I. Select the Correct Option:
1. The ratio of
hydrogen and oxygen in water is:
o (a) 2:1 Explanation:
The chemical formula of water is H₂O, which means it contains two atoms of
hydrogen and one atom of oxygen.
2. An element that
kills living germs found in water is:
o (b) chlorine Explanation:
Chlorine is commonly used to disinfect water and kill harmful germs and
bacteria.
3. The most impure
water is:
o (c) sea water Explanation:
Sea water contains a high concentration of dissolved salts and minerals, making
it unfit for drinking without treatment.
4. The hardness of
water is due to the presence of:
o (b) calcium and
magnesium salts Explanation: Hard water contains dissolved salts of calcium and
magnesium, which cause hardness.
5. Which of the
following is a source of soft water?
o (d) Rain water Explanation:
Rainwater is naturally soft because it has not yet dissolved minerals from the
ground.
6. Which of the
following statements is correct?
o (a) Pure water is a
bad conductor of electricity Explanation: Pure water does
not contain ions, which are necessary for conducting electricity.
7. The dissolved
impurities in water:
o (b) increase its
boiling point but decrease its freezing point Explanation: Dissolved
impurities raise the boiling point and lower the freezing point of water.
II. Assertion and Reasoning
Questions:
1. Assertion (A): The seawater can
be used for drinking purposes. Reason (R): The seawater contains many
dissolved salts.
o (d) Assertion (A)
is false but Reason (R) is true Explanation: Seawater cannot
be used for drinking due to its high salt content, which makes it unsafe for
consumption.
2. Assertion (A): Water is a
precious resource to maintain life on Earth. Reason (R): The World Water
Day is celebrated on 22nd January.
o (d) Assertion (A)
is true but Reason (R) is false Explanation: World Water Day
is celebrated on 22nd March, not January.
3. Assertion (A): Pure water is a
good conductor of heat and electricity. Reason (R): Pure water boils at
273 K and freezes at 373 K.
o (b) Both Assertion
(A) and Reason (R) are false Explanation: Pure water is a bad
conductor of heat and electricity. Pure water boils at 373 K (100°C)
and freezes at 273 K (0°C).
4. Assertion (A): Typhoid is an
acute illness associated with fever caused by Salmonella typhi bacteria.
Reason (R): Cholera is an infection of the small intestine caused by
bacterium Vibrio cholera.
o (a) Both Assertion
(A) and Reason (R) are true Explanation: Both statements are
scientifically accurate.
5. Assertion (A): The solution
obtained when the maximum possible substance is dissolved in a given mass of
water is called a saturated solution. Reason (R): If a saturated
solution is cooled, some of the solute can be seen at the bottom of the
container.
o (a) Both Assertion
(A) and Reason (R) are true Explanation: Both statements correctly
describe the properties of a saturated solution.
III. State if the Following
Statements Are True or False:
1. Water helps in
maintaining body temperature.
o True Explanation:
Water regulates body temperature through sweating and evaporation.
2. Water is an
important man-made resource.
o False Correction:
Water is a natural resource.
3. The human body has
about 50% of water by weight.
o False Correction:
The human body is about 70% water by weight.
4. Water is essential
for the germination of seeds.
o True Explanation:
Seeds require water to begin the germination process.
5. Oceans are the main
source of water.
o False Correction:
Oceans contain most of the Earth's water, but rain is the main source of
freshwater.
IV. Fill in the Blanks:
1. The amount of
usable water on Earth is small.
2. In a sugar and
water solution, sugar acts as a solute.
3. Solubility is the amount of
solute that can dissolve in 100 mL of water.
4. Water liberates
dissolved gases on heating.
5. Materials that we
get from the environment to meet our needs are called resources.
V. Match the Following:
|
Column A |
Column B |
|
1. Saline water |
(c) Water containing more than 2% of dissolved salts and unfit for
human consumption. |
|
2. Saturated solution |
(d) The solution which cannot dissolve any more of a solute at a given
temperature. |
|
3. Solution |
(b) Homogeneous mixture of solute and solvent. |
|
4. Water pollution |
(e) Adding harmful and unwanted substances to water. |
|
5. Potable water |
(a) Water used for drinking purposes. |
VI. Answer in One Word or One
Sentence:
1. Name a chemical
substance used to kill germs in water.
o Chlorine
2. What is a resource?
o Materials that we
get from the environment to meet our needs are called resources.
