6a. Making a soluble salt by neutralising a soluble acid and an alkali (a soluble base)

[Author © Dr Phil Brown PhD: Doc Brown's chemistry exam revision notes on pH-reactions-acids-bases-neutralisation-salt preps, suitable for students of UK GCSE level and international IGCSE/O level chemistry courses, ~US grades 9-10 chemistry notes [page updated Mar 11th 2026 *]

Introduction

One important point is to recognise that all the reactants and salt product are soluble here, which is why you need a titration procedure to work out how much of the acid is to be added to a given volume of alkali.

e.g. the hydroxide of an alkali metal like sodium hydroxide, potassium hydroxide or ammonia solution (wrongly called )ammonium hydroxide. Steps (1) to (3) below is called a titration.

Typical common soluble bases (alkalis) used for preparing soluble salts:

NaOH sodium hydroxide, KOH potassium hydroxide and some soluble carbonates

Typical examples of word and symbol equations for neutralisation are shown below:

(The equations are identical for potassium hydroxide, KOH, just swap Na with a K)

 

sodium hydroxide + hydrochloric acid ==> sodium chloride + water

NaOH_(aq) + HCl_(aq) ==> NaCl_(aq) + H₂O_(l)

sodium hydroxide + sulfuric acid ==> sodium sulfate + water

2NaOH_(aq) + H₂SO_4(aq) ==> Na₂SO_4(aq) + 2H₂O_(l)

 

potassium hydroxide + sulfuric acid ==> potassium sulfate + water

2KOH_(aq) + H₂SO_4(aq) ==> K₂SO_4(aq) + 2H₂O_(l)

sodium hydroxide + nitric acid ==> sodium nitrate + water

NaOH_(aq) + HNO_3(aq) ==> NaNO_3(aq) + 2H₂O_(l)

 

ammonia + nitric acid ==> ammonium nitrate

NH_3(aq) + HNO_3(aq) ==> NH₄NO_3(aq)

 

potassium hydroxide + hydrobromic acid ==> potassium bromide + water

KOH_(aq) + HBr_(aq) ==> KBr_(aq) + H₂O_(l)

 

sodium carbonate + hydrochloric acid ==> sodium chloride + water + carbon dioxide

Na₂CO_3(s) + 2HCl_(aq) ==> 2NaCl_(aq) + H₂O_(l) + CO_2(g)

Note that, unusually for most carbonates, sodium carbonate and potassium carbonate are soluble bases.

 

More examples of neutralization equations are given in section 4.

(1) A known volume of acid is pipetted into a conical flask and universal indicator added. The acid is titrated with the alkali from the burette.

(2) The acid is added until the indicator turns green, pH 7 neutral. This means all the acid has been neutralised to form the salt. I've illustrated the method using universal indicator BUT it isn't that accurate an indicator for titrations.

You should use a more precise indicator like phenolphthalein or methyl orange. I didn't repeat all the titration details here again, I've just kept to the basic ideas and description, but there lots of detailed examples on another page in the calculation sections (more examples - diagrams, descriptions of titration procedures, calculations)

(3) The volume of alkali needed for neutralisation is then noted, this is called the endpoint volume.

(1)-(3) are repeated with both known volumes mixed together BUT without the contaminating indicator, such as phenolphthalein or methyl orange.

You can use any volumes as long as they are the same ratio from the initial titration.

All that's left in solution is the salt.

(4) The solution is transferred to an evaporating dish and heated to partially evaporate the water causing crystallisation or it can be left to very slowly evaporate - which tends to give bigger and better crystals, but should not be heated-evaporated to dryness.

This evaporation can be done safely with an electric heater of a hot water bath.

Then hot concentrated solution is left to cool and crystallise.

(5) The residual liquid can be decanted away and the crystals can be carefully collected and dried by 'dabbing' with a filter paper OR the crystals can be collected by filtration and dried (as above).

See also the preparation of ammonium salts using this method.

AND also more examples - diagrams, descriptions of titration procedures

Extra guidance notes

(i) You can put the acid in the burette and the alkali in the flask.

(ii) Parts (1) to (3) are known specifically as an acid-base (alkali) titration, and the general method is known as a volumetric titration by which it possible to find out exactly what volume ratios are needed for neutralisation.

So knowing one concentration, you can calculate the other.

(iii) Concentration calculations are on calculations pages sections 11. and 12.

(iv) Apparatus used: (1) pipette and conical flask; (2)-(3) burette and conical flask; (4) evaporating (crystallising) dish, bunsen burner, tripod and gauze; (5) filter paper.

(v) Other indicators e.g. phenolphthalein can be used instead (pink alkaline, colourless acid).

(vi) The burette and pipette are both used for the accurate measurement of volume.

(vii) The pH changes in this preparation are described in section 7

Neutralisation equation questions - just select a few different preparation equations

Write down your answer and click on link for answers below

(and I've added a note on their uses, these are not just abstract equations, they represent the preparation of useful chemicals)

Q1 Write down the equations for the preparation of ....

lithium chloride,  lithium nitrate  and  lithium sulfate

Lithium Compound Uses

Q2 Write down the equations for the preparation of ....

sodium chloride,  sodium nitrate  and  sodium sulfate

Sodium Compound Uses

Q3 Write down the equations for the preparation of ....

potassium chloride,  potassium nitrate,  potassium sulfate

Potassium Compound Uses

Q4 Write down the equations for the preparation of ....

rubidium chloride,  rubidium nitrate  and  rubidium sulfate

Rubidium Compound Uses

These compounds are less common than lithium, sodium, or potassium salts, but they play important roles in precision technologies and experimental chemistry.

Q5 Write down the equations for the preparation of ....

caesium chloride,  caesium nitrate  and  caesium sulfate

Caesium Compound Uses

These compounds are less common than lighter alkali metal salts but play key roles in precision science and niche industrial processes.

MOH + HCl:  LiCl  NaCl  KCl  RbCl  CsCl

MOH + HNO₃: LiNO₃  NaNO₃  KNO₃  RbNO₃  CsNO₃

MOH + H₂SO₄: Li₂SO₄  Na₂SO₄  K₂SO₄  Rb₂SO₄  Cs₂SO₄