When metals react with acids, the reaction is an example of a redox reaction. In these reactions, the metal is oxidised (loses electrons), and the hydrogen ions in the acid are reduced (gains electrons), producing hydrogen gas and a salt.

The general reaction between a metal and an acid can be written as:

For example, when zinc reacts with hydrochloric acid, zinc chloride and hydrogen gas are produced:

• Oxidation: Zinc (Zn) loses two electrons to form $\ce{Zn2+}$, which means zinc is oxidised.
• Reduction: The hydrogen ions $\ce{(H+)}$ from the acid gain electrons to form hydrogen gas $\ce{(H2​)}$, meaning the hydrogen is reduced.

Some metals will react with acids to produce salts and hydrogen gas, depending on their reactivity.

Not all metals will react with acids. The reactivity of the metal and the strength and concentration of the acid determine whether a reaction will occur:

• Highly reactive metals: Sodium, lithium, and magnesium react readily, even with weak or dilute acids.
• Less reactive metals: Copper, mercury, and silver require strong and concentrated acids to react.
• Inert metals: Platinum is so unreactive that it won't react with acids under any conditions.