Gold generally does not react with dilute acids. This inertness is a key characteristic of gold, contributing to its value and use in various applications.
Why Gold Doesn't React with Dilute Acid
The primary reason gold does not react with dilute acids lies in its position on the metal reactivity series.
Metals are ranked in the reactivity series based on their tendency to lose electrons and form positive ions. Hydrogen is included in this series as a reference point.
According to the reference:
- Metals below hydrogen in the reactivity series do not react with dilute acids.
- Gold (and platinum) are placed below hydrogen in the reactivity series.
Therefore, because gold is less reactive than hydrogen, it cannot displace hydrogen from dilute acids. Unlike more reactive metals that produce hydrogen gas when reacting with acids (as hydrogen is always given off when a metal reacts with water, steam or a dilute acid if the reaction occurs), gold does not undergo this reaction.
Understanding the Reactivity Series
The reactivity series is a list of metals arranged in order of their decreasing reactivity. A simplified view relative to hydrogen is:
- More Reactive Metals (Above Hydrogen): React with dilute acids to produce hydrogen gas.
- Less Reactive Metals (Below Hydrogen): Do not react with dilute acids.
| Reactivity Status | Examples | Reaction with Dilute Acid? |
|---|---|---|
| Above Hydrogen | Zinc, Iron, Lead (some) | Yes (produces H₂) |
| At Hydrogen | Hydrogen (reference) | N/A |
| Below Hydrogen | Gold, Platinum, Silver | No |
Note: While some sources place lead slightly above hydrogen, it reacts very slowly or not at all with dilute HCl or H₂SO₄ due to the formation of insoluble chloride/sulfate layers.
Practical Implications
Gold's lack of reaction with dilute acids makes it ideal for:
- Jewelry: It resists corrosion from environmental exposure, including mild acids.
- Coinage: Gold coins remain stable over long periods.
- Electronics: Used in connectors and wiring where corrosion resistance is critical.
While gold resists most single acids, it can be dissolved by a mixture of concentrated nitric acid and hydrochloric acid called aqua regia, which is a much stronger and more complex reagent than simple dilute acids. However, when considering only dilute acids, gold remains inert.
