GL TEACHER SCHOOL EDUCATION
DEPARTMENT JAMMU AND KASHMIR
Water ..........Lesson no 16
Points to Remember.
- We all including plants and animals live on water.
- Water is used for drinking, bathing, washing and many other purposes.
- Water is essential for sustenance of life.
- It is important medium for all life processes.
- Water is a universal solvent.
- India has rich water bodies (Rivers, lakes, streams and ponds) both as surface and ground water.
- Water cycle maintains ecological balance in nature.
- Indiscriminate felling of plants has upset water cycle and resulted in water shortage.
- Water is renewable if it is protected against wastage and pollution.
- Every organism consists mostly of water.
- We must take 2.4 litres of water daily which may be in the form of water we drink or other soft drinks and food we eat.
- The fluidity and solubility are the two main properties which make it useful in the processes of digestion, blood circulation and excretion.
- Water helps to regulate temperature of our body.
- Each person in a day may use 50 litres of water on the average.
- To raise crops we need to irrigate crops.
- Seeds of plants are transported by water.
- Water is used in food processing and for making soft drinks.
- Water is also used for cooling gases produced in refining oil and hot steel.
- Water is also used for generating electricity, for transporting goods and heavy machinery and for water recreations,
- Sources of water-Taps, Tube wells, Rivers, Lakes, Sea water, Ground water and spring etc.
- The molecules that make water are always moving.
- Water exists in three states-solid, liquid and gaseous,
- Interconversion of states of water is brought about by change of temperature and pressure.
- Oxygen and carbon dioxide are soluble in water.
- Dissolved oxygen helps aquatic organisms to survive in water.
- Aquatic plants use carbon dioxide dissolved in water for preparation of their food.
- During summer the amount of oxygen dissolved in water reduces.
- Population explosion and large scale industrialization has resulted in water pollution.
- Oil refineries situated near the sea shore also pollute water.
- Potable water should not contain suspended or soluble impurities and harmful bacteria.
- Alum is added to water for settling suspended materials.
- Bleaching powder kills bacteria present in water.
- Aeration improves taste and odour of water.
- The molecular formula of water is H₂O which suggests that water molecule is made of two atoms of hydrogen and one atom of oxygen.
- Water molecules can be split into its constituting elements hydrogen and oxygen by passing current.
- Pure water freezes at 0°C and boils at 100°C.
- Pure water is a bad conductor of heat and electricity.
- In a desert cooler, the evaporating water absorbs heat from air and cools it.
- Density of a substance is the amount of mass it contains in unit volume of it.
- Water has maximum density at 4°C.
- Most substances contract when they freeze whereas water expands when it freezes.
- Because of low density ice floats on water surface.
- Saline water corrodes metals.
- Sea water is salty which makes it unfit for drinking.
- Removing dissolved salt from saline water is called desalination.
SOME IMPORTANT DEFINITIONS
Hydroelectricity. Electricity produced by the use of energy of falling water to turn water turbines that drive a generator
Water table. The upper layer of saturated zone of underground water that has collected above watertight rocks is called water table.
Interchangeability. The phenomenon of change of one state of water into another and back to the original state is called interchangeability.
Universal solvent. The property of water to dissolve many substances is called universal solvent.
Boiling point. The temperature at which a liquid changes into its vapour is called boiling point.
Freezing point. The fixed temperature at which a liquid changes into its solid state is called freezing point.
Water cycle. The evaporation of water into air and then formation of water droplets by condensation and then falling as heavy drops as rain on the earth is called water cycle.
Cloud. The condensed group of water droplets which come together with dust form cloud.
Polluted water. The change of quality and composition of water due to addition of undesirable substance into it make it polluted water.
Potable water. The water which is suitable for drinking purpose is known as potable water. It does not contain any suspended soluble impurities and harmful bacteria.
Electrolysis. The split up of water molecules into its constituents by the passage of electricity is called Electrolysis.
Heat capacity. It is the ability of a substance to absorb heat without becoming much warmer itself.
Density. The density of substance is the amount of mass it contains for each unit of its volume. It is measured in g/cc
Desalination. The process of removing dissolved salts from saline water is called desalination.
