Yes, platinum can dissolve under specific conditions.
Platinum, generally considered a very inert metal, can indeed dissolve. It's not a spontaneous process in most common environments, but with the right chemical or electrochemical environment, dissolution is possible. The question that needs rephrasing to clarify is, "Under what conditions can platinum dissolve?" The subsequent sections elaborate on these conditions.
Conditions for Platinum Dissolution
Electrochemical Dissolution (Electrolysis)
One established method for dissolving platinum is through electrolysis, particularly in chloride solutions.
- Process: When platinum is used as an anode during electrolysis of chloride solutions, it dissolves.
- Product: This process leads to the formation of platinum(IV) compounds, specifically [PtCl6]2-.
- Reference: This phenomenon was recognized as early as the 1920s (1962).
- Current Density: At low current densities (below 10 A m−2), platinum dissolves in accordance with Faraday's laws of electrolysis.
Chemical Dissolution
Platinum can also be dissolved chemically, though it requires very aggressive reagents.
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Aqua Regia: A well-known solvent for platinum is aqua regia, a highly corrosive mixture of concentrated nitric acid and hydrochloric acid, optimally in a molar ratio of 1:3.
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Mechanism: Nitric acid acts as an oxidizer and is used to form platinum ions (Pt2+). Hydrochloric acid is then required to react with the platinum ions to form tetrachloroplatinate(II) anions ([PtCl4]2−), also in solution. The reaction with hydrochloric acid is an equilibrium reaction that favors the formation of tetrachloroplatinate(II) anions. This reaction results in the removal of platinum ions from solution and allows the further oxidation of platinum to proceed. The relevant reaction equation is:
Pt + 4 HNO3 + 6 HCl → [PtCl6]2− + 4 NO2 + 4 H2O + 2 H+
Summary Table: Platinum Dissolution
| Method | Environment | Product |
|---|---|---|
| Electrolysis | Chloride solutions | [PtCl6]2− |
| Chemical Dissolution | Aqua Regia (HNO3 + HCl) | [PtCl6]2− |
