Water Class 8 Questions and Answers Notes Basic Science Chapter 14 Kerala Syllabus

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Class 8 Basic Science Chapter 14 Water Question Answer Notes

Class 8 Basic Science Chapter 14 Notes Kerala Syllabus Water Question Answer

Water Class 8 Questions and Answers Notes

Let’s Assess

Question 1.
What changes will occur on heating water that has already reached boiling point?
Answer:
When water has reached its boiling point (100°C at 1 atm pressure), further heating will cause it to change state from liquid to gas (steam). The temperature will remain constant at the boiling point during this phase change, as the extra heat energy (latent heat) is used to overcome the forces of attraction between water molecules.

Question 2.
Explain how the boiling point of water varies under the following conditions:
a. In high-altitude areas:
b. At sea level:
c. In vacuum containers:
d. In pressure cookers:
Answer:
a. In high-altitude areas, the atmospheric pressure is lower. A decrease in pres¬sure causes the boiling point of water to decrease (become lower than 100°C).

b. At sea level, the atmospheric pressure is considered normal (approximately 1 atm). Under this standard pressure, the boiling point of water is 100°C.

c. In vacuum containers, the pressure is significantly reduced. This drastic decrease in pressure will cause the boiling point of water to decrease considerably, potentially allowing it to boil even at room temperature or lower.

d. In pressure cookers, steam is trapped, causing the pressure inside to increase. An increase in pressure causes the boiling point of water to increase (become higher than 100°C, e.g., 120°C).

Question 3.
Due to the intermolecular attraction between water molecules, a force arises that tends to minimize the surface area of water. How can this be demonstrated?
Answer:
This force is surface tension. It can be demonstrated in several ways:

1. Floating a Blade/Needle: Gently place a razor blade or a needle flat on the surface of still water. Due to surface tension acting like a stretched skin, the blade/needle can float even though it’s denser than water.
2. Water Striders: Observe insects like water striders walking on the surface of a pond. They distribute their weight, and the surface tension supports them.
3. Spherical Drops: Observe water drop¬lets on a surface that water doesn’t wet (like a lotus leaf or plastic sheet). Surface tension pulls the water into a shape with the minimum possible surface area, which is a sphere.
4. Soap Film Experiment: Dip a wire ring with a thread tied across it into soap solution. Break the soap film on one side of the thread. The surface tension of the remaining film will pull the thread into a curved arc, minimizing the film’s surface area.

Question 4.
Write any three special properties of water and explain situations in daily life where we make use of these properties.
Answer:
High Heat Capacity:
Property: Water can absorb a large amount of heat without a significant rise in its own temperature.
Application: It is used as a coolant in vehicle radiators to absorb excess engine heat and prevent overheating. It also helps regulate body temperature.

Universal Solvent:
Property: Water can dissolve a wide variety of substances.
Application: This allows us to make various solutions for daily use (like salt water, sugar syrup, medicines), enables nutrients to be transported in living organisms (in blood, plant sap), and unfortunately, also contributes to water pollution as harmful substances dissolve in it.

Anomalous Expansion (Ice Floats):
Property: Unlike most substances, water expands when it freezes into ice, making ice less dense than liquid water.
Application: Because ice floats, lakes and rivers freeze from the top down. The surface ice layer insulates the water below, allowing aquatic life to survive during winter in cold climates.

Question 5.
Observe the picture.
Compare the attraction between water molecules and the attraction between water and other substances, and explain why the water level rises inside a glass tube.

Answer:
The picture shows capillary rise.
Forces Involved:
Cohesion: The attraction between water molecules themselves.
Adhesion: The attraction between water molecules and the molecules of the glass tube.
Explanation: In the case of water and glass, the adhesive force (attraction between water and glass) is stronger than the cohesive force (attraction between water molecules). This stronger attraction pulls the water molecules up along the surface of the glass tube, causing the water level inside the narrow tube to rise above the level in the surrounding beaker.

