HOTS Questions: Separation of Substances | Class 6: Additional Practice PDF Download

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Q1: You are given a mixture of sand and water. How do you separate them?
Ans: To separate a mixture of sand and water, follow these steps:

• Sedimentation: Leave the mixture undisturbed for some time. The sand will settle down at the bottom due to its higher density.
• Decantation: Carefully pour the clear water from the top into another container. Make sure not to disturb the settled sand.

Q2: You are asked to dissolve sugar in water. You kept on adding sugar to water till some of the sugar is not dissolving at all by stirring with the spoon. How can you dissolve the left-out sugar?
Ans: To dissolve the remaining sugar, you can:

• Heat Water: Gently heat the water while stirring. More sugar might dissolve as warm water can hold more sugar.
• Crush Sugar: Crush the remaining sugar to smaller pieces. Smaller pieces dissolve faster.
• Stir Continuously: Keep stirring the mixture to help the sugar dissolve.

Q3: If you keep ice pieces in a glass tumbler, you observe a lot of water droplets on the surface of the tumbler. Why?
Ans: Water droplets form on the tumbler due to condensation. The cold tumbler cools the surrounding air, causing moisture in the air to turn into water droplets.

Q4: River water is clear whereas sea water is not, even though both contain mud and sand. Why?
Ans: River water appears clear compared to sea water due to a few reasons:

• Water Movement: Rivers have a consistent flow that helps carry away mud and sand particles. This movement prevents particles from settling and keeps the water relatively clear.
• Deposition: Rivers deposit sediments in their beds, helping to remove particles from the water column. In contrast, sea water often contains suspended sediments due to waves and currents.
• Tidal Action: The tides and waves in the sea constantly stir up the water, causing particles like mud and sand to remain suspended and making the sea water appear cloudy.
• Depth: Oceans are much deeper than rivers. The greater volume of water in the oceans provides more space for particles to remain suspended, resulting in the cloudiness of sea water.

In summary, the consistent flow, deposition, and shallower nature of rivers, along with the constant motion and greater depth of the sea, contribute to the difference in clarity between river water and sea water, even though both contain mud and sand.

Q5: You are given a mixture of water and oil. Using an empty cool drink bottle, how do you separate them?
Ans: You can separate water and oil using a funnel:

• Funnel: Attach a funnel to the mouth of the bottle.
• Pour Mixture: Gently pour the mixture into the funnel.
• Separation: Due to their different densities, oil will float on top of water. Oil goes through the funnel first, and water follows.

Q6: After the games period, you had come back to your classroom and sat under a fan. Your body becomes so cool, and you feel so comfortable. Why?
Ans: Sitting under a fan after playing feels cool because of evaporation. When you sweat, the fan helps the sweat evaporate faster, taking away heat and making you feel cooler.

Q7: River water is clear whereas sea water is not, even though both contain mud and sand. Why?
Ans: Rivers flow continuously, carrying away mud and sand particles. Sea water is often disturbed by waves and tides, which keep particles suspended, making it look cloudy.