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It is the acidic anhydride of chromic acid, and is sometimes marketed under the same name. [6] This compound is a dark-purple solid under anhydrous conditions and bright orange when wet. The substance dissolves in water accompanied by hydrolysis. [clarification needed] Millions of kilograms are produced annually, mainly for electroplating. [7]
Because of its considerable stability, chromia is a commonly used pigment. It was originally called viridian. It is used in paints, inks, and glasses. It is the colorant in "chrome green" and "institutional green." Chromium(III) oxide is a precursor to the magnetic pigment chromium dioxide, by the following reaction: [7] Cr 2 O 3 + 3 CrO 3 → ...
Chromium(III) hydroxide (Cr(OH) 3) is amphoteric, dissolving in acidic solutions to form [Cr(H 2 O) 6] 3+, and in basic solutions to form [Cr(OH) 6] 3−. It is dehydrated by heating to form the green chromium(III) oxide (Cr 2 O 3), a stable oxide with a crystal structure identical to that of corundum. [6]
It is readily oxidized by the atmosphere. CrO is basic, while CrO 3 is acidic, and Cr 2 O 3 is amphoteric. [3] CrO occurs in the spectra of luminous red novae, which occur when two stars collide. It is not known why red novae are the only objects that feature this molecule; one possible explanation is an as-yet-unknown nucleosynthesis process. [4]
This kind of chromic acid may be used as a cleaning mixture for glass. Chromic acid may also refer to the molecular species, H 2 CrO 4 of which the trioxide is the anhydride. Chromic acid features chromium in an oxidation state of +6 (and a valence of VI or 6). It is a strong and corrosive oxidizing agent and a moderate carcinogen.
A basic oxide, also called a base anhydride (meaning "base without water"), is usually formed in the reaction of oxygen with metals, especially alkali (group 1) and alkaline earth (group 2) metals. Both of these groups form ionic oxides that dissolve in water to form basic solutions of the corresponding metal hydroxide: Alkali metals (Group 1)
The water molecule is amphoteric in aqueous solution. It can either gain a proton to form a hydronium ion H 3 O +, or else lose a proton to form a hydroxide ion OH −. [5] Another possibility is the molecular autoionization reaction between two water molecules, in which one water molecule acts as an acid and another as a base.
Pure water has a pH of 7 at 25°C, meaning it is neutral. When an acid is dissolved in water, the pH will be less than 7, while a base, or alkali, will have a pH greater than 7. A strong acid, such as hydrochloric acid, at concentration 1 mol dm −3 has a pH of 0, while a strong alkali like sodium hydroxide, at the same concentration, has a pH ...