Which term refers to the weight per unit volume of a substance?

The term that refers to the weight per unit volume of a substance is density. Density is defined as the mass of an object divided by its volume, and it is typically expressed in units such as grams per cubic centimeter (g/cm³) or kilograms per cubic meter (kg/m³). Understanding density is crucial in water treatment processes, as it helps in identifying how substances will behave in water, such as whether they will float or sink, which can be important for processes like sedimentation and flotation.

Mass refers to the amount of matter in an object, but it does not account for the volume of the substance involved. Volume is simply the amount of space that a substance occupies, independent of its weight or mass. Concentration measures how much of a substance is present in a given volume of solution, typically in terms of moles per liter or grams per liter, but it does not specifically address the relationship between weight and volume in the way that density does. Therefore, density is the most accurate term for describing weight per unit volume.