Basic Science Class 8 Chapter 14 Question Answer Kerala Syllabus

Question 1.
Why does the panchayat give importance to the conservation of water resources? (Discussion)?
Answer:
The panchayat gives importance to water conservation because water is essential for the origin and survival of life on Earth. Water is crucial for agriculture, industry, energy production, and transportation. Conserving water bodies like wells, streams, and rivers, which are the wealth of the country, is a collective responsibility to protect this resource from pollution and ensure its availability for vital functions and growth.

Question 2.
Why do people think that if there is water, there is a possibility of life? (Discussion)
Answer:
People believe that where there is water, there is a possibility of life because water is the precious gift of nature responsible for the origin and survival of life on Earth. Water is essential for all vital functions in living organisms, such as respiration, digestion, and excretion, as well as maintaining body temperature and keeping eyes moist. Plants also need it for growth and photosynthesis. This fundamental necessity is why scientists search for water when looking for life on other planets.

Question 3.
What are the uses of water?
Answer:

1. For drinking.
2. For bathing.
3. For cooking.
4. It’s also essential for vital functions like respiration, digestion, and excretion, regulating body temperature, and keeping eyes moist.
5. It’s needed for plant growth and photosynthesis.
6. It is crucial for agriculture, industry, energy production, and transportation.

Question 4.
Why can water be used for so many purposes?
Answer:
Water can be used for so many purposes primarily because of its special property as a universal solvent. Water can dissolve a wide variety of substances, and the nature of the water changes depending on what is dissolved in it, allowing it to be used to make different types of solutions. This solubility is one of solubility is one of the main reasons for its varied uses.

Textbook Page No : 235 & 236

Question 5.
Complete the Table (Table 14.1 – Litmus Test)

Answer:

Pure Water / Substance Added to Water	Blue / Red Litmus Paper Experiment – Observation	Inference
Pure Water	No change in the colour of the litmus paper	Water has no acidic or basic property.
Common Salt	No change	Common Salt solution is Neutral
sugar	No change	Sugar solution is Neutral
honey	No change	Honey solution is Neutral
vinegar	Turns blue litmus red	Vinegar solution is Acidic
Soap Powder	Turns red litmus blue	Soap Powder solution is Basic
Lime juice	Turns blue litmus red	Lime juice solution is Acidic
Sodium hydroxide (Alkali)	Turns red litmus blue	Sodium hydroxide solution is Basic

Question 6.
What could be the reason for the hardness of water? (Discussion)
Answer:
The hardness of water is caused by dissolved salts that water picks up as it flows through the soil. Specifically, the hardness is caused by some salts of metals like magnesium and calcium. If the hardness is caused by bicarbonates of calcium and magnesium, it is temporary hardness. If it is caused by sulphates or chlorides of metals such as magnesium or calcium, it is permanent hardness.

Question 7.
Complete the Table (Table 14.2 – Hardness Test)

Answer:

Substance added to water	Soap lathers well/ Doesn’t lather well	Conclusion
Pure water (nothing added)	Lathers well	Pure water is soft water.
Magnesium bicarbonate/ Calcium bicarbonate	Doesn’t lather well	These salts cause hardness.

Question 8.
How does the water level appear inside the glass tube? (Question from Experiment)
Answer:
The water level inside the thin glass tube appears to be higher than the water level in the beaker. This phenomenon is due to capillary action.

Textbook Page No : 237

Question 9.
Now pour a little water on a leaf of colocasia. Does it wet the surface?
Answer:
No, the water does not wet the surface of the colocasia leaf easily.
Explanation: The reason is that the molecules in the leaf and the water molecules have very little attraction between them (poor adhesion).

Question 10.
Can you list some materials around you that water cannot wet? (Discussion)
Answer:
Water does not wet a surface when the attraction between the molecules in the surface and the water molecules is very little.
Materials that water cannot easily wet (hydrophobic materials) include:

1. A colocasia leaf.
2. Waxy or oily surfaces (like a car that’s been waxed).
3. Plastic or synthetic materials (like a plastic sheet, which is why drops are spherical).
4. Teflon (used in non-stick pans).
5. The feathers of some water birds due to their oily coating.

Question 11.
What is the shape of the water drops (on a plastic sheet)?
Answer:
If a surface is not getting wet, the water drops will be spherical in shape. This occurs because the attraction between water molecules (cohesion) is stronger than the attraction between water and the surface (adhesion).

