Typical Reactions of Acids

Equations and Reaction Types

What is the general equation for a metal reacting with an acid?

metal + acid → salt + hydrogen

What is usually observed when a reactive metal reacts with an acid?

Bubbles of hydrogen gas are produced.

What forms when a metal reacts with an acid?

A salt and hydrogen gas.

What happens if the salt formed in a metal–acid reaction is soluble?

A solution of the salt forms.

Do all metals react with dilute acids?

No. The metal must be sufficiently reactive.

Does magnesium react with dilute acids?

Yes.

Does copper normally react with dilute hydrochloric or sulfuric acid?

No.

What is the equation for magnesium reacting with hydrochloric acid?

Mg + 2HCl → MgCl₂ + H₂

What is the ionic equation for magnesium reacting with acid?

Mg(s) + 2H⁺(aq) → Mg²⁺(aq) + H₂(g)

What happens to H⁺ ions when a metal reacts with an acid?

They gain electrons and form hydrogen gas.

Are metal–acid reactions redox reactions?

Yes.

Why is a metal–acid reaction a redox reaction?

Electrons are transferred from the metal to H⁺ ions.

What happens to H⁺ ions during a metal–acid reaction in terms of oxidation and reduction?

H⁺ ions are reduced.

Why is the reaction between a metal and an acid not classified as neutralisation?

The H⁺ ions are reduced rather than neutralised.

What is the general equation for a metal oxide reacting with an acid?

metal oxide + acid → salt + water

What is the general equation for a metal hydroxide reacting with an acid?

metal hydroxide + acid → salt + water

What type of reaction occurs between an acid and a metal oxide?

Neutralisation.

What type of reaction occurs between an acid and a metal hydroxide?

Neutralisation.

Does the reactivity of the metal matter when a metal oxide reacts with an acid?

No, because the metal is present as metal ions rather than metal atoms.

What is usually observed when an insoluble metal oxide or hydroxide reacts with acid?

The solid dissolves and a solution forms.

What is the equation for copper(II) oxide reacting with sulfuric acid?

CuO + H₂SO₄ → CuSO₄ + H₂O

What is the ionic equation for copper(II) oxide reacting with acid?

CuO(s) + 2H⁺(aq) → Cu²⁺(aq) + H₂O(l)

What is the equation for zinc hydroxide reacting with sulfuric acid?

Zn(OH)₂ + H₂SO₄ → ZnSO₄ + 2H₂O

What is the ionic equation for zinc hydroxide reacting with acid?

Zn(OH)₂(s) + 2H⁺(aq) → Zn²⁺(aq) + 2H₂O(l)

Why are acid reactions with metal oxides and hydroxides neutralisation reactions?

H⁺ ions react with O²⁻ or OH⁻ ions.

Are acid reactions with metal oxides and hydroxides redox reactions?

No.

Why are acid reactions with metal oxides and hydroxides not redox reactions?

There is no change in oxidation number.

What is an alkali?

A metal hydroxide that dissolves in water.

What is the general equation for an alkali reacting with an acid?

alkali + acid → salt + water

What type of reaction occurs between an acid and an alkali?

Neutralisation.

What is the ionic equation for an acid reacting with an alkali?

H⁺(aq) + OH⁻(aq) → H₂O(l)

What happens to H⁺ and OH⁻ ions during neutralisation?

They combine to form water.

Are acid–alkali reactions redox reactions?

No.

Why are acid–alkali reactions not redox reactions?

There is no change in oxidation number.

What visible change usually occurs when an acid reacts with an alkali?

Usually no visible change.

What change may be detected when an acid reacts with an alkali?

A temperature change.

Why can phosphoric acid react with different amounts of sodium hydroxide?

Phosphoric acid has three replaceable hydrogen ions.

How many replaceable hydrogens are present in phosphoric acid?

Three.

What is the formula of phosphoric acid?

H₃PO₄

What is the equation when one mole of NaOH reacts with one mole of H₃PO₄?

NaOH + H₃PO₄ → NaH₂PO₄ + H₂O

What is the equation when two moles of NaOH react with one mole of H₃PO₄?