3. What is the percentage
of water, on average, that a living organism has?
o 70%
4. Name any two
waterborne diseases.
o Cholera, Typhoid
5. What is the water
below the surface of the Earth called?
o Groundwater
VII. Define the Following Terms:
1. Solute
Definition: A solute is a substance that dissolves in a solvent to form a solution.
It can be a solid, liquid, or gas.
Example:
- When you add sugar
(solute) to water (solvent), the sugar dissolves, forming a sugar
solution.
- In a cup of tea, tea
leaves or tea powder act as the solute, dissolving in hot water to
give the tea its flavor and color.
2. Solvent
Definition: A solvent is a substance (usually a liquid) that dissolves a solute to
form a solution. It is the medium in which the solute dissolves.
Example:
- Water is the most common solvent.
It dissolves sugar, salt, and many other substances.
- In nail polish remover, acetone
acts as the solvent, dissolving the nail polish (solute).
3. Solution
Definition: A solution is a homogeneous mixture of a solute and a solvent. This
means the solute is evenly distributed in the solvent, and you cannot see
separate particles of the solute.
Example:
- Saltwater: When you mix salt (solute)
in water (solvent), it forms a saltwater solution where the salt is evenly
distributed.
- Lemonade: Lemon juice and sugar
(solutes) dissolve in water (solvent) to form a homogeneous lemonade
solution.
4. Saturated Solution
Definition: A saturated solution is a solution that cannot dissolve any more solute
at a given temperature. Any additional solute added will not dissolve and will
remain as a solid at the bottom of the container.
Example:
- Imagine adding sugar to a
glass of water while stirring. At first, the sugar dissolves easily.
However, after adding a certain amount, the sugar stops dissolving and
settles at the bottom. At this point, the water has reached its saturation
point for sugar at that temperature.
- Rock candy formation: When a sugar solution is
saturated and allowed to cool, sugar crystals form because the solution
can no longer hold all the dissolved sugar.
5. Unsaturated Solution
Definition: An unsaturated solution is a solution that can dissolve more solute at
a given temperature. The solvent has not yet reached its maximum capacity to
dissolve the solute.
Example:
- If you add a spoonful of
sugar to a glass of water and it dissolves completely, the solution is
unsaturated because it can still dissolve more sugar.
- Making tea: When you add tea powder to
hot water and it dissolves completely, the solution is unsaturated because
you can still add more tea powder until it stops dissolving.
VIII. Answer the Following Questions
in Short:
1. How does sweating
help us to keep our body cool?
o Sweating cools the
body through evaporation, which absorbs heat from the skin.
2. List any three
sources of water on Earth.
o Rainwater, River
water, Groundwater
3. What is meant by
the term 'potable water'?
o Potable water is safe
for drinking and free from harmful bacteria and impurities.
4. How does boiling
help to make water fit for drinking?
o Boiling kills
germs and bacteria, making water safe for consumption.
5. Why is water known
as a universal solvent?
o Water can dissolve
a wide variety of substances, making it a universal solvent.
6. What are the
different methods to make water fit for drinking?
o Filtration,
Boiling, Chlorination, Aeration
7. How will you show
that water contains dissolved salts?
o Heat water in a
beaker; bubbles of dissolved gases will appear, indicating the presence
of dissolved salts.
8. Explain the process
of transpiration during the water cycle.
o Plants release water
vapor into the atmosphere through their leaves, contributing to the water
cycle.
IX. Answer the Following Questions in
Detail:
1. Explain the importance of water for the sustenance of life on Earth.
Water is the most vital substance on
our planet, as it is a prerequisite for the survival of all plants and animals
·
Daily Survival: Human beings and animals rely on water for essential daily
activities such as drinking, cooking, bathing, and washing
·
Biological Processes: Within the body, water acts as a medium for critical life
processes, including blood circulation, the digestion of food, and the
excretion of waste
·
Cellular Composition: All living things are composed of one or more cells, and the proportion
of water in these cells is approximately 80%
·
Temperature Regulation: Water helps maintain our body temperature through the
physiological processes of sweating and evaporation
·
Agriculture and Industry: Beyond biological needs, water is required for the irrigation of
crops
The interaction between water and
gas molecules allows life to thrive in aquatic environments
·
Aquatic Respiration: Dissolved oxygen in water is essential for the respiration and
survival of aquatic animals
·
·
Marine Protection: Carbon dioxide dissolved in water helps marine animals form hard
shells around themselves for their protection
3.
