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Concentration and dilution

Molarity (concentration) is the number of moles of substance per liter of solution, with the unit mol/L, often written M. When a solution is diluted, the volume changes but the number of moles of substance stays the same — giving a simple relationship between concentration and volume before and after dilution.

c = \frac{n}{V}

concentration (molarity)

c_1V_1 = c_2V_2

the dilution equation (same number of moles)

Symbols

$c$	concentration	mol/L
$n$	amount of substance	mol
$V$	volume of solution	L

Example

10 mL of a 1 M solution diluted to 1000 mL:

$c_2 = c_1V_1/V_2 = 1\cdot 10/1000 = 0.01$ M.

Use the same volume unit on both sides of

c_1V_1 = c_2V_2

— it does not need to be liters, just consistent.

Practise moles and stoichiometry for free →

← Moles and molar mass · Balanced equations and limiting reactant →

Part of General Chemistry: Moles and stoichiometry.