1.(a) A salt is an ionic compound formed when the cation from a base combine with the anion derived from an acid.
A salt is therefore formed when the hydrogen ions in an acid are replaced wholly/fully or partially/partly, directly or indirectly by a metal or ammonium radical.
(b) The number of ionizable/replaceable hydrogen in an acid is called basicity of an acid.
Some acids are therefore:
(i)monobasic acids generally denoted HX e.g.
HCl, HNO3,HCOOH,CH3COOH.
(ii)dibasic acids ; generally denoted H2X e.g.
H2SO4, H2SO3, H2CO3,HOOCOOH.
(iii)tribasic acids ; generally denoted H3X e.g.
H3PO4.
(c) Some salts are normal salts while others are acid salts.
(i)A normal salt is formed when all the ionizable /replaceable hydrogen in an acid is replaced by a metal or metallic /ammonium radical.
(ii)An acid salt is formed when part/portion the ionizable /replaceable hydrogen in an acid is replaced by a metal or metallic /ammonium radical.
Table showing normal and acid salts derived from common acids
| Acid name | Chemical formula | Basicity | Normal salt | Acid salt |
| Hydrochloric acid | HCl | Monobasic | Chloride(Cl–) | None |
| Nitric(V)acid | HNO3 | Monobasic | Nitrate(V)(NO3–) | None |
| Nitric(III)acid | HNO2 | Monobasic | Nitrate(III)(NO2–) | None |
| Sulphuric(VI)acid | H2SO4 | Dibasic | Sulphate(VI) (SO42-) | Hydrogen sulphate(VI) (HSO4–) |
| Sulphuric(IV)acid | H2SO3 | Dibasic | Sulphate(IV) (SO32-) | Hydrogen sulphate(IV) (HSO3–) |
| Carbonic(IV)acid | H2CO3 | Dibasic | Carbonate(IV)(CO32-) | Hydrogen carbonate(IV) (HCO3–) |
| Phosphoric(V) acid | H3PO4 | Tribasic | Phosphate(V)(PO43-) | Dihydrogen phosphate(V) (H2PO42-) Hydrogen diphosphate(V) (HP2O42-) |
The table below show shows some examples of salts.
| Base/alkali | Cation | Acid | Anion | Salt | Chemical name of salts |
| NaOH | Na+ | HCl | Cl– | NaCl | Sodium(I)chloride |
| Mg(OH)2 | Mg2+ | H2SO4 | SO42- | MgSO4 Mg(HSO4)2 | Magnesium sulphate(VI) Magnesium hydrogen sulphate(VI) |
| Pb(OH)2 | Pb2+ | HNO3 | NO3– | Pb(NO3)2 | Lead(II)nitrate(V) |
| Ba(OH)2 | Ba2+ | HNO3 | NO3– | Ba(NO3)2 | Barium(II)nitrate(V) |
| Ca(OH)2 | Ba2+ | H2SO4 | SO42- | MgSO4 | Calcium sulphate(VI) |
| NH4OH | NH4+ | H3PO4 | PO43- | (NH4 )3PO4 (NH4 )2HPO4 NH4 H2PO4 | Ammonium phosphate(V) Diammonium phosphate(V) Ammonium diphosphate(V) |
| KOH | K+ | H3PO4 | PO43- | K3PO4 | Potassium phosphate(V) |
| Al(OH)3 | Al3+ | H2SO4 | SO42- | Al2(SO4)2 | Aluminium(III)sulphate(VI) |
| Fe(OH)2 | Fe2+ | H2SO4 | SO42- | FeSO4 | Iron(II)sulphate(VI) |
| Fe(OH)3 | Fe3+ | H2SO4 | SO42- | Fe2(SO4)2 | Iron(III)sulphate(VI) |
(d) Some salts undergo hygroscopy, deliquescence and efflorescence.
(i) Hygroscopic salts /compounds are those that absorb water from the atmosphere but do not form a solution.
Some salts which are hygroscopic include anhydrous copper(II)sulphate(VI), anhydrous cobalt(II)chloride, potassium nitrate(V) common table salt.
(ii)Deliquescent salts /compounds are those that absorb water from the atmosphere and form a solution.
