Density = mass ÷ volume, or d = m/V.
The concentration of a substance in a solution can be determined by measuring the density of the solution. Density measurements are useful in identifying minerals and other solids. In addition, the molecular weight of a gas can be calculated from its density.The density of a liquid can be determined by measuring the mass needed to fill a container of a known volume. In most cases, a device called a pycnometer, which has a precisely known volume, is used for this purpose. An instrument called a hydrometer is also used to determine the density of a liquid.
The density of a regularly shaped solid is determined by simply measuring the object's mass, calcu-lating its volume, and dividing the mass by the volume. The density of an irregularly shaped solid is determined by submerging it in a known quantity of liquid and measuring the volume of the liquid displaced. The volume of the displaced liquid equals the volume of the solid. The mass of the object is then determined and is divided by the volume.
The density of a gas is difficult to measure because it is extremely low and changes greatly with varia-tions in temperature and pressure. The mass of a gas is determined by subtracting the mass of an empty container from the mass of the same container filled with the gas. The volume of the container can be found by measuring the amount of water the container holds. The specific gravity of a substance is related to its density. Specific gravity is the ratio of the mass of a given volume of the substance to the mass of an equal volume of water. It is found by dividing the density of the substance by the density of water at either
4° C (39° F.) or 20° C (68° F.).
