THESE NOTES ARE PREPARED ACCORDING TO JKBOSE SYLLABI IN SIMPLIFIED AND CONCISE PATTERN
Exercises
I. Answer the following questions in one word or a figure.
1. What is the apparatus used for the electrolysis of water called?
Ans: Voltameter (Hoffman's Voltameter)
2. What is the volume ratio for hydrogen to oxygen in water?
Ans: 2:1.
3. At what temperature does water change into steam?
Ans: 100° Celsius.
4. At what temperature does water change into ice?
Ans: 0° celsius
5. At what temperature is the density of water maximum?
Ans: 4° celsius
6. What is the composition of water?
Ans: Hydrogen and Oxygen in the ratio of 2:1
7. Which is lighter: water or ice?
Ans: Ice is lighter than water.
8. Name the largest source of water on earth.
Ans: The Oceans.
9. Name a liquid which is heavier than water.
Ans: Glycerine, Honey etc.
10. Name a chemical which is used to kill germs in water.
Ans: Chlorine, Ozone etc.
II. Fill in the blanks:
1. Water helps in the dispersal and growth of seeds and fruits.
2. About 97% of water is in the Oceans.
3. The property of Solubility makes water useful in the process of digestion.
4. The human body has about 70% of water by Weight.
5. Seed cannot germinate with out water.
6. Removing dissolved salts from saline water is called Desalination.
7. The process of using electricity to split water molecule is called Electrolysis.
8. The Density of liquid water is 1g/cc.
9. The density of water is maximum at 4°C.
10. The freezing point of water is 100°C.
III. Write 'True' or 'False' against each of the following statements:
1. Ice has lower density than water: True
2. Rain water is the purest form of natural water: True
3. The solubility of gases in water increases with the increase in temperature True
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:
1. State any three physical properties of water.
Ans: The three states of water are:
1. Solid state in form of Ice
2. Liquid state in form of water
3. Gaseous state in form of water vapour
2. How will you determine the freezing point of water?
Ans: We will take some ice in a beaker and put a thermometer in it.
The thermometer will show the reading at 0°C till all the ice melts.
In this way we can determine the freezing point of water.
3. How will you determine the boiling point of water?
Ans: We will take some water in a beaker and put thermometer in it.
The thermometer will show the reading at 100°C when the water starts boiling.
In this way we can determine the boiling point of water.
4. Briefly describe the water cycle in nature.
Ans: Water cycle in nature occurs in three steps:
1. Evaporation: The water from the surface of water bodies converts into vapour and rises up.
2. Condensation: Due to low temperature at higher altitudes, The vapour condenses to form clouds.
3. Precipitation: The water from clouds fall down as rain.
5. Mention five uses of water.
Ans: Water is life. It has many uses such as;
1. Water is important to sustain life on earth.
2. Water is used in our homes for daily activities.
3. Water is used for irrigation.
4. Water is used in industries and factories.
5. Water is used for power generation.
6. Water is used for transport.
6. How is water polluted?
Ans: Water pollution is biggest problem humanity is facing currently. Water is polluted by many ways:
1. By discharge of domestic sewage.
2. By discharge of industrial wastes.
3. By discharge of agriculture wastes.
4. Oil spill in oceans.
7. How can pollution of water be prevented?
Ans: Water pollution can be prevented by following ways:
1. Use of Septic tanks.
2. Treatment of sewage and industrial waste water.
3. Less use of fertilizers and pesticides.
4. Regular cleaning of water bodies.
5. Planting trese along banks of rivers.
8. What is electrolysis? Describe in brief the electrolysis of water.
Ans: Electrolysis is the method of splitting a molecule or compound with the help of electricity.
Electrolysis of water:
Take water in a voltameter.
Take water in two test tubes and invert them over two electrodes of a voltameter.
Connect the voltameter with a battery.
You will see hydrogen and oxygen getting collected in the two test tubes in the ratio of 2:1.
9. Mention the names of some industries which pollute water.
Ans: Almost all the industries pollute water. Some of them include oil refineries, Pesticide, fertilizer, Leather, textile industries, sugar mills etc.
10. Give the names of some metals whose compounds are toxic.
Ans: The metals whose compounds are toxic include copper, zinc, lead, nickel, mercury, arsenic etc.
11 Why is saline water not suitable for drinking?
Ans: Saline water is not suitable for drinking because it causes vomiting in a person.
12. What is potable water?Give its characteristics.
Ans: Thevwater which is used for drinking purposes is called potable water.
The characteristics of potable water are:
1. It should be fresh and clean.
2. It should not contain impurities.
3. It should be free from germs.
13. Name the elements that water is composed of.
Ans: Water is composed of Hydrogen and Oxygen in the ratio of 2:1 by volume.
14. Name two physical changes that take place in the water cycle.
Ans: The two physical changes that take place in water cycle are evaporation and condensation.
15. How will you determine that a given sample of water is pure or polluted?
Ans: If the given sample of water has colour, odour, or taste, then it is polluted.
16. What is salinity? Describe the process of desalination.
Ans: Salinity means the presence of dissolved salt in the water.
The water should be desalinated before use. Desalination is done as follows:
The water is collected in huge tank connected to another tank via semi permeable membrane.
High pressure is applied on saline water.
The water moves via semi permeable into another tank and is desalinated.
V. Choose the correct answer:
1. At which temperature is the density of water maximum?
(a) 0C (b) 4 C (c) -4C (d) 100C
Ans: (b) 4°C
2. What is the volume ratio of oxygen to hydrogen in water?
(a) 1:2 (b)1:3 (c) 2:1 (d)3:1
Ans: (a) 1:2
3. Which one of the following liquids has the greatest heat capacity?
(a) Water (b) Glycerine
(c) Kerosene (d) Oil
Ans: (a) Water
4. Which one of the following metals is not affected by water?
(a) Sodium (b) Potassium (c) Calcium (d) Boron
Ans: (d) Boron
Ans: (a) Water
4. Which one of the following metals is not affected by water?
(a) Sodium (b) Potassium (c) Calcium (d) Boron
Ans: (d) Boron
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