Definition:
Molarity (M) is defined as the number of moles of solute present in one litter (1 L) of solution. It is one of the most commonly used units of concentration in pharmaceutical and analytical chemistry.
Formula:
Unit:
The unit of molarity is moles per litter (mol/L), often written as M (e.g., 0.5 M HCl).
Calculation Example:
Example 1:
Calculate the molarity of a solution prepared by dissolving 10 g of NaCl in 500 mL of solution.
Solution:
- Find the molar mass of NaCl: Na (Sodium) = 23 g/mol
- Cl (Chlorine) = 35.5 g/mol
- Molar mass of NaCl = 23 + 35.5 = 58.5 g/mol
- Calculate the number of moles of NaCl:
3. Convert volume to liters:
4. Calculate molarity:
Answer: The molarity of the NaCl solution is 0.342 M.
Applications of Molarity in Pharmaceuticals
- Used in preparing standard solutions for titrations.
- It helps in determining the exact concentration of drug solutions.
- it is essential in chemical reactions, where the stoichiometric ratio is based on molar concentration.
- It is important in buffer preparation for maintaining pH in formulations.
Factors Affecting Molarity
- Temperature: Since molarity depends on volume, temperature variations can change solution volume, thus affecting molarity.
- Solute Dissociation: In electrolytes, dissociation increases the number of particles, influencing molarity-related calculations.
Conclusion
Molarity (M) is a crucial unit of concentration in pharmaceutical and analytical chemistry, as it provides a precise measure of solute quantity in a given volume of solution. It is widely used in titrations, drug formulations, and buffer preparations. However, since molarity depends on solution volume, factors like temperature changes and solute dissociation can influence its accuracy. Understanding molarity is essential for accurate chemical reactions, solution standardization, and pharmaceutical applications.