2NaOH + H₃PO₄ → Na₂HPO₄ + 2H₂O

What is the equation when three moles of NaOH react with one mole of H₃PO₄?

3NaOH + H₃PO₄ → Na₃PO₄ + 3H₂O

What determines which salt forms when phosphoric acid reacts with sodium hydroxide?

The relative amounts of acid and alkali used.

What is the general equation for a metal carbonate reacting with an acid?

metal carbonate + acid → salt + water + carbon dioxide

What gas is produced when a carbonate reacts with an acid?

Carbon dioxide.

What is observed when a carbonate reacts with an acid?

Effervescence or bubbling due to carbon dioxide gas.

What happens if the salt produced in an acid–carbonate reaction is soluble?

A solution forms.

What is the equation for lithium carbonate reacting with hydrochloric acid?

Li₂CO₃ + 2HCl → 2LiCl + H₂O + CO₂

What is the ionic equation for a carbonate reacting with an acid?

CO₃²⁻(aq) + 2H⁺(aq) → H₂O(l) + CO₂(g)

What type of reaction occurs between a carbonate and an acid?

Neutralisation.

Why is an acid–carbonate reaction a neutralisation reaction?

H⁺ ions react with carbonate ions.

Is an acid–carbonate reaction a redox reaction?

No.

Why is an acid–carbonate reaction not a redox reaction?

There is no change in oxidation number.

What is a hydrogencarbonate?

A compound containing the hydrogencarbonate ion, HCO₃⁻.

What is the formula of the hydrogencarbonate ion?

HCO₃⁻

How do hydrogencarbonates react with acids?

In the same general way as carbonates, producing a salt, water and carbon dioxide.

What is the general equation for a hydrogencarbonate reacting with an acid?

hydrogencarbonate + acid → salt + water + carbon dioxide

What common substance contains sodium hydrogencarbonate?

Baking soda or bicarbonate of soda.

What is the formula of sodium hydrogencarbonate?

NaHCO₃

What happens when sodium hydrogencarbonate reacts with an acid?

Carbon dioxide gas is produced along with water and a sodium salt.

Why do cakes rise when baking soda reacts with acids?

Bubbles of carbon dioxide become trapped in the mixture and cause it to rise.

What is the word equation for sodium hydrogencarbonate reacting with citric acid?

sodium hydrogencarbonate + citric acid → sodium citrate + water + carbon dioxide

How can carbonate or hydrogencarbonate ions initially be tested for?

Add aqueous acid and observe whether a gas is produced.

How can the gas produced from a carbonate–acid reaction be identified?

Test it with limewater.

What happens when carbon dioxide is passed through limewater?

The limewater turns milky/cloudy.

What salt is normally produced when hydrochloric acid reacts?

A chloride salt.

What salt is normally produced when sulfuric acid reacts?

A sulfate salt.

What salt is normally produced when nitric acid reacts?

A nitrate salt.

What salts can phosphoric acid produce?

Phosphate or partially neutralised hydrogen phosphate salts.

What are the four common acids discussed in typical acid reactions?

Hydrochloric acid, nitric acid, sulfuric acid and phosphoric acid.

What substance is always formed in the typical acid reactions shown in this topic?

A salt.

What are the products of acid + metal?

Salt + hydrogen.

What are the products of acid + metal oxide?

Salt + water.

What are the products of acid + metal hydroxide?

Salt + water.

What are the products of acid + alkali?

Salt + water.

What are the products of acid + carbonate?

Salt + water + carbon dioxide.

What are the products of acid + hydrogencarbonate?

Salt + water + carbon dioxide.

Write the full equation for zinc reacting with sulfuric acid.

Zn + H₂SO₄ → ZnSO₄ + H₂

Write the simplest ionic equation for zinc reacting with hydrochloric acid.

Zn(s) + 2H⁺(aq) → Zn²⁺(aq) + H₂(g)

Write the full equation for aluminium oxide reacting with hydrochloric acid.

Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O

Write the simplest ionic equation for magnesium carbonate reacting with nitric acid.

MgCO₃(s) + 2H⁺(aq) → Mg²⁺(aq) + H₂O(l) + CO₂(g)