Density
Density is a property due to the nature of a particular material. The density of a particular material is not dependent on the amount of the material examined. Therefore, density is a characteristic property. It is a ratio of the mass of an object to its volume. The mathematical equation is
Density is a property that must be computed from measurements. In the lab, the mass is usually measured by weighing the material on a balance. For a solid, depending on the shape of the object, its volume could be determined using various formulae.
Volume of a cube = a3, where a is the side of the cube.
Volume of a rectangular block = l · w · h, where l is the length, w is the height, and h is the height of the rectangular block.
Volume of a cylinder = <math>\pi</math> · r2 · h, where r is the radius and h is the height of the cylinder.
Volume of a sphere = (4/3) · <math>\pi</math> · r3, where r is the radius of the sphere.
For a liquid, the volume is usually measured using a measuring device called the graduated cylinder.
Typical units of density measurements are:
- for solids, g/cm3
- for liquids, g/mL
- for gases, g/L
Density and temperature
Density is temperature dependent (i.e. - it varies with temperature).
eg - Mercury
| Temperature | Density | Notation |
| at 20°C | 13.55 g/mL |  = 13.55 g/mL
|
| at 270°C | 12.95 g/mL |  = 12.95 g/mL
|
Compare the densities of some common materials:
| Material | Density at room temperature | |
| Solid: | Aluminum | 2.70 g/cm3 |
| Lead | 11.4 g/cm3 | |
| Liquid: | Gasoline | 0.67 g/mL |
| Mercury | 13.55 g/mL | |
| Water | 1 g/mL | |
| Gas: | Air | 1.3 g/L |
| Chlorine | 3.17 g/L |
Example
When mercury, gasoline and water are mixed at room temperature, we would observe three layers because these liquids are immiscible. Look at the densities of these liquids given above, can you predict the order of these layers?
At room temperature, the densities are:
- Mercury: 13.55 g/mL
- Gasoline: 0.67 g/mL
- Water: 1 g/mL
Since these liquids are immiscible, they separate into 3 layers, with the liquid that is the most dense on the bottom. The liquid that is the least dense will rest on top.
External link
zeroBio - Irregular shaped objects can be determined by displacement of water method.