Question 12.
Why is the water surface behaving like this (when coins are added)?
Answer:
The water surface will appear to bulge or rise above the rim of the beaker, behaving like a stretched, elastic film or membrane.

Question 13.
Why is the water surface behaving like this?
Answer:
The water surface is behaving like this due to surface tension. The mutual attraction between water molecules causes a force to act on the water surface, making it behave like a stretched film.

Question 14.
Why can some insects walk on the surface of water?

Answer:
Insects can walk on water because of surface tension. The mutual attraction between water molecules creates a force that makes the water surface behave like a stretched, flexible film, which is strong enough to support the light weight of the insects.

Question 15.
Gently place a blade on the surface of water. Can you explain why the blade stays on top without sinking?

Answer:
The blade stays on top of the water without sinking because of surface tension. The mutual attraction between water molecules creates a force at the water surface that makes it behave like a stretched film. This stretched film is strong enough to support the light weight of the blade without breaking.

Textbook Page No : 238 & 239

Question 16.
From the figure can you say in which direction the force acts on the water molecules on the surface? (Discussion)
Answer:
Based on the text explaining surface tension, the force acts on the water molecules on the surface in a direction that tries to minimize the surface area. This force is an inward pull (towards the bulk of the liquid), which causes the surface to behave like a stretched film.

Question 17.
What is the shape of the soap film now (after breaking it on one side of the thread)?
Answer:
When the soap film on one side of the thread is broken, the remaining film on the other side will pull the thread, causing the thread to take a circular or curved shape that maximizes the area of the side where the film remains, and minimizes the area of the film itself. The intact film pulls the thread to try and reduce its own surface area.

Question 18.
Is it easier to clean dirty clothes with plain water or with soap water? Clothes get cleaner in cold water or hot water? (Discussion)
Answer:
It is easier to clean dirty clothes with soap water and hot water.

• Plain water has a high surface tension, meaning it doesn’t easily wet the clothes.
• When you add soap or heat the water, the surface tension decreases.
• This decrease in surface tension allows the water to wet the clothes better and clean them more easily, helping the water penetrate the fabric and lift the dirt.

Question 19.
What change happens to water at this point (when temperature stops increasing despite continued heating)?
Answer:
At this point, the water starts to boil. The water molecules begin to change their state from liquid to gas (steam). This temperature is the boiling point of water, which is 100°C (at normal atmospheric pressure).

Question 20.
Why doesn’t the temperature rise once the water starts boiling?
Answer:
Once water starts boiling, the temperature doesn’t rise because the extra heat energy is used to overcome the force of attraction between the water molecules. In other words, the heat is used for the change of state (liquid to gas) rather than to increase the temperature of the liquid water.

Question 21.
Which contains more energy boiling water or steam? Which can cause severe burn? Boiling water or steam? (Discussion)
Answer:
Steam contains more energy than boiling water. The extra heat energy (called latent heat of vaporization) added to boiling water to turn it into steam without increasing the temperature is stored in the steam. Therefore, steam can cause a more severe burn. When steam condenses back into liquid water on the skin, it releases that extra latent heat, causing a much more intense burn than boiling water at 100°C.

Textbook Page No : 240

Question 22.
Why does cooking in open vessels take more time in high mountain regions? (Discussion)
Answer:
In high mountain regions, the atmospheric pressure is lower because height increases as pressure decreases. Since the boiling point of a liquid is related to atmospheric pressure, when the pressure decreases, the boiling point of water also decreases. This means water boils at a temperature lower than 100°C. Food takes longer to cook because the boiling water, the medium of cooking, is at a lower maximum temperature.

Question 23.
What change happens to the boiling point when pressure increases? How does cooking become easier in pressure cookers?
Answer:

• When pressure increases, the boiling point of water increases.
• Cooking becomes easier in pressure cookers because they are sealed and the steam cannot escape. As a result, the pressure inside increases. This increased pressure raises the boiling point of the water well above 100°C. Cooking at a higher temperature significantly reduces the cooking time.

Question 24.
When the same amount of heat is given to water and coconut oil, which one’s temperature rises faster in a fixed time? Why?
Answer:
The coconut oil’s temperature will rise faster.