Some salts which are deliquescent include: Sodium nitrate(V),Calcium chloride, Sodium hydroxide, Iron(II)chloride, Magnesium chloride.
(iii)Efflorescent salts/compounds are those that lose their water of crystallization to the atmosphere.
Some salts which effloresces include: sodium carbonate decahydrate, Iron(II)sulphate(VI)heptahydrate, sodium sulphate (VI)decahydrate.
(e)Some salts contain water of crystallization.They are hydrated.Others do not contain water of crystallization. They are anhydrous.
Table showing some hydrated salts.
| Name of hydrated salt | Chemical formula |
| Copper(II)sulphate(VI)pentahydrate | CuSO4.5H2O |
| Aluminium(III)sulphate(VI)hexahydrate | Al2 (SO4) 3.6H2O |
| Zinc(II)sulphate(VI)heptahydrate | ZnSO4.7H2O |
| Iron(II)sulphate(VI)heptahydrate | FeSO4.7H2O |
| Calcium(II)sulphate(VI)heptahydrate | CaSO4.7H2O |
| Magnesium(II)sulphate(VI)heptahydrate | MgSO4.7H2O |
| Sodium sulphate(VI)decahydrate | Na2SO4.10H2O |
| Sodium carbonate(IV)decahydrate | Na2CO3.10H2O |
| Potassium carbonate(IV)decahydrate | K2CO3.10H2O |
| Potassium sulphate(VI)decahydrate | K2SO4.10H2O |
(f)Some salts exist as a simple salt while some as complex salts. Below are some complex salts.
Table of some complex salts
| Name of complex salt | Chemical formula | Colour of the complex salt |
| Tetraamminecopper(II)sulphate(VI) | Cu(NH3) 4 SO4 H2O | Royal/deep blue solution |
| Tetraamminezinc(II)nitrate(V) | Zn(NH3) 4 (NO3 )2 | Colourless solution |
| Tetraamminecopper(II) nitrate(V) | Cu(NH3) 4 (NO3 )2 | Royal/deep blue solution |
| Tetraamminezinc(II)sulphate(VI) | Zn(NH3) 4 SO4 | Colourless solution |
(g)Some salts exist as two salts in one. They are called double salts.
Table of some double salts
| Name of double salts | Chemical formula |
| Trona(sodium sesquicarbonate) | Na2CO3 NaHCO3.2H2O |
| Ammonium iron(II)sulphate(VI) | FeSO4(NH4) 2SO4.2H2O |
| Ammonium aluminium(III)sulphate(VI) | Al2(SO4) 3(NH4) 2SO4.H2O |
(h)Some salts dissolve in water to form a solution. They are said to be soluble. Others do not dissolve in water. They form a suspension/precipitate in water.
Table of solubility of salts
| Soluble salts | Insoluble salts |
| All nitrate(V)salts | |
| All sulphate(VI)/SO42- salts except | Barium(II) sulphate(VI)/BaSO4 Calcium(II) sulphate(VI)/CaSO4 Lead(II) sulphate(VI)/PbSO4 |
| All sulphate(IV)/SO32- salts except | Barium(II) sulphate(IV)/BaSO3 Calcium(II) sulphate(IV)/CaSO3 Lead(II) sulphate(IV)/PbSO3 |
| All chlorides/Cl– except | Silver chloride/AgCl Lead(II)chloride/PbCl2(dissolves in hot water) |
| All phosphate(V)/PO43- | |
| All sodium,potassium and ammonium salts | |
| All hydrogen carbonates/HCO3– | |
| All hydrogen sulphate(VI)/ HSO4– | |
| Sodium carbonate/Na2CO3, potassium carbonate/ K2CO3, ammonium carbonate (NH4) 2CO3 | except All carbonates |
| All alkalis(KOH,NaOH, NH4OH) | except All bases |
13 Salts can be prepared in a school laboratory by a method that uses its solubility in water.
- Soluble salts may be prepared by using any of the following methods:
(i)Direct displacement/reaction of a metal with an acid.
By reacting a metal higher in the reactivity series than hydrogen with a dilute acid,a salt is formed and hydrogen gas is evolved.
Excess of the metal must be used to ensure all the acid has reacted.
When effervescence/bubbling /fizzing has stopped ,excess metal is filtered.
