what is the formula for chromium ii hydroxide

Breiz Heurope

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10-03-2025

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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. Let's break it down.

Understanding the Components

To determine the formula, we need to understand the components:

• Chromium(II): This tells us we're dealing with chromium (Cr) in its +2 oxidation state. The Roman numeral II is crucial because chromium can exist in multiple oxidation states (+2, +3, +6 being the most common).

• Hydroxide: This is the polyatomic ion OH⁻, which carries a -1 charge.

Deriving the Formula

The formula reflects the balance of charges within the compound. Since chromium(II) has a +2 charge (Cr²⁺) and hydroxide has a -1 charge (OH⁻), we need two hydroxide ions to balance the charge of one chromium(II) ion.

Therefore, the formula for chromium(II) hydroxide is Cr(OH)₂.

Properties and Reactions

Chromium(II) hydroxide is a relatively unstable compound. It readily oxidizes in the presence of air, converting to chromium(III) hydroxide. This makes it difficult to obtain and study in its pure form. It's typically a pale blue solid, but its exact appearance can depend on its purity and hydration.

The instability of chromium(II) compounds in general is a key factor in their chemistry. The +2 oxidation state isn't as stable as the +3 state for chromium, meaning reactions often lead to the formation of chromium(III) species.

Related Compounds

Understanding the formula for chromium(II) hydroxide allows you to predict the formulas of other related chromium(II) compounds. For example, chromium(II) chloride would be CrCl₂, as chloride (Cl⁻) also has a -1 charge, requiring two chloride ions to balance one chromium(II) ion.

Conclusion

The formula for chromium(II) hydroxide is Cr(OH)₂. Remember, the Roman numeral II is essential for specifying the oxidation state of chromium and understanding the correct formula. This simple formula underlies the more complex chemistry of this fascinating and reactive compound.