Types of Solutions

There are lots of different criteria or factors based on which a solution can be of different types. Let us see the types of solution based on these different factors.

1) Based on the Solvent

Although, water is a universal solvent, there are also various other solvents such as alcohol. So, based on whether the solvent is water or not, a solution can be of the following two types.

• Aqueous solution: The solutions that contain water as a solvent or in which water is present in large amount are known as aqueous solutions. So, in aqueous solutions, the solutes are dissolved in water. For example, sugar or salt dissolved in water.
• Non-aqueous solution: It is a solution in which solvent is not water or solutes are dissolved in a solvent other than water. For example, iodine dissolved in alcohol, sulphur in carbon disulphide, and phosphorus in ethyl alcohol.

2) Based on solute added to the solvent I amount of solute

• Dilute solution: It is made of a small amount of solute but a large amount of solvent. We can say that a very small amount of solute is present in a large amount of solvent.
• Concentrated solution: A solution in which a large amount of solute is dissolved in a small amount of solvent is called a concentrated solution.

3) Based on the dissolution of solute

Based on the dissolution of solute, a solution can be of the following three types;

i) Saturated solution

It refers to a solution in which we cannot dissolve any more solute at a specific temperature. We can say that a solution, which contains the maximum amount of solute at a given temperature is called a saturated solution. For example, at 20 degree centigrade, we can dissolve a maximum of 36 gm of NaCl in 100 gm of water. So, a solution made by dissolving 36 gm of sodium chloride in 100 gm of water is a saturated solution. If we add more NaCl past this point, it will not dissolve in the water.

Let us understand it with an example;

When we add sugar to water and stir it the sugar dissolves quickly if we add more sugar the process of dissolution becomes slower and a stage comes when no more sugar can be dissolved in water and the extra sugar if added, will settle down at the bottom of the beaker. However, a dynamic equilibrium will be created between the dissolved particles and undissolved solute particles. For example, if ten undissolved particles are dissolving, an equal number of dissolved particles will become undissolved. Such solutions are known as saturated solution which cannot dissolve solutes beyond their capacity at a given temperate and amount.

How to prepare a saturated solution:

It is easy to prepare a saturated solution. You are required to add solute continuously and slowly to the solvent until no more solute can be dissolved into the solution or the solute starts to appear as crystal or precipitate. For example, a saturated solution of sugar and water can be made easily by adding sugar into the water. The dissolution of sugar in water takes place quickly in the beginning but afterwards, a stage comes when the extra sugar starts to settle down at the bottom and does not dissolve in water even after stirring. At this stage, we can say that a saturated solution has been prepared.

Common examples of saturated solutions:

• Beverages like coca cola, pepsi, etc., in which the carbon dioxide gas is dissolved in the solvent under pressure until a saturated solution is formed.
• The soil is also a saturated solution of soil and nitrogen as a solute. When the concentration of nitrogen increases further, it is released into the air in the form of gas.

There are certain factors that affect the dissolution or solubility of the solute in a saturated solution, such as;

• Temperature: The solubility or dissolution of solute increases when the temperature is increased. For example, we can dissolve more salt in hot water.
• Pressure: By increasing pressure, more solute can be dissolved into the solution. For example, gases are dissolved in liquids by applying pressure such as carbonated water.
• Chemical composition: The solubility in saturated solutions is also affected by the chemical nature of solute and solvent and the presence of other chemicals. For example, more sugar can be dissolved in water as compared to salt, and water and ethanol are completely soluble in each other.

Properties of Saturated Solutions:

• The solvent contains the maximum amount of dissolved solute.
• The extra solute settles down at the bottom of the container when left undisturbed.
• There exists a dynamic equilibrium between the dissolved and undissolved solute particles of the solute.

ii) Unsaturated Solution

It refers to a solution in which we can dissolve more solute at the given temperature. So, an unsaturated solution contains less amount of solute than the maximum amount of solute that can be dissolved in it and thus it also contains no residual substances. For example, a solution that can dissolve 40 gm of a solute in it if contains only 20 gm of that solute, is an unsaturated solution.

Common examples of unsaturated solutions:

• A pinch of salt in a glass of water produces an unsaturated sugar solution.
• Vinegar (acetic acid in water).
• Sugar in tea, coffee, water, etc.
• Mist (water vapours in the air)
• Smoke in the air
• 01 M HCl (hydrochloric acid in water).

Preparation of unsaturated solution:

The unsaturated solutions are very easy to prepare. For example, just by adding and dissolving 10 gm sugar crystals in 200 ml of water, you can create an unsaturated solution as we still can add more sugar crystals in this solution.

Properties of Unsaturated Solutions:

• The amount of dissolved solute is less than the saturation point of the solvent at a given temperature.
• They are generally more reactive than saturated solutions.

iii) Supersaturated Solution

A solution that contains more dissolved substances than the maximum amount of solute that can be dissolved in it at a given temperate is called a supersaturated solution.

For example, 36 gm of sodium chloride can be added or dissolved in 100 ml of water at 20 degree centigrade to create a saturated solution. If we add more solute or sodium chloride to it by increasing temperature, it will become a supersaturated solution.

How to make a supersaturated solution:

They are generally prepared by dissolving solutes in the heated solvent and then cooling it slowly. They are mostly prepared by cooling, however, there are also many other methods that can be used to prepare supersaturated solution such as solvent evaporation, changing temperature, changing pH or by changing solvent composition.

