Dissolving in Water

• Define dissolving and identify soluble and insoluble materials.
• Recognise that a solute seems to disappear but is still present.
• Compare how fast different materials dissolve in water.
• Connect dissolving to cooking, medicine, and drinking water at home.

Level 1 - Meaning of dissolving

When a solid mixes completely with a liquid and seems to disappear, we say it has dissolved. The liquid with the dissolved material is called a solution. Salt and sugar dissolve easily in water.

Level 2 - Soluble and insoluble materials

Materials that dissolve in water are called soluble, like salt, sugar, and washing soda. Materials that do not dissolve are called insoluble, like sand, chalk powder, and small stones.

Level 3 - Daily observations

Stirring sugar into hot tea makes it disappear, sweetening the tea evenly. Adding sand to water and stirring shows the sand settling at the bottom instead of dissolving. Stirring speeds up dissolving because it spreads the solute through the water faster.

Level 4 - Indian context

Making nimbu paani involves dissolving sugar and salt in water along with lemon juice. Oral rehydration solution (ORS) packets are dissolved in clean water to treat dehydration. Salt pan workers in Gujarat and Tamil Nadu rely on the reverse of dissolving — evaporation — to get back solid salt from seawater.

NCERT anchor: Looking Around 4, Ch 18 — Too Much Water, Too Little Water (water quality and use)

Sugar dissolving in water

Step 1 - Add one spoon of sugar to a glass of water.
Step 2 - Stir with a spoon for 30 seconds.
Step 3 - Observe the glass; no sugar grains are visible.
Step 4 - Taste a drop; the water tastes sweet.
Answer: Sugar has dissolved completely in the water.

Sand in water test

Step 1 - Add one spoon of sand to a glass of water.
Step 2 - Stir with a spoon for 30 seconds.
Step 3 - Let the glass stand for a minute.
Step 4 - Sand grains are still visible, settled at the bottom.
Answer: Sand is insoluble; it does not dissolve in water.

• What does it mean when a material dissolves?
• Name one material that dissolves in water and one that does not.
• How can you prove dissolved sugar is still present in water?
• Why does stirring help sugar dissolve faster?
• Stretch: Compare how quickly a sugar cube dissolves in hot water versus cold water and explain the difference.

Revision tip: Soluble materials dissolve and seem to disappear; insoluble materials stay visible and settle.

Open the Practice tab for graded questions on Dissolving.