Concept in Definition ABC

Candela Rocío Barbisan | Oct. 2021
Chemical engineer

It is important not to confuse density with concentration, since concentration is the amount of solute contained in a given amount of solution or solvent. A simple home experiment that we can carry out in our homes to determine density involves mixing a certain amount of sugar with water and dissolving it. To be able to estimate the density of this solution we must take a glass with graduation used for cooking recipes and weigh it in a balance table.

Once the glass is placed on top of the balance, the mass of this empty glass can be recorded or the balance can be "tared" if it has this function.

Then, a certain volume of solution is taken and placed inside the beaker, the volume precisely measured in the graduated beaker is then recorded and the mass contained within it is recorded. This can be repeated with different mass and volume pairs. In this way, there are different density values ​​when making the relationship between the mass and the registered volume.

The important thing to note is that the density is expected to be the same at each point, since it is an intensive property that does not depend on the amount of matter in the body. In this case, the density value can be estimated as a weighted average of the different mass and volume pairs.

Density estimation

The same experience can be replicated in the laboratory, working with calibrated glass materials and perfectly calibrated and balances with a higher degree of precision, resulting in estimated calculations much closer to the value real. Likewise, there is an instrument that allows the density of a liquid to be measured using Archimedes' Principle as a basic concept.

In general, a hydrometer is a hollow rod of glass material whose hole is enlarged in the lower section and has a weight (for example, lead), it also has a scale graduated at the top. its functioning and determination of the density depends on the degree of subsidence when submerged, since depending on the density of the liquid where it is immersed, by Archimedes' Principle, the instrument will float and a certain value corresponding to the density will be read on the scale relative. That is why there are two types of density meters, those for densities greater than water and less than water.

There are other types of instruments for the estimation of densities, among which we can mention digital density meters and pycnometers.

Factors capable of affecting density

As we well know, density is a physical property and a scalar quantity. But what can make the density of a certain compound vary? Mainly the factor of temperature it is an important parameter when determining density. It is very logical to to thinkWhen we increase the temperature, the agitation of the molecules and their vibration increases, which leads the particles to tend to separate and occupy more volume. Consequently, the density will be decreased since the volume will tend to increase while conserving the amount of matter. If, on the contrary, we decrease the temperature, the volume will decrease and the density will tend to increase.

That is why, every time we take a tabulated data for a certain pure substance or solution, we must verify that said data is referenced to the temperature of interest, otherwise it may be corrected. For its correction it is necessary to take into account several factors like the heat of vaporization, for instance.

Water is an exception to the aforementioned, and we can easily check it when we put liquid water in the freezer, since it will freeze and increase its volume. It is also for this reason that ice floats on liquid water and this is explained through the hydrogen bridging forces that form water.

Finally, in the case of compressible fluids (gases, in general) such as the airThese will vary their volume with pressure differences, which undoubtedly generates a change in their density, therefore, in these cases, the density will also depend on the pressure exerted.