Chemistry
Like sulfuric acid, selenic acid is a strong acid that is hygroscopic and extremely soluble in water. Concentrated solutions are viscous. Crystalline mono- and di-hydrates are known. The monohydrate melts at 26°C, and the dihydrate melts at −51.7°C.
Selenic acid is a stronger oxidiser than sulfuric acid, capable of liberating chlorine from chloride ions, being reduced to selenous acid in the process:
- H2SeO4 + 2 H+ + 2 Cl− → H2SeO3 + H2O + Cl2
It decomposes above 200°C, liberating oxygen gas and being reduced to selenous acid:
- 2 H2SeO4 → 2 H2SeO3 + O2
Selenic acid reacts with barium salts to precipitate BaSeO4, analogous to the sulfate. In general, selenate salts resemble sulfate salts, but are more soluble. Many selenate salts have the same crystal structure as the corresponding sulfate salts.
Treatment of selenic acid with fluorosulfuric acid gives the dioxydifluoride (b.p. −8.4 °C):
- H2SeO4 + 2 HO3SF → SeO2F2 + 2 H2SO4
Hot, concentrated selenic acid is capable of dissolving gold, forming a reddish-yellow solution of gold(III) selenate:
- 2 Au + 6 H2SeO4 → Au2(SeO4)3 + 3 H2SeO3 + 3 H2O
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