Molarity Calculator

The Formula

Molarity (M) is the number of moles of solute per liter of solution. It is calculated by dividing the moles of solute (n) by the volume of solution in liters (V). The moles of solute are found by dividing the mass (m) by the molar mass (MM).

Variable Definitions

How to Use This Calculator

1. 1

   Select the calculation mode: Molarity (from mass & volume), Mass (from molarity & volume), or Volume (from mass & molarity).

2. 2

   Optionally enter a compound name (e.g., NaCl, H2SO4) to auto-fill the molar mass.

3. 3

   Fill in the required fields based on the selected mode.

4. 4

   Select the appropriate volume unit (L, mL, or µL).

5. 5

   Results will show the calculated value, moles, step-by-step solution, and formulas used.

Molarity = moles of solute per liter of solution

Understanding the Concept

Molarity is one of the most common units of concentration in chemistry. A 1 M (1 molar) solution contains 1 mole of solute dissolved in enough solvent to make 1 liter of solution. The mole is a counting unit representing Avogadro's number (6.022 × 10²³) of particles. To prepare a solution of known molarity, measure the required mass of solute and dilute to the desired volume. Practical example: to prepare 500 mL of 0.1 M NaCl solution. First, find the molar mass of NaCl: 58.44 g/mol. The moles needed = 0.1 M × 0.5 L = 0.05 mol. The mass needed = 0.05 × 58.44 = 2.922 g. Weigh 2.922 g of NaCl, dissolve in about 400 mL of distilled water, then dilute to exactly 500 mL in a volumetric flask. The resulting solution contains 0.1 moles of NaCl per liter. Edge cases: molarity is temperature-dependent because the volume of the solution changes with temperature. A solution that is 0.1000 M at 20°C becomes approximately 0.0995 M at 30°C due to thermal expansion. For precise analytical work, solutions should be used at the temperature at which they were prepared. For very dilute solutions (below 0.001 M), the assumption that the solute volume is negligible becomes less accurate, and molality (moles per kg of solvent) may be preferred. For concentrated solutions (above 1 M), the volume change upon mixing can be significant — for example, mixing 50 mL of water with 50 mL of ethanol yields only about 97 mL of solution, not 100 mL. For acids and bases, always add acid to water (not water to acid) when diluting concentrated solutions, especially for sulfuric acid which generates significant heat upon dilution.

Frequently Asked Questions

Sources & References