Molarity is the most common unit of concentration in chemistry. It measures the number of moles of solute dissolved per liter of solution. Molarity is essential for stoichiometric calculations, dilutions, and preparing solutions in laboratory settings.
M = n / V
Molarity equals moles divided by volume
Units: mol/L (moles per liter) or M (molar)
Meaning: The concentration of solute in the solution
Units: mol (moles)
Meaning: The amount of substance dissolved in the solution
💡 To find moles: n = mass / molar mass
Units: L (liters)
Meaning: The total volume of the solution (not just solvent)
⚠️ Convert mL to L by dividing by 1000
The molarity formula can be rearranged to solve for different variables depending on what you know:
n = M × V
Use when you know molarity and volume
V = n / M
Use when you know moles and molarity
M = n / V
The original formula
Molar mass of NaCl = 58.5 g/mol
n = 5.85 g ÷ 58.5 g/mol = 0.100 mol
V = 250 mL ÷ 1000 = 0.250 L
M = n / V = 0.100 mol / 0.250 L = 0.400 M
Answer: The molarity is 0.400 M (or 0.400 mol/L)
Always convert volume to liters! 250 mL = 0.250 L, not 250 L
Don't plug grams directly into the formula. Convert to moles first using molar mass.
V is the total solution volume, not just the volume of water added. The final volume may differ!
Your answer should have the same number of significant figures as your least precise measurement.
Use these interactive calculators to apply the molarity formula:
The molarity formula is M = n / V, where M is molarity (mol/L), n is moles of solute, and V is volume of solution in liters. It calculates the concentration of a solution.
Molarity (M) is expressed in mol/L or M. Moles (n) are in mol, and volume (V) must be in liters (L). Always convert mL to L by dividing by 1000.
Yes! You can rearrange it to n = M × V (to find moles) or V = n / M (to find volume). The rearrangement depends on which variable you're solving for.
Divide the mass in grams by the molar mass: n = mass (g) / molar mass (g/mol). For example, 10 g of NaCl (58.5 g/mol) = 10 / 58.5 = 0.171 mol.
Molarity (M) uses liters of solution, while molality (m) uses kilograms of solvent. Molarity changes with temperature because volume changes, but molality doesn't.
Molarity is easy to measure (volume is simpler than mass), directly relates to stoichiometry, and works well for most laboratory calculations and reactions in solution.
Use the dilution formula M₁V₁ = M₂V₂, where subscript 1 is the concentrated solution and subscript 2 is the diluted solution. This formula derives from the molarity formula.
Use these calculators to apply the molarity formula in practical chemistry problems: