Structure of salts and nomenclature

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Link to the lesson

Before you start you should know

that hydroxides react with acids;
that as the result of the reaction of sodium hydroxide with hydrochloric acid salt – sodium chloride – and water are formed;
that the neutralization reaction is a transformation in which the hydroxide anions combine with the hydrogen cations to form neutral water molecules.

You will learn

to describe the structure of salt;
to create salt names;

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Nagranie dostępne na portalu epodreczniki.pl

Nagranie dźwiękowe abstraktu

What are salts?

Salt is the common name of cooking salt, whose main ingredient is sodium chloride. However, this is not the only compound that can be determined by this name. It also applies to other substances, e.g. potassium chloride, copper mono‑sulphide. SaltssaltsSalts are a huge number of compounds with some characteristic features.

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Zdjęcie przedstawia kryształ halit o kształcie sześcianu. Jego struktura charakteryzuje się regularnym ułożeniem jonów Cl minus i z wypełnieniem wolnych przestrzeni przez Na plus. Halit ma kolor półprzezroczysty i szarym odcieniem — Sodium chloride is the main component of the mineral called halite.
Source: domena publiczna.

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Zdjęcie przedstawia minerał sól kamienną. Sól jest skałą osadową. Na zdjęciu ściana w jaskini pokryta kryształami soli — In addition to sodium chloride, other salts are also found in rock salt, e.g. potassium chloride.

Are all salts salty?

Not every salt is salty. There are tasteless salts (e.g. calcium carbonate). There are also salts that are described in the literature as spicy or refreshing (potassium nitrate). Magnesium sulphate due to its taste has been called bitter salt.

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Zdjęcie przedstawia szalkę Petriego, na której znajdują się kryształy azotanu pięć potasu. Mają one kształt wielu cienkich igieł poukładanych w skupiska. Kryształy mają biały kolor — Potassium nitrate crystals after evaporation of water from the solution
Source: Adam Rędzikowski, [online], dostępny w internecie: https://pl.wikipedia.org/wiki/Azotan_potasu#/media/File:Potassium_nitrate_crystals.jpg [dostęp 2018.03.28 r.].

Salts are built of metal cations (or ammonium cation as following ${NH}_{4}^{+}$ ) and anions of acid residue. General formula is:

${Me}_{m} R_{n}$

where:

$Me$ – symbol of metal, which cation is in salt,
$R$ – symbol of acid residue, which anion creates salt,
$n, m$ – stoichiometric indices determined on the basis of the valence of the metal and the acid residue.

The valency of the acid residue is equal to the absolute value of its ion charge, e.g. the valence of the sulphate ion, ${SO}_{4}^{2-}$ , equals 2.

Salts are made of ions, so they belong to the group of ionic compounds. As solids they form crystals with an ordered structure.

Molecular formulas of salts

Task 1

Look at the table with the molecular formulas of the selected salts. How these formulas are created?

Type of anion	Type of cation	Molecular formula of salt composed of indicated ions
ClIndeks górny -	NaIndeks górny +	NaCl
	CaIndeks górny 2+	CaClIndeks dolny 2
	AlIndeks górny 3+	AlClIndeks dolny 3
${SO}_{4}^{2 -}$	NaIndeks górny +	NaIndeks dolny 2SOIndeks dolny 4
	CaIndeks górny 2+	CaSOIndeks dolny 4
	AlIndeks górny 3+	${Al}_{2} ({SO}_{4})_{3}$
${PO}_{4}^{3 -}$	NaIndeks górny +	NaIndeks dolny 3POIndeks dolny 4
	CaIndeks górny 2+	${Ca}_{3} ({PO}_{4})_{2}$
	AlIndeks górny 3+	AlPOIndeks dolny 4

Names of salts

The salt names consist of two parts: the first refers to the type of the acid residue, the second refers to the metal. The part derived from the name of the acid residue has an ending the tip - ate (-ite) (in the case of salts of oxoacids) or - ide (for salts of hydracids). For example, salts derived from sulphuric or sulphurous acid will be called sulphates/sulphites, and hydrogen sulphide derivatives – sulphides. Sometimes the names of salts include the valence of the non‑metal, which is part of the acid residue, and metal.

Type of acid	Molecular formula of acid	Name of acid	Ion of acid residue	Second part of name of the salt, the derivative of the acid
oxyacid	$H_{2} {SO}_{4}$	sulphuric acid	${SO}_{4}^{2-}$	sulphate
	$H_{2} {SO}_{3}$	sulphurous acid	${SO}_{3}^{2-}$	sulphite
	$H_{2} {CO}_{3}$	carbonic acid	${CO}_{3}^{2-}$	carbonate
	$H {NO}_{3}$	nitric acid	${NO}_{3}^{-}$	nitrate
	$H_{3} {PO}_{4}$	phosphoric acid	${PO}_{4}^{3-}$	phosphate
hydracid	$HCl$	hydrochloric acid	${Cl}^{-}$	chloride
hydracid	$H_{2} S$	hydrosulphuric acid	$S^{2-}$	sulphide

First part is the name of the metal. If it can have different valency it can be sometimes added to the name. So, iron trichloride (iron(III) chloride), ${FeCl}_{3}$ , is other substance than iron dichloride (iron(II) chloride), ${FeCl}_{2}$ .

