Atoms, Elements And Compounds – Session 3

As we know, a solution is formed when a solute dissolves in a solvent. The ability of the solute to dissolve in the solvent under specific conditions is called solubility. Specific conditions include particular values of temperature and pressure. The solubility is usually measured in grams per litre.

The table salt is soluble in water. The solubility of the table salt in water is 360 g/L. This means that maximum of three hundred and sixty grams of table salt can be dissolved in water. This solubility value is valid only at room temperature and standard pressure.

Various factors affect the solubility of the solute in the solvent. In most cases, the solubility of the solids in liquids increases with a rise in temperature. For example, take one litre of water. Add as much sugar as you can in this water. Stir it constantly to dissolve the sugar.

After a particular point, more sugar will not dissolve in water. Now heat it up a bit and add more sugar in water. You will see that sugar will start dissolving. This is because, as you heated it up raising it’s temperature, the solubility of the sugar increases.

But, why does the solubility of solids in liquids rise with temperature. When we increase the temperature of the solution, the energy of the solute and the solvent molecules rise.This energy is enough to break the intermolecular forces holding the solute particles together. When these forces are overcome, more solute particles can mix with the solvent. This results in higher solubility.

A saturated solution contain the maximum amount of solute that can be dissolved in a particular solvent under specific conditions. Specific conditions are usually standard temperature and pressure. If you add more solute to the saturated solution, it will not dissolve. The undissolved solute will accumulate as a solid at the bottom of the container.

A supersaturated solution contains more solute than it would normally be able to hold at a particular temperature and pressure. In the supersaturated solution, the amount of solute there is exceeds its normal solubility. The supersaturation is achieved by dissolving the solute in a solvent at an elevated temperature. After that it is slowly cooled to prevent the excess solute from precipitating out.

The supersaturated solutions are highly unstable. This is because they contain more solute than the solvent can normally hold at that temperature. Any disturbance can trigger rapid crystallization or precipitation. The supersaturated solutions have practical applications. For example, the production of particular types of candies involves creating supersaturated sugar solutions. The solution then crystallizes upon cooling to create a smooth texture.

In an unsaturated solution, the solvent has not dissolved the maximum amount of solute possible under a given set of conditions. It is the solution that can dissolve more solute because it has not reached its saturation point. The unsaturated solutions are common in daily life. For example, when you add sugar to a cup of tea and stir it until the sugar completely dissolves, you can say that you have created an unsaturated sugar solution. This is because you could add more sugar before it becomes saturated.

Imagine you have a mixture of different inks. You want to know which colored inks were mixed to create this mixture. How would you do it? We can do it with the help of chromatography. The chromatography is a laboratory technique used for separating mixtures into their individual components. There are different types of chromatography techniques.

Here, we will use the paper chromatography technique to separate a mixture of inks. There are two phases in paper chromatography. These are called stationary phase and mobile phase. The stationary phase does not move. In paper chromatography, a piece of filter paper is used as the stationary phase.

The mobile phase moves up the stationary phase. The mobile phase is usually a solvent or a mixture of solvents. In paper chromatography, the mobile phase moves up the filter paper. This happens due to the affinity of the liquid with the filter paper.

The mixture to be separated is usually dissolved in a small amount of solvent. A small spot of this solution is applied near the bottom of the filter paper. The filter paper is then placed in a container with a lid. The container is lined with a small amount of the mobile phase. The lid is closed, creating a sealed environment. The mobile phase travels up the paper via capillary action.

As the solvent travels up the paper, it carries the mixture's components with it. Different components move at different rates. This leads to their separation along the paper. Once the solvent front reaches a particular point on the paper the paper is removed from the container. The separated components are then visualized. In the case of colored substances, this can be done by looking at the colored bands or spots on the paper. As you can see the mixture of inks is separated.