Acids and bases neutralise to give a salt and water

Definition

Base

A substance that neutralises an acid, such as a metal oxide, a metal hydroxide or a metal carbonate.

Definition

Neutralisation

The reaction of an acid with a base in which hydrogen ions and hydroxide ions combine to form water.

A base is a substance that neutralises an acid; a soluble base is called an alkali.

In neutralisation, an acid reacts with a base to make a salt and water.

acid+base→salt+water\text{acid} + \text{base} \rightarrow \text{salt} + \text{water}

Metal oxides and metal hydroxides are bases, so both follow this pattern.

Sulfuric acid and copper oxide:

H2SO4(aq)+CuO(s)→CuSO4(aq)+H2O(l)\text{H}_2\text{SO}_4(aq) + \text{CuO}(s) \rightarrow \text{CuSO}_4(aq) + \text{H}_2\text{O}(l)

Hydrochloric acid and sodium hydroxide:

HCl(aq)+NaOH(aq)→NaCl(aq)+H2O(l)\text{HCl}(aq) + \text{NaOH}(aq) \rightarrow \text{NaCl}(aq) + \text{H}_2\text{O}(l)

Key Idea

Acid + metal oxide gives a salt and water.
Acid + metal hydroxide gives a salt and water.

Acids and carbonates also give off carbon dioxide

Definition

Metal carbonate

A compound of metal ions and carbonate ions that reacts with acids to give a salt, water and carbon dioxide.

A metal carbonate reacts with an acid to give a salt, water and carbon dioxide.

dioxide\text{acid} + \text{metal carbonate} \rightarrow \text{salt} + \text{water} + \text{carbon dioxide}

Hydrochloric acid and calcium carbonate:

2HCl(aq)+CaCO3(s)→CaCl2(aq)+H2O(l)+CO2(g)2\text{HCl}(aq) + \text{CaCO}_3(s) \rightarrow \text{CaCl}_2(aq) + \text{H}_2\text{O}(l) + \text{CO}_2(g)

Test the gas by bubbling it through limewater, which turns milky if it is carbon dioxide.

Example

Dropping marble chips (calcium carbonate) into dilute hydrochloric acid gives steady fizzing as carbon dioxide escapes.
Bubbling that gas through limewater turns it cloudy white, confirming carbon dioxide.

The acid decides the ending of the salt name

Definition

Chloride ion

A negatively charged chlorine ion with the formula $Cl−\text{Cl}^-$ that forms chloride salts.

Definition

Nitrate ion

A negatively charged group of atoms with the formula $NO3−\text{NO}_3^-$ that forms nitrate salts.

Hydrochloric acid makes chloride salts.

Sulfuric acid makes sulfate salts.

Nitric acid makes nitrate salts.

The metal in the salt comes from the base, so copper oxide and sulfuric acid give copper sulfate.

Exam technique

Build the salt name from two parts: the metal from the base and the ending from the acid.
Nitric acid plus potassium hydroxide gives potassium nitrate, not potassium nitrite.

Choosing the right base for the salt you want

Use a soluble alkali when both reactants are in solution, so the salt can be found by titration.

Use an insoluble base, such as a metal oxide or carbonate, when you can add it in excess and filter off what is left.

Either route gives the same salt; the choice depends on whether the base dissolves.

Self review

What two products form when an acid neutralises a base?
What extra product forms when an acid reacts with a metal carbonate?
Which salt forms from nitric acid and sodium hydroxide?
Describe the test for carbon dioxide and its result.
Write the balanced equation for hydrochloric acid reacting with calcium carbonate.

Acids and bases neutralise to give a salt and water

Definition

Base

A substance that neutralises an acid, such as a metal oxide, a metal hydroxide or a metal carbonate.

Definition

Neutralisation

The reaction of an acid with a base in which hydrogen ions and hydroxide ions combine to form water.

A base is a substance that neutralises an acid; a soluble base is called an alkali.
In neutralisation, an acid reacts with a base to make a salt and water.
$acid+base→salt+water\text{acid} + \text{base} \rightarrow \text{salt} + \text{water}$
Metal oxides and metal hydroxides are bases, so both follow this pattern.
Sulfuric acid and copper oxide: $H2SO4(aq)+CuO(s)→CuSO4(aq)+H2O(l)\text{H}_2\text{SO}_4(aq) + \text{CuO}(s) \rightarrow \text{CuSO}_4(aq) + \text{H}_2\text{O}(l)$
Hydrochloric acid and sodium hydroxide: $HCl(aq)+NaOH(aq)→NaCl(aq)+H2O(l)\text{HCl}(aq) + \text{NaOH}(aq) \rightarrow \text{NaCl}(aq) + \text{H}_2\text{O}(l)$

Key Idea

Acid + metal oxide gives a salt and water.
Acid + metal hydroxide gives a salt and water.

