What happens when concentrated HNO3 is mixed with gold (Au) at room temperature?

• A. Nitric acid reduces to NO2 gas and gold forms a soluble complex.
• B. Gold dissolves, forming Au(NO3)3.
• C. No reaction occurs; gold remains unchanged.
• D. Gold is oxidized to Au2O3.

Answer: (C)

Verified step by step guidance

1. Recall the chemical properties of gold (Au), especially its reactivity with acids. Gold is a noble metal known for its resistance to corrosion and oxidation by most acids, including concentrated nitric acid (HNO3).
2. Understand that concentrated nitric acid is a strong oxidizing agent and can dissolve many metals by oxidizing them and producing nitrogen dioxide (NO2) gas. However, gold is an exception due to its high standard reduction potential.
3. Recognize that gold does not react with concentrated nitric acid alone because the acid cannot oxidize gold to form soluble gold ions or complexes under normal conditions (room temperature).
4. Note that gold can be dissolved by aqua regia, a mixture of concentrated nitric acid and hydrochloric acid, which provides both oxidizing power and complexing chloride ions, but not by nitric acid alone.
5. Conclude that when concentrated HNO3 is mixed with gold at room temperature, no reaction occurs, and gold remains unchanged.