Standard density

The standard density is defined as the density of a substance , mixture of substances or element under the following standard conditions : ${\displaystyle \rho _{n}}$

1. Temperature = 273.15  K corresponding to 0 ° C and ${\displaystyle T_{n}}$
2. Pressure = 101 325  Pa = 101 325  N / m² = 1 013.25 hPa = 101.325 kPa = 1 013.25 mbar = 1.01325  bar ${\displaystyle p_{n}}$

By determining the mass  m and the standard volume , the standard density results in ${\displaystyle V_{n}}$

${\displaystyle \rho _{n}={\frac {m}{V_{n}}}}$

The standard density has the unit :

${\displaystyle {\frac {\text{Kilogramm}}{\text{Kubikmeter}}}={\frac {\mathrm {kg} }{\mathrm {m^{3}} }}={\frac {\text{Gramm}}{\text{Liter}}}={\frac {\mathrm {g} }{\mathrm {l} }}}$

For an ideal gas , the standard density is calculated according to the thermal equation of state of ideal gases as:

${\displaystyle \rho _{\text{n}}={\frac {p_{\text{n}}}{R_{\text{i}}\cdot T_{\text{n}}}}}$

Here are:

• ${\displaystyle p_{\text{n}}}$the absolute pressure and the absolute temperature of the defined standard or norm condition ${\displaystyle T_{\text{n}}}$
• ${\displaystyle R_{\text{i}}}$the specific or individual gas constant of the gas.

Under the physical standard conditions z. B. dry air has a density of = 1.293 kg / m ³ . ${\displaystyle \rho _{\text{n}}}$

determination

The standard density of an element in solid form can be determined experimentally as follows: a measuring cylinder is filled with any amount of water and the current level is read off. Then a portion of the element concerned, usually 1  g , is placed in the measuring cylinder. The water level is read again; the difference in water levels before the addition of the element and afterwards corresponds to the volume of the body. If you divide the mass of the body by its volume, you get the standard density of this element.

The density of liquids can be determined with the help of a pycnometer or a Mohr balance . With gaseous elements one determines the volume z. B. with the help of a piston sampler .

See also

• DIN 1306