• This is because water is a liquid with a very high heat capacity.
• Heat capacity is the amount of heat energy required to raise the temperature of a given substance by 1 °C.
• Due to its high heat capacity, the temperature of water does not rise quickly.

Question 25.
How can we make use of high heat capacity of water?
Answer:
The high heat capacity of water is utilized in the following ways:

• Water is used to cool hot objects.
• The radiators in vehicles use a mixture containing a special coolant and water to cool the engine.
• Water helps in maintaining the body temperature within a limit.

Textbook Page No : 241

Question 26.
In which state is oxygen usually seen? What about hydrogen? But in which state is water usually found?
Answer:

• Oxygen is usually seen in the gaseous state.
• Hydrogen is usually seen in the gaseous state.
• Water is usually found in the liquid state.

Question 27.
What could be the reason for water to occur in the liquid state?
Answer:
The reason water occurs in the liquid state at room temperature, even though its components (hydrogen and oxygen) are gases, is the existence of a special kind of attractive force between water molecules. This attractive force is strong enough to keep the water in a liquid form at room temperature.

Question 28.
Now think, what would happen if this force between water molecules did not exist?
Answer:
If the attractive force between water molecules did not exist, water would stay only in the gaseous state. The gas would not condense to form liquid water, meaning there would be no rivers, no seas, and probably no living things on earth.

Textbook Page No : 242

Question 29.
What happened to the volume of the water in the bottle when it turned into ice?
Answer:
When water turns into ice, its volume increases. This is an unusual property for a substance when cooled.

Question 30.
Can you now explain why a piece of ice floats on the surface of water when you put it in water?
Answer:
A piece of ice floats on the surface of water because its density decreases when it turns from liquid water into solid ice. This is because, unlike most substances, the volume of water increases when it freezes. Since density is mass divided by volume (D = m/V), an increase in volume for the same mass results in a lower density. Since the density of ice is less than that of liquid water, it floats.

Question 31.
What if the water in rivers and lakes there turns completely into ice? Wouldn’t aquatic life get trapped in the ice and die? Does that happen? What could be the reason?
Answer:
Aquatic life generally does not get trapped and die because the rivers and lakes do not freeze completely from top to bottom. The reason is:

• The maximum density of water is at 4°C. As the surface water cools to 4°C, it sinks, and warmer water rises.
• Once the surface water cools below 4°C and starts freezing, its volume increases, and its density decreases.
• This less-dense ice (and near-freezing water) floats on top, forming an insulating layer that protects the underlying water from freezing completely. This allows fish and other aquatic life to survive in the colder regions.

Textbook Page No : 243

Question 32.
What could be the reasons for water pollution?
Answer:

• Chemicals from agricultural fields.
• Chemicals from factories.
• Oils from vehicles.
• Other reasons not explicitly listed but implied by the images are dumping of solid waste into water bodies and the release of untreated sewage/industrial discharge.

Question 33.
What are the main problems caused by water pollution?
Answer:

• Destruction of aquatic plants.
• Damage to the food chain.
• Soil pollution.
• Diseases.
• Millions of people suffer from water-borne diseases every year, leading to many deaths, and a lack of access to clean water.

Class 8 Basic Science Chapter 14 Question Answer Extended Activities

Question 1.
Investigate and prepare a study report on the efforts taken in your locality to conserve water sources.

Question 2.
Based on rainfall availability across Kerala, prepare a rainfall distribution map.

Water Class 8 Notes

Class 8 Basic Science Water Notes Kerala Syllabus

The Importance of Water
Water is a precious gift of nature, and its conservation is a collective responsibility. The presence of water is what scientists look for on other planets (like the Moon) as evidence for the possibility of life.

Why water is essential:

• For Life (ജീവന്റെ നിലനിൽപ്പിന്):
  1. Water is responsible for the origin and survival of life on Earth.
  2. It’s essential for vital bodily functions like respiration, digestion, and excretion.
  3. It helps to regulate body temperature and keeps the eyes moist.
  4. Plants need water for growth and photosynthesis.
• For Development (വികസനത്തിന്):
  • Water is crucial for agriculture, industry, energy production, and transportation.
• Daily Uses: We use water for drinking, bathing, cooking, and many other purposes.

