A man went door to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was upset but after a futile argument the man beat a hasty retreat. Can you play the detective to find out the nature of the solution he had used?

Aqua regia, a term derived from Latin meaning 'royal water,' is renowned for its ability to dissolve noble metals like gold and platinum. It's a powerful and highly corrosive mixture composed of nitric acid (HNO₃) and hydrochloric acid (HCl) in a ratio of 1:3. The unique property of aqua regia lies in its combined chemical strength; while neither of the individual acids can dissolve noble metals completely, together they form a potent solution capable of breaking down these stubborn metals. When gold comes into contact with aqua regia, the nitric acid oxidizes a small portion of the gold into gold ions, and the hydrochloric acid then forms chloroauric acid, making the gold soluble. This process effectively removes a thin layer of gold, exposing a fresh, shiny layer beneath and reducing the overall weight of the original piece. Thus, this explains how the jewelry in the problem became shiny but lighter.

The dissolution of metals is a chemical process that involves breaking down a metal into its ionic form. This occurs when a metal reacts with an acid or another chemical solution. In the context of gold, which is generally unreactive, only a few specific solutions like aqua regia can cause dissolution. The dissolution process is as follows:
- The metal (in this case, gold) is exposed to a chemical like aqua regia.
- The nitric acid component in aqua regia oxidizes a portion of the gold to form gold ions.
- These gold ions then react with the hydrochloric acid to form a soluble complex known as chloroauric acid.
This process not only dissolves a part of the gold but also leaves the remaining part clean and shiny. The significant reduction in weight observed in the problem signifies that the dissolution process went beyond just surface cleaning, removing a substantial amount of material.

Gold is an element with unique chemical properties. It is one of the least reactive metals, which is why gold objects do not tarnish or corrode easily, maintaining their luster over time. However, gold can be reactive under certain conditions, particularly with aqua regia.
- Gold's atomic number is 79, and it belongs to group 11 of the periodic table, which includes other noble metals like silver and copper.
- Aqua regia is one of the few chemical mixtures capable of dissolving gold due to its highly reactive combination of acids.
- In aqua regia, gold is converted into chloroauric acid through a redox reaction where gold initially forms gold ions.
Understanding the chemistry of gold is crucial because it explains why typical cleaning agents would not affect gold, while a specialized mixture like aqua regia can dissolve it. This knowledge also underscores the importance of handling such powerful reagents with care, as their misuse can lead to significant material loss, as illustrated by the reduced weight of the bangles in the problem.