The filtrate is heated to concentrate then allowed to crystallize.
Washing with distilled water then drying between filter papers produces a sample crystal of the salt. i.e.
M(s) + H2X -> MX(aq) + H2(g)
Examples
Mg(s) + H2SO4(aq) -> MgSO4 (aq) + H2(g)
Zn(s) + H2SO4(aq) -> ZnSO4 (aq) + H2(g)
Pb(s) + 2HNO3(aq) -> Pb(NO3) 2(aq) + H2(g)
Ca(s) + 2HNO3(aq) -> Ca(NO3) 2(aq) + H2(g)
Mg(s) + 2HNO3(aq) -> Mg(NO3) 2(aq) + H2(g)
Mg(s) + 2HCl(aq) -> MgCl 2(aq) + H2(g)
Zn(s) + 2HCl(aq) -> ZnCl 2(aq) + H2(g)
(ii)Reaction of an insoluble base with an acid
By adding an insoluble base (oxide/hydroxide) to a dilute acid until no more dissolves, in the acid, a salt and water are formed. Excess of the base is filtered off. The filtrate is heated to concentrate, allowed to crystallize then washed with distilled water before drying between filter papers e.g.
PbO(s) + 2HNO3(aq) -> Pb(NO3) 2(aq) + H2O (l)
Pb(OH)2(s) + 2HNO3(aq) -> Pb(NO3) 2(aq) + 2H2O (l)
CaO (s) + 2HNO3(aq) -> Ca(NO3) 2(aq) + H2O (l)
MgO (s) + 2HNO3(aq) -> Mg(NO3) 2(aq) + H2O (l)
MgO (s) + 2HCl(aq) -> MgCl 2(aq) + H2O (l)
ZnO (s) + 2HCl(aq) -> ZnCl 2(aq) + H2O (l)
Zn(OH)2(s) + 2HNO3(aq) -> Zn(NO3) 2(aq) + 2H2O (l)
CuO (s) + 2HCl(aq) -> CuCl 2(aq) + H2O (l)
CuO (s) + H2SO4(aq) -> CuSO4(aq) + H2O (l)
Ag2O(s) + 2HNO3(aq) -> 2AgNO3(aq) + H2O (l)
Na2O(s) + 2HNO3(aq) -> 2NaNO3(aq) + H2O (l)
(iii) Reaction of insoluble /soluble carbonate /hydrogen carbonate with an acid.
By adding an excess of a soluble /insoluble carbonate or hydrogen carbonate to a dilute acid, effervescence /fizzing/bubbling out of carbon (IV) oxide gas shows the reaction is taking place. When effervescence /fizzing/bubbling out of the gas is over, excess of the insoluble carbonate is filtered off. The filtrate is heated to concentrate, allowed to crystallize then washed with distilled water before drying between filter paper papers e.g.
PbCO3 (s) + 2HNO3(aq) -> Pb(NO3) 2(aq) + H2O (l)+ CO2(g)
ZnCO3 (s) + 2HNO3(aq) -> Zn(NO3) 2(aq) + H2O (l)+ CO2(g)
CaCO3 (s) + 2HNO3(aq) -> Ca(NO3) 2(aq) + H2O (l)+ CO2(g)
MgCO3 (s) + H2SO4(aq) -> MgSO4(aq) + H2O (l)+ CO2(g)
Cu CO3 (s) + H2SO4(aq) -> CuSO4(aq) + H2O (l) + CO2(g)
Ag2CO3 (s) + 2HNO3(aq) -> 2AgNO3(aq) + H2O (l) + CO2(g)
Na2CO3 (s) + 2HNO3(aq) -> 2NaNO3(aq) + H2O (l) + CO2(g)
K2CO3 (s) + 2HCl(aq) -> 2KCl(aq) + H2O (l) + CO2(g)
NaHCO3 (s) + HNO3(aq) -> NaNO3(aq) + H2O (l) + CO2(g)
KHCO3 (s) + HCl(aq) -> KCl(aq) + H2O (l) + CO2(g)
(iv) neutralization/reaction of soluble base/alkali with dilute acid
By adding an acid to a burette into a known volume of an alkali with 2-3 drops of an indicator, the colour of the indicator changes when the acid has completely reacted with an alkali at the end point. The procedure is then repeated without the indicator .The solution mixture is then heated to concentrate, allowed to crystallize ,washed with distilled water before drying with filter papers. e.g.