Acids and carbonates also give off carbon dioxide

Definition

Metal carbonate

A compound of metal ions and carbonate ions that reacts with acids to give a salt, water and carbon dioxide.

A metal carbonate reacts with an acid to give a salt, water and carbon dioxide.
$dioxide\text{acid} + \text{metal carbonate} \rightarrow \text{salt} + \text{water} + \text{carbon dioxide}$
Hydrochloric acid and calcium carbonate: $2HCl(aq)+CaCO3(s)→CaCl2(aq)+H2O(l)+CO2(g)2\text{HCl}(aq) + \text{CaCO}_3(s) \rightarrow \text{CaCl}_2(aq) + \text{H}_2\text{O}(l) + \text{CO}_2(g)$
Test the gas by bubbling it through limewater, which turns milky if it is carbon dioxide.

Example

Dropping marble chips (calcium carbonate) into dilute hydrochloric acid gives steady fizzing as carbon dioxide escapes.
Bubbling that gas through limewater turns it cloudy white, confirming carbon dioxide.

The acid decides the ending of the salt name

Definition

Chloride ion

A negatively charged chlorine ion with the formula $Cl−\text{Cl}^-$ that forms chloride salts.

Definition

Nitrate ion

A negatively charged group of atoms with the formula $NO3−\text{NO}_3^-$ that forms nitrate salts.

Hydrochloric acid makes chloride salts.
Sulfuric acid makes sulfate salts.
Nitric acid makes nitrate salts.
The metal in the salt comes from the base, so copper oxide and sulfuric acid give copper sulfate.

Exam technique

Build the salt name from two parts: the metal from the base and the ending from the acid.
Nitric acid plus potassium hydroxide gives potassium nitrate, not potassium nitrite.

Choosing the right base for the salt you want

Use a soluble alkali when both reactants are in solution, so the salt can be found by titration.
Use an insoluble base, such as a metal oxide or carbonate, when you can add it in excess and filter off what is left.
Either route gives the same salt; the choice depends on whether the base dissolves.

Self review

What two products form when an acid neutralises a base?
What extra product forms when an acid reacts with a metal carbonate?
Which salt forms from nitric acid and sodium hydroxide?
Describe the test for carbon dioxide and its result.
Write the balanced equation for hydrochloric acid reacting with calcium carbonate.

A base is a substance that neutralises an acid. Metal oxides, metal hydroxides and metal carbonates are bases; a soluble base is called an alkali.

In neutralisation with a metal hydroxide or alkali, an acid reacts with the base to produce a salt and water. The ionic explanation is that hydrogen ions and hydroxide ions combine to form water: $H++OH−→H2OH^+ + OH^- \rightarrow H_2O$ . Metal oxides supply oxide ions rather than hydroxide ions, so their ionic reaction is $2H++O2−→H2O2H^+ + O^{2-} \rightarrow H_2O$ . When an acid reacts with a metal carbonate, the products are a salt, water and carbon dioxide.

For metal oxides and metal hydroxides, the general word equation for a neutralisation reaction is:

\text{acid} + \text{metal oxide or hydroxide} \rightarrow \text{salt} + \text{water}

For metal carbonates, the word equation is:

\text{acid} + \text{metal carbonate} \rightarrow \text{salt} + \text{water} + \text{carbon dioxide}

4.2.2 Neutralisation of acids and salt production

Acids and bases neutralise to give a salt and water

Acids and carbonates also give off carbon dioxide

The acid decides the ending of the salt name

Choosing the right base for the salt you want

Review 4.2.2 Neutralisation of acids and salt production by teaching Genie

Recap your knowledge with an interactive lesson

Remember key concepts with flashcards

4.2.2 Neutralisation of acids and salt production

Acids and bases neutralise to give a salt and water

Acids and carbonates also give off carbon dioxide

The acid decides the ending of the salt name

Choosing the right base for the salt you want

Review 4.2.2 Neutralisation of acids and salt production by teaching Genie

Recap your knowledge with an interactive lesson

Remember key concepts with flashcards

4.2.2 Neutralisation of acids and salt production

Acids and bases neutralise to give a salt and water

Acids and carbonates also give off carbon dioxide

The acid decides the ending of the salt name

Choosing the right base for the salt you want

Review 4.2.2 Neutralisation of acids and salt production by teaching Genie

Recap your knowledge with an interactive lesson

Remember key concepts with flashcards

4.2.2 Neutralisation of acids and salt production Revision Guide

4.2.2 Neutralisation of acids and salt production

Acids and bases neutralise to give a salt and water

Acids and carbonates also give off carbon dioxide

The acid decides the ending of the salt name

Choosing the right base for the salt you want

Review 4.2.2 Neutralisation of acids and salt production by teaching Genie

Recap your knowledge with an interactive lesson

Remember key concepts with flashcards

4.2.2 Neutralisation of acids and salt production Revision Guide