Take any saturated solution then heat it and add more solute to it. By heating, you can add more solute to it. Thereafter, allow the solution to cool down gently. When its temperature decreases, excess solute remains dissolved for a while and later it may crystalize.

Let us understand it by an example;

When we add sugar to water at 25 degree centigrade, we can dissolve 210 gm of sugar in 100 ml of water. But, when we heat the solvent and raise its temperature up to 80 degree centigrade, we can dissolve 360 gm of sugar in the same amount of water. After heating, let the solution cool down and reach 25 degree centigrade, it still has 360 gm of sugar dissolved in it, though it can dissolve only 210 gm at this temperature. Thus, a supersaturated solution can be prepared.

Examples of supersaturated solution:

• Sodium acetate and sodium thiosulphate easily form a supersaturated solution
• Honey is a supersaturated solution of sugars in water.

4) Types of solutions based on the concentration of solute in two solutions

A solution can be of three types based on the concentration of the solute in two solvents separated by a membrane or barrier that allows the movement of a solvent such as a cell placed in beaker containing a solution.

i) Hypertonic Solution: It is a solution in which the concentration of the solute in a beaker is higher than the concentration of solute in the cell present in it. Due to this difference in concentration, the solvent tends to come out of the cell that causes the cell to shrink or plasmolyze.

ii) Hypotonic Solutions: It refers to a solution in which the concentration of solute in a beaker is less than the concentration of solute in the cell contained in the beaker. So, in this case, due to the difference in concentration, the solvent from the beaker tend to move into the cell due to which the cell swells and may burst.

iii) Isotonic Solution: A solution in which the concentration of solute in the container and in the cell is the same is called an isotonic solution. So, in this case, the solvent moves in equal parts from the container into the cell and vice versa.

5) Types of Solutions based on Physical State

The components of a solution like solute and solvent can be present in any physical state or phase such as solid, liquid and gas. For example, a solute can be a solid, liquid or gas, similarly, a solvent can be a solid, liquid or gas. Accordingly, there can be nine types of binary solutions if we make the combination of solute and solvent in their different physical states, for example, 3 solid solutions, 3 liquid solutions and 3 gaseous solutions.

Solid solutions

In these solutions, the solvent is a solid or a substance present in its solid state and solute can be solid, liquid or gas. So, there can be three types of solid solutions such as solid in solid, liquid in solid and gas in solid. They are described as follows;

i) Solid in solid solutions: In this type, both solvent and solute are in solid state. For example, alloys are homogenous mixtures of two metals or a mixture of metal and non-metal. Steel is an alloy that is made of 98 % iron, which is a metal and 2 % carbon, which is non-metal. Iron is present in the largest amount in steel so, it is a solvent. Whereas, carbon, which is present in the smallest amount, acts as a solute.

Another example is brass, which is also an alloy that contains two metals, zinc and copper. In brass, the copper's amount ranges from 60 to 80%, so it acts as a solvent, whereas, zinc, which accounts for 20 to 40 % of copper's weight is a solute.

ii) Liquid in solid: In this type, the solute is liquid or is present in the liquid state in the solid solvent. For example, the hydrated salts, the salts that contain moisture are liquid in solid solutions. The water molecules are enclosed within the crystal lattice structure of hydrated salts. The common examples of hydrates salts include copper sulphate (blue vitriol), hydrated ferrous sulphate (green vitriol) and hydrated magnesium sulphate (white vitriol), etc.

iii) Gas in solid: In this type of solid solution, the solute is a gas or a substance in its gaseous state and solvent is a solid or a substance in its solid state. For example, a gas adsorbed on the surface of a metal such as nickel, platinum, etc., forms gas in a solid solution.

Liquid solutions

The solvent is a liquid or is present in a liquid state and the solute can be present in or can be a solid, liquid or gas. So, there can be three types of liquid solutions that include solid in liquid, liquid in liquid and gas in the liquid. They are described as follows;

i) Solid in liquid: Solute is solid and the solvent is a liquid. Its common examples include saltwater in which salt is solute and water is solvent and tincture of iodine in which iodine is a solute and alcohol is a solvent.

ii) Liquid in liquid: In this case, both solute and solvent are liquids. For example, alcohol in water, solution of ethyl alcohol in water, and vinegar, which is a solution of ethanoic acid in water.

iii) Gas in liquid: It is a type of liquid solution in which solute is a gas and solvent is a liquid. For example, carbonated drinks such as soda water, Coca-Cola, Pepsi, etc. They are prepared by dissolving carbon dioxide in a liquid solvent.

Gaseous solutions

The solvent is a gas or is present in the gaseous state and solute can be or can be present in the liquid, solid or gaseous state. So, there can be three types of gaseous solutions; solid in gas, liquid in gas and gas in gas. They are described as follows;

i) Solid in gas: In this gaseous solution, the solute is a solid or a substance in its solid state and solvent is a gas. Some common examples include iodine in air, camphor in air, etc.

ii) Liquid in gas: In this gaseous solution, the solute is a liquid or a substance in its liquid state and solvent is a gas. Its common examples include clouds in the air, fog in the air and mist in air, etc.

iii) Gas in gas: In this gaseous solution, both solute and solvents are gases. Its common examples include air that is a mixture of different gases some of which are present in large amount some are present in a small amount. The two main gases present in the air are Nitrogen, which is 78% and oxygen, which is around 22 %.