what is the formula for chromium ii hydroxide

Charlotte

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26-02-2025

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Chromium(II) hydroxide, also known as chromous hydroxide, is an inorganic compound with a fascinating chemistry. Understanding its formula requires a grasp of basic chemical nomenclature and the oxidation states of chromium. Let's break it down.

Understanding Chromium's Oxidation States

Chromium (Cr) is a transition metal, meaning it can exist in multiple oxidation states. This means it can lose different numbers of electrons to form ions with varying charges. The most common oxidation states for chromium are +2, +3, and +6.

• Chromium(II): This refers to chromium in its +2 oxidation state. It means a chromium atom has lost two electrons.
• Chromium(III): This indicates a chromium ion with a +3 charge.
• Chromium(VI): This is a highly oxidized form of chromium, with a +6 charge.

Deriving the Formula for Chromium(II) Hydroxide

The hydroxide ion is OH⁻, carrying a -1 charge. Since chromium(II) has a +2 charge (Cr²⁺), we need two hydroxide ions to balance the charge in the compound. Therefore, the formula for chromium(II) hydroxide is Cr(OH)₂.

This formula indicates that one chromium(II) ion is bonded to two hydroxide ions, resulting in a neutral compound.

Properties and Reactions of Chromium(II) Hydroxide

Chromium(II) hydroxide is a relatively unstable compound. It is a light blue solid, and it is easily oxidized to chromium(III) hydroxide in the presence of air. This oxidation reaction is what causes it to change color to a darker green over time.

Further Considerations

• Solubility: Chromium(II) hydroxide is largely insoluble in water.
• Preparation: It can be prepared by reacting a chromium(II) salt solution with a base. The exact procedure requires careful control of conditions to prevent oxidation.
• Applications: Due to its instability and reactivity, it doesn't have widespread industrial applications. Its primary significance lies in its role in illustrating the chemistry of chromium in different oxidation states.

Conclusion

The formula for chromium(II) hydroxide is Cr(OH)₂. This formula arises from the +2 charge of the chromium(II) ion and the -1 charge of the hydroxide ion. Understanding the oxidation states of transition metals is essential for correctly predicting the formulas of their compounds. Remember that Cr(OH)₂ is a relatively unstable compound, readily oxidizing to higher oxidation states.