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Zinc hydroxide is an inorganic compound formed when zinc ions (Zn²⁺) combine with hydroxide ions (OH⁻). The correct chemical formula is Zn(OH)₂. In this compound, one zinc ion with a +2 charge is balanced by two hydroxide ions, each carrying a -1 charge. This maintains electrical neutrality, which is a fundamental rule in writing chemical formulas.
Zinc hydroxide is an amphoteric hydroxide, meaning it can act as both a weak base and a weak acid. It is usually obtained as a white, gelatinous precipitate when a solution of zinc salt, such as zinc sulfate (ZnSO₄), is treated with sodium hydroxide (NaOH) or ammonia solution. For example:
ZnSO₄ + 2NaOH → Zn(OH)₂ ↓ + Na₂SO₄
The precipitate of Zn(OH)₂ is insoluble in water but dissolves in strong bases like NaOH, forming soluble zincates, and also dissolves in acids, showing its amphoteric nature.
Examining the options:
Zn(OH)₂ is correct, as it reflects the +2 oxidation state of zinc.
ZnO₂ represents zinc peroxide, which is a different compound.
Zn₂(OH)₃ is not a valid or stable formula for zinc hydroxide.
ZnOH is incorrect because zinc requires two hydroxide ions to balance its +2 charge.
Zinc hydroxide has important applications in medicine, chemistry, and industry. It is used in ointments, as a precursor for zinc oxide, and in various laboratory reactions. Its amphoteric property makes it significant in analytical and industrial chemistry.
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