Chapter-5 Separation of Substances

Explanation:

Mixing two or more substances results in a mixture, which may need to be separated into its individual components. Separation is necessary when certain components may not be useful, or if they could potentially spoil the useful components of the mixture.

For example:

In tea preparation, a strainer is used to separate the tea leaves from the liquid.

When processing wheat, rice, or pulses, any stone pieces are removed by hand to ensure that they do not spoil the quality of the final product.

Explanation:

Winnowing is a process that involves separating the lighter components of a mixture, such as chaff or dust, from the heavier ones, such as grains or seeds, by subjecting the mixture to a wind or blowing air. This is usually done by tossing the mixture in the air and allowing the wind or a fan to blow away the lighter components, leaving behind the heavier ones.

Winnowing has been used for thousands of years in agriculture to separate grain from chaff or husks. It is still used today in many parts of the world, especially in rural areas where modern technology is not available. It is useful for small-scale farmers who cannot afford expensive machinery.

Explanation:

There are a few different methods you can use to separate husk or dirt particles from a sample of pulses before cooking. Here are three common methods:

1. Handpicking: This is a simple method that involves visually inspecting the pulses and removing any husk or dirt particles by hand. This is best done on a small scale, such as when preparing a meal for a few people.

2. Water flotation: In this method, the pulses are soaked in water and stirred, causing any husk or dirt particles to float to the surface. The floating particles can then be discarded, leaving the clean pulses at the bottom of the container.

3. Sieving: This method involves passing the pulses through a fine-mesh sieve. The sieve catches any large husk or dirt particles, which can then be removed by hand. This method is best for removing larger particles and may not be as effective for very fine particles.

4. Winnowing: can also be used to remove lighter dust or husk particles from the heavier pulses.

Explanation:

Sieving is a method of separating particles of different sizes by passing a mixture through a sieve or a screen with uniform holes. The smaller particles can pass through the holes while the larger particles are retained on the sieve.

Sieving is commonly used to separate different grades of flour or to remove impurities from spices, sugar, and other food ingredients.

Explanation:

To separate sand and water from their mixture, you can use the process of sedimentation and decantation. Here are the steps involved:

1. Allow the mixture of sand and water to stand undisturbed for some time. The sand will settle at the bottom due to its higher density, while the water will remain on top.

2. Carefully pour off the water from the top of the container, leaving behind the sand at the bottom. You can do this by tilting the container and pouring the water out slowly, being careful not to disturb the sand.

3. Once most of the water has been poured off, you can remove any remaining water by using a filter paper or a sieve. This will allow you to collect the sand and remove any remaining water or small particles

Explanation:

Explanation:

To obtain clear water from a sample of muddy water, you can use a process called filtration.

Here are the steps involved:

1. Set up a filter consisting of a funnel, filter paper, and a clean container to collect the filtered water.

2. Place the funnel in the mouth of the clean container and fold a filter paper to fit into the funnel.

3. Pour the muddy water into the filter paper slowly, being careful not to overfill the funnel.

4. Wait for the water to filter through the paper, leaving behind the mud and other solid particles.

5. Collect the filtered water in the clean container.

6. If the water is still not completely clear, you can repeat the filtration process using a fresh filter paper until the water is clear.

Explanation:

(a) The method of separating the seeds of paddy from its stalks is called threshing.

(b) When milk, cooled after boiling, is poured onto a piece of cloth, the cream (malai) is left behind on it. This process of separating cream from milk is an example of filtration.

(c) Salt is obtained from seawater by the process of evaporation.

(d) Impurities settled at the bottom when muddy water was kept overnight in a bucket. The clear water was then poured off from the top. The process of separation used in this example is called sedimentation or decantation.

Explanation:

(a) False. A mixture of milk and water cannot be separated by filtration as both milk and water pass through the filter paper due to their small particle sizes.

(b) False. A mixture of powdered salt and sugar cannot be separated by the process of winnowing. Winnowing is a process used to separate solids of different sizes and densities by blowing air through them. However, salt and sugar have similar particle sizes and densities, so they cannot be separated by winnowing.

(c) False. Separation of sugar from tea cannot be done with filtration as sugar dissolves in water and passes through the filter paper along with the tea.

(d) False. Grain and husk cannot be separated with the process of decantation. Decantation is a process used to separate a liquid from a solid that has settled at the bottom of a container. However, grain and husk are both solid components and have similar densities, so they cannot be separated by decantation. Threshing or sieving is the appropriate method for separating grain and husk.

Explanation:

It is better to dissolve the sugar in water before adding ice to the lemonade. This is because sugar dissolves more easily in warm water than in cold water. If you add ice to the lemonade before dissolving sugar, the water will be colder, which will make it more difficult for the sugar to dissolve.

If you dissolve sugar in warm water first and then add ice, the water will cool down, but the sugar will still remain dissolved.