Making Salts

Soluble salt

Acid + reactive metal

Acid + base

Acid + carbonate

Acid + excess insoluble solid

Acid + alkali titration

Insoluble saltPrecipitation

Direct combination

Neutralisation of:

hydrochloric acid gives a chloride

sulphuric acid gives a sulphate

nitric acid gives a nitrate

Acid + metal salt + hydrogen

Acid + base* salt + water

Acid + carbonate salt + water + carbon dioxide

*Base: A metal oxide or metal hydroxide.

An alkali is a water-soluble base.

Reactions of acids

Salts

A salt is an ionic compound which is neither an acid (containing H+) or a base (containing O2- or OH-). A salt is formed whenever an acid is neutralised.

Ionic compounds

Acids, containing H+

Bases, containing OH- or O2-

Salts

Uses of Salts

• Plant fertilisers (NPK)– (NH4)2SO4, NH4NO3, KH2PO4, …….

• Food flavour and preservation– NaCl, KCl, KNO3…….

• In toothpaste– NaF

• Photographic film– AgCl, AgBr

Salts are important also in:

• Proteins and enzymes– The molecules that carry out the chemical

reactions of life

• DNA and RNA– the molecules of inheritance

• Transmission of electrical impulses along nerves

Neutralisation of:

hydrochloric acid gives a chloride (containing Cl-)

sulphuric acid gives a sulphate (containing SO42-)

nitric acid gives a nitrate (containing NO3-)

Acid + metal salt + hydrogen

Acid + base salt + water

Acid + carbonate salt + water + carbon dioxide

Acid Neutralisation reactions

Acid + alkali salt + water

HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l)

Titration of acid against alkali for soluble salts of group 1 metals and ammonium

5 cm3 sodium hydroxide solution was measured using a pipette and transferred to the conical flask. 2 drops of methyl orange indicator were added. Hydrochloric acid was poured into the burette and the starting reading was recorded. The acid was added to the sodium hydroxide, drop by drop, until the indicator turned from yellow to orange (or red). Charcoal was added to the mixture to absorb the indicator and was removed by filtration. Water was evaporated from the filtrate, leaving sodium chloride crystals.

Methods of salt making (1)

Methods of salt making (2)

• Acid + excess insoluble solid– For all other soluble salts

– Solid is either a moderately reactive metal, a base or a carbonate

– Excess solid to react with all the acid• Removed by filtration

Methods of salt making (3)

• Precipitation reactions– To make insoluble salts– 2 solutions each containing one of the ions in

the salt are mixed.– Salt is precipitated– Salt is filtered, residue is washed on filter paper

and dried.

Methods of salt making (4)

• Direct combination of the elements

sodium (l) + chlorine (g) sodium chloride (s)

2 Na (l) + Cl2 (g) 2 NaCl (s)

aluminium (s) + bromine (l) aluminium bromide (s)

2 Al (s) + 3 Br2 (l) 2 Al Br3 (s)

barium hydroxide (aq) + nitric acid (aq)

Ba(OH)2 (aq) + HNO3 (aq)

barium nitrate (aq) + water (l)

Ba(NO3)2 (aq) + H2O (l)

2

2

(a)

Methods of salt making (1)

ammonium carbonate (aq) + sulphuric acid (aq)

(NH4)2CO3 (aq) + H2SO4 (aq)

ammonium sulphate (aq) + water (l) + carbon dioxide (g)

(NH4)2SO4 (aq) + H2O (l) + CO2 (g)

(b)

Methods of salt making (1)

ammonium hydroxide (aq) + nitric acid (aq)

NH4OH (aq) + HNO3 (aq)

ammonium nitrate (aq) + water (l)

NH4NO3 (aq) + H2O (l)

(c)

Methods of salt making (1)

potassium hydroxide (aq) + nitric acid (aq)

KOH (aq) + HNO3 (aq)

potassium nitrate (aq) + water (l)

KNO3 (aq) + H2O (l)

(e)

Methods of salt making (1)

Methods of salt making (2)

Acid + insoluble base salt + water

H2SO4 (aq) + CuO (s) CuSO4 (aq) + H2O (l)

calcium (s) + nitric acid (aq)

Ca (s) + HNO3 (aq)

calcium chloride(aq) + hydrogen (g)

Ca(NO3)2 (aq) + H2 (g)

2

(g)

Methods of salt making (2)

iron (s) + sulphuric acid (aq)

Fe (s) + H2SO4 (aq)

iron (II) sulphate (aq) + hydrogen (g)

FeSO4 (aq) + H2 (g)

(f)

Methods of salt making (2)

calcium carbonate (s) + nitric acid (aq)

CaCO3 (s) + HNO3 (aq)

calcium nitrate (aq) + water (l) + carbon dioxide (g)

Ca(NO3)2 (aq) + H2O (l) + CO2 (g)

2

(d)

Methods of salt making (2)

Acid + metal salt + hydrogen

Magnesium + hydrochloric acid magnesium chloride + hydrogen

Mg (s) + 2 HCl (aq) MgCl2 (aq) + H2 (g)

Mg (s) + 2 H+ 2 Cl- (aq) Mg2+ 2 Cl- (aq) + H2 (g)

copper + hydrochloric acid no reaction

Cu (s) + 2 HCl (aq)

Cu (s) + 2 H+ 2 Cl- (aq)

2 e-

Metal Reactivity Series

Potassium

Sodium

Lithium

Calcium

Magnesium

Zinc

Iron

Lead

Hydrogen

Copper

Silver

Gold

Platinum

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Acid + base salt + water

Sulphuric acid + copper oxide copper sulphate + water

H2SO4 (aq) + CuO (s) CuSO4 (aq) + H2O (l)

2 H+ SO42- (aq) + Cu2+ O2- (s) Cu2+ SO4

2- (aq) + H2O (l)

Sulphuric acid + copper hydroxide copper sulphate + water

H2SO4 (aq) + Cu(OH)2 (s) CuSO4 (aq) + 2 H2O (l)

2 H+ SO42- (aq) + Cu2+ 2 OH- (s) Cu2+ SO4

2- (aq) + 2 H2O (l)

Carbonic acid

• H2CO3 (aq)

• 2 H+ CO32- (aq)

• Present in fizzy drinks:H2CO3 (aq) CO2 (g) + H2O (l)

Acid +carbonate salt + water + carbon dioxide

Sulphuric acid + nickel carbonate nickel sulphate + water + carbon dioxide

H2SO4 (aq) + NiCO3 (s) NiSO4 (aq) + H2O (l) + CO2 (g)

2 H+ SO4

2- (aq) + Ni2+ CO32- (s) Ni2+ SO4

2- (aq) + H2CO3 (aq)+ H2O (l) + CO2 (g)