NaOH (aq) + HNO3(aq) -> NaNO3(aq) + H2O (l)
KOH (aq) + HNO3(aq) -> KNO3(aq) + H2O (l)
KOH (aq) + HCl(aq) -> KCl(aq) + H2O (l)
2KOH (aq) + H2SO4(aq) -> K2SO4(aq) + 2H2O (l)
2 NH4OH (aq) + H2SO4(aq) -> (NH4)2SO4(aq) + 2H2O (l)
NH4OH (aq) + HNO3(aq) -> NH4NO3(aq) + H2O (l)
(iv) Direct synthesis/combination.
When a metal burn in a gas jar containing a non metal , the two directly combine to form a salt. e.g.
2Na(s) + Cl2(g) -> 2NaCl(s)
2K(s) + Cl2(g) -> 2KCl(s)
Mg(s) + Cl2(g) -> Mg Cl2 (s)
Ca(s) + Cl2(g) -> Ca Cl2 (s)
Some salts once formed undergo sublimation and hydrolysis. Care should be taken to avoid water/moisture into the reaction flask during their preparation. Such salts include aluminum (III) chloride (AlCl3) and iron (III) chloride (FeCl3)
1. Heated aluminium foil reacts with chlorine to form aluminium(III)chloride that sublimes away from the source of heating then deposited as solid again
2Al(s) + 3Cl2(g) -> 2AlCl3 (s/g)
Once formed aluminium(III)chloride hydrolyses/reacts with water vapour / moisture present to form aluminium hydroxide solution and highly acidic fumes of hydrogen chloride gas.
AlCl3(s)+ 3H2 O(g) -> Al(OH)3 (aq) + 3HCl(g)
2. Heated iron filings reacts with chlorine to form iron(III)chloride that sublimes away from the source of heating then deposited as solid again
2Fe(s) + 3Cl2(g) -> 2FeCl3 (s/g)
Once formed , aluminium(III)chloride hydrolyses/reacts with water vapour / moisture present to form aluminium hydroxide solution and highly acidic fumes of hydrogen chloride gas.
FeCl3(s)+ 3H2 O(g) -> Fe(OH)3 (aq) + 3HCl(g)
(b)Insoluble salts can be prepared by reacting two suitable soluble salts to form one soluble and one insoluble. This is called double decomposition or precipitation. The mixture is filtered and the residue is washed with distilled water then dried.
CuSO4(aq) + Na2CO3 (aq) -> CuCO3 (s) + Na2 SO4(aq)
BaCl2(aq) + K2SO4 (aq) -> BaSO4 (s) + 2KCl (aq)
Pb(NO3)2(aq) + K2SO4 (aq) -> PbSO4 (s) + 2KNO3 (aq)
2AgNO3(aq) + MgCl2 (aq) -> 2AgCl(s) + Mg(NO3)2 (aq)
Pb(NO3)2(aq) + (NH4) 2SO4 (aq) -> PbSO4 (s) + 2NH4NO 3(aq)
BaCl2(aq) + K2SO3 (aq) -> BaSO3 (s) + 2KCl (aq)
14. Salts may lose their water of crystallization, decompose, melt or sublime on heating on a Bunsen burner flame.
The following shows the behavior of some salts on heating gently /or strongly in a laboratory school burner:
(a)effect of heat on chlorides
All chlorides have very high melting and boiling points and therefore are not affected by laboratory heating except ammonium chloride. Ammonium chloride sublimes on gentle heating. It dissociate into the constituent ammonia and hydrogen chloride gases on strong heating.
NH4Cl(s) NH4Cl(g) NH3(g) + HCl(g)
(sublimation) (dissociation)
(b)effect of heat on nitrate(V)
(i) Potassium nitrate(V)/KNO3 and sodium nitrate(V)/NaNO3 decompose on heating to form Potassium nitrate(III)/KNO2 and sodium nitrate(III)/NaNO2 and producing Oxygen gas in each case.
