of another molecule. This is hydrogen bonding. As, one water molecule has two partial positive hydrogen atoms and two lone pairs on oxygen atom. Therefore, a water molecule forms four hydrogen bonds with other water molecules in tetrahedral manner.

Due to hydrogen bonding, polar molecules like sugar, glucose, alcohols are dissolved in water. On the other hand non-polar molecules like alkanes, alkenes, alkynes,’ benzene etc. is not dissolved in water.

(Water)

Ethyl alcohol) Hydrogen bond

XI

‘Figure: Hydrogen bonding between ethanol and water molecules

2. Explain why it is advisable to drink boiled water?

Ans. Reason for boiled water:

When water is boiled the disease causing micro-organisms are killed. Besides this the temporary hardness of water which is also dangerous for health is removed. That is why it is advisable to drink boiled Later

3.Why ice floats on the surface of water?

Ans. Reason for floating of ice on water surface:

The density of ice (0.917g/ml). It is less than the density of water (1g/m1) because in ice, the water molecules are arranged hexagonally in which six molecules of water are arranged in the form of a ring having empty spaces due to which the volume of ice increases and density decreases. Thus due to low: density, ice floats on water surface.

Q 4: Explain the importance of water and its quality?

Aps:For answer see questions no. 1 and 2

Q 5. What is eutrophication? How does it pollute water?

• Ans. Eutrophication:

The enrichment of nutrients (nitrogen. phosphorus etc.) in water bodies to enhance the harmful overgrowth of algae is called eutrophication.”

Eutrophication:

I Eutrophication cause nutrient pollution. Red and brown algae etc. are toxic and they have a direct effect to pollute water

ii. Algae also p011ute water when they die they are decomposed during which oxygen is used and shortage of oxygen occur in water in which fish species and other aquatic animal die.

I-. • Algal growth also blocks the sunlight which is needed by sea grasses which serve as food and shelter for many fish species

Q 6.How chemistry helps to maintain clean swimming pools?

Ans. swimming pools:

Chlorine gas is a chemical element produced through chemical processes. It is used in calculated amount in swimming pools to kill micro-organisms.

Actually, chlorine reacts with water to form hydrochloric acid(HCI) and Hypochlorus acid(HOCI). Then the Hypochlorus acid decomposes to produce atomic oxygen and HCI. The atomic oxygen kills the germs. It also acts as bleaching agent. The reactions are given below:

H20 (1) + Cl2 (g) —-, HCI (aq) + HOCI (aq)

HOCI (aq) —* HG1 (aq) + [0]

Waver, the amount of chlorine must be in the range of 0.5mg/dm3 to g/m3. Because, in excess amount it causes eye irritation.

Make the distinction between soft water and hard water.

Ans. Distinction between hard and soft water:

The distinction between hard and soft water below: Soft water hard water

  1. “Water which produces lather “Water which do not why water is universal solvent? \…—-‘—’

Ans. Water as universal solvent:

For answer see question no.7

Q 9. Give some disadvantages of detergents?

Ans. Disadvantages of detergents:

Some of the disadvantages of detergents are given below:

i. Non-biodegradable:

The major disadvantage of detergents is that they are non-biodegradable.

ii. Cause water and soil pollution:

They cause water and soil pollution.

iii. Damage to fabric:

Excessive alkalies used in some detergents can damage the fabric.

iv. Wastage of water:

Detergents waste large amount of water, as more amount of water is required for rinsing and removing foam.

Q 10. Identify the toxic substances in household wastes.

Ans.Toxic substances in household wastes:

Household wastes are classified into three categories. These categories and their toxic substances are given below:

a. Waste water or grey water

B .Untreated sewage or black water

C.Solid wastes

a. Was water or grey water:

It includes the water we use in kitchens, washrooms and cleaning floors etc. It contains harmful chemicals because in most washing detergents and powder are used which contain phosphates to soften water. Besides these it may also contains acids, medicines, bleaches, dyes, insecticides, rodent killer, waxes, hair color etc. which badly affect aquatic life.

Untreated sewage or black water:

Untreated sewage is the major source of water pollution because it contains pathogens such as bacteria, viruses and protozoans.

c. Solid wastes:

It is also called domestic waste or urban waste. It is either in solid or semisolid form. It contains newspapers. Glasses, glass bottles, cans, metals, plastics etc.

