## What is a Solution?

A solution is a homogeneous mixture of two or more substances. This means that there is no chemical reaction between the components, and that the mixture is a single phase.

An example of a solution is the mixture of sodium chloride and water. The water component is in lager quantity and is referred to as the solvent, while the sodium chloride component is of lower quantity and is called the solute.

Therefore, in a solution, the solvent is the component in which the solute is dissolved.

Another common example of a solution is sugar solution, comprising water and sugar.

### Saturated Solution

A saturated solution is a solution which contains as much solute as it can dissolve at a particular temperature, in the presence of the crystals of the solute.

To Prepare a Saturated Solution

The procedure for preparing a saturated solution at a particular temperature is quite simple. For example, to prepare a saturated solution of sodium chloride at 25oC, get a given volume of distilled water in a beaker, heat it to a temperature above 25oC, say 40-60oC. Then begin to add sodium chloride crystals with continuous stirring until no more dissolved. Cool the beaker and its content to 25oC.

At this point you will observe some crystals of the salt which have come out of the solution settled on the bottom of the container. These are the ones from the whole that are not soluble in the volume of water used at 25oC. Now separate the clear solution from the crystals by decantation (i.e., run off the clear solution into another container, while leaving the undissolved sodium chloride crystals behind).

The clear solution that you have is the saturated solution.

### Supersaturated Solution

A supersaturated solution is one which contains more solute than it can hold at a particular temperature if crystals of the solute were present.

Note:

- Supersaturated solutions are not stable, they easily form precipitate with slight disturbance (e.g. by shaking or adding a tiny crystal of the solute).

- They can be obtained from few compounds. E.g. sodium tetraoxo- sulphate(VI) decahydrate (Na2SO4.10H2O), sodium trioxosulphursulphate(VI) pentahydrate (Na2S2O3.5H2O) by: i. Preventing dust (which might act as centers of crystallization) from entering the solution. ii. Slowly cooling the solution. iii. Avoiding any form of disturbance, like shaking the container.

- When crystals separate from a supersaturated solution, the solution becomes saturated.

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