Molarity: definition in chemistry
Molarity: The concentration of a solution expressed as moles of solute per liter of solution, written mol/L or M.
To find molarity, divide the number of moles of solute by the total volume of the solution in liters, not the volume of solvent added. Solutions of a set molarity are prepared by dissolving a measured amount of solute and adding solvent up to the mark on a volumetric flask. Because liquids expand when warmed, molarity changes slightly with temperature, so very precise work sometimes uses molality, the moles of solute per kilogram of solvent.
Examples
- 58.44 g of NaCl made up to 1.00 L of solution — 1.00 M
- 0.50 mol of sugar in 250 mL of solution — 2.0 M
- Concentrated sulfuric acid — about 18 M
- Laboratory bench acids — often 1 M or 2 M
On the periodic table
To calculate molarity from a mass, you need the solute's molar mass, which you add up from the atomic masses shown on the periodic table.