Cation Anion	${SO}_{4}^{2-}$	${SO}_{3}^{2-}$	${CO}_{3}^{2-}$	${NO}_{3}^{-}$	${PO}_{4}^{3-}$	${Cl}^{-}$	$S^{2-}$
${Na}^{+}$	${Na}_{2} {SO}_{4}$ sodium sulphate	${Na}_{2} {SO}_{3}$ sodium sulphite	${Na}_{2} {CO}_{3}$ sodium carbonate	$Na {NO}_{3}$ sodium nitrate	${Na}_{3} {PO}_{4}$ sodium phosphate	$NaCl$ sodium chloride	${Na}_{2} S$ sodium sulphide
$K^{+}$	$K_{2} {SO}_{4}$ potassium sulphate	$K_{2} {SO}_{3}$ potassium sulphite	$K_{2} {CO}_{3}$ potassium carbonate	$K {NO}_{3}$ potassium nitrate	$K_{3} {PO}_{4}$ potassium phosphate	$KCl$ potassium chloride	$K_{2} S$ potassium sulphide
${Ca}^{2+}$	$Ca {SO}_{4}$ calcium sulphate	$Ca {SO}_{3}$ calcium sulphite	$Ca {CO}_{3}$ calcium carbonate	$Ca {(NO}_{3})_{2}$ calcium nitrate	${Ca}_{3} {(PO}_{4})_{2}$ calcium phosphate	${CaCl}_{2}$ calcium chloride	$CaS$ calcium sulphide
${Mg}^{2+}$	$Mg {SO}_{4}$ magnesium sulphate	$Mg {SO}_{3}$ magnesium sulphite	$Mg {CO}_{3}$ magnesium carbonate	$Mg {(NO}_{3})_{2}$ magnesium nitrate	${Mg}_{3} {(PO}_{4})_{2}$ magnesium phosphate	${MgCl}_{2}$ magnesium chloride	$MgS$ magnesium sulphide
${Fe}^{3+}$	${Fe}_{2} {(SO}_{4})_{3}$ Iron(III) sulphate	compound made of these ions does not exist	compound made of these ions does not exist	$Fe {(NO}_{3})_{3}$ Iron(III) nitrate	$Fe {PO}_{4}$ Iron(III) phosphate	${FeCl}_{3}$ Iron(III) chloride	${Fe}_{2} S_{3}$ Iron(III) sulphide
${Al}^{3+}$	${Al}_{2} {(SO}_{4})_{3}$ aluminium sulphate	compound made of these ions does not exist	compound made of these ions does not exist	$Al {(NO}_{3})_{3}$ alumiumiun nitrate	$Al {PO}_{4}$ aluminium phosphate	${AlCl}_{3}$ alumiunium chloride	${Al}_{2} S_{3}$ the compound consisting of these ions is unstable

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Exercise 1

Check what you remember about salts. Complete the sentences with the words below.

anion, valence, acid residue, charge, ionic, acidic residue, valence, cation, ate/ite, metal, lower, non-metal, ide

Salts are substances of ............................ structure, composed of ............................ cations and anions of ............................. The salt formulas are determined on the basis of the ............................ of the metal and the acid residue. The valence of the metal equals the ............................ of the ............................ it creates, and the valence of the ............................ equals the charge of the ............................ formed by it. These numbers are inscribed on the cross as ............................ indexes. If the valences of ions are equal, then the corresponding indexes are equal to 1, and the number 1 in the formula of total salts is omitted. The salts of hydracids have the ending - ............................, and the salts of oxoacids have the ending - ............................. When creating a systematic name of salt, the ............................ of the metal and ............................ belonging to the acidic residue should be given if these elements in their compounds have various valences, e.g. copper(II) phosphate.

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Exercise 2

Add salts to the correct group:

Lead(II) nitrate, Calcium carbonate, Calcium nitrate, Potassium phosphate, Tin(II) sulphide, Aluminium carbonate, barium sulphate, Iron(III) chloride, Silver chloride, Barium sulphide, Sodium sulphide, magnesium phosphate, Iron(III) sulphate, Potassium sulphite, Aluminium chloride

Salts of hydracids:
Salts of oxoacids:

Summary

Salts are a group of ionic chemical compounds that consist of metal cations (or an ammonium cation of the formula ${NH}_{4}^{+}$ ) and anions of the acid residue.
The name of the salt consists of two parts: the name of the acid residue and the name of the metal. When the salt comes from the oxyacid, the ending is - ate/ite, and when from hydracid – ending is - ide.
Sometimes in the salt name the valence of the metal is included, which can take on a different numerical value.

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Source: GroMar Sp. z o.o., licencja: CC BY-SA 3.0.

Keywords

Salts, salt, molecular formula of salt, nomenclature of salts, anion, cation

Glossary

salts

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