ഭൂമിയിലെ ജീവന്റെ ഉത്ഭവത്തിനും നിലനിൽപ്പിനും ജലം അത്യന്താപേക്ഷിതമാണ്. ദഹനം, ശ്വസനം തുടങ്ങിയ ശാരീരിക പ്രവർത്തനങ്ങൾക്കും കൃഷി, വ്യവസായം, ഊർജ്ജ ഉത്പാദനം തുടങ്ങിയ കാ ര്യങ്ങൾക്കും ജലം കൂടിയേ തീരൂ. അതിനാൽ, നമ്മുടെ ജലസ്രോതസ്സുകളെ (കിണറുകൾ, പുഴ കൾ) മലിനീകരണത്തിൽ നിന്ന് സംരക്ഷിക്കേണ്ട ത് നമ്മുടെ എല്ലാവരുടെയും ഉത്തരവാദിത്തമാണ്.

Characteristics of Water: Solubility (ജലത്തിന്റെ സവിശേഷത ലായകത്വം)
One of the most important characteristics of water is its ability to dissolve many other substances.

• Universal Solvent (സാർവിക ലായകം):
  • “Since water can dissolve a wide variety of substances, it is known as universal solvent”.
• Nature of Pure Water:
  • Observation: Pure water shows no change in the colour of blue or red litmus paper.
  • Inference: This means pure water has no acidic or basic property; it is neutral.
• Nature of Solutions:
  • The nature of water changes depending on the substances dissolved in it. If you dissolve an acid (like vinegar), the solution becomes acidic. If you dissolve a base (like soap), the solution becomes basic.

ധാരാളം പദാർത്ഥങ്ങളെ ലയിപ്പിക്കാൻ (dissolve) ജലത്തിന് കഴിവുണ്ട്. ഈ സവിശേഷതകൊ ണ്ടാണ് ജലത്തെ “സാർവിക ലായകം’ (Universal Solvent) എന്ന് വിളിക്കുന്നത്. ശുദ്ധജലം (Pure water) നിർവീര്യമാണ് (netural), അതായത് ഇതിന് ആസിഡിന്റെയോ ബേസിന്റെയോ സ്വഭാ വമില്ല. എന്നാൽ ജലത്തിൽ ലയിക്കുന്ന പദാർത്ഥം ഏതാണോ, അതിനനുസരിച്ച് ആ ലായനിയുടെ സ്വഭാവം (ആസിഡ് ബേസ്) മാറുന്നു.

Litmus Test Observations (Indicating pH Nature)

Substance Added to Water	Inference
Pure Water, Common Salt, Sugar, Honey	Neutral (No change in litmus paper color)
Vinegar, Lime juice	Acidic (Turns blue litmus red)
Soap Powder, Sodium hydroxide	Basic (Alkaline) (Turns red litmus blue)

Hard Water and Soft Water (കഠിനജലവും മൃദുജലവും)

• Soft Water: Water in which soap lathers well. Example: Rainwater.
• Hard Water: Water in which soap does not lather well. Example: Bore well water.
• Cause of Hardness: As water flows through the soil, salts of metals like magnesium and calcium dissolve in it. These dissolved salts make the water hard.

സോപ്പ് എളുപ്പത്തിൽ പതയുന്ന ജലമാണ് മൃദു ജലം (ഉദാ: മഴവെള്ളം). സോപ്പ് എളുപ്പത്തിൽ പ തയാത്ത ജലമാണ് കഠിനജലം (ഉദാ: കിണറ്റിലെ വെള്ളം). ജലം മണ്ണിലൂടെ ഒഴുകുമ്പോൾ, കാൽ സ്യം, മഗ്നീഷ്യം എന്നിവയുടെ ലവണങ്ങൾ (salts) അതിൽ ലയിക്കുന്നതാണ് ജലം കഠിനമാകാൻ കാരണം.

Types of Hardness

Type of Hardness	Cause	Removal Method
Temporary Hardness	Bicarbonates of calcium and magnesium	Removed by boiling the water.
Permanent Hardness	Sulphates or chlorides of metals such as magnesium or calcium	Cannot be removed by boiling.