2KNO3 (s) -> 2KNO2(s) + O2(g)
2NaNO3 (s) -> 2NaNO2(s) + O2(g)
(ii)Heavy metal nitrates(V) salts decompose on heating to form the oxide and a mixture of brown acidic nitrogen(IV)oxide and oxygen gases. e.g.
2Ca(NO3)2 (s) -> 2CaO(s) + 4NO2(g) + O2(g)
2Mg(NO3)2(s) -> 2MgO(s) + 4NO2(g) + O2(g)
2Zn(NO3)2(s) -> 2ZnO(s) + 4NO2(g) + O2(g)
2Pb(NO3)2(s) -> 2PbO(s) + 4NO2(g) + O2(g)
2Cu(NO3)2(s) -> 2CuO(s) + 4NO2(g) + O2(g)
2Fe(NO3)2(s) -> 2FeO(s) + 4NO2(g) + O2(g)
(iii)Silver(I)nitrate(V) and mercury(II) nitrate(V) are lowest in the reactivity series. They decompose on heating to form the metal(silver and mercury)and the Nitrogen(IV)oxide and oxygen gas. i.e.
2AgNO3(s) -> 2Ag (s) + 2NO2(g) + O2(g)
2Hg(NO3)2 (s) -> 2Hg (s) + 4NO2(g) + O2(g)
(iv)Ammonium nitrate(V) and Ammonium nitrate(III) decompose on heating to Nitrogen(I)oxide(relights/rekindles glowing splint) and nitrogen gas respectively.Water is also formed.i.e.
NH4NO3(s) -> N2O (g) + H2O(l)
NH4NO2(s) -> N2 (g) + H2O(l)
(c) effect of heat on nitrate(V)
Only Iron(II)sulphate(VI), Iron(III)sulphate(VI) and copper(II)sulphate(VI) decompose on heating. They form the oxide, and produce highly acidic fumes of acidic sulphur(IV)oxide gas.
2FeSO4 (s) -> Fe2O3(s) + SO3(g) + SO2(g)
Fe2(SO4) 3(s) -> Fe2O3(s) + SO3(g)
CuSO4 (s) -> CuO(s) + SO3(g)
(d) effect of heat on carbonates(IV) and hydrogen carbonate(IV).
(i)Sodium carbonate(IV)and potassium carbonate(IV)do not decompose on heating.
(ii)Heavy metal nitrate(IV)salts decompose on heating to form the oxide and produce carbon(IV)oxide gas.Carbon (IV)oxide gas forms a white precipitate when bubbled in lime water. The white precipitate dissolves if the gas is in excess. e.g. CuCO3 (s) -> CuO(s) + CO2(g)
CaCO3 (s) -> CaO(s) + CO2(g)
PbCO3 (s) -> PbO(s) + CO2(g)
FeCO3 (s) -> FeO(s) + CO2(g)
ZnCO3 (s) -> ZnO(s) + CO2(g)
(iii)Sodium hydrogen carbonate(IV) and Potassium hydrogen carbonate(IV)decompose on heating to give the corresponding carbonate (IV) and form water and carbon(IV)oxide gas. i.e.
2NaHCO 3(s) -> Na2CO3(s) + CO2(g) + H2O(l)
2KHCO 3(s) -> K2CO3(s) + CO2(g) + H2O(l)
(iii) Calcium hydrogen carbonate (IV) and Magnesium hydrogen carbonate(IV) decompose on heating to give the corresponding carbonate (IV) and form water and carbon(IV)oxide gas. i. e.
Ca(HCO3) 2(aq) -> CaCO3(s) + CO2(g) + H2O(l)
Mg(HCO3) 2(aq) –
Name…………………………………………….Class…………….Adm No….…..
CHEMISTRY Practice balancing Chemical equations
Date done………………..Date marked……………….Date revised……..…..
Balance the following chemical equations in the spaces provided on the question paper.
