Concepts

Examples of Density

We explain the examples of density. The density , represented by the Greek letter ρ is the physical property of matter which tells us how much mass to (m) for each unit volume (V) that this covers. It is a more relevant magnitude than it seems, since it directly determines the physical state of substances. The density depends on the closeness between the atoms or molecules that compose them. When they are very compact and take on a clear geometry, the substance is solid and very dense .

When they are relatively close and move in layers over each other, the substance is liquid and can have very different density values . On the other hand, when the particles are extremely far from each other without taking physical form, the substance is gaseous and very thin . Density is so useful because it allows us to relate the mass and volume of a body when one of them is unknown, which on a practical level is a great tool.

The formula to calculate the density of a body when its mass and volume are known is:

ρ = m / V

And it reads as density has been defined: “Density is equal to the amount of mass for each unit of volume.”

Density types

Depending on the practical approach that density has, this magnitude will be classified into three types:

Real density
Apparent density
Relative density

Real density

The true density indicates the exact amount of mass that there is for each unit volume of the substance in question. This density is a data that is obtained by means of precision instruments, and is tabulated in laboratory manuals. When handling chemicals as practically relevant as sulfuric acid (H ₂ SO ₄ ), there will be very extensive tables for their densities, even with the corresponding data for different temperatures.

Apparent density

The apparent density is the one used in school laboratories for the preparation of aqueous solutions and mixtures. Your data is obtained at a glance through the scales of the materials used. For example, to measure the bulk density of a viscous liquid mixture such as lime with a little water, you can fill a measuring cylinder with it. First of all, the mass of the empty specimen is measured to exclude it from the measurement.

It is filled with the mixture and placed on top of a scale. Two pieces of information can be read: the mass of the full specimen (which by subtracting the empty specimen will leave the mass of the mixture inside it as data ) on the scale screen ; and the volume that the mixture covers, according to the level it reaches on the scale of the test tube . Having already the mass of the mixture and its volume, we proceed to calculate its density. It is a result obtained in a practical way, but it is very useful.

Relative density

The relative density is the ratio of the density of any substance to the density of the water standard, that is 1 g / mL. The result is a unitless number (density over density is canceled), which is often used in engineering books to make the data easier to read. For example, the true density of sulfuric acid H ₂ SO ₄ is known to be 1.83 g / mL. Its relative density will be: (1.83 g / mL) / (1.00 g / mL) = 1.83 .

To make the relative density clear, its formula is written like this:

ρ _R = ρ _substance / ρ _water

Density in other areas

In demography , density indicates the number of people that inhabit for each square kilometer of a geographic site. It is therefore called population density , and it is one of the main socioeconomic indicators that are taken into account to outline the situation of a country.