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How to separate a Mixture of Two Solids?

  • Last Updated : 16 Sep, 2021

As we look at our surroundings, we see many things with different shapes, sizes and textures. Everything in this universe is made up of material which scientists call matter. The air we breathe, the food we eat, stones, clouds, stars, plants and animals, even a small drop of water or a particle of sand – everything is matter. These substances have different natures, different properties. They can be pure or there can be some impurities in them. We can also see as we look around that all the things mentioned above occupy space and have mass. 

Types of Mixtures

  1. Homogeneous Mixture: They are the mixtures that possess the same properties and combination throughout their masses. e.g. Sugar mixed in water.
  2. Heterogeneous Mixture: They possess different properties and compositions in various parts. e.g. Sand mixed with salt.

Characteristics of Mixtures

  1. There is an absence of chemical force acting between its constituents, yet they exist together.
  2. They can either be heterogeneous or homogeneous in nature.
  3. The proportions of the substances vary in an indefinite manner.
  4. The constituents of the mixture can be separated by physical methods.
  5. Their boiling and melting point depends upon the characteristic of the constituents.
  6. During the formation of a mixture, there is no change in energy.
  7. All the states of matter can combine to form mixtures.

Separation of Mixture

A separation process is a method that converts a mixture of chemical substances into two or more distinct product mixtures. In some cases, a separation may fully divide the mixture into pure constituents. It exploit differences in chemical or physical properties between the constituents of a mixture.

Heterogeneous mixtures can be separated into their respective constituents by simple physical methods like handpicking, sieving, filtration that we use in our day-to-day life. 



Methods of Separation of Mixtures

Most of the time, the chemicals we encounter are not in their purest form. They are essentially a combination of two or more chemicals. Surprisingly, mixes appear in a variety of ways. As a result, there are several sorts of separation procedures utilised in segregating a combination of components. As for the need for separation, it is usually done to remove all the unwanted materials and obtain useful components. 

The separation of mixtures refers to the process or methods of physically separating distinct components of a mixture.

The procedure used to separate a mixture is determined by the type of combination and the differences in the chemical characteristics of the mixture’s components. 

Separation of Mixture of two Solids

There are many methods to achieve the following target which are discussed below:

1. Mechanical Picking or Handpicking: 

In this method, components are separated on the basis of physical characteristics like size and shape. Example- Removing stones from grains. This technique in which a mixture can be separated by picking them out by hand is called Handpicking. This method can be used to separate slightly larger pieces of dirt, stones and husk from the grains because the quantity of such impurities is usually not very large.

2. By using a suitable solvent:

Here, a mixture of two solids can be separated from each other by using a solvent which will make one of the substances soluble in the solvent, thus separating the two substances. E.g. A mixture of sugar and sand can be separated by using water as a solvent as sugar is soluble in water and sand is insoluble in water. This difference in the solubility of sugar and sand in water is used to separate them.  



3. Separation by sublimation: 

The changing of a solid directly into vapours on heating, and of vapours into solid on cooling is called sublimation. The process of sublimation is used to separate those substances from a mixture that sublime on heating. E.g. Ammonium chloride, iodine, camphor, naphthalene etc. sublime on heating and can be recovered in the form of a sublimate by cooling into vapours. Most of the substances do not undergo sublimation. When some molecules absorb heat energy, they are at a much higher energy state than their neighbours, thus, they overcome the force of attraction and escape into the vapour phase. Then sublimation is defined as heat or energy required to change the state from solid to gas.

4. Magnetic Separation:

If a mixture contains iron as one of the constituents, it can be separated by using a magnet. E.g. A mixture of iron fillings and Sulphur powder can be separated by a magnet. Iron filings will get attracted to the magnet and Sulphur won’t. This technique is useful for few minerals which contain magnetic properties and also for minerals with paramagnetic (materials that are less affected) properties. Not all metals are magnetic; gold, silver and aluminium are some examples. 

5. Gravity Separation:

A mixture containing two components having different densities but both being insoluble in a solvent can be separated by using this method. Example- Mixture of chalk powder and sand in water. As sand is denser, they settle at the bottom of the water container, while chalk being less dense floats in it. The most notable advantages are their cost-effectiveness and excellent reduction. Gravity separation is an attractive unit operation as it generally has low capital and operating costs, uses few if any chemicals that might cause environmental concerns. The ores of metals are heavier than gangue particles. This process uses this property for the concentration of ore. Hematite ore is concentrated using the gravity separation process. Hematite is a common ore of iron oxide.

Hydraulic Washing is a type of gravity separation. Here, the ore is concentrated by passing it through an upward stream of water where all the lighter particles of gangue are separated from the heavier metal ore.

Sample Problems

Problem 1: What is centrifugation?

Solution: 

Centrifugation is used to separate tiny solid particles that pass through a filter paper which is carried out with the process of centrifugation which in turn, is based on the shape and size of particles, viscosity of the medium and speed of rotation. On rotating the rotor, due to centrifugal force the denser insoluble particles separate from liquid and ends up at the bottom of the tube and the liquid gets collected at the top.



Problem 2: What is mechanical picking?

Solution:

It is a technique of separating two components on the basis of physical characteristics like size and shape. Example- Removing stones from grains.

Problem 3: Explain the process of separation by sublimation.

Solution:

The changing of a solid directly into vapors on heating, and of vapors into solid on cooling is called sublimation. The process of sublimation is used to separate those substances from a mixture which sublime on heating. E.g. Ammonium chloride, iodine, camphor, naphthalene etc. sublime on heating and can be recovered in the form of a sublimate by cooling into vapors. Most of the substances do not undergo sublimation.

Problem 4: What are the various types of mixtures?

Solution:

Mixtures can be classified into two types- homogeneous mixture and heterogeneous mixture. The former is a mixture which possess same properties and combination throughout their masses. while the latter possess different properties and compositions in various parts.

Problem 5: Define chromatography. How many types of chromatography are there?



Solution:

It is used to separate components in a liquid mixture and is based on different properties of compounds in two phases: stationary and mobile phase. It is of four types-

  1. Adsorption Chromatography
  2. Thin Layer Chromatography
  3. Column Chromatography
  4. Partition Chromatography

Problem 6: What is gravity separation?

Solution:

Mixture containing two components having different densities but both being insoluble in a solvent can be separated by using this method. Example- Mixture of chalk powder and sand in water. As sand is more dense, they settle at the bottom of the water container, while chalk being less dense floats in it.

Problem 7: Compare sublimation and Evaporation.

Solution:

Both are useful in describing phase transitions of matter. The properties of matter are uniform in the phase of matter. The conversion of the phase of matter from one phase to another is a phase transition. In sublimation, the initial phase is solid-phase whereas in evaporation the initial phase is a liquid phase. Also, in sublimation, the enthalpy gives the amount of energy that is required for sublimation to occur.

Problem 8: What is the Magnetic Separation process of ore?

Solution:

An electromagnetic separator is required. A brass belt moves over two rollers, one of which encloses magnets in it. The powdered ore is dropped over the moving belt at one end. The non-magnetic part of the ore is not attracted by the magnet and falls, forming a separate heap at a distance. The magnetic part clings to the belt and forms another heap.




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