Molarity (M) is defined as:

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Moles of solute per liter of solution. Molarity (M) is defined as the number of moles of solute dissolved per liter of total solution. It is the most commonly used concentration unit in chemistry and is calculated as M = moles of solute / liters of solution. For example, a 1.0 M NaCl solution contains 1.0 mole of NaCl (58.44 grams) dissolved in enough water to make exactly 1.0 liter of total solution. Note that molarity is based on the volume of the total solution, not the volume of the solvent alone.

Moles of solute per kilogram of solvent defines molality (m), a different concentration unit that is temperature-independent (since it is based on mass rather than volume). Molality is preferred for colligative property calculations. Grams of solute per liter of solvent is not a standard concentration unit; it mixes mass and volume units without using moles. Mass percent represents the mass of solute divided by the total mass of the solution, multiplied by 100%, which is another valid concentration expression but not molarity.

Understanding different concentration units and being able to convert between them is essential for the CLEP Chemistry exam. Molarity is particularly important because it is used in stoichiometric calculations involving solutions (MV = moles), dilution problems (M₁V₁ = M₂V₂), and calculating the amounts of reactants and products in solution-based reactions. Being able to prepare solutions of specific molarities and to use molarity in quantitative calculations is a fundamental laboratory and analytical skill.

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