Matter in Our Surroundings

Separation of Mixtures by Using More Than One Method

A mixture which has only two components (or constituents) can be usually separated by a single method.On the other hand, a mixture which has more than two components can be separated into individual components by a combination of methods of separation. These methods are applied turn by turn. The separation of mixtures by using a combination of methods will become clear from the following examples.
Sample Problem 1. How will you separate iron filings, ammonium chloride and sand from their mixture ?
Answer Whenever we want to separate the components of a mixture, we should first find out some properties which are different for different components. In this question we have three components to be separated These are : iron filings, ammonium chloride and sand. Now, iron is attracted by a magnet whereas ammonium chloride undergoes sublimation. But sand does not have any of these properties. So, this difference in the properties of iron filings, ammonium chloride and sand will be used to separate them from their mixture.
The mixture containing iron filings, ammonium chloride and sand is separated as follows :
(i) Iron filings are attracted by a magnet so they are removed by the method of magnetic separation. When a magnet is moved in this mixture, iron filings cling to the magnet and get separated. We are then left with ammonium chloride and sand.
(ii) Ammonium chloride sublimes on heating whereas sand does not sublime. So, ammonium chloride is separated from sand by the process of sublimation. When the mixture containing ammonium chloride and sand is heated, then ammonium chloride forms vapours easily. These vapours on cooling give pure ammonium chloride. Sand is left behind.
From the above discussion we conclude that a mixture of iron filings, ammonium chloride and sand has been separated into its components by a combination of two methods: magnetic separation an sublimation. Please note that we have given so many details in answering this question just to make you understand clearly. There is no need for the students to write so many details while writing their answers.
Sample Problem 2. Describe a method of separating common salt from a mixture of common salt and chalk powder.
Answer This mixture contains two constituents : common salt and chalk powder. Now, common salt is soluble in water whereas chalk powder is insoluble in water. So, this difference in their solubility will be used to separate them. This is done as follows :
(i) Some water is added to the mixture of common salt and chalk powder,and stirred. Common salt dissolves in water to form salt solution whereas chalk powder remains undissolved.
(ii) On filtering, chalk powder is obtained as a residue on the filter paper and salt solution is obtained as filtrate.
(iii) The salt solution (filtrate) is evaporated to dryness when common salt is left behind.
Sample Problem 3. You are given a mixture of sand, water and mustard oil.How will you separate the components of this mixture ?
Answer. This mixture contains three components: sand, water and mustard oil.Now, sand is a solid which is insoluble in water as well as mustard oil. Water and mustard oil are immiscible liquids.
(i)The mixture of sand, water and mustard oil is filtered. Sand is left on the filter paper as residue.Water and mustard oil collect as filtrate.
(ii) The filtrate containing water and mustard oil is put in a separating funnel. Water forms the lower layer and mustard oil forms the upper layer in separating funnel. The lower layer of water is run out first by opening the stop-cock of the separating funnel. Mustard oil remains behind in the separating funnel and can be removed separately.We are now in a position to answer the following questions :