Chemicals from these wastes dissolve in rain water which is called leaching and the resulting mixture is called leachate. It contains decomposed organic matter, newspaper ink, pesticides, fertilizer and other dangerous chemicals.

i. We make a large number of solutions in water which are used for drinking, washing and other purposes.

ii. A large number of medicines are made by dissolving chemical substances in it.

iii. Water plays an important role in removing waste materials from the body by dissolving them which are removed in the form of sweat.

iv. Water dissolves many salts and minerals which are then taken by plants and enhances their growth:

v. Rain water and irrigation water dissolves the fertilizers given to the plants which are then taken by plant. As these fertilizers cannot be used by plants in solid state.

Harmful effects of water as an excellent solvent;

As water is an excellent solvent therefore, a large number of harmful

Substances also get dissolved in it making it unsuitable for drinking.

: This water causes various diseases in humans and other organisms.

Ii It causes hardness of water by dissolving bicarbonates, sulphates and chlorides of calcium and magnesium.

Q 3. (a) Classify temporary hard and permanent hard water?

Ans.Classification of temporary hard water:

“The water which contains dissolved calcium bicarbonate or magnesium bicarbonate is called temporary hard water.”

It is called temporary hard water because it can by removed simply by boiling.

Thus temporary hard water types:

i. Due to bicarbonates of calcium

ii. Due to bicarbonates of magnesium

iii. Due to mixture of above salts

These salts exist in the form ions in water i.e.

Ca (HCO3)2(aq) ► Ca#2(aq) + 2 HCO; (aq)

Mg (HCO3)2(aq) l• Mg-2(aq) + 2 NCO,- (aq)

ii. Classification of permanent hard water:

“The water which contains dissolved sulphates and chloride of calcium and magnesium is called permanent hard water.”

It cannot be removed by boiling therefore; it is called permanent hard water. Thus permanent hard water has the following types:

i. Due to sulphates of calcium

ii. Due to sulphates of magnesium

iii. Due to chlorides of calcium

iv. Due to chlorides of magnesium

  1. Due to mixture of above above salts

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Q 1. (a)Enlist the main sources of water.

Ans. For answer see question no.1

(b)How would you categorize physical properties of water?

Ans. For answer see question no.5

(c)Predict the products of reaction with water?

Is K ii. Cl2 iii.CaO IV. CH3COONa v. C

Ans:

i. Reaction of water with potassium:

Potassium reacts vigorously with cold water, forming potassium hydroxide and hydrogen gas. This is an exothermic reaction and due to the heat produced the liberated hydrogen catches fire.

2K(s) + 2H20(I) 2KOH (aq) + H2 (g)

Ii.Reaction with chlorine:

Water reacts with chlorine to hydrochloric acid (HC!) and hypochlorousacid (HOCI). Hypochlorus acid is unstable and decomposes to hydrochloric acid and atomic oxygen which decolorizes the dye molecule and also kills the gems. So chlorine can be used as bleaching agent and germicide in water.

H200) + Cl2 (9) – ► HCI (aq) + HOCI (aq)

HOCI (aq) ♦ HCI (aq) + [0]

Dye + [0] colorless dye

iii. Reaction with calcium oxide:

Water reacts with calcium oxide to form slaked lime or calcium hydroxide.

H20 (1) + Ca0 Ca (OH) 2(aq)

iv. Reaction with sodium acetate:

Water reacts with sodium acetate to form acetic acid and sodium hydroxide.

CH3COONa(s) + H20 (1) CH3COOH (aq) + NaOH (aq)

v. Reaction with carbon:

Water in the form of steam reacts with red hot coke to form a mixture ribbon monoxide and hydrogen which is called water gas. Water gas is Ed as fuel.

H20 (g) + C(s) CO (g) + H2 (g)

(Water gas)

Q: Water is an excellent solvent. Explain how this property is beneficial for life but sometimes harmful for us?

Ans: Benefits of water as an excellent solvent:

Water is an excellent solvent and dissolved a large number of solutes in it. This property of water is very beneficial for us for example: These salts are dissolved by water from the earth. They are present in water in ionic form e g.

CaCl2 (aq) -0. Ca+2(aq) + 2Crom

MgCl2 (aq) l• Mg+2(aq) + 2C1— (aq)

CaSO4 (aq) Ca+2(ac) + SO4 (aq)

MgSO4 (aq) IP” Mg+2(aq) + SO4 2 (aq)

(b)What methods could be adopted to remove temporary hardness of water?

Ans. For answer see question no.10

(c)What methods could be adopted to remove permanent hardness of water?

Ans. For answer see question no.11

Q 4. (a)Why water is important for us?

Ans: For answer see question no.2

(b) Write disadvantages of hard water.

Ans. For answer see question no.12

(c)Enlist the advantages of waste water treatment.