List any four major remedies for water pollution.
To protect our environment, several
steps must be taken to prevent the contamination of water bodies
·
Waste Treatment: Sewage and industrial factory wastes must be treated for toxic
matter and cleaned before they are allowed to flow into water reservoirs
·
Minimal Chemical Use: The use of chemical fertilizers and herbicides should be
judicious and minimal to prevent harmful runoff into lakes and rivers
·
Proper Waste Disposal: Dead bodies of humans and animals should not be thrown into
rivers; instead, excreta and other garbage should be treated in a biogas plant
to produce fuel and manure
·
Afforestation: Planting a large number of trees along river banks helps protect
the water environment and maintain the natural landscape
4.
List several strategies for conserving water in your own words.
Conservation involves managing fresh
water sustainably to meet current and future human demands
·
Maintenance: We should regularly check for and fix any leakages in taps and
pipes to prevent the constant waste of water
·
·
Controlled Usage: We must minimize wastage during daily routines, such as turning
off the tap while brushing teeth or avoiding the over-watering of garden plants
·
5.
State the three states of water and how interchangeability is achieved.
Water exists in three physical
states: solid (found as ice or snow), liquid (found in rivers and seas), and
gaseous (found as vapor in the atmosphere)
·
The Role of Temperature: The change from one state to another is achieved by varying the
temperature of the water
·
Heating: When solid ice is heated, it melts into liquid water; if heating
continues, the water boils and turns into gaseous steam or vapor
·
Cooling: Conversely, removing heat causes water vapor to condense back
into liquid water, and further cooling (freezing) turns the liquid back into
solid ice
6.
Explain the steps involved in the water cycle.
The water cycle is the continuous
movement of water from the Earth's surface to the atmosphere and back again
·
Evaporation and Transpiration: Heat from the sun causes water in oceans and lakes to turn into
vapor (evaporation)
·
·
Precipitation: When these droplets collect to form bigger, heavier drops, they
fall back to Earth as rain, snow, or hail
·
Surface Run-off and Collection: The fallen water flows over the ground into rivers and lakes or
is absorbed by the soil as groundwater, eventually returning to the sea to
start the cycle again
7.
What are the steps involved in the purification of water?
Natural water must be treated
through several stages to make it safe for human consumption
·
·
·
Aeration: Simple exposure of water to air or spraying it through fountains
improves its taste and odor, while the dissolved oxygen helps kill certain
bacteria
HOTS and Critical Thinking:
1. Vaanya's detergent
issue:
o The water is hard
(contains calcium/magnesium salts), which prevents lather formation. Use soft
water or a water softener.
2. Water Cycle
Diagram:
o Evaporation: Water → Vapor
(from oceans/rivers).
o Condensation: Vapor → Clouds.
o Precipitation: Clouds →
Rain/Snow.
o Surface Runoff: Rainwater →
Rivers/Lakes.
o Transpiration: Plants release
water vapor.
3. Sources of water in
homes:
o Taps (municipal
supply), Wells, Tubewells, Rainwater harvesting
4. Rainwater impurity:
o The first rain
carries dust and pollutants from the atmosphere, making it impure.
5. Robin's activity:
o Solute: Sodium chloride
(salt)
o Solvent: Water
o Solution: Sodium chloride
solution
6. Impact of 10
tubewells:
o Over-extraction can
lower the water table, leading to water scarcity.
Diagram-Based Question:
- A: Melting (Solid →
Liquid)
- B: Freezing (Liquid →
Solid)
- C: Condensation (Gas →
Liquid)
- D: Sublimation (Solid →
Gas)
Crossword Puzzle Answers:
Across:
1. Chlorination
2. Salinity
3. Rainwater
4. Soft water
Down:
3. Solvent
4. Diarrhoea
5. Photosynthesis
6. Lagoon
7. Saturated solution
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