TEXT BOOK EXERCISES
(I) Answer the following questions in one word or a figure.
Q. 1. What is the apparatus used for the electrolysis of water called?
Ans. Voltameter.
Q. 2. What is the volume ratio for hydrogen to oxygen in water ?
Ans. Hydrogen: Oxygen (Volume) = 2 : 1.
Q. 3. At what temperature does water change into steam?
Ans. 100°C.
Q. 4. At what temperature does water change into ice ?
Ans. 0° C.
Q. 5. At what temperature is the density of water maximum ?
Ans. 4° C.
Q. 6. What is the composition of water.
Ans. Water is composed of two atoms of hydrogen and one atom of oxygen. (i.e. Hydrogen: Oxygen = 2 : 1)
Q. 7. Which is lighter: water or ice ?
Ans. Ice.
Q. 8. Name the largest source of water on earth.
Ans. Sea.
Q. 9. Name a liquid which is heavier than water.
Ans. Honey.
Q. 10. Name a chemical which is used to kill germs in water.
Ans. Bleaching powder.
(II) Fill in the blanks :
1. Water helps in the.........of seeds and fruits.
2. About 97% of water is in the...........
3. The property of............ makes water useful in the process of digestion
4. The human body has about 70% of water by............
5. Seed cannot.............. without water.
6. Removing dissolved salts from saline water is called...........
7. The process of using electricity to split water molecule is called ...............
8. The.............. of liquid water is 1 g/co.
9. The density of water is maximum at...............
10. The freezing point of water is...........
Ans. 1. Germination 2. Tomato 3. Solubility 4. Weight 5. Grow 6. Desalination 7. Electrolysis 8. Density 9. 4°C 10.0°C.
(III) Write "True' or 'False' against each of the following statements :
1, Ice has lower density than water.
2. Rain water is the purest form of natural water.
3. The solubility of gases in water increases with the increase in temperature.
4. During the summer, the amount of oxygen dissolved in water is increased and fish die..
5. Pure water tastes sweet.
6. The use of fertilizers pollutes water.
7.The ratio of oxygen to hydrogen in water is 2: 1.
8. The states of water are interchangeable.
Ans. 1, Ice has lower density than water.
True
2. Rain water is the purest form of natural water.
False
3. The solubility of gases in water increases with increase of temperature.
False
4. During the summer, the amount of oxygen dissolved in water is increased and fish die.
False
5. Pure water tastes sweet.
False
6. The use of fertilizers pollutes water.
True
7. The ratio of oxygen to hydrogen in water is 2: 1. False
8. The states of water are interchangeable.
True
(IV) Answer the following questions:
Q. 1. State any three physical properties of water.
Ans. Physical Properties of water
1. Nature. Pure water is colourless, tasteless and odourless
2. Boiling point. Pure water boils at 100°C.
3. Freezing point, Pure water freezes at 0°C. The presence of impurities lowers the freezing point.
4. Density. The density of water is 1g/cc at 4°C
5. Solubility, Water can dissolve almost all the substances.
Q. 2. How will you determine the freezing point of water?
Ans. Determination of Freezing point of water
1. Take some dried broken pieces of ice in a glass beaker.
2. Fix a celsius thermometer in a stand.
3. Lower the bulb of a celsius
thermometer inside the beaker so
that its bulb is well within ice as
shown in fig.
4. Note the temperature of ice..
5. Go on measuring the
temperature at intervals. You will
notice that the temperature shown
by the thermometer remains
constant at 0°C till all the ice has
melted.
This constant temperature is called freezing point of ice which is also the melting point of ice.
Q. 3 How will you determine the boiling point of water ?
Ans. Determination of Boiling point of water
1. Take a glass beaker.
2. Fill half of the beaker with water.
3. Fix a half degree celsius
thermometer in a stand and lower
its bulb inside water.
4. Heat the beaker from below as shown in the fig
5. Go on heating till the water
in the beaker begins to boil.
6. Note this temperature which
would be about 100°C and is called
boiling point of water.
