Important Questions Test: Separation of Substances - UPSC MCQ

• Sedimentation is the process where solid particles settle at the bottom of a liquid.
• It occurs when the particles are denser than the liquid and can no longer remain suspended.
• This is a common method used to separate mixtures, particularly in water treatment and sedimentary rock formation.

Seawater contains a large amount of common salt and the salts of other metals dissolved in it. Near the sea-shore, the sea water is collected in shallow pits and allowed to evaporate in the sunshine. In a few days, the water evaporates, leaving behind salt. Hence it is obtained by evaporation.

X is winnowing, a process which uses the difference in weights of solids in a solid- solid mixture for separating the components.

A solution that has reached the maximum solubility is called a saturated solution . It means you can no longer add solute to the solution . Saturated solution are required for the process of crystallization.

We separate substances in a mixture for several reasons:
(i) To separate two different but useful components : This allows us to utilize each component effectively. For example, separating cream from milk.
(ii) To remove useless components : This process helps in obtaining the desirable part by removing unwanted parts, like removing husks from grains.
(iii)To remove impurities : This ensures the purity and quality of substances, such as purifying water by removing dirt and bacteria.
Hence, option D, which includes all three reasons, is correct.

Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. This is the method used to separate a dissolved solid component from its solution as after evaporation only salt remains.

Answer : D

• Handpicking is a separation technique used to separate a solid-solid mixture.
• In this method, the individual components of the mixture are picked out by hand based on their physical properties.
• It is commonly used when the solid components have distinct differences in size, color, or shape, making them easy to separate manually.
• Handpicking is a simple and cost-effective method, but it may not be suitable for mixtures with very fine particles or similar properties

Filtration is the process of separating suspended solid matter from a liquid, by causing the latter to pass through the pores of some substance, called a filter. The liquid which has passed through the filter is called the filtrate.

Paneer is separated from curdled milk through filtration.

• Filtration is a process used to separate solids from liquids.
• When few drops of lemon juice are added to milk as it boils, this gives mixture of particles of solid paneer and a liquid.
• The paneer is then seprated by filtering  the mixture through fine cloth or a strainer.
• This process effectively separates the paneer from the mixture.

Winnowing is the process of separation of the heavier components from the lighter components of a mixture by wind or by blowing air. It is generally used by farmers to separate the lighter impurities such as husk particles from the heavier grains.

The easiest method to separate mixture of sugar and water is evaporation as it will evaporate water and will leave behind the sugar molecules. 

When a saturated solution is heated, it can dissolve more of the substance. This is because heating increases the solubility of most substances, allowing more particles to mix with the solvent. For example, more sugar can dissolve in hot water than in cold water.

• X - Winnowing: This method uses the weight difference between components and depends on air to separate lighter particles (like husk) from heavier ones (like grains). Requires air.

• Y - Threshing: This method involves beating or mechanical action to separate grains from stalks. It does not rely on air for separation. Does not require air.

• Z - Sieving: This method involves passing a mixture through a sieve with appropriate-sized holes to separate particles based on size. It does not rely on air. Does not require air.

Correct Answer: b) Only Y, Z

• Sieving is used when particles are too small to be picked by hand and the quantity is large.
•  It is done to separate mixtures that contain substances mostly of different sizes.
• The mixture is passed through the pores of the sieve.
• All the smaller substances pass through easily while the bigger components of the mixture are retained.

Condensation is the process by which water vapour changes into liquid water when it comes into contact with a cooler surface. It is a crucial part of the water cycle and plays a significant role in various natural phenomena, such as the formation of clouds and dew.