Reactions of acids with metals
Emmanuel Opoku
Teacher
Contents
What Are Acids?
Definition:
An acid is a substance that produces hydrogen ions when dissolved in water.
These ions are responsible for the characteristic acidic properties and for reactions with metals, bases, and carbonates.
Common Acids and the Salts They Produce
Acid | Formula | Salt Produced | Example Salt | Found in… |
Hydrochloric acid | Chloride | Sodium chloride | Stomach acid | |
Sulfuric acid | Sulfate | Zinc sulfate | Car batteries | |
Nitric acid | Nitrate | Magnesium nitrate | Fertilisers | |
Citric acid | Citrate | Sodium citrate | Citrus fruits / food acids |
Tip:
The first part of the salt’s name comes from the metal (or base), and the second part comes from the acid (chloride, sulfate, nitrate, citrate).
No answer provided.
Example:
Magnesium + Hydrochloric acid → Magnesium chloride + Hydrogen
Zinc + Sulfuric acid → Zinc sulfate + Hydrogen
Sodium + Citric acid → Sodium citrate + Hydrogen
No answer provided.
General Reaction
When a metal reacts with an acid, the products are a salt and hydrogen gas.
Metal + Acid → Salt+Hydrogen
Definition of a Salt:
A salt forms when the hydrogen ion from an acid is replaced by a metal ion.
Common Examples
Word Equation | Symbol Equation |
Magnesium + Hydrochloric acid → Magnesium chloride + Hydrogen | |
Zinc + Sulfuric acid → Zinc sulfate +Hydrogen | |
Iron + Nitric acid → Iron(II) nitrate + Hydrogen |
Naming Tip:
Combine the metal name with the acid’s ending (chloride, sulfate, nitrate, citrate).
No answer provided.
Reactivity and Hydrogen
Only metals above hydrogen in the reactivity series react with acids to produce hydrogen gas.
Reactivity | Reaction with Acids |
Metals above hydrogen (Mg, Zn, Fe) | React to give hydrogen gas |
Metals below hydrogen (Cu, Ag, Au) | Do not react |
Example observation:
Magnesium reacts vigorously with acid (rapid fizzing/bubbling/effervescence), while iron reacts more slowly.
Test for Hydrogen Gas
Test: Bring a lit splint near the gas.
Result: A squeaky pop sound confirms hydrogen gas.
Hydrogen burns explosively in air, causing the pop sound.
Type of Reaction (HT Only)
Reactions of acids with metals are redox reactions, because:
The metal atoms are oxidised (lose electrons).
The hydrogen ions are reduced (gain electrons).
Ionic and Half Equations (HT Only)
Let’s take magnesium reacting with hydrochloric acid for example…
Full Equation:
Ionic equation:
This shows the electron transfer without spectator ions.
Higher Tier Only Content
Half Equations (HT Only)
Process | Half Equation | Explanation |
|---|---|---|
Oxidation | Metal loses electrons | |
Reduction | Hydrogen ions gain electrons |
HT Key Idea:
Electrons are lost by the metal and gained by hydrogen ions redox reaction.
Remember: OIL RIG (HT Only)
Process | Meaning | Electron Change |
|---|---|---|
Oxidation | Is Loss | Loses electrons → more positive |
Reduction | Is Gain | Gains electrons → more negative |
OIL RIG - Oxidation Is Loss, Reduction Is Gain (of electrons)
Ionic vs Full Equations (HT Only)
Full Equation | Ionic Equation | Spectator Ions |
Spectator ions appear on both sides and are not involved in the redox reaction.
HT Concept Extension - Why Copper Doesn’t React
Copper lies below hydrogen in the reactivity series.
It cannot displace hydrogen ions from acids - so no reaction occurs.
Exam Tip
When explaining why hydrogen forms:
The metal is oxidised (loses electrons) and hydrogen ions are reduced (gain electrons) to form hydrogen gas.
No answer provided.
Check Your Understanding
Recall
a) What ions do all acids produce in solution?
Answer
a) Hydrogen ions .
b) State the general word equation for a metal reacting with an acid.
Answer
b) Metal + Acid → Salt + Hydrogen.
c) Which gas is released, and what is its test?
Answer
c) Gas: Hydrogen . Test: Squeaky pop with a lit splint.
d) Name four common acids and the salts they form.
Answer
d)
Acid | Salt Formed | Example |
|---|---|---|
Hydrochloric acid | Chloride | Sodium chloride |
Sulfuric acid | Sulfate | Zinc sulfate |
Nitric acid | Nitrate | Magnesium nitrate |
Citric acid | Citrate | Sodium citrate |
e) What is the definition of a salt?
Answer
e) A salt forms when the hydrogen ion in an acid is replaced by a metal ion.
Apply
f) Write the word and symbol equations for the reaction between zinc and sulfuric acid.
Answer
f) Word: Zinc + Sulfuric acid → Zinc sulfate + Hydrogen
Symbol:
g) What salt is produced when magnesium reacts with citric acid?
Answer
g) Magnesium citrate + Hydrogen gas.
h) Why does copper not react with hydrochloric acid?
h) Copper is below hydrogen in the reactivity series - it cannot displace hydrogen ions.
i) (HT only) Write the ionic equation for the reaction between magnesium and hydrochloric acid, and identify any spectator ions.
Answer
i) ; spectator ion = .
j) (HT only) Write the oxidation and reduction half-equations for the reaction in (i).
Answer
j) Oxidation:
Reduction:
Challenge (HT only)
k) Explain why reactions between acids and metals are redox reactions.
Answer
k) Metals are oxidised (lose ) and hydrogen ions are reduced (gain ).
l) For the reaction , identify which species is oxidised and which is reduced.
Answer
l) Feoxidised, reduced.
m) Predict the salt name and products when iron reacts with nitric acid. Write a word and symbol equation.
Answer
m) Word: Iron Nitric acid Iron(II) nitrate Hydrogen
Symbol: