Olympiad Test: Separation of Substances - Class 6 MCQ

Winnowing is a method used to separate lighter impurities from heavier substances in a mixture. This technique is commonly employed in agriculture, particularly for separating husk from grain.

• The process involves releasing the mixture into the air.
• Wind blows away the lighter husk particles.
• Heavier grains fall back down, allowing for easy recovery.

For example, when separating husk from wheat:

• The husk is carried away by the wind.
• The heavier wheat grains form a heap on the ground.

This method not only helps in cleaning the grains but also allows the husk to be used for various purposes, such as fodder for cattle.

The correct answer is A: Sugar.

• The separation technique used is crystallization, which separates solids from a solution.
• Sugar can be extracted from a sugar-water solution through this method.
• In crystallization, sugar dissolves in water, is heated to dissolve more, and then cooled to form sugar crystals.
• Other substances like chalk powder, glass, and oxygen cannot be separated using crystallization.

Thus, R must be a substance that is soluble in water, which in this case is sugar.

The process of evaporation involves converting water into vapour by heating. This method effectively separates salt from salty water. When the water is boiled, it evaporates, leaving the salt behind.

Key points about evaporation:

• Evaporation occurs continuously wherever water is present.
• Sea water contains various salts, including common salt.
• When sea water is placed in shallow pits, sunlight heats it, causing the water to evaporate.
• After several days, the water evaporates completely, leaving behind solid salts.
• Common salt can be obtained from these salts through further purification.

In summary, evaporation is a simple and effective method for extracting salt from water.

• 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 combines evaporation and condensation to separate liquids. Here’s how it works:

• The liquid is heated, causing it to evaporate into vapour.
• The vapour is then cooled, leading to condensation back into liquid form.
• This method is effective for separating mixtures based on their boiling points.

For example, in the distillation of water:

• Water is boiled to produce steam.
• The steam is cooled and collected as pure water.

This process is widely used in laboratories and industries for various applications.

Filtration is the method used to separate tea leaves from prepared tea. This process involves the following steps:

• The tea is poured through a filter.
• The liquid tea passes through while the solid tea leaves are trapped.
• This method effectively removes solid particles from liquids.

In comparison to other methods:

• Decantation may leave some leaves in the tea.
• Strainers can also be used, but filtration is more effective.

Overall, filtration is a common and reliable technique for ensuring a clear cup of tea.

To obtain salt from seawater, the method used is evaporation.

This process involves the following steps:

• Seawater is heated, which causes the water to evaporate.
• As the water evaporates, it leaves behind the salt as a solid residue.
• This method is effective because water has a lower boiling point than salt.

In summary, evaporation is a reliable way to extract salt from seawater by taking advantage of the different boiling points of water and salt.

The process of separating butter from curd is called churning. This method involves:

• Vigorously stirring or rotating the curd.
• Separating the butterfat from the liquid, known as buttermilk.
• Causing the butter to solidify and detach from the buttermilk.

Churning is a common technique used in dairy processing to obtain butter from curd.

Sedimentation is the process of separating solid particles suspended in a liquid by allowing them to settle due to gravity. Key points include:

• The heavier solid particles gradually settle at the bottom of the container.
• The clearer liquid can then be decanted or removed from the top.
• This method is commonly used in water treatment and other scenarios where particles need to be eliminated from liquids.

Additionally, sedimentation can be applied to mixtures of two immiscible liquids, such as oil and water:

• When allowed to stand, they form two distinct layers.
• The top layer can be separated through decantation.

In practical applications, consider:

• When preparing tea, using a strainer to remove tea leaves is a form of filtration.
• Decantation can also be used to separate impurities from muddy water, allowing clear water to be poured off.

The method used to separate a mixture of wheat and rice is sieving. This process involves:

• Using a sieve with a mesh of suitable size.
• Allowing smaller particles, like rice, to pass through.
• Retaining larger particles, such as wheat.

Sieving is effective for separating mixtures based on particle size. It is commonly used in various applications, including:

• Removing impurities from flour.
• Separating pebbles and stones from sand.

In summary, sieving is a practical method for sorting materials with different sizes, making it an essential technique in both cooking and construction.

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 an effective tool for separating two immiscible liquids, which are liquids that do not mix, such as oil and water. Here’s how it works:

• The denser liquid settles at the bottom.
• 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.

This method is particularly useful when dealing with mixtures where the components have different densities, allowing for a clear separation.

Evaporation is the method used to separate soluble substances from a liquid. This process involves the following steps:

• When a liquid containing a dissolved substance is heated, the liquid evaporates.
• This leaves behind the soluble substance, such as salt or sugar, as a solid residue.
• The effectiveness of this method is due to the fact that the solvent, typically water, has a lower boiling point than the dissolved substance.

For example, in the case of sea water:

• Sea water contains various salts, including common salt.
• When allowed to stand in shallow pits, sunlight heats the water, causing it to evaporate.
• After several days, the water completely evaporates, leaving behind solid salts.
• These salts can then be further purified to obtain common salt.

In summary, evaporation is a crucial method for separating soluble substances from liquids, making it widely used in various applications.

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 traditional farming technique used to separate lighter components from heavier ones in a mixture. It is particularly effective for separating grain from chaff.

Key points about winnowing:

• It involves using air or wind to blow away lighter particles.
• This method is ideal for heterogeneous solid-solid mixtures.
• Winnowing is commonly employed by farmers to separate husk from heavier seeds.
• The lighter husk is carried away by the wind, while the heavier seeds form a pile.

Winnowing is often preceded by threshing, which loosens the grain from its husks and straw. This method is not only effective for grains but can also be adapted for other 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 where a gas transforms into a liquid when it is cooled or compressed. Here’s how it works:

• When water vapour in the air cools down, it turns into liquid water.
• For example, steam from a kettle condenses on a cold surface.
• As the steam meets a cool surface, like a metal plate with ice, it forms water droplets.
• This process is commonly observed when water vapour condenses under a lid covering hot liquids.

In summary, condensation is crucial for understanding how gases can change into liquids through cooling.

Winnowing is a method used to separate chaff or husk from grains like wheat. This process relies on the application of wind to distinguish between heavier and lighter components.

Key points about winnowing:

• It is commonly employed by farmers to remove lighter husk particles from heavier seeds.
• The wind carries away the husk, allowing the seeds to form a heap.
• The separated husk can be repurposed, for example, as fodder for cattle.

In summary, winnowing effectively uses the natural force of wind to facilitate the separation of different components in a mixture.

The process of obtaining clear water from muddy water using alum is called loading. This method involves the following steps:

• Alum Addition: Alum is added to the muddy water.
• Clumping: The fine dirt and impurities clump together, a process known as flocculation.
• Settling: The larger particles settle to the bottom due to gravity, resulting in clearer water.
• Separation: The clearer water can then be separated using decantation or filtration.

An unsaturated solution contains less solute than the saturation level, allowing it to dissolve more solute.

In the case of a sugar solution:

• If it can still dissolve more sugar without changing temperature, it is classified as an unsaturated solution.
• This means that additional sugar can be added and will dissolve.

Therefore, a sugar solution that can hold more solute without altering its temperature is indeed an unsaturated solution.