What is the primary unit of concentration used in expressing molarity?

Molarity is a specific way to express concentration, defined as the number of moles of solute per liter of solution. Therefore, the primary unit of concentration in expressing molarity is indeed moles per liter. This measurement is crucial because it allows chemists to quantify how much of a substance is dissolved in a given volume of solvent, facilitating calculations in stoichiometry and analytical methods.

Other concentration measurements, like grams per liter or percent by mass, serve different purposes and are not tailored specifically for molarity. Grams per liter gives a different perspective on concentration, focusing on the mass of solute, whereas percent by mass expresses the mass of solute relative to the total mass of the solution. Milliliters per solution is not a unit of concentration, but rather a volume measurement that does not relate directly to the amount of substance and is not used in calculating molarity. Thus, moles per liter remains the definitive unit for expressing molarity.