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Neutralisation for SQA National 5 Chemistry

Neutralisation

This page covers the following topics:

1. Neutralisation reactions
2. Neutralising carboxylic acids
3. Spectator ions
4. Production of soluble salts
5. Production of insoluble salts

A neutralisation reaction is a reaction between an acid and a base during which a salt and water is formed. The salt is usually named by using a combination of the base positive ion and an acid negative ion. For example, sodium hydroxide with sulphuric acid would produce sodium sulphate and water. Many neutralisation reactions can be simplified to just Hโบ + OHโป โ†’ Hโ‚‚O.

Acids react with some metal oxides and metal hydroxides to produce a salt and water.
CaO + Hโ‚‚SOโ‚„ โ†’ CaSOโ‚„ + Hโ‚‚O
KOH + HCl โ†’ KCl + Hโ‚‚O

Acids can also be neutralised when reacting with carbonates. Acids, both strong and weak, react with metal carbonates to produce a salt, water and carbon dioxide.
MgCOโ‚ƒ + 2HCl โ†’ MgClโ‚‚ + Hโ‚‚O + COโ‚‚

Neutralisation reactions

Carboxylic acids react with some metal oxides and metal hydroxides to produce a salt and water.
CaO + 2CHโ‚ƒCOOH โ†’ (CHโ‚ƒCOO)โ‚‚Ca + Hโ‚‚O
KOH + CHโ‚ƒCOOH โ†’ CHโ‚ƒCOOK + Hโ‚‚O

Carboxylic acids react with metal carbonates to produce a salt, water and carbon dioxide.
MgCOโ‚ƒ + 2CHโ‚ƒCOOH โ†’ (CHโ‚ƒCOO)โ‚‚Mg + Hโ‚‚O + COโ‚‚

Neutralising carboxylic acids

Spectator ions are aqueous ions that appear the same and can be cancelled out from both sides of a chemical equation without affecting the reaction between other particles.

When acids react with some metal oxides and metal hydroxides, reactions without spectator ions are respectively:
Oยฒโป + 2Hโบ โ†’ Hโ‚‚O (soluble oxides)
MO + 2Hโบ โ†’ Hโ‚‚O + Mยฒโบ (some insoluble oxides)
OHโป + Hโบ โ†’ Hโ‚‚O (soluble hydroxides)
MOH + Hโบ โ†’ Hโ‚‚O + Mโบ (some insoluble hydroxides)

When acids react with metal carbonates, reaction without spectator ions is:
COโ‚ƒยฒโป + 2Hโบ โ†’ Hโ‚‚O + COโ‚‚ (soluble carbonates)
MCOโ‚ƒ + 2Hโบ โ†’ Hโ‚‚O + COโ‚‚ + Mยฒโบ (some insoluble carbonates)

Spectator ions

Soluble salts can be difficult to separate from other soluble compounds once dissolved in water. Therefore, pure soluble salts are usually produced by reacting an acid with an excess of insoluble metal or insoluble metal oxide/hydroxide/carbonate. This ensures that there is no acid left once the reaction is finished but the insoluble metal or insoluble metal oxide/hydroxide/carbonate is removed using filtration. The filtrate is then evaporated to produce crystals of the soluble salt.

If a soluble salt is prepared by reacting an acid with a metal that reacts with water or a soluble metal oxide/hydroxide/carbonate, titration is used. Titration ensures that exact amounts of each compound are mixed since soluble metal oxides/hydroxides/carbonates cannot be removed from a solution by using filtration. After the salt solution is obtained using titration, evaporation is used to crystallise the salt.

Production of soluble salts

Insoluble salts are much easier to separate from a solution than soluble salts as filtration can be used even if there are other compounds dissolved in the solution. Once an insoluble salt is produced by precipitation, that is the formation of a solid within a reaction mixture, the mixture is filtered to separate the salt as a residue. It can then be further washed with a solvent and dried to produce pure dry salt crystals.

Production of  insoluble salts

1

Provide a balanced chemical equation for the reaction between butanoic acid and sodium oxide.

Carboxylic acids react with some metal oxides and metal hydroxides to produce a salt and water.

Naโ‚‚O + 2CHโ‚ƒCHโ‚‚CHโ‚‚COOH โ†’ 2CHโ‚ƒCHโ‚‚CHโ‚‚COONa + Hโ‚‚O

Provide a balanced chemical equation for the reaction between butanoic acid and sodium oxide.

2

Simplify the reaction equation provided to exclude the spectator ions.

Ba(OH)โ‚‚ + 2HNOโ‚ƒ โ†’ Ba(NOโ‚ƒ)โ‚‚ + 2Hโ‚‚O

Spectator ions are aqueous ions that appear the same and can be cancelled out from both sides of a chemical equation without affecting the reaction between other particles.

2OHโป + 2Hโบ โ†’ 2Hโ‚‚O

Simplify the reaction equation provided to exclude the spectator ions. 

Ba(OH)โ‚‚ + 2HNOโ‚ƒ โ†’ Ba(NOโ‚ƒ)โ‚‚ + 2Hโ‚‚O

3

What is a balanced equation for the reaction of butanoic acid with strontium oxide?

Carboxylic acids react with some metal oxides and metal hydroxides to produce a salt and water.

SrO + 2CHโ‚ƒCHโ‚‚CHโ‚‚COOH โ†’ (CHโ‚ƒCHโ‚‚CHโ‚‚COO)โ‚‚Sr + Hโ‚‚O

What is a balanced equation for the reaction of butanoic acid with strontium oxide?

4

Describe how a pure dry sample of NaCl can be produced from the two solutions provided in the image. The amount of each material present in the beakers and the volumes of the solutions are known.

Both HCl and NaOH are soluble in water. If a soluble salt is prepared by reacting an acid with a soluble metal hydroxide, titration is used. Titration ensures that exact amounts of each compound are mixed since soluble metal hydroxides cannot be removed from a solution by using filtration. After the salt solution is obtained using titration, evaporation is used to crystallise the salt.

The two solutions are mixed using titration and the salt crystals are obtained using crystallisation.

Describe how a pure dry sample of NaCl can be produced from the two solutions provided in the image. The amount of each material present in the beakers and the volumes of the solutions are known.

5

What are the two main ions responsible for the production of Hโ‚‚O in a reaction between an acid and an alkali?

Many neutralisation reactions can be simplified to just Hโบ + OHโป โ†’ Hโ‚‚O.

Hโบ, OHโป

What are the two main ions responsible for the production of Hโ‚‚O in a reaction between an acid and an alkali?

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