Concentration

The concentration of a solution can be defined as the amount or quantity of a substance in a defined volume of solution. It can also be given as the abundance of any constituent divided by the total volume of a mixture. This term is generally used to refer to solutes and solvents in solutions.

There are two parts in an aqueous solution: solute and solvent. The solute is combined or mixed with the solvent to produce a solution.

• If a solution contains more amount of solute, then it is said to be a concentrated solution.
• If a solution contains a very low amount of solute, then it is said to be a dilute solution.

Percentage Concentration

The concentration of a particular solution can be further defined based on the percentage of solute present in the solution.

The percentage concentration can be determined using any one of these three ways

• The mass of the solute (w) is divided by the mass of the solution (w),
• The volume of the solute (v) is divided by the volume of the solution (v),
• The mass of the solute (w) is divided by the volume of the solution (v)

The Mass Percentage of Concentration

Whenever a solid is used as the solute in a solution, the percentage of concentration can be expressed as the total number of grams of solute per 100g of solution.

It can also be given as the amount or fraction of a solute in a solution multiplied by 100.

Percent by mass = mass of solute/mass of solution × 100%

To understand this concept better, let us consider an example.

A solution is prepared by the addition of 25.0g of sugar with 100g of water. The percentage of concentration can be calculated as

Percent by mass = 25g sugar / 125g solution × 100% = 20% sugar

The volume percentage of concentration

Whenever a liquid is considered to be used as the solute in a solution, then the concentration percentage can be easily determined as both the solute and solvent are liquids. Dividing the volume of the solution by the volume of the solution gives us the percent by volume of the solution. 

Percent by volume = volume of solute/volume of solution × 100%

To understand this concept better, let us consider an example.

If a solution was prepared by dissolving 40 mL of ethanol in enough water to produce 240 mL of solution, then the percentage of concentration can be calculated as:

Percent by volume = 40mL ethanol / 240mL solution × 100% = 16.7% ethanol

However, it should be kept in mind that, unlike in the case of mass, one cannot simply get the final solution volume by adding the volumes of solute and solvent together. This is because, while adding a solute and solvent together, only the mass is conserved, but the volume doesn’t. So, while considering the above-mentioned example, simple mixing of 40ml of ethanol and 200ml of water would not give the expected result, and the final volume would not be 240ml. Therefore, the solution can be made by adding 40ml of ethanol and a sufficient quantity of water to make 240mL of solution.

Units of Concentration

The most basic way of expressing concentration is as the mass per unit volume. It can be expressed as percent by mass (%w/w) and percent by volume (%v/v). The mixed concentration values of mass and volume can be expressed as percent w/v (%w/v) and per cent v/w (%v/w).

• Parts per million (ppm)

This is a type of expressing very small concentrations of solute like, for example, the amount of lead present in drinking water.

Let us consider a suitable example, such as taking a percentage as parts per hundred. In this case, a solution is said to be 15ppm which means 15 parts solute per 1 million parts solution.

• Parts per billion (ppb)

This is another type of expression for the concentration of small quantities of solute. Considering the same example as taking a percentage as parts per hundred, a solution is said to be 22ppb, which means 22 parts solute per billion parts solution.

Frequent Terms used for Expressing Concentration

In terms of quantitative titrimetric analysis, the concentration of a solution can be expressed in chemical quantities known as moles. All definitions and chemical quantities used are based on the rules put forward by the International Union of Pure and Applied Chemistry (IUPAC). 

Conclusion

Solutions are either diluted or concentrated based on the quantity of solute present in them. Concentration also has a high value in our daily lives regarding beverages such as tea and coffee. It also plays an important part in healthcare when expressed in terms of equivalents for dosing medicines, blood.. This concentration study material covers various aspects of concentration and helps us understand this concept better.