Molarity Calculator - Calculate Solution Concentration

Molarity (M)

Molarity is the most common concentration unit in chemistry. It measures the number of moles of solute per liter of solution.

Formula: M = moles of solute / liters of solution

Example: A 2 M NaCl solution contains 2 moles of NaCl in every liter of solution.

Molality (m)

Molality measures the number of moles of solute per kilogram of solvent (not solution).

Formula: m = moles of solute / kilograms of solvent

Key difference: Molality uses mass of solvent, while molarity uses volume of solution. Molality is temperature-independent because mass doesn't change with temperature, unlike volume.

Normality (N)

Normality measures the number of equivalents per liter of solution. It depends on the reaction type.

Formula: N = equivalents of solute / liters of solution

Example: For H2SO4 (which can donate 2 H+ ions), a 1 M solution is 2 N in acid-base reactions.

When to Use Each Unit

• Molarity: General chemistry, most lab work, reactions in solution
• Molality: Colligative properties (boiling point elevation, freezing point depression)
• Normality: Acid-base titrations, redox reactions (less common in modern chemistry)

What is the difference between molarity and molality?

Molarity (M) is moles per liter of solution, while molality (m) is moles per kilogram of solvent. Molarity changes with temperature because volume expands or contracts, but molality remains constant since it's based on mass.

How do I convert between molarity and normality?

Normality = Molarity × n, where n is the number of equivalents. For acids, n equals the number of H+ ions it can donate. For bases, n equals the number of OH- ions or H+ ions it can accept.

Why is molarity temperature-dependent?

Molarity depends on volume, and volume changes with temperature. When solutions are heated, they expand, increasing volume and decreasing molarity. This is why molality is preferred for studies involving temperature changes.

How do I prepare a solution with specific molarity?

1. Calculate the mass needed: mass = Molarity × Volume (L) × Molar Mass (g/mol)
2. Weigh out the calculated mass of solute
3. Dissolve in a small amount of solvent
4. Transfer to a volumetric flask and fill to the mark with solvent

What is the molarity of pure water?

Pure water has a molarity of approximately 55.5 M. This is calculated using the density of water (1 g/mL) and its molar mass (18.015 g/mol): 1000 g/L ÷ 18.015 g/mol = 55.5 mol/L.