A Journey through States of Water

Given: An ice cube is left in a cup at room temperature.

Observation: The ice cube gradually melts and turns into water (liquid).

Conclusion: Ice and water are the same substance. Ice is the solid state of water, and when heat from the surroundings is absorbed by the ice, it melts and becomes liquid water. Both ice and water are made of the same substance — they are simply two different states of water.

- Water flows but ice does not.
- Water splashes but ice does not.

These differences in behaviour are due to the different states (solid and liquid) of the same substance.

Yes, water in puddles does disappear over time. It disappears due to two main reasons:

1. Evaporation: Water on the surface of the puddle absorbs heat from the sun and surroundings, converts into water vapour, and mixes with the air. This is the primary reason.
2. Seeping into the ground: Some water may seep through the soil into the ground (especially if the ground is not paved).

Therefore, water from puddles disappears mainly due to evaporation and partly due to seeping into the ground.

Examples of water disappearing:

1. Wet clothes dry after some time when hung out.
2. Water on a mopped floor dries up.
3. Sweat on our body dries up.
4. Water left on utensils after washing dries up.
5. Water sprinkled on a hot pan disappears instantly.

Reason: In all these cases, water undergoes evaporation — it absorbs heat from the surroundings and converts into water vapour, which mixes with the air and becomes invisible. This is why water seems to 'disappear'.

Activity Design (Activity 8.2):

Materials needed: A steel plate, a tablespoon of water.

Steps:
1. Place a steel plate on a flat surface.
2. Put a tablespoon of water on the top surface of the steel plate.
3. Observe whether any water appears on the underside (bottom surface) of the plate.
4. Keep observing at regular intervals until the water on top completely disappears.

Expected Observation: No water appears on the underside of the steel plate. The water on top gradually disappears without seeping through.

Inference: Water does not seep through the steel plate. Therefore, Thirav is correct. The water disappears because it converts into water vapour through the process of evaporation, not because it seeps through the plate.

Answer: The water that was placed on the steel plate has been converted into its gaseous state, called water vapour.

- The process by which water converts into water vapour is called evaporation.
- Evaporation takes place continuously, even at room temperature.
- The water vapour mixes with the surrounding air and becomes invisible, which is why it appears that the water has 'disappeared'.

Examples of evaporation in daily life:
- Drying of wet clothes
- Drying of a mopped floor
- Evaporation of sweat from our body

Answer: (iii) Both seeping of water into the ground AND evaporation of water.

Explanation:
- Evaporation: The sun heats the water in the puddle, causing it to convert into water vapour and mix with the air. This is the major reason for water disappearing from puddles.
- Seeping into the ground: If the ground is made of soil (not paved), some water also seeps through the soil into the ground.

Therefore, both processes contribute to the disappearance of water from puddles, with evaporation being the more significant factor.

Answer: When we rub hand sanitiser on our hands, it evaporates rapidly.

Reason:
- Hand sanitiser contains alcohol (like ethanol or isopropanol), which evaporates much faster than water.
- The friction from rubbing and the warmth of our hands provides the heat needed for evaporation.
- As the sanitiser evaporates, it takes heat from our hands, which is why we feel a cooling sensation when we apply sanitiser.

This is the same process as evaporation of water, but it happens much more quickly because alcohol evaporates faster than water.

Observation: No water appears on the underside of the steel plate. The water on the top surface gradually disappears over time.

Inference: Water does not seep through the steel plate. The water disappears because it evaporates — it converts into water vapour and mixes with the air.

Is this activity enough? Yes, this activity is sufficient to conclude that water does not seep through a steel plate, because:
- If water had seeped through, we would see water droplets on the underside of the plate.
- Since no water appears on the underside, and the water on top disappears, it confirms that the water has evaporated, not seeped through.

However, to be more thorough, we could repeat the activity multiple times and with different amounts of water to confirm the conclusion.

Observation: Water droplets appear on the outer surface of the glass tumbler containing cold water and ice cubes.

Possible Reasons:

1. Condensation of water vapour (Most likely reason): The air around us contains water vapour. When this water vapour comes in contact with the cold outer surface of the glass tumbler, it loses heat and converts into liquid water droplets. This process is called condensation.

2. Seeping of water through the glass: Water might be seeping through the walls of the glass tumbler from inside to outside. (This can be tested by Activity 8.4.)

Evidence for Condensation:
- We observe dew drops on plants in the morning — this is also due to condensation of water vapour on the cool surface of leaves.
- When we boil water in a covered utensil, water drops form on the inner side of the lid — this is also condensation.

Conclusion: The most likely reason is condensation of water vapour present in the surrounding air on the cold outer surface of the glass tumbler.

Answer: We see dew drops more in the morning because:

1. During the night, the temperature drops significantly.
2. The surfaces of plants, grass, and other objects become very cold.
3. The water vapour present in the air comes in contact with these cold surfaces.
4. This water vapour condenses (converts from gaseous state to liquid state) and forms tiny water droplets called dew drops.
5. In the morning, before the sun heats up the surfaces, these dew drops are still visible.
6. As the day progresses and the sun heats up the surfaces, the dew drops evaporate and disappear.

Therefore, dew drops are seen more in the morning because the surfaces are coldest at that time, favouring condensation.

Answer: The water drops on the inner side of the steel plate come from the condensation of steam (water vapour).

