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How to find the relative density

How to find the relative density

In chemical laboratories and conduct chemical experiments at home is often necessary to determine the relative density of a substance.

Relative density isratio of the density to the density of a particular substance under certain other conditions or to the density of the reference material, for which the distilled water is taken.

Relative density is expressed in an abstract number.

You will need

  • - Tables and spravochniki-
  • - Hydrometer, pycnometer or special scales.



The relative density of the substance in relation to thedistilled water density is determined by the formula: d = p / p0, where d - the desired relative density, p - the density of the substance, p0 - the density of the reference material. The last parameter table and defined quite accurately: at 20 ° C distilled water has a density of 998.203 kg / m³ and a maximum density at 4 ° C, it reaches - 999.973 kg / cu.m. Before calculations do not forget that p and p0 must be expressed in the same units.


In addition, the relative density of the materialcan be found in the physical and chemical handbooks. The numerical value of the relative density is always equal to the relative specific gravity of the same substance in the same conditions. Conclusion: Use the tables relative specific weights the same as if it were a relative density of the table.


Determining the relative density, alwaysconsider the temperature of the test and reference substances. The fact that the substance density decreases by heating and increases with cooling. If the temperature of the substance is different from the reference temperature, amended. It is calculated as the average change in the relative density at 1 ° C. The required data on search nomograms temperature corrections.


For a quick calculation of the relative densityliquids, in practice, using a hydrometer. To measure the relative density of gases and solids using pyknometers and special scales. Classic hydrometer is a glass tube, flared at the bottom. At the lower end of the tube there is a tank with a shot or a special substance. On the upper part of the tube division plotted showing the numerical value of the relative density of the substance. Many hydrometers additionally equipped with a thermometer for temperature measurement of the test substance.


Immerse the hydrometer to test liquid orsolution. The lower the relative density of the test liquid, the deeper it will sink hydrometer under its own weight. Therefore, when measuring device should not hold his hand. Having waited until the surface of the substance to calm down and freeze hydrometer, by division of the scale to find the relative density of the test liquid.

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