What is a Solution

Different types of substances are present around us. These may vary in composition, or in their physical state. One of these types of substances is solution. But what is a solution? To understand this, we need to first look at two more terms – solute and solvent.The substance that is dissolved in a liquid to make solution is called solute and the liquid in which solute is dissolved is called solvent.

Most common solutes are solids but liquid and gases can also be solutes. Similarly, most common solvent is water but organic liquids such as alcohol, acetone, carbon tetrachloride, carbon disulphide and benzene can also be used as solvents.

So, let us start by defining solutions

A solution is a homogenous mixture of two or more substances. Homogenous mixture means that mixture is just the same throughout. For example – salt solution, sugar solution, vinegar, metal alloys (such as brass) and air.

Salt solution is a homogenous mixture of two substances salt and water whereas sugar solution is a mixture of two substances sugar and water. Salt solution and sugar solution are also called true solutions because in these solutions, the particles of salt and sugar are mixed so well with water that we cannot distinguish one from the other. The true solutions are also known as molecular solutions because the size of dissolved particles in such solutions is the same as that of a molecule. Some more examples of a solution are – sea-water, copper sulphate solution, alcohol and water mixture, petrol and oil mixture, soda water, soft drinks and lemonade.




The substances like salt, sugar etc. which dissolve in water completely are said to be soluble in water. Only soluble substances form true solutions.

To study the properties of a solution –

If we shake some sugar with water in a beaker, the sugar seems to disappear in water and we get a transparent sugar solution. The dissolved sugar particles cannot be seen even with a microscope, and the sugar does not settle down even on keeping the solution for quite some time. if we filter the sugar solution, the whole solution passes through the filter paper and no residue is left behind.

From these observations we can conclude that sugar solution is a homogenous mixture having the same composition throughout. Sugar solution is a true solution. In a true solution, the particles of the solute break up to such an extent that they disappear into the spaces between the water molecules. A sugar solution does not scatter a beam of light passing through it and render its path visible because the sugar particles present in it are so small that they cannot reflect light rays falling on them.

Based on these observations we can now state some of the properties of solutions.

Properties of a solution –

The important characteristic properties of a solution are as follows –

  1. A solution is a homogenous mixture.
  2. The size of solute particles in a solution is extremely small. It is less than 1 nm in diameter. (1nm = 10-9 m).
  3. The particles of a solution cannot be seen even with a microscope.
  4. The particles of a solution pass through the filter paper. So, a solution cannot be separated by filtration.
  5. The solutions are very stable. The particles of solute present in a solution do not separate out on keeping.
  6. A true solution does not scatter light. This is because of the fact that its particles are very, very small).

Types of solutions –

Usually it is thought that solutions are formed when solid substances are dissolved in liquids. Though most of the common solutions are made by dissolving solids in liquids, but this is not always so. In fact, solutions can be made by dissolving: solids in solids, solids in liquids, liquids in liquids, gases in liquids and gases in gases. As long as the mixture is homogenous, the term solution applies to it.

  1. Solution of solid in a solid : Metal alloys are the solutions of solids in solids. For example – brass is a solution of zinc and copper. Brass is prepared by mixing molten zinc with molten copper and cooling their mixture.
  2. Solution of solid in liquid : This is the most common type of solutions. Sugar solution and salt solution are the solutions of solids in liquids. A solution of iodine in alcohol called ‘tincture of iodine’ is also a ‘solid in a liquid’ type of solution. This is because it contains a solid iodine dissolved in a liquid alcohol.
  3. Solution of liquid in a liquid :Vinegar is a solution of acetic acid (ethanoic acid) in water. It is a liquid in liquid type of solution.
  4. Solution of gas in a liquid :Soda-water is a solution of carbon-dioxide gas in water. It is a gas in a liquid type of solution.
  5. Solution of a gas in a gas :Air is a solution of gases like oxygen, argon, carbon dioxide and water vapour etc. in nitrogen gas. Nitrogen is the solvent in air and all the other gases are solutes.




NCERT textbook Questions – Page 28, 29 and 30

Question 8:-

Identify the solution among the following mixtures –

(a)  soil
(b)  sea-water
(c)  air
(d)  coal
(e)  soda water

Answer:-

Sea-water, air an

 

In our daily life we observe around us some pure and some impure substances. The mixtures are impure substances and they are further classified into solutions, colloids and suspensions. What is a solution? A solution is a homogenous mixture of two or more than two substances. For example – sugar solution, vinegar etc. Solutions have various properties like – they have uniform composition, the size of solute particles in a solution is very small, the particles of solute do not separate out on keeping, they do not scatter light. Many types of solutions are possible like – solution of solids in solids, solids in liquids, liquids in liquids, gases in liquids and gases in gases.

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