Chromic acid

Japanese: クロム酸 - くろむさん(英語表記)chromic acid
Chromic acid

The oxoacid of chromium(VI), H 2 CrO 4 , has never been isolated. Because an aqueous solution of chromium(VI) oxide, CrO 3 , is a chromic acid solution, chromium(VI) oxide was sometimes called chromic acid.

CrO3 + H2OH2CrO4
A low concentration chromic acid solution is yellow-red, but as the concentration increases, it turns red or dark red, becoming darker in color. Ions such as CrO 4 2- , HCrO 4 - , and Cr 2 O 7 2- are present in the solution, and at high concentrations, polyacid ions Cr 3 O 10 2- and Cr 4 O 13 2- are produced. Chromate ions are stable in alkaline conditions, but reversibly change to dichromate ions Cr 2 O 7 2- when the solution becomes acidic.

2CrO 4 2- +2H + Cr 2 O 7 2- +H 2 O
[Iwamoto Shinbu]

[Reference] | Oxoacids

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

クロム(Ⅵ)のオキソ酸H2CrO4であるが、この酸自体は単離されていない。酸化クロム(Ⅵ)CrO3の水溶液がクロム酸溶液であるため、酸化クロム(Ⅵ)がクロム酸といわれたこともあった。

  CrO3+H2O→H2CrO4
 低濃度のクロム酸溶液は黄赤色であるが、濃度が高くなるにしたがって赤色ないし濃赤色を呈し、黒ずんだ色となる。溶液中にはCrO42-、HCrO4-、Cr2O72-などのイオンが存在し、高濃度になるとポリ酸イオンCr3O102-、Cr4O132-を生ずる。クロム酸イオンは塩基性では安定であるが、酸性になると可逆的に二クロム酸イオンCr2O72-に変化する。

  2CrO42-+2H+Cr2O72-+H2O
[岩本振武]

[参照項目] | オキソ酸

出典 小学館 日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について 情報 | 凡例

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