Capillary Rise

• Capillary Rise (Fig 14.3): The water level inside a thin glass tube is higher than the water in the beaker.

Reason: Aattraction between water and glass is stronger than the attraction between water and water, so the water is “pulled up” the glass tube.

• Water on a Leaf (Fig 14.4): Water forms spherical drops on a colocasia (ചേസില) leaf and does not wet it.

Reason: Attraction between water and the leaf is very weak. Therefore, the water’s its attraction to itself is stronger, pulling the water into a tight, spherical drop.

Surface Tension (പ്രതലബലം)

• The surface of the water behaves like a stretched film or membrane.
• “Due to the mutual attraction (cohesion) between water molecules, a force acts on the water surface, making its surface area as small as possible. This force is called surface tension.”
• Surface Tension and Cleaning:
  1. Water has a high surface tension, which prevents it from “wetting” clothes easily.
  2. To clean clothes, we need to reduce this tension. We can do this by:
     • Adding soap or detergent
     • Heating the water (using hot water)
  3. This decreases the surface tension, allowing the water to soak into the fabric and clean more effectively.

Boiling Point (തിളനില)

• The boiling point is the specific temperature at which a liquid (like water) starts to change into a gas (steam).
• Boiling Point of Water: 100°C.
• Phenomenon: When water reaches 100°C and starts to boil, its temperature stops increasing, even if you continue to add more heat.
• Reason: This extra heat energy is not used to raise the temperature. It is used to overcome the forces of attraction between the molecules and complete the change of state from liquid to gas.
• Application:
  1. Steam (at 100°C) contains more energy than boiling water (at 100°C) because it holds this extra “hidden” heat.
  2. This is why steam causes more severe burns than boiling water.

ജലം തിളയ്ക്കുമ്പോൾ (100°C-ൽ), നാം തുടർ ന്നും ചൂട് നൽകിയാലും അതിന്റെ താപനില (temperature) കൂടുന്നില്ല. ഈ അധിക ഊർജ്ജം ഉപയോഗിക്കുന്നത് ജലം നീരാവിയാക്കി (change of state) മാറ്റാനാണ്. ഈ ‘ഒളിഞ്ഞിരി ക്കുന്ന’ ഊർജ്ജം (ലീനതാപം) കൂടി നീരാവിയി ൽ ഉള്ളതുകൊണ്ടാണ്, തിളച്ച വെള്ളത്തേക്കാൾ കൂടുതൽ പൊള്ളൽ നീരാവി ഏൽപ്പിക്കുന്നത്.

Pressure and Boiling Point (മർദ്ദവും തിളനിലയും)
□ The boiling point of a liquid is directly related to the atmospheric pressure acting on it.

□ Standard Boiling Point: The boiling point of water is 100°C at the normal atmospheric pressure of 1 atmosphere (1 atm).

□ Relationship:

1. Pressure Decreases → Boiling Point Decreases:

• Experiment (Fig 14.8): Water is boiled and the flame is turned off. When the piston of a syringe is pulled back, the pressure inside the tube decreases. This causes the water to start boiling again, even at a lower temperature.
• Application: In high mountain regions, the atmospheric pressure is low. Because pressure is low, water boils at a lower temperature (e.g., 80°C or 90°C). This temperature is not high enough to cook food properly, so cooking takes more time.

2. Pressure Increases → Boiling Point Increases:
Application (Pressure Cooker, Fig 14.9): A pressure cooker traps the steam, not allowing it to escape. This causes the pressure inside to increase significantly. Because the pressure is high, the boiling point of the water increases (e.g., to 120°C). Food cooks much faster at this higher temperature.
മർദ്ദം (Pressure) കൂടുമ്പോൾ തിളനില (Boiling Point) കൂടുന്നു; മർദ്ദം കുറയുമ്പോൾ തിളനില കുറയുന്നു.

