How are salts made and named?

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+acid base a salt

How are salts made and named?

When an acid reacts with a base, a neutralization reaction occurs and produces a chemical called a salt.

The name of the salt depends on the names of the reactants.

The first part of the salt’s name comes from the base:

e.g. sodium hydroxide sodium…

The second part of the salt’s name comes from the acid:

e.g. sulfuric acid sulfate…

For example, if sodium hydroxide neutralizes sulfuric acid, the product is a salt called sodium sulfate.


What is the name of the salt?


What are salts used for?

Table salt is sodium chloride. This is the salt used to flavour and preserve food.

Indigestion remedies often contain magnesium salts.

Salts can also be used as coloured pigments in paints, and to help fuels burn better.

The colours of fireworks are formed when certain salts burn. Calcium chloride, for example, burns a bright red colour.


Water is formed because OH– ions from the alkali react with H+ ions from the acid to produce molecules of water (H2O).

Making salts 1: acid + alkali

When an acid reacts with an alkali, the products are a salt and water.

acid alkali salt water+ +

For example:

+ +

++

sodiumhydroxide

NaOH (aq)

sodiumchloride

NaCl (aq)

water

H2O (aq)

hydrochloricacid

HCl (aq)


When is the reaction complete?

There is no obvious sign when this reaction is complete, so an indicator is used to show when the solution is neutral.

This process is called titration.

The reaction between sodium hydroxide and hydrochloric acid produces sodium chloride, which is soluble in water.

+ +

++

sodiumhydroxide

NaOH (aq)

sodiumchloride

NaCl (aq)

water

H2O (aq)

hydrochloricacid

HCl (aq)


What is a titration?


Making salts 2: acid + metal

When a metal is added to an acid, the products are a salt and hydrogen gas.

For example:

This method of making salts only works with some metals.

hydrochloricacid

2HCl (aq)

+

+

+

+

zinc

Zn (aq)

zincchloride

ZnCl2 (aq)

hydrogen

H2 (aq)

acid metal a salt hydrogen+ +

What would happen if potassium was used? Or copper?


Which metal will react the most?


Making salts 3: acid + metal oxide

When a metal oxide is mixed with an acid, the products are a salt and water.

calciumchloride + water

calciumoxide

CaO (aq)

hydrochloricacid

2HCl (aq) CaCl2 (aq) +

+

+ H2O (aq)

For example:

acid metal oxide salt water+ +

Water forms because oxygen ions from the oxide join up with H+ ions from the acid to produce molecules of water (H2O).


Obtaining salts from metal oxides

When a metal oxide is added to an acid, it dissolves as it reacts.

How could the solid copper sulfate salt be separated from the water?

You know when you have added enough of the metal oxide because it stops dissolving.

+ +copperoxide

CuO (s)

sulfuricacid

H2SO4 (aq)

coppersulfate

CuSO4 (aq)

water

H2O (aq)


Obtaining salts from copper oxide


Making salts 4: acid + carbonate

When a carbonate is mixed with an acid, the products are a salt, carbon dioxide and water.

coppernitrate + water +

carbondioxide

coppercarbonate

CuCO3 (s)

nitricacid

2HNO3

(aq)

Cu(NO3)2

(aq)+

+

+ H2O(aq)

+ CO2

(g)

For example:

What would you expect to observe in this reaction?

acid carbonate salt water+ +carbondioxide+

Water and carbon dioxide are formed because the carbonate ions (CO3

2-) react with H+ ions from the acid.


Making salts – summary

Salts can be made by reacting acids with bases.

acid + alkali a salt + water

acid + metal a salt + hydrogen

acid + metal oxide a salt + water

acid + carbonate a salt + carbon dioxide + water

There are four ways of making salts from acids:


Matching reactants and salts


Complete the neutralization reaction


Sometimes when two solutions are mixed, they react to form an insoluble solid product.

For example, mixing solutions of lead nitrate and sodium chloride produces a yellow precipitate of lead chloride.

What is a precipitation reaction?

The insoluble solid product is called a precipitate.

You can spot a precipitate because the mixture goes cloudy.

leadnitrate

Pb(NO3)2 (aq)

sodiumchloride

2NaCl (aq)

leadchloride

PbCl2 (s)

sodiumnitrate

2NaNO3 (aq)

+

+

+

+


How can hard water be softened?

Hard water contains magnesium and calcium ions, which can clog up pipes and heating elements. These ions can be removed using precipitation reactions.

The magnesium ions are removed by this reaction:

What are the word and symbol equations for the removal of the calcium ions?

Sodium carbonate is added to the hard water to form precipitates, which can then be removed by filtration.

sodiumcarbonate

Na2CO3 (aq)

magnesiumchloride

MgCl2 (aq)

sodiumchloride

2NaCl (aq)

magnesiumcarbonate

MgCO3 (s)+ +

+ +


Many metals form hydroxide precipitates, which have characteristic colours.

Precipitates of hydoxides

For example, when sodium hydroxide solution is added to a solution of iron(III) chloride, the reaction produces a brown precipitate of iron(III) hydroxide.

+ +

FeCl3 (aq) 3NaOH (aq) Fe(OH)3 (s) ++ 3NaCl (aq)

iron(III)chloride

sodiumhydroxide

iron(III)hydroxide

sodiumchloride


Identifying precipitates


Identifying metals


Precipitation – true or false?


Glossary

acid – A substance that releases H+ ions in solution.alkali – A substance that releases OH- ions in solution.base – Any substance that reacts with an acid.decomposition – A type of reaction in which a compound

is broken down into two or more substances.neutralization – A type of reaction in which an acid reacts

with a base to produce a salt.precipitate – A solid, insoluble product of a reaction.precipitation – A type of reaction in which two aqueous

solutions react to form an insoluble product.salt – A substance formed when an acid reacts with a base.titration – A method of indicating when an undetectable

reaction, such as neutralization, is complete.


Anagrams


Completing equations


Multiple-choice quiz

How are salts made and named?

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