Density is a physical property describing the amount of matter packed into a given space. It is mathematically defined as the mass of a substance divided by the volume it occupies. In chemistry and physics, measurable characteristics of matter are grouped based on whether they change with the sample size. This categorization helps scientists identify substances and determines how density is classified.
What are Intrinsic Properties?
An intrinsic property is a characteristic of a material that does not rely on the size of the sample being measured. If a scientist measures a small or large quantity of the same substance, the measurement remains the same. These characteristics are sometimes referred to as intensive properties. They reflect the inherent nature and composition of the material itself.
The temperature of a substance, for example, will not change if the sample size is cut in half. The boiling point of pure water remains 100°C at standard pressure, whether heating a cup or a barrel. Other examples include melting point and electrical conductivity. These properties are often used by scientists to identify unknown substances.
What are Extrinsic Properties?
Extrinsic properties are characteristics that directly depend on the amount of substance present in the sample. If the sample size is doubled, the measurement of the property will also double. These properties are also known as extensive properties because their value is proportional to the size of the system.
Classic examples of extrinsic properties include the mass of an object and the volume it occupies. A large block of wood has a greater mass and occupies a larger volume than a small splinter from the same block. Length and the total energy content of a system are also categorized as extrinsic characteristics.
The measurement of an extrinsic property alone is not enough to identify a substance because the value changes with the amount of matter. For instance, mass alone does not distinguish between a large piece of aluminum and a large piece of gold.
Why Density is an Intrinsic Property
Density is classified as an intrinsic property because its value does not change regardless of the amount of substance measured. This characteristic makes density a reliable feature for identifying specific materials, such as pure silver or ethanol. Every unique substance generally has its own corresponding density value under the same conditions.
The fundamental calculation for density is mass divided by volume (D = M/V), which utilizes two extrinsic properties. This relationship demonstrates how the ratio of two extensive properties results in an intensive property. If a sample is doubled in size, both the mass (M) and the volume (V) double simultaneously.
Because both the numerator and the denominator increase by the same factor, the resulting ratio remains constant. For example, the density of liquid water is approximately one gram per milliliter (1 g/mL). This value holds true whether measuring a single drop or an entire lake of water.
If a scientist measures a teaspoon of water (5 grams/5 milliliters), the density is 1 g/mL. If they measure a full cup of water (250 grams/250 milliliters), the density is still 1 g/mL. Density only changes significantly if external factors like temperature or pressure are altered.