Exploring the States of Water: A Must-Have Lesson for Grade 3 Students

States of Water

Penelope is very curious about everything related to science. One day she was thinking about how miraculous water is. She talked to her science teacher Mrs. Peterson about it.

Penelope: Mrs. Peterson, I am really awed about what a miraculous thing water is. It is really remarkable that it can exist in three states.

Mrs. Peterson: Yes, Penelope, water can change its state when it gains or loses heat. What we call as water exists in liquid form. In room temperature. When it is heated to 100°C, what will happen? It will change to a gas called steam. We know this is called boiling.

Penelope: When my mother heats water to make coffee, I can see it boiling. So, at that time water turns into steam?

Mrs. Peterson: Yes, so we have a name for the temperature at which water changes to steam. It is called its boiling point.

Penelope: Wow! Awesome!

Mrs. Peterson: You should also know what evaporation is.

Penelope: What is evaporation, Mrs. Peterson? I have only a rough idea.

Mrs. Peterson: When water gains enough heat from its surroundings, it will change from a liquid to a gas called water vapour. This is known as evaporation. It occurs all the time, at any temperature.

Penelope: So, evaporation and boiling are similar in some ways. But they are different in some other ways, right?

Mrs. Peterson: Yes, boiling happens only at a fixed temperature. That is the boiling point. But evaporation can occur at any temperature. Also, boiling takes place throughout the liquid. Evaporation? On the surface of the liquid.

Pene

lope: Oh, are there more differences?

Mrs. Peterson: Yes, there are some more. During boiling, bubbles form throughout the liquid. In evaporation there are no bubbles. Also, during boiling the temperature of the water remains constant. But during evaporation, it is not constant.

Penelope: Remarkable!

Mrs. Peterson: Do you drink Coca Cola?

Penelope: Yes, Mrs. Peterson.

Mrs. Peterson: Ok. Imagine this. You have taken out the can of Coca Cola from the fridge. It is now left on the table. Do you see droplets of water on the outside of the can?

Penelope: I have noticed that Mrs. Peterson.

Mrs. Peterson: Well, when warm water vapour from the surrounding air touches the cooler surface of the can, it loses heat. This is known as condensation.

Penelope: How amazing!

Mrs. Peterson: Do you know what is water in solid state?

Penelope: Yup, it is ice.

Mrs. Peterson: Right. When taken out of the freezer, what happens? The Ice cubes are brought into higher temperature than inside the freezer. This causes the change from a solid to a liquid. This is known as melting. The melting point of ice is 0°C.

Penelope: Oh, I see!

Mrs. Peterson: During melting, heat is absorbed. The particles of water in the solid state gain more energy. They vibrate more vigorously and become randomly arranged.

Penelope: When does water change to ice?

Mrs. Peterson: When water is cooled, it changes from a liquid to a solid. This is known as freezing.

Penelope: Mrs. Peterson, how is snow formed?

Mrs. Peterson: Water in the atmosphere freezes. Ice crystals are formed. These ice crystals may remain in the atmosphere. Or they may fall to Earth as snowflakes.

Penelope: Ok. Mrs. Peterson, you said the boiling point of water is 100°C. How about the boiling point of water after something is added to it? For example, after sugar is added to it? Or salt?

Mrs. Peterson: The boiling point of water can increase to above 100°C. When? When salt, sugar or even honey is added.

Penelope: How about freezing point?

Mrs. Peterson: Yes, the freezing point of water can decrease. When does that happen? When other substances are added to it. When we say water boils at 100°C and freezes at 0°C, we are talking about pure water.

Penelope: Oh, I see. Water is so basic to our human civilization, right Mrs. Peterson?

Mrs. Peterson: Yes, Penelope. Water is the elixir for all living things. Besides drinking, water is widely used in homes and industries for various purposes.

Penelope: Oh yes. Just the other day I read in a magazine that water is used to generate electricity.

Mrs. Peterson: Yup, Penelope.

Penelope: Thanks a lot Mrs. Peterson. I wish to talk to you again on science-related topics. I find it really interesting to talk to you.

Mrs. Peterson: My pleasure.