Explanation:
1. When water is boiled, it converts into steam (water vapour).
2. This steam rises upward and comes in contact with the steel plate covering the utensil.
3. The steel plate is cooler than the steam.
4. When the hot water vapour touches the cool steel plate, it loses heat and condenses — converting back into liquid water droplets.
5. These water droplets accumulate on the inner side of the steel plate.

This is the same process of condensation — the conversion of water vapour into its liquid state upon contact with a cool surface.

Table 8.1: Observations and Questions

| I observe | I wonder |
|---|---|
| Water droplets appear on the outer surface of the glass tumbler. | Where do these water droplets come from? |
| The outer surface of the glass feels wet and cold to touch. | Is the water seeping through the glass from inside? |
| Initially small droplets form, then they combine to form bigger drops. | Is the water coming from the air around the glass? |
| The glass tumbler feels very cold on the outside. | Why does the outside of the glass become cold? |

Inference: The water droplets on the outer surface of the glass tumbler are formed due to condensation of water vapour present in the surrounding air. The cold surface of the glass causes the water vapour in the air to cool down and convert into liquid water droplets.

Prediction: The mass of the cold water (glass tumbler with cold water and ice cubes) kept on the digital weighing balance will increase.

Reason:
- The cold surface of the glass tumbler causes the water vapour present in the surrounding air to condense on its outer surface.
- This condensed water (from the air) gets deposited on the outer surface of the glass tumbler.
- Since extra water from the air is being added to the outer surface of the glass, the total mass of the system increases.

Conclusion from Activity 8.4: The increase in mass confirms that:
1. Water is not seeping from inside the glass to the outside (if it were, the mass would remain the same).
2. Extra water from the surrounding air is condensing on the cold outer surface of the glass.
3. This proves that the water droplets on the outer surface are due to condensation of water vapour from the air.

Table 8.3: Comparison of Different States of Water

| Property | Ice (Solid state) | Water (Liquid state) | Water vapour (Gaseous state) |
|---|---|---|---|
| Shape | Has a definite, fixed shape. Does not change shape when transferred to another container. | Has no fixed shape. Takes the shape of the container it is poured into. | Has no fixed shape. Spreads in all directions and fills the entire space available. |
| Ability to flow | Cannot flow. It is rigid and stays in one place. | Can flow easily from one place to another. Flows from higher level to lower level. | Can flow (move) in all directions. Spreads throughout the available space. |
| Ability to spread | Does not spread. Stays in its original form. | Spreads on a flat surface but stays on the surface. | Spreads in all directions and fills the entire container or space. |

Summary:
- Solid (Ice): Fixed shape, cannot flow, does not spread.
- Liquid (Water): No fixed shape, flows easily, spreads on surfaces.
- Gas (Water vapour): No fixed shape, flows in all directions, spreads to fill entire available space.

Given: The diagram shows the three states of water and the processes of conversion between them.

Filling the blanks:

States of water (Boxes A, B, C):
- A = Ice (Solid state)
- B = Water (Liquid state)
- C = Water Vapour (Gaseous state)

Processes of conversion (Boxes 1, 2, 3, 4):
- 1 = Melting (Ice → Water; on heating)
- 2 = Freezing (Water → Ice; on cooling)
- 3 = Evaporation (Water → Water Vapour; on heating)
- 4 = Condensation (Water Vapour → Water; on cooling)

Summary of conversions:
$$\text{Ice} \xrightarrow{\text{Melting (heating)}} \text{Water} \xrightarrow{\text{Evaporation (heating)}} \text{Water Vapour}$$
$$\text{Water Vapour} \xrightarrow{\text{Condensation (cooling)}} \text{Water} \xrightarrow{\text{Freezing (cooling)}} \text{Ice}$$

Conditions that affect the rate of evaporation:

1. Temperature: Higher temperature → faster evaporation. On a hot day, water evaporates much faster than on a cold day because more heat energy is available for the water molecules to escape into the air.

2. Exposed surface area: Larger surface area → faster evaporation. Water in a plate evaporates faster than water in a bottle cap because more water surface is exposed to air.

3. Air movement (wind): More wind → faster evaporation. A windy day causes faster evaporation because the water vapour formed is quickly carried away, allowing more water to evaporate.

4. Humidity: Lower humidity → faster evaporation. On a rainy day, the air already contains a lot of water vapour (high humidity), so water evaporates slowly. On a dry day, evaporation is faster.

Hot day vs. Cold day:
- On a hot day: Evaporation is fast. Clothes dry quickly, puddles disappear faster.
- On a cold day: Evaporation is slow. Clothes take longer to dry, puddles last longer.

Given: Equal amounts of water are taken in a bottle cap (small exposed area) and in a plate (large exposed area).

Expected Observation: The water in the plate evaporates faster (in less time) than the water in the bottle cap.

Conclusion: The exposed surface area of water affects the rate of evaporation.
- Greater the exposed surface area, faster is the rate of evaporation.
- The plate has a larger surface area exposed to air, so more water molecules can escape into the air at the same time, causing faster evaporation.

Table 8.4:

| Container | Exposed Surface Area | Time taken for complete evaporation |
|---|---|---|
| Bottle cap | Small | More time |
| Plate | Large | Less time |

Application: This is why wet clothes are spread out (not bunched together) to dry — spreading increases the surface area and speeds up evaporation.