Acid–Metal Reactions — Quick Reference

Reaction Overview

• An acid–metal reaction: an acid reacts with a metal to form a salt and hydrogen gas.

• Hydrogen is produced by removing H from the acid; metal combines with the remaining part to form a salt.

• General equation: $\text{Acid} + \text{Metal} \rightarrow \text{Salt} + \text{H}_2 \text{(gas)}$

Gas Evolution and Testing

• Hydrogen gas appears as bubbles rising to the surface.

• Pop test: insert a lit splint; a loud pop confirms hydrogen gas.

Example

• Hydrochloric acid + Magnesium → Magnesium chloride + hydrogen gas

• Equation: $\text{HCl} + \text{Mg} \rightarrow \text{MgCl}<em>2 + \text{H}</em>2$

• Observed as bubbling during the reaction.

Reaction Type and Concept

• This is a single displacement reaction: the metal displaces hydrogen from the acid.

• Concept: the positive ion of hydrogen is replaced by the positive metal ion.

• Compare with double displacement (neutralisation) where two ions swap partners; here only one substance is swapped.

Metal Reactivity Series

• Reactivity is inferred from the rate of bubble production (faster rate = more reactive).

• Reactivity order (example): \text{Ca} > \text{Mg} > \text{Zn} > \text{Cu}