NCERT Summary: Separation of Substances | Science Class 6 PDF Download

What is Separation?

• The removal of substances from a mixture of two or more substances is known as separation.
• Some examples of separation are:
  (i) Separating stones from rice
  (ii) Churning milk to obtain butter

Why do we need to separate substances? 

• To obtain two different components
• To remove impurities or harmful components
• To group substances of different sizes

Methods of Separation

Mixtures of solid with solid 

(i) Hand picking

• Handpicking is a method used to manually remove larger impurities like stones, husks, or dirt from food grains such as wheat, rice, or pulses. 
• It is a simple and effective way to separate unwanted items when the quantity of impurities is small.

Handpicking

(ii) Threshing

• The process in which the stalks are beaten to free the grain seeds.
• Threshing is done with the help of bullocks. For large quantities of grains, machines are used for threshing.
• This method is used by the farmers to separate the grains from the stalks after harvesting.

Threshing

(iii) Winnowing

• It is the process which is used to separate heavier and lighter components of a mixture by wind or by blowing air.
• This method is used by farmers to separate lighter husk particles from heavier seeds of grain.

(iv) Sieving

• It is a process in which components of a mixture of different sizes can be separated by a sieve.
• The smaller particles are removed out through the pore of the sieve and the larger particles are left behind.
• This method is used to separate wheat bran (the bigger particles) from flour.

Seiving

Separation of solids that do not dissolve in liquids

(i) Sedimentation

• This process involves allowing the heavier particles in a mixture to settle down at the bottom when water is added. 
• For example, dust particles settle at the bottom when rice is washed.

Sedimentation

(ii) Decantation

• After sedimentation, decantation is used to carefully pour off the liquid, leaving the settled heavier particles behind. 
• This is how we remove dirty water from washed rice.
• This method is used to separate liquids that don’t mix, like oil from water.

Decantation

(iii) Filtration

• The process in which separation of solid from liquid by filter paper or strainer.
• Example: separating mud from water by using filter paper.

Filteration

Mixtures of solids with liquids

(i) Evaporation

• This process is used to separate a solid dissolved in a liquid. 
• Water is heated until it turns into vapor, leaving the solid behind.
• In this process, liquid changes into gaseous form on heating.

(ii) Condensation

• It is the process when water vapour turns into liquid water, usually by cooling down.
•  It happens when warm, moist air cools down, causing the vapor to change back into liquid form. 
• For example, when steam from boiling water hits a cold surface, it condenses into droplets of water.

Can water dissolve any amount of a substance?

• Saturation Point: Adding more salt to water eventually leads to a point where no more salt can dissolve; the solution is saturated.
• Heating to Dissolve More: Heating a saturated solution allows more salt to dissolve. When cooled, excess salt may settle.
• Different Solubilities: Water dissolves different substances in varying amounts. Each substance has its own saturation limit.