Ca (OH)2(aq) + Cl2(g) → CaCl2(aq) + CaOCl2(aq) + H2O(l)
(Cold/dilute) (Calcium Chlorate(I))
Ca (OH)2(aq) +Cl2(g) → CaCl2(aq) +Ca(ClO3)2(aq) +H2O(l)
(Hot/Concentrated) (Calcium Chlorate(V))
NaOH + Cl2(g) → NaClO3 (aq) + NaCl(aq) + 3H2O(l) (Sodium Chlorate (V)
KOH + Cl2(g) → KClO3 (aq)+ KCl(aq) + H2O(l) (Potassium Chlorate (V)
Ca (OH)2(aq)+ Cl2(g) → CaCl2(aq)+CaOCl2(aq)+ H2O(l)
(Cold/dilute) (Calcium Chlorate(I))
NaCl(s) + H2SO4(l) -> NaHSO4(aq) + HCl(g)
KCl(s) + H2SO4(l) -> KHSO4(aq) + HCl(g)
CaO(s) + 2H2O(l) -> Ca(OH)2(aq) + H2O(l)
Ca(OH)2(aq) + Cl2 (g) -> CaOCl2(aq) + H2O(l)
HCl(s) + NH3(g) -> NH4Cl(s)
Fe(s) + 2HCl(aq) -> FeCl2(aq + H2 (g)
Zn(s) + 2HCl(aq) -> ZnCl2(aq + H2 (g)
Mg(s) + 2HCl(aq) -> MgCl2(aq + H2 (g)
2Li(s) + 2HCl(aq) -> 2LiCl(aq + H2 (g)
Ca (OH)2(aq) +Cl2(g) → CaCl2(aq) +Ca(ClO3)2(aq) +H2O(l)
(Hot/Concentrated) (Calcium Chlorate(V))
CaCO3 (s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)
(Colourless solution)
1.Chemical equation:
Ionic equation:
CaCO3 (s) + 2H+(aq) → Ca2+(aq) + H2O(l) + CO2(g)
2.Chemical equation:
Ag2CO3 (s) + 2HCl(aq) → 2AgCl(s) + H2O(l) + CO2(g)
(Coats/Cover Ag2CO3)
3.Chemical equation:
NaHCO3 (s) + HCl(aq) → NaCl(aq) +H2O(l) +CO2(g)
(colourless solution)
Ionic equation:
NaHCO3 (s) + H+(aq) → Na+(aq) + H2O(l) + CO2(g)
4.Chemical equation:
CuCO3 (s) + 2HCl(aq) → CuCl2(aq)+ H2O(l) + CO2(g)
(Blue Solution)
Ionic equation:
CuCO3 (s) + 2H+(aq) →Cu2+(aq) + H2O(l) + CO2(g)
5.Chemical equation:
FeCO3 (s) + 2HCl(aq) →FeCl2(aq)+ H2O(l) + CO2(g)
(green solution)
Ionic equation:
FeCO3 (s) + 2H+(aq) → Fe2+(aq) + H2O(l)+ CO2(g)
6.Chemical equation:
(NH4) 2CO3 (s)+2HCl(aq) →2NH4 Cl(aq)+H2O(l)+ CO2(g)
Ionic equation:
(NH4) 2CO3 (s)+2H+ (aq) →2NH4 + (aq)+H2O(l)+ CO2(g)
Chemical equation:
NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)
Ionic equation:
OH–(aq) + H+(aq) → H2O(l)
Chemical equation:
KOH(aq) + HCl(aq) → KCl(aq) + H2O(l)
Ionic equation:
OH–(aq) + H+(aq) → H2O(l)
Chemical equation:
NH4OH(aq) + HCl(aq) → NH4Cl(aq) + H2O(l)
Ionic equation:
OH–(aq) + H+(aq) → H2O(l)
CuO(s) + 2HCl (aq) → CaCl2(aq) + H2O(l)
Ionic equation:
CuO(s) + 2H+(aq) → Cu2+(aq) + H2O(l)
Chemical equation:
CaO(s) + HCl (aq) → CaCl2 (aq) + H2O (l)
Ionic equation:
CuO(s) + 2H+(aq) → Cu2+(aq) + H2O(l)
Chemical equation:
PbO(s) + 2HCl (aq) → PbCl2 (s) + H2O (l)
No ionic equation
Chemical equation:
ZnO(s) + HCl (aq) → ZnCl2 (aq) + H2O (l)
Ionic equation:
ZnO(s) + 2H+(aq) → Zn2+(aq) + H2O(l)
H2(g) + Cl2(g) → 2HCl(g)
HCl(g) + (aq) → HCl(aq)
NH4Cl(s) -> HCl(g) + NH3 (g)
