How it works
Molarity (M) is moles of solute per liter of solution. It is the standard way chemists express concentration because reactions happen mole-for-mole.
To make a solution, weigh the mass shown, dissolve it in less solvent than the final volume, then top up to the mark in a volumetric flask. Adding the solute to a full liter of water gives slightly more than a liter of solution and a lower concentration.
Molar mass is the sum of the atomic masses in the formula, in g/mol. For hydrated salts, include the water of crystallization.
Formula
M = n ÷ V = (mass ÷ molar mass) ÷ volume (L)
Questions people ask
How do I make 500 mL of 0.5 M NaCl?
Moles = 0.5 × 0.5 L = 0.25 mol. Mass = 0.25 × 58.44 = 14.61 g. Dissolve and dilute to 500 mL total.
What is the difference between molarity and molality?
Molarity is moles per liter of solution and changes slightly with temperature. Molality is moles per kilogram of solvent and does not.
What does 1 mM mean?
One millimolar, or 0.001 mol/L. Biological buffers are often given in mM.