What is a Solution?

Do you know what is a solution? Do you think that the water you drink or the cola that you enjoy are solutions? Let us tell you more about it in this section. At times we think, every liquid we see around us are solutions. However, that is not the case! There are many solid solutions as well! Surprised? In this chapter, we will discuss more on what is a solution and which is a type a mixture.

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What is a Solution?

What is a solution? Solutions are a homogeneous mixture of two or more substances. It has homogeneity at the particle level. Usually, people think of it as some liquid with either a solid or a liquid or a gas dissolved in it. However, this is not entirely true. We can also have solid solutions like alloys. For example:

• Air: It is a mixture of gas in gas. Air is a homogeneous mixture of a number of gases. The two main constituents of gases are oxygen (21%) and Nitrogen (78%)
• Alloys: Alloys are homogeneous mixtures of metals. They cannot be separated into their individual components by physical methods. Irrespective of that, an alloy is considered as a mixture. It is because an alloy shows the properties of its constituents and can have variable composition. For example, brass is a mixture of 30% zinc and 70% copper.

Components of a Solution

The substances that make up a homogeneous solution are called components of the solution. It has basically has two components i.e. a solvent and a solute.

• Solvent: The component of a solution which dissolves the other component in itself is called solvent. A solvent constitutes the larger component of the solution. For example, a solution of sugar in water is solid in the liquid. Here, sugar is the solute and water is the solvent.
• Solute: The component of the solution which dissolves in the solvent is called solute. The solute is the smaller component of the solution. For example, a solution of iodine in alcohol known as ‘tincture of iodine’, iodine is the solute. Similarly, in carbonated drinks (Soda water), carbon dioxide gas is the solute.

Characteristics of Solutions

• It is a homogeneous mixture
• The size of solute particles in the solutions is extremely small. It is less than 1 nm in diameter.
• The particles of a solution cannot be seen even with a microscope.
• The particles of a solution pass through the filter paper. Thus filtration cannot separate the solution.
• It is very stable. The particles of solute present in a solution do not separate out on keeping.
• A true solution does not scatter light (because its particles are very small).

Concentration of a Solution

The concentration of a solution is the amount of solute present in a given quantity of it. In other words, the concentration of a solution is the mass of the solute in grams, which is present in 100 g of a solution. Depending upon the amount of solute present, it is called a dilute, concentrated or a saturated solution.

Different substances in a given solvent have different solubilities at the same temperature. The most common method for expressing the concentration of a solution is the percentage method. The concentration of the solutions refers to the percentage of solute present in the solutions. The percentage of solute can be expressed in terms of the following two quantities:

• Concentration of solutions in terms of mass of solute

If the solutions have solid solute dissolved in a liquid, then we consider the ‘mass percentage of solute’ in calculating the concentration of the solutions. So, in the case of a solid solute dissolved in a liquid solvent. Mass by mass percentage of the solutions is given by the percentage of the mass of solute in 100 grams of solvent.

• Concentration by mass by volume percentage of a solution

Mass by volume percentage of a solute is the percentage of the mass of the solute present in the specific volume of the solvent. Depending upon the unit of the mass and volume, the mass by volume percentage of solute in solutions can have following units as gram/ml or gram/litre.

• Solubility of a Solute

Solubility is the amount of solute (in gram), which dissolves in 100 g of water (solvent), at a given temperature.

Types of Solutions

• Saturated Solutions: Saturated solutions are solutions dissolving as much solute as it is capable of dissolving at a given temperature.
• Unsaturated Solutions: Unsaturated solutions are the ones with a lesser amount of solute than what we require for saturation. Sometimes, by applying external forces like heat energy, you can increase the solubility of the solutes in the solutions.
• Supersaturated Solutions: Supersaturated solutions contain more solute than saturated solutions.

Solved Examples for You

Question: Write a note on Brownian movement in colloids.

Answer: The colloidal particles move at random and zig-zag motion in all directions. This type of random motion of the particles denotes the Brownian movement. The main reason behind such. movement is the collision of various particles against each other.