Syllabus Study Notes

Class VI >> Science >> Separation of substances >> Free Detailed Study Notes

IMPORTANT TERMS

Mixture                                 Mixture is made up of two or more pure substance. Sea water is a mixture containing water, common salt and other various salts and minerals.

Types of mixture                    Mixtures are of two types—homogeneous and heterogeneous. Solutions are homogeneous mixtures, while suspensions and emulsions are heterogeneous mixtures.

Pure substance                      Substance which consists of only one kind of particle is termed as pure substance. A mixture is made up of two or more pure substance.

Impure substance                  Substance which contains different kind of particle is termed as impure substance.

Solution                                  The mixture of a solute and a solvent is called as solution.

Saturated solution                 A solution which cannot dissolve more of a given substance at a given temperature is called as saturated solution.

Unsaturated solution            A solution which can dissolve more of a given substance at a given temperature is called as unsaturated solution.

Components of mixture        The pure substances which are present in a mixture are called components of the mixture.

 

REASON FOR SEPARATING MIXTURES INTO THEIR COMPONENT: – The mixtures are separated into their components for various purposes, such as:

  • To remove an undesirable component: Tea leaves are separated from tea mixture by using tea- strainer.
  • To remove harmful component: We separate the small pieces of stones and insects from rice, wheat and pulses before using them.
  • To obtained a useful component: Butter is a useful component which is separated from a mixture called milk.

 

METHODS OF SEPARATION OF MIXTURES: – Some of the methods which are commonly used for separating the component of mixtures are threshing, winnowing, hand-picking, sieving, magnetic separation, decantation, loading, filtration, evaporation, distillation, condensation, chromatography and crystallization

 

SEPARATING A SOLID FROM A SOLID

  1. THRESHING: - The process that is used to separate grain from stalks is called threshing. In this process, the stalks are beaten to free grain seeds to separate it from the stalks.
  1. WINNOWING: - The process that is used to separate heavier and lighter components of a mixture by wind or by blowing air is called winnowing. Wind is essential to perform winnowing process.
  1. HAND-PICKING: - The process that is used to separate slightly large particle impurities like the pieces of dirt, stone, and husk from wheat, rice or pulses is called handpicking.
  1. SIEVING: - The process that is used to separate components of a mixture having different sizes is called sieving. It is used to separate pebbles and stones from the sand.
  1. MAGNETIC SEPARATION: - Magnetic separation means 'separation of a mixture by using a magnet'. A mixture of iron fillings and sulphure powered can be separated by using a magnet.   

 

SEPARATING A SOLID FROM A LIQUID

Solid substance may be soluble or insoluble in a solvent like salt is soluble in water but chalk is insoluble in water in it, so we have to use different methods of separation for soluble and insoluble substance in their respective solvents.

 

  1. SEPARATING SOLUBLE SOLIDS FROM THEIR SOLUTION: - The soluble solid can be separated from liquid by using following methods

 

  1. EVAPORATION: - Evaporation is the process that involves heating of a solution until the liquid changes into gaseous state leaving behind a solid residue. It is used to separate sugar dissolved in water.
  • Evaporating basin – the solution can be placed in the evaporating basin for the process of evaporation.

 

  1. DISTILLATION: - Distillation is the process of heating water to form water vapour, and then cooling the hot water vapour to get back liquid water. A special apparatus is used in this process known as ‘Liebig condenser’. The clear liquid obtained by the process is called as distillate.

 

  1. SEPARATING INSOLUBLE SOLIDS FROM THEIR SOLUTION: - The solids like chalk, sand and dust particles are insoluble in water. Particles of such solids can be separated from their solution by using following method.

 

  1. DECANTATION: - Decantation is a process for the separation of mixtures, by removing a layer of liquid, generally one from which a precipitate has settled. The purpose may be either to produce a clean decant, or to remove undesired liquid from the precipitate.

 

  1. LOADING: - Loading is the process in which alum particles are deposited on suspended clay particles of muddy water to make them heavy and settle down rapidly.

 

  1. SEDIMENTATION: - When the heavier component in a mixture settles after water is added to it, the process is called as sedimentation. The solid matter that settles down at the bottom of the liquid is called sediment.

 

  1. FILTRATION: - Filtration is a process that is used for separation of solids from liquids by interposing a medium through which only liquids can pass. It is used in the process of preparing cottage cheese.
  • Filter paper – It is used to filter the substance.
  • Filtrate - The liquid obtained by the process of filtration is called a filtrate.
  • Residue - The solid substance left behind on the filter paper in filtration process is called as residue.

 

SOME OTHER IMPORTANT METHODS OF SEPARATIONS

  1. CONDENSATION: - The process of conversion of water vapour into its liquid form is called condensation.
  1. CENTRIFUGATION: - Centrifugation process uses centripetal force for the sedimentation of heterogeneous mixtures. An example of centrifugation is used in washing machine to dry clothes by the spinner.
  1. CHROMATOGRAPHY: - Chromatography separates a mixture based on the component's movement at different rates, when introduced through a medium. It used to separate the color in food dyes.
  1. CRYSTALLIZATION: - Crystallization is a chemical solid–liquid separation technique, wherein solute from the liquid solution changes to a pure solid crystalline. It is a technique which is used to obtain pure salt from impure salt.
  1. SUBLIMATION: - Sublimation is a process where a solid turns into a gas without going through a liquid stage. An example of sublimation is when ice cubes shrink in the freezer.
  • Sublime- Condensed solid produced during sublimation is called sublime.

 

SOLUBILITY: -    The maximum amount of a substance which can be dissolved in 100g of water                   at a given temperature is known as solubility of the substance in water.

  • The solubility of a common salt in water is 36 g at 20 degree C. 
  • The solubility of a sugar in water is 204 g at 20 degree C. 
  • The solubility of a copper sulphate in water is 21 g at 20 degree C. 
  • The solubility of a potassium nitrate in water is 32 g at 20 degree C. 

 

INTERESTNG FACTS

  • Ice cubes do shrink in their trays, especially in frost-free refrigerators by the process of sublimation.
  • High speed centrifuges can spin up to 30,000 times a minute in centrifugation.
  • Painting uses the separation process of evaporation. When the solvent dries and evaporates, only the colour pigment is left.
  • Glaciers in Polar Regions can experience the loss of water due to sublimation process even when there isn't enough energy to lose water mass from evaporation.
  • Chromatography is used extensively in forensics, for analysing drugs in body fluid, and at airports to detect explosives.