Note. The presence of impurities in water raises the boiling point of water above 100°C,
Q. 4 Briefly describe the water cycle in nature.
Ans. Water Cycle. The water from the earth get evaporated from oceans, rivers and ponds and reaches high up in the atmosphere. The water vapours condense to form clouds and fall back on the earth in the form of rain. constitutes water cycle in nature.
 |
| Fig. Water cycle in nature. |
Q. 5. Mention five uses of water.
Ans. Uses of Water
1. Water has property of fluidity and solubility. These properties make it useful in the process of digestion, blood circulation and excretion.
2. Water helps in regulating body temperature.
3. In our homes, we need water for cleaning, cooking, bathing and carrying away wastes.
4. Water is also used in irrigating agricultural fields.
5. Water is used in food processing industry, soft drinks.
6. Water cools the hot gases produced in refining oil, hot steel made in steel mills.
7. Water is used to produce electric power at hydroelectric power stations for lighting homes and to run industry.
8. We depend on water for transportation of heavy products such as coal, grains and machinery etc.
Q. 6. How is water polluted ?
Ans. Pollution of water, water is polluted in variety of the ways given below;
1. Domestic sewage, Discharge of sewage water
containing human urine and faeces, animal dung, cloth washing etc are sources which pollute water,
2. Pollution of water also results from excessive use of fertilizers and animal wastes for increasing agriculture yields.
3. Hunting of water birds and migratory birds and weed infestation also results in water pollution.
4. Release of toxic industrial wastes into water bodies,
5. Oil refineries near the sea shore and discharge of crude oil during transportation also causes water pollution.
Q. 7. How can pollution of water be prevented?
Ans. Prevention of water pollution. The pollution of water can be prevented by the following ways:
1. For each individual house separate septic tank should be used.
2. Before allowing the sewage from houses or wastes from factories to flow into water reservoirs it should be cleaned.
3. Biological treatment for the sewage should be carried out.
4. The use of fertilizers should be judicious and minimal.
5. The use of synthetic detergents should be minimized.
6. Dead animals and human bodies should not be thrown into water bodies.
Q. 8. What is electrolysis ? Describe briefly the
electrolysis of water.
Ans. Electrolysis. The process of splitting molecules of water by the passage of current, is called electrolysis.
Electrolysis of water
1. Take a voltameter.
2. Fill 4th of the volume of voltameter with water.
3. Add 2-3 drops of sulphuric acid to make water good conductor of electricity.
4. Set up the apparatus and connections as shown in the Fig.
5. Fill two graduated test tubes with water and close them with your thumbs.
6. Invert each of these test tubes on the two electrodes without splitting water.
7. Connect electrodes to the terminals of the source of electricity (say battery) with connecting wires.
8. Press the switch and allow the current to pass through water. You will see bubbles being formed on the two electrodes and rising into the test tubes. After some time you will notice
that one test tube has collected more gas than the other.
9. Test the gases collected by bringing burning match stick near the mouth of the test tube having been removed from the electrodes. The test tube with more gas burns with popping
sound is hydrogen. The burning matchstick brought to the other test tube burns brightly. It is oxygen gas.
Q. 9. Mention the names of some industries which pollute water.
Ans. Industries which contribute to water pollution
1. Industry manufacturing paint and varnishes.
2. Industry manufacturing sulphuric acid and nitric acid.
3. Industry engaged in manufacturing synthetic detergent, urea and other fertilizers.
4. Industry engaged in manufacturing insecticides and other toxic substances.
5. Oil refinery
Q. 10 Give the names of some metals whose
compounds are toxic.
Ans. Names of metals whose compounds are toxic in nature Copper, zinc, lead, nickel, mercury and arsenic are some of the metals the compounds of which are toxic in nature.
Q. 11. Why is saline water not suitable for drinking?
Ans. Saline water means water that contains salt. Drinking salty water makes a person vomit. Therefore, saline water cannot be used for drinking.
Q. 12. What is potable water? Give its characteristics,
Ans. Potable Water. The water which is used for drinking, purpose is known as potable water,
Characteristics of Potable water
Potable water should be clean, fresh and free from suspended or soluble impurities and harmful germs such as bacteria.
Q. 13. Name the elements that water is composed of.
Ans. Elements of water
Water is composed of two elements :
(i) Hydrogen (ii) Oxygen.
