Which term refers to the number of moles of solute per kilogram of solvent?

The term that refers to the number of moles of solute per kilogram of solvent is known as molality. Molality is an important concentration unit in chemistry that measures how concentrated a solution is by relating the amount of solute to the mass of the solvent.

In calculating molality, you take the number of moles of the dissolved substance (solute) and divide it by the mass of the solvent in kilograms. This is particularly useful in situations where temperature changes may affect the volume of a solution, as molality remains constant because it is based solely on the mass of the solvent.

Normality, on the other hand, refers to the concentration of a solution expressed in equivalents per liter of solution, and molarity measures the number of moles of solute per liter of solution, which can vary with temperature. Equivalency is a term that typically relates to the number of reactive units in a given solution but does not directly address concentration in a manner tied to mass and moles. This makes molality distinct and essential for specific types of chemical calculations, especially those involving properties that depend on the mass of the solvent, such as boiling point elevation or freezing point depression.