Define density. What units do chemists normally use for density? Is density an intensive or extensive property?

Understanding the difference between intensive and extensive properties is fundamental in the study of chemistry. Intensive properties are independent of the amount of substance present. For example, melting point, boiling point, and indeed, density are all intensive properties. They do not change when you take a sample of the substance or when you have the entire bulk of it. This is why, no matter how much gold you have, its density remains constant at approximately 19.32 g/cm³.

On the other hand, extensive properties scale with the amount of substance. Mass and volume are quintessential examples of extensive properties because they depend directly on how much material you're dealing with. If you double the amount of water you have, both its mass and volume will double, but its density will not change because density is an intensive property.

Density is a measurable physical property, and as such, it requires units for its expression. In chemistry, the most common units are grams per cubic centimeter (g/cm³) for solids, and grams per milliliter (g/mL) for liquids. These units conveniently convey the mass to volume relationship, allowing chemists to compare the densities of different substances effectively.

Conversion and Versatility

A variety of other units can also be used depending on the context, like kilograms per cubic meter (kg/m³) in physics or pounds per cubic foot in engineering. Since density units are all about the relationship between mass and volume, they are easily interchangeable through conversion factors. This flexibility allows scientists and engineers to use the units most appropriate for their field or the scales at which they are working.

Physical properties of matter are aspects that can be measured or observed without changing the substance into another chemical compound. These properties include color, odor, phase of matter (solid, liquid, gas), boiling point, melting point, and of course, density. They are distinctive for particular materials and can be used to identify and classify substances.

Understanding and Application

By understanding the physical properties, chemists can predict behavior under different conditions, separate mixtures, and purify substances. For instance, knowing the density of oil and water helps explain why oil floats on water and also guides the design of separation techniques for these two liquids. Physical properties are integral in the development of new materials and products, and they influence our everyday life from cooking to the development of space materials.