In chemical laboratories and during chemical experiments at home, it is often necessary to determine the relative density of a substance.
The relative density isThe ratio of the density of a particular substance to the density of another under certain conditions or to the density of the reference substance for which distilled water is taken.
Relative density is expressed by an abstract number.
You will need
- - tables and directories-
- - hydrometer, pycnometer or special scales.
Relative density of substances in relation toThe density of distilled water is determined by the formula: d = p / p0, where d is the required relative density, p is the density of the test substance, p0 is the density of the reference substance. The last parameter is tabular and is defined quite accurately: at 20oC distilled water has a density of 998.203 kg / m3, and its maximum density reaches 499 at 999.973 kg / m3. Before computing, do not forget that p and p0 should be expressed in the same units.
In addition, the relative density of matterCan be found in physical and chemical reference books. The numerical value of the relative density is always equal to the relative specific gravity of the same substance under the same conditions. Conclusion: use tables of relative weights in the same way as if they were tables of relative density.
Determining the relative density, alwaysTake into account the temperature of the test and reference substance. The matter is that the density of substances decreases with heating and increases with cooling. If the temperature of the test substance is different from the reference temperature, make a correction. Calculate it as the average change in the relative density by 1 ° C. Search for the correct data on the nomograms of the temperature corrections.
To quickly calculate the relative densityLiquids in practice use a hydrometer. To measure the relative density of gases and solids, use pycnometers and special scales. A classical hydrometer is a glass tube expanding at the bottom. At the lower end of the tube there is a reservoir with a shot or special substance. On the upper part of the tube there are fissions showing the numerical value of the relative density of the substance under study. Many areometers are additionally equipped with thermometers for measuring the temperature of the test substance.
Immerse the hydrometer in the test liquid orsolution. The lower the relative density of the liquid being studied, the deeper the hydrometer will plunge into it under the influence of its own weight. Therefore, do not hold the device with your hand when making measurements. After waiting, when the surface of the substance calms down and the hydrometer is frozen, determine the relative density of the liquid under study by the scale divisions.