The 'royal water' that can dissolve gold and platinum is a mixture of:
- AConc. HNO₃ and HCl in the ratio 1 : 3
- BConc. HNO₃ and HCl in the ratio 3 : 1
- CConc. H₂SO₄ and HCl in the ratio 1 : 3
- DHNO₃, HCl and H₂SO₄ in the ratio 3 : 1 : 1
Show answer and explanation
Correct answer: (a) Conc. HNO₃ and HCl in the ratio 1 : 3
Explanation
Aqua regia ("royal water") is a mixture of concentrated nitric acid and concentrated hydrochloric acid in the ratio 1 : 3 by volume. It is called royal because it dissolves the "royal" or noble metals, gold and platinum, which neither acid dissolves alone.
The nitric acid oxidises the metal, and the chloride ions from hydrochloric acid hold the metal ions as complex ions (such as AuCl₄⁻), so the reaction keeps going.