Short Answer

Molarity (M) is a unit used to express the concentration of a solution. It tells how many moles of solute are present in one litre of solution. The formula for molarity is:
M = moles of solute ÷ litres of solution.

Molarity is commonly used in chemistry because it clearly shows how strong or dilute a solution is. It helps chemists prepare solutions accurately and perform stoichiometric calculations in reactions that occur in solutions.

Detailed Explanation

Molarity

Molarity (M) is one of the most widely used ways to express the concentration of a solution in chemistry. It describes the number of moles of a solute dissolved in exactly one litre of solution. Since chemical reactions in solutions depend on the number of molecules present, molarity provides a convenient and accurate way to measure concentration.

Molarity is especially useful in laboratory work, titrations, stoichiometry, and industrial solution preparation because it relates directly to moles—the fundamental counting unit in chemistry.

Meaning of molarity

Molarity tells how much solute is present in a given amount of solution. It answers questions such as:

• How concentrated is the solution?
• How many moles of solute are dissolved?
• How much solute is needed to prepare a certain volume of solution?

The unit of molarity is mol/L (moles per litre), but it is commonly written as M.

Examples:

• A 1 M solution has 1 mole of solute in 1 litre of solution.
• A 0.5 M solution has 0.5 moles of solute in 1 litre of solution.
• A 2 M solution has 2 moles of solute in 1 litre of solution.

Formula of molarity

The molarity of a solution is calculated using the formula:

M = moles of solute ÷ litres of solution

This formula shows that molarity depends on two things:

1. The amount of solute (in moles)
2. The total volume of solution (in litres)

If either value changes, the molarity changes.

How to calculate molarity

To calculate molarity:

1. Convert the mass of solute into moles
   – Use: moles = mass ÷ molar mass
2. Measure the final volume of the solution in litres
3. Divide moles of solute by litres of solution

Example:
If 2 moles of NaCl are dissolved in 1 litre of water, the molarity is:
M = 2 mol ÷ 1 L = 2 M

Why molarity is important

Molarity is widely used because it:

1. Helps in stoichiometric calculations

Chemical reactions in solutions are often based on volume and concentration. Molarity makes it easy to determine how much reactant is needed.

2. Makes solution preparation accurate

By knowing the molarity, chemists can prepare solutions of exact concentration for experiments.

3. Helps compare concentrations

Different solutions can be compared easily using molarity values.

4. Is essential in titrations

Titrations use molarity to find the concentration of unknown solutions.

5. Is useful in industrial processes

Industries rely on molarity to make chemicals, medicines, and food products in correct proportions.

Effect of temperature on molarity

Molarity depends on the volume of the solution, and volume changes with temperature. When temperature increases:

• The solution expands
• Volume increases
• Molarity decreases

When temperature decreases:

• The solution contracts
• Volume decreases
• Molarity increases

Thus, molarity is temperature-dependent. This is why molarity is always measured at a specific temperature.

Difference between molarity and other concentration units

Molarity is often compared with:

Molality (m)

• Based on mass of solvent, not volume
• Not affected by temperature

Normality (N)

• Depends on the number of equivalents
• Used in acid–base and redox reactions

Mass percentage or volume percentage

• Based on mass or volume ratios
• Used in industry and everyday materials

Molarity is the most commonly used method in chemistry labs because it directly relates to moles.

Real-life applications of molarity

Molarity is used in many practical areas:

1. Pharmaceuticals

Medicines must be prepared with exact concentrations.

2. Food industry

Acidity, sugar concentration, and preservatives are measured using molarity.

3. Water purification

Chemical dosages for treatment are calculated using molarity.

4. Environmental testing

Pollutant concentrations in water are expressed using molarity.

5. Academic experiments

Students use molarity to prepare solutions and perform titrations.

These applications show how important molarity is in everyday life and scientific processes.

Conclusion

Molarity (M) is a measure of how concentrated a solution is, defined as the number of moles of solute per litre of solution. It is one of the most important and commonly used units of concentration in chemistry. Molarity helps chemists prepare solutions, perform stoichiometric calculations, and analyse chemical behaviour in solutions. Because it is easy to use and closely related to reaction processes, molarity remains a fundamental concept in both laboratory and industrial chemistry.