CBSE Class 5 EVS: Experiments with Water (Chapter 7)

Understanding Water's Properties

Water is one of the most common substances on Earth, and it has some very special properties. In this chapter, we focus on two main ideas: solubility and floating/sinking. When you put something into water, one of two things usually happens: either it mixes completely and 'disappears' (we say it dissolves), or it remains visible and separate from the water. The things that dissolve form a solution. Some things, like sand, do not dissolve but settle down, while oil doesn't mix at all. Another interesting property is whether an object floats on the surface of the water or sinks to the bottom. This happens because some things are lighter than water, and some are heavier for their size. We'll explore these ideas with everyday examples to make them easy to understand.

Key Terms for Our Experiments

Dissolve

When a solid substance mixes completely with a liquid, becoming invisible and forming a uniform mixture. For example, sugar dissolves in water.

Soluble

A substance that can dissolve in a liquid. Sugar and salt are soluble in water.

Insoluble

A substance that cannot dissolve in a liquid. Sand and oil are insoluble in water.

Solution

The clear mixture formed when a soluble substance dissolves completely in a liquid. For example, sugar water is a solution.

Float

When an object stays on the surface of a liquid without sinking. Objects that are lighter than water, for their size, float.

Sink

When an object goes to the bottom of a liquid. Objects that are heavier than water, for their size, sink.

How to Make Things Dissolve Faster

1. Using Stirring — Imagine you put a spoonful of sugar in a glass of water. If you just leave it, it will take a long time to dissolve. But if you take a spoon and stir the water, the sugar crystals move around, come into contact with fresh water more often, and dissolve much faster. Stirring helps the water molecules quickly spread out the dissolving substance.
2. Using Heat — Have you ever seen your parents make tea? They add sugar to hot tea, and it dissolves very quickly. This is because heating the water makes its molecules move faster. These faster-moving water molecules bump into the sugar crystals more often and with more energy, helping them break apart and dissolve much quicker than in cold water. So, hot water dissolves many things faster than cold water.
3. Breaking into Smaller Pieces — If you have a big lump of sugar and some powdered sugar, which do you think will dissolve faster in water? The powdered sugar! When you break a substance into smaller pieces, more of its surface comes into contact with the water. This increased contact area allows the water to dissolve the substance more easily and quickly. Think about crushing a hard candy before putting it in your mouth – it dissolves faster!

What Floats and What Sinks? (With Examples)

• An empty plastic bottle: An empty plastic bottle is mostly filled with air, which is very light. So, the overall weight of the bottle and the air inside it is much less than the weight of the water it pushes aside. Therefore, it floats.
• A stone: A stone is a solid, compact object. It is much heavier than the same amount (volume) of water it displaces. Because of its weight relative to its size, a stone will always sink to the bottom.
• A dry leaf: A dry leaf is very light and often has tiny air pockets within its structure. This makes it less heavy than the water it displces. So, a dry leaf will typically float on the surface of the water.
• A coin: Coins are made of metal, which is a heavy material. Even a small coin is much heavier than the amount of water it displaces. So, a coin will quickly sink.
• Oil drops: Oil and water do not mix. If you put drops of cooking oil in water, you will see the oil drops stay on top and form a layer. This is because oil is lighter than water. So, oil floats on water.
• A wooden block: Wood is generally lighter than water. That's why big logs and boats made of wood float. A wooden block will float.

Always Observe Carefully and Record!

In EVS, and especially when doing experiments, observation is key! Don't just look; really see what's happening. Notice details: Does it dissolve immediately or slowly? Does it float completely or partially? Does the water change colour? What happens if you stir it?

After observing, it's very important to record your findings. You can draw pictures, make a table, or write down sentences about what you saw. This helps you remember and understand the results of your experiments better, and also helps you answer questions correctly in exams. A good scientist (and a good student!) always observes carefully and records accurately.

Practice Questions with Solutions

• Q: You put a spoonful of salt into a glass of water. What will happen to the salt? Why?
  A: Step 1: When salt is put into water, it will mix completely.
  Step 2: The salt will 'disappear' and make the water taste salty.
  Final answer: The salt will dissolve in the water because it is a soluble substance.

• Q: Name two things that float on water and two things that sink in water.
  A: Step 1: Think of light objects that stay on top of water.
  Step 2: Think of heavy objects that go to the bottom of water.
  Final answer: Things that float: a dry leaf, an empty plastic bottle. Things that sink: a stone, a coin.

• Q: Imagine you want to dissolve sugar in water as quickly as possible. What two things can you do to speed up the dissolving process?
  A: Step 1: Recall the methods discussed that help substances dissolve faster.
  Step 2: Identify the actions that increase contact between sugar and water molecules or increase their movement.
  Final answer: To dissolve sugar quickly, you can 1) stir the water, and 2) use warm or hot water.

• Q: If you mix sand with water, will it form a solution like sugar water? Explain why or why not.
  A: Step 1: Think about what happens when you mix sand and water. Does the sand disappear?
  Step 2: Compare this to what happens when sugar mixes with water.
  Final answer: No, sand will not form a solution with water. This is because sand is an insoluble substance; it does not dissolve but instead settles down at the bottom of the glass.

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