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More about density
What is density?
The density (ρ) of a sample is defined as the relationship between the mass (m) and the volume (V) of a specific amount of material. The density of a sample can therefore be determined by dividing the mass of the sample by its volume:
The density (ρ) of a sample is defined as the relationship between the mass (m) and the volume (V) of a specific amount of material. The density of a sample can therefore be determined by dividing the mass of the sample by its volume:
In the International System of Units (SI) the unit of density is kg/m3. However, for applications in the laboratory, a more suitable unit is g/cm3. For conversion between these units, the applicable formula is:
To determine the density of a sample, both the mass and the volume of the sample must be known. The mass can be determined easily using a weighing instrument. However, the volume of the sample cannot be determined directly. To determine the volume of a sample, use is made of Archimedes' principle.
Density determination using Archimedes' principle
Density determinations are frequently performed by means of Archimedes' principle (buoyancy method), which is also the method used by the density determination kit for balances. Archimedes' principle states that a body immersed in a fluid apparently loses weight by an amount equal to the weight of the fluid it displaces. When using Archimedes' principle for density determination, the procedure used depends on whether the density of solids or of liquids is being determined.
The density of a solid is determined with the aid of a liquid whose density is known. In a first step, the weight (mass)of the sample is determined by weighing the sample in air. In a second weighing, the volume of the sample is determined indirectly from the weight the sample displaces in the liquid of known density. From these two weighings, the density of the sample can be calculated.
Density determinations are frequently performed by means of Archimedes' principle (buoyancy method), which is also the method used by the density determination kit for balances. Archimedes' principle states that a body immersed in a fluid apparently loses weight by an amount equal to the weight of the fluid it displaces. When using Archimedes' principle for density determination, the procedure used depends on whether the density of solids or of liquids is being determined.
The density of a solid is determined with the aid of a liquid whose density is known. In a first step, the weight (mass)of the sample is determined by weighing the sample in air. In a second weighing, the volume of the sample is determined indirectly from the weight the sample displaces in the liquid of known density. From these two weighings, the density of the sample can be calculated.
For the density determination of liquids, a glass sinker of known volume is used. The sinker is first weighed in air, and then in the liquid whose density needs to be determined.
Influencing factors:
As the density is very much dependent on the temperature, the temperature must be recorded and controlled very precisely. In addition to the temperature, air buoyancy, and surface tension of the liquid, the following factors can also affect the experimental results:
· Immersion depth of the holder or sinker
· Air bubbles
· Porosity of the solid body
As the density is very much dependent on the temperature, the temperature must be recorded and controlled very precisely. In addition to the temperature, air buoyancy, and surface tension of the liquid, the following factors can also affect the experimental results:
· Immersion depth of the holder or sinker
· Air bubbles
· Porosity of the solid body