The chemical reaction between magnesium and hydrochloric acid is a classic example of a single displacement reaction where magnesium displaces hydrogen from the acid, producing a salt and hydrogen gas.
The Chemical Process
When solid magnesium metal (Mg) is added to aqueous hydrochloric acid (HCl), a chemical reaction occurs. This reaction involves the transfer of electrons, making it a redox (reduction-oxidation) reaction. Magnesium, a reactive metal, loses electrons and is oxidized, while hydrogen ions from the acid gain electrons and are reduced to form hydrogen gas.
As referenced, when magnesium reacts with hydrochloric acid, the salt magnesium chloride is formed along with hydrogen gas.
The Chemical Equation
The balanced chemical equation representing this reaction is:
Mg (s) + 2HCl (aq) → MgCl₂ (aq) + H₂ (g)
Let's break this down:
- Mg (s): Solid magnesium metal (the reactant).
- HCl (aq): Aqueous hydrochloric acid (the reactant).
- MgCl₂ (aq): Aqueous magnesium chloride (the salt product).
- H₂ (g): Hydrogen gas (the gaseous product).
Observable Changes During the Reaction
During the reaction between magnesium and hydrochloric acid, several observations are typically made. These help confirm that a chemical change is taking place. As referenced, during the reaction the following observations would be made:
- Bubbles of colourless gas: This is the visible evidence of hydrogen gas (H₂) being produced. The rate of bubbling indicates the speed of the reaction.
- Exothermic (heat given out): The reaction releases energy in the form of heat, causing the temperature of the solution to rise. This classifies the reaction as exothermic.
- The magnesium metal itself will gradually disappear as it reacts and is converted into magnesium chloride dissolved in the solution.
Products of the Reaction
The two main products of this reaction are:
- Magnesium Chloride (MgCl₂): This is an ionic salt that dissolves in water, forming a colourless solution. It is the result of the magnesium atoms bonding with chloride ions from the hydrochloric acid.
- Hydrogen Gas (H₂): This is a colourless, odourless diatomic gas. It is produced when hydrogen ions from the acid gain electrons from magnesium and combine to form H₂ molecules. Hydrogen gas is highly flammable.
Summary of the Reaction
| Reactants | Products | Type of Reaction | Observations |
|---|---|---|---|
| Magnesium (Mg) | Magnesium Chloride (MgCl₂) | Single Displacement | Bubbles of colourless gas |
| Hydrochloric Acid (HCl) | Hydrogen Gas (H₂) | Redox | Exothermic (Heat is given out) |
This reaction is commonly demonstrated in laboratories to show the reactivity of metals with acids and to produce hydrogen gas.
