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.”
Depending on the practical approach that density has, this magnitude will be classified into three types:
- Real density
- Apparent density
- Relative 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.
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.
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.
Examples of density
- The density of steel is higher than that of cotton, since a kilo of steel occupies less volume than a kilo of cotton.
- The density of water is greater than that of water vapor, since there are more molecules in a liter of water than in a liter of steam.
- The population density of a city refers to the number of inhabitants per square kilometer.
- The density of attendance at a stadium is given by the division between the people who attended it, divided by the number of places available in it.
- The density of a forest refers to the number of trees per square hectare.
- The traffic density of a city is higher at 3 in the afternoon than at 2 in the morning.
- A person’s hair density is higher at 18 than when they are 50.
- The density of flights at an airport is the number of flights per hour it has.
- Ice floats in water because its density is lower, that is, there are fewer molecules in a liter of ice than in the same volume of water.
- A nail sinks in water because it is denser than it, but in mercury it floats because it is more dense than the nail.
- The density of gold is greater than that of aluminum, so a kilo of aluminum takes up more space than a kilo of gold.
- Bone density is the proportion of bone matter in the bones (calcium), in bones with lower bone density fractures and injuries of the bones occur frequently, while in denser bones this does not usually happen.
23 examples of density of some substances
- The density of ice (at 0 ° C) is 0.92 g / mL
2. The density of uranium is 18.7 g / mL
3. Density of helium (a gas) is 0.000178 g / mL
4 Platinum has a density of 21.50 g / mL
5. Palladium has a density of 12.023 g / mL
6. Rhodium has a density of 12.41 g / mL
7. 24 k gold has a density of 19.32 g / mL
8. The 18 k gold has a density of 15.58 g / mL
9. The density of mercury is 13.50 g / mL
10. The density of 14 k gold is 13.07 g / mL
11. The gold of 10 k its density is 11.57 g / mL
12. The density of lead is 11.30 g / mL
13. Silver of purity .999 has a density of 10.49 g / mL
14. Silver with a purity of .925 its density is 10.36 g / mL
15. The density of copper is 9.00 g / mL
16. The density of brass is between 8.40 to 8.70 g / mL
17. The density of nickel is 8.29 g / mL
18. Iron its density is 7.87 g / mL
19. The density of bronze is 7.40 to 8.90 g / mL
20. The density of tin is 7.29 g / mL
21. Zinc has a density of 7.10 g / mL
22. Chromium has a density of 7.10 g / mL
23. Aluminum has a density of 2.70 g / mL