About the sample
Selenium is a chemical element that occurs in several allotropic modifications. The most stable is exhibited here and it is called gray selenium. It has been donated by Metodija Najdoski.
A new sample of red amorphous selenium has been added on May 17th 2023. This sample is donated by our exceptional student Mihail Trajkov. The exhibited sample was prepared by the reduction of selenous acid with sulfur dioxide.
Sulfur dioxide is generated by the reaction of sodium disulfite and sulfuric acid.
Na2S2O5 + H2SO4 = Na2SO4 + 2SO2 + H2O
Then, this gas is passed through an aqueous solution of selenous acid, additionally acidified with hydrochloric acid at a temperature of 15 to 20 °C. The red selenium is obtained according to the reaction:
H2SeO3 + SO2 + 2H+ = Se + H2SO4 + H2O
ρ / g/cm34.82
tt, mp / °C221
tv, bp / °C685
Electronegativity, (X)2.55
Crystal structureMonoclinic
Extended informationhttps://www.webelements.com/selenium/