Q. 14. Name two physical changes that take place in the water cycle.
Ans. Physical changes taking place in water cycle.
1. Evaporation. Change of water into its vapours with increase of temperature
2. Condensation. Change of water vapours into drops of liquid water on cooling at high altitudes.
Q. 15. How will you determine that a given sample of water is pure or polluted ?
Ans. Determination of Purity of water
1. For suspended Impurities.
To look for any suspended impurity present in given sample of water, add alum piece. If some particles settle down then it shows the presence of suspended impurities in the sample.
2. For dissolved Impurities.
(i) Take some drop of water on a watch glass. Heat it on a burner flame to evaporate it to become dry. If some deposit is seen on the watch glass then it confirms the presence of soluble salt in the sample.
(ii) Determine the boiling point of the given sample of water If it happens to be 100°C then the sample of water is pure and in case the boiling point of water is more than 100°C
then it contains some soluble salts so that it is polluted water.
3. Presence of Germs and bacteria. Take a drop of the given sample of water on watch glass. Observe it under microscopic for the presence of some germs. It they do not appear then sample is pure otherwise polluted.
Q. 16. What is salinity ? Describe the process of desalination
Ans, Salinity. It is the property of water containing soluble salts.
Process of Desalination. The process of removing dissolved salts from water is called desalination. It is done in the following ways:
i) Take two huge tanks A and B connected with each other through semipermeable membrane.
(ii) Collect sea water (saline water) in tank A.
(iii) Apply pressure on saline water in tank A with an external source.
(iv) The increased pressure would retain salt only, pure water would be allowed to pass through semipermeable membrane.
(v) Water so collected in tank B would be of pure water.
(V) Choose the correct answer :
1. At which temperature is the density of water
maximum ?
(a) 0°C
(c) -4°C
(b) 4°C
(d) 100°C.
Ans. (b) 4°C.
2. What is the volume ratio of hydrogen to oxygen in water ?
(a) 1:2
(c) 2:1
(b) 1:3
(d) 3:1.
Ans. (c) 2:1.
3. Which one of the following liquids has the greatest heat capacity ?
(b) Glycerine
(d) Oil.
(a) Water
(c) Kerosene
Ans. (a) Water.
4. Which one of the following metals is not affected by water?
(a) Sodium
(c) Calcium
(b) Potassium.
(d) Boron.
Ans. (d) Boron.
IN-TEXT QUESTIONS
WORKSHEET 16.1. (Text Book Page 243)
Q. 1. By what per cent water is present in your body?
Ans. About 65%.
Q. 2. By what per cent water is present in a potato?
Ans. 80%.
Q. 3. How much water do you require for different activities ? Calculate the quantity of water used for different activities and put them in a tabular form.
Ans
Activities where water is used. Water is used in litres
Bathing. 30
Drinking 10
Washing clothes 50
Cleaning utensils 15
Cleaning house 15
Q. 4. List any four uses of water in industries.
Ans. Uses of water industry.
1. Water is used as raw material in soft drinks, canned foods and many more products.
2. Water is used in the industry for cooling hot gases produced during refining of oil.
3. In electric power stations water is used for generating steam that supplies energy to run machines that produce electricity .
4. For industrial production of Hydrogen and Oxygen water is electrolysed.
5. Water is used in transport industry for carrying heavy machinery, grains etc.
Q. 5. What is the use of water in hydroelectric power stations?
Ans. Use of water in Hydroelectric Power stations
In hydroelectric power stations, water is made to fall from a height of dams or waterfalls on wheels of turbines. The potential energy of water at height is converted into kinetic energy of running water which when falls on the turbines
rotates it to convert into mechanical energy for driving a generator where electric energy is produced.
WORK SHEET 16.2. (Text Book Page 246)
Q. 1. Name the main source of water.
Ans. Rain.
Q. 2. Name the main source of water of your home.
Ans. Tap water.
Q. 3. What is the source of underground water.
Ans. Well or spring.
Q. 4. Why do we not use sea water?
Ans. Because it is polluted water and contains dissolved salts.
Q. 5. From where does water come in rivers and
streams?