Ans. Advantages of waste water treatment:

Some of the advantages of waste water treatment are given below:

i. Quality improvement:

Waste water treatment improves the quality of water and makes it fit for drinking.

ii. Germs removal:

Waste water treatment also eliminated germs from water which are dangerous to health:

iii. Prevention from diseases:

Waste water treatment protects us from various waterborne diseases.

iv. Water preservation:

It also preserves water as it makes large amount of water fit for use. Otherwise it could be wasted.

Q: How would you relate agricultural wastes and water pollution?

Ans. Agricultural wastes and water pollution:

Agricultural wastes are produced as a result of various agricultural activities. It includes manure, waste from poultry forms and slaughterhouses, harvest waste, fertilizer run off from fields, pesticides and insecticides etc.

Non-natural or synthetic waste includes packaging, agrochemicals, used syringes, oils, tyres, batteries and building wastes like asbestos sheeting. These pollutants are very dangerous and harmful.

Thus, agricultural wastes pollute the water through various toxic pollutants.

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1, choose the correct answer.

1. Human body contains about of water.

(a) 70% (b) 60% (c) 90% (d) 80%

2. Plant contains about of water.

(a) 70% (b) 60% (c) 90% (d) 80%

3. The density of water by cooling below 4°c.

(a) Increase (b) decrease (c) remain same (d) negligible.

4. Glycol is added to car radiator to prevent of water.

(a) Freezer (b) boiling

(c) Contaminating (d) evaporation.

5. one gram of water requires of heat to raise its temperature by one

Degree centigrade:

(a) 4.2 joules (b) 4.9 joules (c) 5.6joules (d) 4.18 joules.

6. The vital function of protoplasm is due to the presence of,

(a) Water (b) minerals (c) fats (d) calcium.

7. The quantity of fresh water present on earth surface is only about.

(a) 2.5% (b) 2.2% (c) 0.04% (d) 0.2%.

8. In water, ratio of oxygen and hydrogen by mass is,

(a) 2:1 (b) 1:2 (c) 8:1 (d)1:8.

9. The reason of unusual physical properties of water is due to the presence of,

(a) Hydrogen bonding (b) covalent bond

(c) Coordinate covalent bond (d) none of these.

10. The density of water is one gram per centimeter cube at,

(a) 0°c (b) 4°c (c) 60°c (d)100°c.

11. The volume of water increase, when its temperature decreases below,

(a) 4°c (b) 5°c (c) 10°c (d) 20°c.

12. The enormous quantity of water present on earth surface act as giant thermostat, due to its high,

(a) Boiling point (b) density

(c) Heat capacity (d) latent heat values.

13. The latent heat of fusion of water is,

(a) 333kj/kg (b) 6kj/Mol (c) 4.2kj/mol (d) 2.4kj/mol.

14. Water gas is a mixture of,

(a) Steam &air (b) hydrogen &oxygen

(c)CO & Hydrogen gas (d) H2O & 02.

15. Chlorine acts as bleaching agent in the presence of,

(a) HCI (b) H2O (c) NaOH (d) HNO3.

16. The chemical formula of magnetic oxide is,

(a) Fe304 (b) Fe203 (c) Fe0 (d) Fe203.H20.

17. Rain water is acidic in nature, because air contain,

(a) Oxygen (b) carbon dioxide (c) nitrogen (d) all of these.

18. Nutrient pollution of water bodies is caused by,

(a) Pathogens (b) calcium &magnesium

(c) Nitrates& phosphates (d) acid rain.

19. Most of the aquatic animals cannot survive above,

(a) 20°c (b) 25°c (c) 30°c (d)40°c.

20.In water, ratio of oxygen and hydrogen by mass is

(a) 2:1 (b) 1:2 (c) 8:1 (d) 1:8.

21. Ocean contain of water.

(a) 97% (b) 80% (c) 50% (d) 60%

22. Small organism that cause diseases are called

(a) Pathogen (b) mucosa (c) pesticides (d) herbicides.

23. The minimum concentration of chlorine in swimming pool is .

(a) 0.5mg/L (b) 0.4mg/L (c) 0.7mg/L (d) 0.3mg/L.

24. The maximum concentration level of chlorine I swimming pobl is .

(a) 1.5mgIL (b) 1-7mg/L (c) 2mg/L (d) 1.9mg/L.

25. The unusual physical properties of water are due to

(a) Covalent bond (b) non-polar (c) hydrogen bond (d) both a & c. 26.Temporary hardness of water is caused by:

(a) CaO (b) Ca (OH) 2 (c) CaCl2 (d) Ca (HCO3)2

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