Question 1 What is sedimentation?
Question 2 What is decantation?
Question 3 How will you separate a mixture of sand and water? Explain with the help of diagram?
Question 4 What substance is used for loading the clay particles suspended in muddy water?
Question 5 Define the term sediment?
Question 6 How will you separate rice and pulses from water after washing?
Question 7 How will you separate a mixture of oil and water?
Question 8 What is filtration?
Question 9 Define the term filter paper, residue and filtrate?
Question 10 How will you separate a mixture of chalk of water?
Question 11 How will you separate a mixture of sand and water?
Question 12 Explain the process by which tea leaves are separated from prepared tea?
Also Read NCERT Solutions for Chapter 5 Separation of Substances
Sedimentation
The solid matter which settles down at the bottom of a liquid is called a sediment. The deposition of solid matter at the bottom of a liquid is called sedimentation.
After sedimentation, we get two layers. The upper layer is of clear liquid and the lower layer is of sediment.
Decantation
The pouring out of a liquid from a vessel without disturbing the sediments is called decantation.
There are some mixtures which contain insoluble solid particles suspended in a liquid. The solid particles which are insoluble in a liquid can be separated by decantation.
A mixture of sand and water contains sand particles suspended in water. Sand can be separated from sand water mixture by the method of decantation.
The sand and water mixture is taken in a beaker. It contains sand particles scattered throughout water. Allow the mixture of sand and water to stand undisturbed for some time. On keeping, the heavier sand particles will settle down at the bottom of the beaker. This layer of sand is called sediment. The deposition of sand at the bottom of a beaker is called sedimentation. When the sand settles down, clear water is left above the layer of sand.
We pour the clear water into another beaker gently with the help of a glass rod, without disturbing the sediment of sand. This process is called decantation. When all the clear water has been poured out, only sand is left at the bottom of the beaker. In this way a mixture of sand and water has been separated into sand and clear water by decantation.
The process of decantation is used in our everyday life
Rice and pulses bought from the market usually have dust or soil particles as impurities in them. So, rice and pulses are always washed before cooking. When we add water to rice or pulses taken in a vessel, then the impurities such as dust and soil particles get separated and go into water. Due to this the water becomes a little dirty. The rice or pulses, being heavy, remain at the bottom of the vessel and dirty water is separated by decantation by tilting the vessel to one side.
The process of decantation can be used for separation only when the solid does not dissolve in the liquid.
Sugar dissolves in water so the mixture of sugar and water cannot be separated by method of decantation.
The method of decantation can also be used for separating two immiscible liquids.
Water and oil are two immiscible liquids which can be separated by decantation. A mixture of water and oil is allowed to stand in a beaker. Since water and oil are immiscible, they form two separate layers in the beaker. Water, being heavier, forms the lower layer and oil, being lighter forms the upper layer in the beaker. We can decant off the upper layer of oil into another beaker carefully. Water will be left behind.
The process of decantation cannot be used for separating two miscible liquids.
For ex: Alcohol and water are miscible with each other, a mixture of alcohol and water cannot be separated by decantation.
kerosene and petrol cannot be separated by decantation because they are miscible liquids.
Loading
Sometimes the water fetched from a river, lake or pond is muddy due to the presence of fine clay particles suspended in it. These suspended clay particles are very small and take a long time to settle down on their own. The settling down of suspended clay particles of muddy water can be made faster by the process of 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.
Muddy water is a mixture of water and suspended clay particles. The muddy water is taken in a beaker. A big piece of alum is taken and a thread is tied to it. The piece of alum is then put in the beaker of muddy water and rotated in it three or four times by holding from thread. After this piece of alum is taken out from the beaker. When the piece of alum is rotated in muddy water, some of the alum dissolves in water. The particle of dissolved alum deposit on the suspended clay particles of muddy water. In this way the suspended clay particles become loaded with heavy alum particles. Due to this the clay particles become quite heavy and settle down at the bottom of beaker quite rapidly. When all the suspended clay particles settle down, the water becomes clear. The clear water is then decanted into another beaker. The loaded clay particles remain behind in the first beaker.
Filtration
A filter paper is round piece of special paper which has millions of tiny holes in it. The holes of filter paper are so small that they cannot be seen with naked eyes. The liquids can pass through tiny holes of paper but solid particles being large cannot pass through the tiny holes of the filter paper.
The solid which remains on the filter paper is called residue.
The liquid which passes through the filter paper is called filtrate.
Before a filter paper can be used for the process of filtration it is folded properly to make a hollow cone.
The process of removing insoluble solids from a liquid by using a filter paper is known as filtration. Filtration is used for separating insoluble substances from a liquid. The mixture of insoluble solid and liquid is poured into a filter paper cone fixed in a funnel by using a glass rod as a guide. The liquid passes through the filter paper and collect in the beaker kept below the funnel. The solid particles do not pass through the filter paper and remain behind on the filter paper. A mixture of insoluble solid in a liquid is separated into the solid and clear liquid.
A mixture of chalk and water is separated by filtration. When the mixture of chalk and water is poured on the filter paper fixed in a funnel, then clear water passes through the filter paper and collects as filtrate. The chalk particles remain behind on filter paper as residue.
A mixture of sand and water can also be separated by filtration. When the mixture of sand and water is poured on a filter paper fixed in funnel, then clear water passes through filter paper and collect as filtrate. The sand remains behind on filter paper in the form of a residue.
In everyday life different kinds of filters are used for example a wire mesh, a piece of cotton, a piece of muslin cloth, tea-strainer.
To separate used tea leaves we pour the prepared tea over the tea strainer. The tea-strainer has a wire mesh in it which acts as a filter. The liquid tea passes through the small holes of tea strainer and collects in the cup below. The tea leaves do not pass through the tea strainer.The tea leaves remain behind on the tea strainer. The used tea leaves are separated from prepared tea by the method of filtration.
Fruit juice is also filtered by using a strainer as filter to remove the seeds and solid particles of pulp.
When milk is cooled after boiling, a layer of cream is formed on its surface. This cream can be removed from the milk by filtering it through a piece of cloth. The milk passes through the clothes whereas cream is left on the cloth.
At water treatment works, the river water or lake water is filtered by using sand filters.
A mixture of two liquids cannot be separated by filtration. A mixture of milk and water cannot be separated by filtration.
| Notes for Chapter 5 Separation of Substances |
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