Question 1

Which of the following best describes condensation?
(i) The conversion of water into its vapour state.
(ii) The process of water changing from a liquid into gaseous state.
(iii) The formation of clouds from tiny water droplets.
(iv) The conversion of water vapour into its liquid state.

Accepted Answer

The correct answer is (iv) The conversion of water vapour into its liquid state. Condensation is the process where water vapour in the air cools down and changes back into liquid water, forming droplets such as clouds. — Condensation is the reverse of evaporation. When water vapour cools, it loses energy and changes into liquid form. This is how clouds form in the atmosphere.

Question 2

Identify in which of the given processes, evaporation is very important—
(i) Colouring with
(a) crayons
(b) water colours
(c) acrylic colours
(d) pencil colours
(ii) Writing on paper with
(a) pencil
(b) ink pen
(c) ball point pen

Accepted Answer

Evaporation is important in:
(i) Colouring with (b) water colours and (c) acrylic colours because the liquid part of the colours evaporates to leave the colour on paper.
(ii) Writing on paper with (b) ink pen and (c) ball point pen because the ink dries by evaporation of the solvent. — In water colours and acrylic colours, the water or solvent evaporates leaving the pigment on the paper. Crayons and pencil colours are solid and do not involve evaporation. Similarly, pencil writing is by solid graphite, so no evaporation is involved, but ink pens and ball point pens use liquid ink which dries by evaporation.

Question 3

We see green coloured plastic grass at many places these days. Space around natural grass feels cooler than space around the plastic grass. Can you find out why?

Accepted Answer

Natural grass feels cooler because it contains water which evaporates, causing cooling. Plastic grass does not have water and hence no evaporation occurs, so it does not cool the surrounding air. — Evaporation of water from natural grass absorbs heat from the surroundings, producing a cooling effect. Plastic grass lacks water and thus cannot cause evaporation or cooling.

Question 4

Give examples of liquids other than water that evaporate.

Accepted Answer

Examples of liquids other than water that evaporate include alcohol, petrol, kerosene, acetone, and cooking oil. — All liquids have some tendency to evaporate depending on their volatility. Alcohol and petrol evaporate quickly at room temperature, while oils evaporate slowly.

Question 5

Fans move air around, creating a cooling sensation. It might seem strange to use a fan to dry wet clothes since fans usually make things cooler, not warmer. Normally, when water evaporates, it requires heat, not cold air. What do you think about this?

Accepted Answer

Fans help dry wet clothes by moving air which increases evaporation. Even though fans blow cooler air, the moving air removes the humid air near the wet clothes, allowing more water to evaporate. Evaporation requires heat, which is taken from the clothes and surroundings, causing a cooling effect. — Evaporation needs heat energy which is absorbed from the wet clothes and surrounding air, cooling them. Fans increase air movement, reducing humidity near the clothes and speeding up evaporation, thus drying clothes faster.

Question 6

Usually, when sludge is removed from drains, it is left in heaps next to the drain for 3–4 days. Afterward, it is transported to a garden or a field where it can be used as manure. This approach reduces transportation cost of the sludge and enhances the safety of individuals handling it. Reflect upon it and explain how.

Accepted Answer

Leaving sludge in heaps for 3–4 days allows it to dry and partially decompose, reducing its volume and making it less smelly and easier to handle. This reduces the weight and amount to be transported, lowering transportation costs. Also, drying reduces harmful pathogens, enhancing safety for handlers. Using it as manure recycles nutrients. — Drying and partial decomposition reduce sludge volume and pathogens. This makes transport cheaper and safer. The sludge becomes nutrient-rich manure beneficial for plants.

Question 7

Observe the activities in your house for a day. Identify the activities that involve evaporation. How does understanding the process of evaporation help us in our daily activities?

Accepted Answer

Activities involving evaporation include drying clothes, boiling water, cooking, sweating, drying wet floors, and using perfumes or deodorants. Understanding evaporation helps us use water wisely, dry clothes efficiently, keep cool by sweating, and understand how liquids dry or cool surfaces. — Evaporation is a common process in daily life. Recognizing it helps in managing water use, improving hygiene, and maintaining comfort.

Question 8

How is water present in the solid state in nature?

Accepted Answer

Water is present in solid state in nature as ice and snow, found in glaciers, polar ice caps, snow on mountains, and hail during storms. — When water freezes due to low temperatures, it becomes solid ice or snow, which is commonly found in cold regions and during winter.

Question 9

Reflect on the statement “Water is our responsibility before it is our right.” Share your thoughts.

Accepted Answer

The statement means that before we claim the right to use water, we must take responsibility to conserve and protect it. Water is a precious resource essential for life, and careless use or pollution harms everyone. Responsible use ensures availability for future generations. — Understanding water as a shared resource encourages conservation, pollution prevention, and wise use, highlighting our duty towards nature and society.

Question 10

The seat of a two-wheeler parked on a sunny day has become very hot. How can you cool it down?

Accepted Answer

You can cool the seat by sprinkling water on it or covering it with a wet cloth. As the water evaporates, it absorbs heat from the seat, causing a cooling effect. — Evaporation requires heat energy which is taken from the hot seat, lowering its temperature and making it cooler to sit on.

Question 11

What are the three states of water observed in daily life?

Accepted Answer

Solid, liquid, and gaseous — Water exists in three states commonly observed in daily life: solid (ice), liquid (water), and gaseous (water vapour). Plasma is not a state water exhibits under normal conditions.

Question 12

Which process describes the change of water from liquid to gaseous state?

Accepted Answer

Evaporation — Evaporation is the process where water changes from liquid to gaseous state (water vapour), usually occurring at room temperature or higher.

Question 13

What is the process called when water vapour changes back into liquid water droplets on a cold surface?

Accepted Answer

Condensation — Condensation is the process where water vapour in the air turns back into liquid water droplets when it comes in contact with a cold surface.

Question 14

Which of the following observations supports that ice and water are the same substance in different states?

Accepted Answer

Ice melts to form water when heated — Ice melting to form water shows that ice and water are different states of the same substance, water. Their chemical formula remains H₂O in both states.

Question 15

During Activity 8.2, water is placed on a steel plate and observed over time. What conclusion can be drawn if water disappears without seeping through the plate?

Accepted Answer

Water evaporates into water vapour — If water disappears without seeping through the steel plate, it means water is changing from liquid to gaseous state by evaporation.

A Journey through

A Journey through — Study Notes

A Journey through States of Water

Investigating Water's Disappearing Act

Another Mystery

Practice Questions — A Journey through

All 12 Chapters in Curiosity