Science STD 6 Chapter 3: Separation of Substances - Exercises

We need to separate the components of a mixture to remove harmful or non-useful substances, or to obtain useful components. For example, stones are separated from rice to remove non-useful components. Butter is churned from milk to obtain a useful component.

Winnowing is a method of separating the heavier and lighter components of a mixture by wind or by blowing air. It is commonly used by farmers to separate lighter husk particles from heavier grain seeds.

To separate husk or dirt particles from pulses, one can use the handpicking method if the impurities are slightly larger in size. Alternatively, the pulses can be washed with water. The lighter husk and dirt particles will float on the water and can be poured off, while the heavier pulses will sink to the bottom. This process uses sedimentation and decantation.

Sieving is a method of separating components of a mixture based on a difference in particle size. A sieve is used, which allows smaller particles to pass through its holes while retaining the larger impurities. It is used in flour mills to separate impurities from wheat before grinding and at construction sites to separate pebbles and stones from sand.

To separate a mixture of sand and water, one can use the process of sedimentation and decantation. First, allow the mixture to stand. The heavier sand particles will settle at the bottom of the vessel (sedimentation). Then, the water can be gently poured off from the top without disturbing the settled sand (decantation).

Yes, it is possible to separate sugar mixed with wheat flour. One method is sieving, as the sugar crystals and flour particles may have different sizes. Alternatively, you can mix the flour and sugar with water. Sugar is soluble in water and will dissolve, while flour is insoluble and will settle down. You can then use decantation or filtration to separate the flour, and then use evaporation to obtain the sugar from the water.

To obtain clear water from muddy water, you can use the following steps:

1. Allow the muddy water to stand undisturbed. The heavier soil particles will settle at the bottom. This is sedimentation.
2. Gently pour the water from the top into another container without disturbing the sediment. This is decantation.
3. Filter the decanted water through a fine cloth or a filter paper to remove any remaining fine impurities. This is filtration.

You should add the ice after dissolving the sugar. It is possible to dissolve more sugar in water when the water is hot or at a higher temperature. Therefore, if you add the ice before the sugar is dissolved, the water temperature will drop and less sugar will dissolve.

Outline: This activity involves a visit to a dairy to learn about industrial separation processes. Students can ask how cream is separated from milk (often through centrifugation, a faster method than churning). The report should describe the process, the equipment used, and how it is a more efficient way of separating components compared to manual methods. This helps connect classroom knowledge to real-world applications.

Outline: This is a hands-on activity about the "loading" process, where alum is used to make fine, suspended mud particles heavier so they settle down faster. Students will observe the muddy water become clear after swirling a piece of alum in it. The mud and impurities will clump together and sink to the bottom. The report should describe this observation and explain that loading is an additional step to improve sedimentation and achieve clearer water.