Ans. Rain fall
Q. 6. Define water table.
Ans. Water table. The upper limit of the zone of rain water collected in water tight layers of rock underground is called water table.
Q. 7. What is a spring ? Is spring water drinkable?
Ans. Spring. The underground water collected in water tight layers of rock finds a way out from some crack in the rock to form a flow of water to the surface is called spring. The spring
water is clean and filtered. Therefore, it is drinkable water.
WORKSHEET 16.3. (Text Book Page 248)
Q. 1. Name the three states of water.
Ans. Different states of water
(i) Solid (ice) (ii) Liquid (water) (u) Gas (water vapours)
Q. 2. Why do fish in shallow ponds die during summer .
Ans. During summer, the water in the shallow pond becomes hot due to heat. As a result of increase of temperature, the amount of oxygen dissolved in water reduces and fishes die.
Q. 3. Name the factors that are responsible for the change of state of substance.
Ans. Temperature and pressure.
Q. 4. Define Temperature.
Ans. Temperature. It is defined as the degree of hotness or coldness of the body. It determines the direction of flow of heat.
Q. 5. Draw a diagram to explain the interchange. ability of states of water,
Ans, Interchangeability of States of Water
Q. 6. Explain water cycle in nature.
Ans. Water Cycle. See Q IV (4) under the heading Textual Exercises.
Q. 7. Give examples to show that water is universal solvent.
Ans. Water as a universal solvent
(1) When water evaporates to form clouds, it is pure water, but when it falls as rain, many gases from air dissolve in rain water.
(2) Rain water when falls on the ground comes in contact with minerals and salts and dissolve of them.
(3) Aquatic animals can survive due to dissolved oxygen present in water.
(4) Aquatic plants use carbon dioxide dissolved in water to prepare their food.
Q. 8. Name two things which cannot dissolve in water
Ans. Substances (Things) which cannot dissolve in water are.
1. Sand 2. Stone 3. Iron Balls.
Q. 9. At what temperature does water boil ?
Ans. At 100°C.
Q. 10. At what temperature does water freeze ?
Ans:- At 0°C
WORKSHEET 16.4. (Text Book Page 251)
Q. 1. What is domestic sewage ? What does it contain?
Ans. Domestic Sewage. Discharge of sewage water containing human urine and faeces, animal dung, cloth washing etc. is called domestic sewage.
Q. 2. Name the metals whose salts are contained in industrial wastes.
Ans. Industrial wastes contains salts of metals like Copper,Zinc, Lead, Nickel and Mercury.
Q. 3. How can you say that given sample of water is polluted ?
Ans. See Q IV (15) under the heading "Textual Exercises".
Q. 4. Why is the river water not fit for drinking purposes ?
Ans. River water contains both suspended and soluble impurities which make it unfit for drinking purposes.
Q. 5. What are the properties of potable water ?
Ans. Properties (characteristics) of potable water.
See Q IV (12) under the heading "Textual Exercises".
Q. 6. What is the importance of aeration for purifying water ?
Ans. Importance of aeration for purifying water Aeration improves taste and odour. In this process water is sprayed through air and the oxygen of the air takes away its bad taste and odour.
Q. 7. Why do we add alum to water tanks ?
Ans. To remove suspended impurities present in water, alum is added. It helps in quick settling of the suspended materials present and making the water partly clean.
WORKSHEET 16.5 Textbook page 256
Q. 1. Which property of water makes the ice float on its surface ?
Ans:- Water unlike other substances contracts and takes up less volume when heated from 0°C to 4°C and its density increases. Water when freezes expands so that its density decreases which makes ice float on water.
Q. 2. What is the formula of density ?
Ans. Density (D) =Mass (M)/Volume (V)
Q. 3. Why is the sea water salty ?
Ans. Rain water falling on the earth flows in the form of rivers into the sea. As it flows over the land, many salts dissolve in it and are carried into the sea.
Q. 4. How can sea water be used for irrigation ?
Ans. Sea water contains salt which make it
unsuitable for agriculture. Before it is used for irrigation, it has to desalinated.
Process of desalination. See Q IV (16) under the heading "Textual Exercises"..
Q. 5. Name the element which is found in sea water but not in water at high mountains.
Ans. Iodine.
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