Olympiad Notes: Separation of Substance | Science Olympiad Class 6 PDF Download

Introduction

• Commonly, substances are separated or purified through various processes in everyday tasks. For instance, when making tea, we filter tea powder, and before cooking, rice is often cleaned with water.
• These processes of separation are widely utilized in our routines to ensure the purification and isolation of different substances.
• Throughout this chapter, we will delve into studying several methods employed for separating substances effectively.

Handpicking

• Handpicking involves the manual separation of stones, dust, husk from grains such as rice and wheat.
• Advantages include its effectiveness in eliminating larger particles of dust from smaller grains.
• However, handpicking is disadvantaged by its time-consuming nature.
• It is not suitable for removing small-sized dust and stone particles efficiently.

Threshing

• Grain stalks undergo sun-drying as a preliminary step.
• Post drying, the stalks are manually beaten vigorously to separate the grains from the stalks, a process known as threshing.
• Occasionally, bullocks or machinery are employed for this purpose.

Winnowing

• A prevalent method used for separating heavier grain particles from lighter dust particles involves a specific technique.
• The mixture, comprising both grain and dust, is elevated to a considerable height, roughly around shoulder or chest level.
• By tilting the mixture slightly and providing a gentle movement, lighter particles such as husk are encouraged to fall out.
• This process is commonly referred to as threshing and is effective in segregating the desired grains from the unwanted lighter particles.

Sieving

• Sieves serve the purpose of filtering out dust particles and are frequently employed in the cleaning of flour.
• This method involves the use of a sieve where fine flour particles pass through the sieve's holes while larger impurities are retained on the sieve.
• Sieving effectively separates finer components from larger impurities, making it a common technique for refining flour.

Sedimentation and Decantation

• Despite previous cleaning processes, residual small particles might remain in purchased rice.
• To address this, rice is washed with water just before cooking, leveraging a separation method.
• Sedimentation occurs as heavier rice particles settle down in the water due to their weight.
• Decantation, a process of separation, involves discarding the water along with lighter dust particles after they float, leaving behind the settled heavier rice particles.
• Similarly, oil and water are separated using a comparable method: water settles as it is heavier than oil, allowing the oil to be separated from the top layer.

Filtration

• Filtration is a separation technique akin to the use of a tea filter, commonly employed to separate substances.
• This process involves passing a liquid containing solid particles through a filter or filter paper, effectively separating the solids from the liquid.
• Fruit and vegetable juices are often subjected to filtration for refining purposes using a similar method.
• Certain substances can also undergo filtration using filter paper, extending the applicability of this separation process.

Evaporation

• The procedure to separate salt from water (seawater) involves heating the water until it completely transforms into vapor, leaving the salt residue behind.
• This transformation of a liquid into its vapor form is termed as evaporation.
• Evaporation serves as the method through which salt is separated from seawater, as the water vaporizes, leaving the salt behind in its solid form.

Salt-Sand mixture

• In scenarios involving mixtures like sand and salt, multiple methods may be necessary for separation.
• Mixing the sand and salt mixture with water initiates a process where salt dissolves in water while the sand remains insoluble.
• Following this, sedimentation occurs as the heavier sand particles settle to the bottom.
• Decantation is then employed, allowing the pouring out of the water mixture containing dissolved salt, while the settled sand remains unaffected.
• Heating the water to induce evaporation separates the salt from the water, leaving the salt behind in the container.
• Cooling down the water vapor using an ice-cold plate initiates condensation, transforming the vapor back into liquid water, which can be collected in a separate container.
• By employing these sequential processes – sedimentation, decantation, evaporation, and condensation – the sand and salt are effectively separated from each other and from the water.

Saturated Solution

• When a solute is added to a solvent, initially, it dissolves into the liquid.
• However, upon continuously adding more solute, a point is reached where the solute no longer dissolves. This indicates that the solvent has reached its 'Saturating point', and further solute cannot be dissolved.
• The saturation point of a solvent is influenced by several factors:
  • Temperature of the solvent
  • Pressure of the solvent
  • Nature of both the solvent and solute
• Understanding the saturation point is crucial as it determines the maximum amount of solute that can be dissolved in a given amount of solvent under specific conditions.