Olympiad Test: Separation of Substances - Class 6 MCQ

In winnowing, light weight impurities are separated from relatively heavier substances. For example, husk is separated from wheat. It is done by releasing the mixture into the air so that the wind blows away the lighter impurities, while the heavier grains fall back down for recovery.

The correct answer is A: Sugar.

• The separation technique shown is crystallization, used to separate solids from a solution.
• Sugar can be separated from a sugar-water solution through crystallization.
• In this process, the sugar is dissolved in water, heated to dissolve more sugar, then cooled to allow sugar crystals to form and separate.
• Chalk powder, glass, and oxygen cannot be separated using crystallization.

R should be a substance which is soluble in water i.e., sugar.

The process of conversion of water into vapour by heating it is called evaporation. The salt can be easily obtained from the salty water by the process of evaporation. If we boil this water, the water evaporates completely, leaving behind only the salt.

• Threshing: This is the primary method where stalks are beaten to release seeds. It can be done manually or with machines.
• Winnowing: After threshing, winnowing helps separate the chaff (outer husk) from the grains using wind or air.
• Sieving: This method can further clean the grains by filtering out smaller debris or broken seeds.
• All these methods are used in grain harvesting, but threshing is the main process for seed removal.

Distillation is a process that involves evaporation followed by condensation. In this process, a liquid is heated to create vapor (evaporation), and then the vapor is cooled down to collect the condensed liquid. This is commonly used to separate mixtures based on different boiling points of the components. For example, in distillation of water, the water is boiled to form steam, and then the steam is condensed back into pure water.

Filtration is used to separate tea leaves from prepared tea. In this method, the tea is poured through a filter, which allows the liquid tea to pass through while trapping the solid tea leaves. This is a common method for separating solid particles from liquids.

To obtain salt from seawater, the method used is evaporation. In this process, seawater is heated, causing the water to evaporate, leaving the salt behind as a solid residue. This method is effective because water has a lower boiling point than salt, so the water evaporates, and the salt is left behind.

The process of separating butter from curd is called churning. In this method, curd is churned to separate the butterfat from the buttermilk. Churning involves rotating or stirring the curd vigorously, which causes the butter to solidify and separate from the liquid (buttermilk).

Sedimentation is the process of separating solid particles suspended in a liquid by allowing them to settle down due to gravity. Over time, the heavier solid particles settle at the bottom of the container, and the clearer liquid can be decanted or removed from the top. This process is commonly used in water treatment and other situations where particles need to be removed from liquids.

Winnowing is the method used to separate a mixture of wheat and rice. In this process, the mixture is tossed into the air, and the wind helps separate the lighter particles (like chaff) from the heavier grains (like wheat and rice). Since wheat and rice have similar densities, winnowing helps separate them based on their size and weight by using air currents.

Brass, Butter-milk, and Steel are all mixtures.

• Brass is an alloy (a mixture of metals like copper and zinc).
• Steel is also an alloy (a mixture of iron and carbon, among other elements).
• Butter-milk is a mixture of water and curd or yogurt.

However, Water is a pure substance, not a mixture, and therefore does not belong to the same group.

Answer: B) Water

A separating funnel is used to separate two immiscible liquids, which are liquids that do not mix, such as oil and water. The denser liquid settles at the bottom, and the less dense liquid forms the upper layer. By opening the tap of the separating funnel, the liquids can be separated based on their densities.

Evaporation is the method used to separate soluble substances from a liquid. When a liquid containing a dissolved substance is heated, the liquid evaporates, leaving the soluble substance (such as salt, sugar, etc.) behind as a solid residue. This method works because the solvent (usually water) has a lower boiling point than the dissolved substance.

In a mixture, the constituent substances are mixed only physically but not combined chemically. A mixture is not a pure substance as its constituents retain their properties. So, a mixture can be either homogeneous or heterogeneous.

Winnowing is a farming method developed by ancient people for separating grain from the chaff. It is also used to remove weevils or other pests from stored grain. Threshing, which is the loosening of grain or seeds from the husks and straw, comes before winnowing. It is used for heterogeneous solid-solid mixtures.

• Sedimentation is used to remove sand from water as sand particles settle down easily.
• Filtration is used to remove sawdust from water as the sawdust can be captured by the filter paper.
• Evaporation can be used to separate salt from water as the water evaporates and salt is left behind.

Condensation is the process by which a gas changes into a liquid when it is cooled or compressed. For example, water vapor in the air condenses into liquid water when it cools down.

Winnowing is a method of separation of chaff or husk from wheat/grains. Also called the process of separation of heavier components from lighter components by the application of wind.

Option B is correct.

The process of obtaining clear water from muddy water using alum is called loading. In this method, alum is added to the muddy water, which causes the fine particles of dirt and impurities to clump together (flocculate). These larger particles then settle down due to gravity, making the water clearer. After this, the clearer water can be separated through decantation or filtration.

If the amount of solute contained in a solution is less than the saturation level, it is called an unsaturated solution. It can dissolve more solute in it. 

So, a sugar solution that can hold more solute in it without changing the temperature is an unsaturated solution.