പ്രഷർ കുക്കർ. ഇതിനുള്ളിൽ മർദ്ദം കൂടുന്നതുകൊ ണ്ട്, ജലം 100°C യിലും ഉയർന്ന താപനിലയിൽ (e.g., 120°C) തിളയ്ക്കുന്നു. ഇത് ആഹാരം വേഗത്തിൽ പാകം ചെയ്യാൻ സഹായിക്കുന്നു.

ഉയർന്ന മലനിരകൾ; അവിടെ മർദ്ദം കുറവായതിനാ ൽ, ജലം 100°C യിലും താഴ്ന്ന താപനിലയിൽ തിളയ്ക്കുന്നു. അതുകൊണ്ട് ആഹാരം പാകമാ കാൻ കൂടുതൽ സമയം എടുക്കുന്നു.

Heat Capacity of Water (ജലത്തിന്റെ തിളനിലയും)

• Observation: When the same amount of heat is given to equal masses of water and coconut oil, the coconut oil’s temperature rises faster. The water’s temperature rises very slowly.
• Reason: Water has a very high heat capacity.
• Heat capacity is the amount of heat energy required to raise the temperature of a given substance by 1°C.
• Applications:
  Because water can absorb a large amount of heat without its own temperature rising quickly, it is an excellent coolant.
  1. Vehicle Radiators: Water is used in radiators to absorb the excess heat from the engine.
  2. Regulating Body Temperature: The water in our bodies helps to maintain a stable internal temperature.

The Special Case of Ice (Anomalous Expansion)

• Normal Behavior: When most substances cool, their volume decreases.
• Water’s Behavior: When water cools and turns into ice, its volume increases.
• Density: Since Density = Mass / Volume, when the volume increases for the same mass, the density of ice decreases.
• Result: Because ice is less dense than water, a piece of ice floats on the surface of water.
• Importance for Aquatic Life:
  In cold countries, when lakes and rivers freeze, the ice (being less dense) forms on the top surface. This ice layer acts as a blanket, insulating the water below and preventing the entire lake from freezing solid. This allows fish and other aquatic life to survive in the liquid water underneath.
• Effect of Solutes on Boiling Point
  1. Observation: The boiling point of water with added substances (like salt) is higher than the boiling point of pure water (100°C).
  2. Reason: When salt is added, more energy is required to boil the water. This is known as boiling point elevation.

Structure and States of Water

• Molecular Structure: A water molecule is made up of two hydrogen atoms and one oxygen atom (H₂O).

• States: Water is a natural substance that can exist in all three states: solid (ice), liquid (water), and gas (steam).
• Liquid State Reason: A special kind of attractive force exists between water molecules. This force is responsible for surface tension and helps water keep its liquid form at room temperature, even though hydrogen and oxygen are gases.

A. Electrolysis

• Water can be split back into hydrogen and oxygen by a process called electrolysis.
• Using the Hoffman water voltameter

• hydrogen is produced at the negative Problems caused by Water Pollution: electrode and oxygen is produced at the positive electrode.

B. Density Anomaly (Unusual Property of Freezing)

• Maximum Density: The maximum density of water is at 4°C.
• Volume Change: When water is cooled or heated from 4C, its volume increases. When water turns into ice (cooled from 4°C to 0°C), its volume increases, and therefore its density decreases.
• Ice Floats: Since ice is less dense than liquid water, it floats on the surface.
• Survival of Aquatic Life: This floating layer of ice acts as an insulator, protecting the underlying water from freezing completely, allowing fish and other living things to survive in cold regions.

C. Effect of Dissolved Substances on Boiling Point

• The boiling point of water with added substances (like salt) is higher than that of pure water.
• This is because more energy is required to boil the water when a substance is added.

Water Pollution ((ജലമലീനീകരണം))
Water’s ability to dissolve many substances (as a universal solvent) also means it can easily become polluted.
Causes/Sources of Pollution:

• Chemicals from agricultural fields
• Chemicals from factories
• Oils from vehicles
• Improper waste disposal (dumping garbage, plastic)
• Sewage discharge

Problems Caused by Water Pollution:

• Destruction of aquatic plants
• Damage to the food chain
• Soil pollution
• Spread of water-borne diseases

Pure water is a basic human need, and millions suffer from diseases due to a lack of it, reinforcing the idea: “Right to water is a birthright”.