The theory of acids and bases is one of the most significant and helpful theories in chemistry. Most of the chemical reactions are categorized as acid-base reactions on the basis of the numerous theories which have been proposed.
Acids, bases and salts are compounds which we see, touch and employ in our everyday life at home. We employ common salt (that is, sodium chloride) on a daily basis in seasoning our food and sterilizing fruits and vegetables. We employ soap everyday in washing. Most of our food items have such compounds. Citrus fruits such as oranges and lemon have citric acid and lactic acid is present in milk. Sodium chloride, tetraoxosulphate (vi) acid and calcium trioxocarbonate (iv) and many others are significant raw materials in the chemical industry.
Water is one of the most plentiful chemical in nature and serves as a good solvent for numerous substances both ionic and covalent. Most of the acids dissolve in water to generate ions. This is as well true of bases and salts. They are electrolytes.
Definition, examples and preparation:
The acid can be stated as a compound:
a) Having hydrogen that can be substituted directly or indirectly via a metal.
b) That generates H+(H3O+) (hydroxonium ion) as the only positive ion in the aqueous solution.
H+ + H2O → H3O+
By the above statements HNO3, H2SO4, CH3COOH are acids. HNO3 and H2SO4 are at times termed to as inorganic or mineral acids whereas CH3COOH is termed to as an organic acid.
Acids are usually made by the given methods.
a) Action of water on acid anhydride (that is, acidic oxides) example:
H2O + SO2 → H2SO3 trioxosulphate (iv) acid
H2O + N2O5 → 2HNO3
b) Displacement of a more volatile acid from its salt.
2KCl + H2SO4 → K2SO4 + 2 HCl
c) Oxidation of the petroleum hydrocarbons:
2C3H8 + 4O2 → 3CH3COOH = 2H2O ethanoic acid.
d) Ethanoic acid can as well be made by the reaction of lead (ii) ethanoate by hydrogen sulphide.
Pb(CH3COO)2 + H2S → PbS(s) + 2CH3COOH
e) Direct reaction of the elements:
Example: H2 (g) + Cl2 (g) → 2 HCl (g)
The first reaction needs a catalyst. The catalyst employed is activated charcoal.
General properties of acids:
Acids usually encompass sour taste and are corrosive. The aqueous solution of an acid turns blue litmus paper red. The chemical properties comprise:
i) Reaction by metals to discharge hydrogen gas example: Zn + 2 HCl (aq) → ZnSO4 + H2
ii) Discharge CO2 from trioxocarbonates and hydrogentrioxocarbonates
Na2CO3 + 2HCl → 2 NaCl + CO2 + H2O
iii) Neutralize bases or alkalis to form only salt and water.
NaOH + HNO3 → NaNO3 + H2O
2NaOH + H2SO4 → Na2SO4 + 2H2O
CaO + 2HNO3 → Ca (NO3)2 + H2O
Uses of acids:
a) In manufacture of fertilizers, dyes, paints, detergents and salts.
b) They serve as electrolytes and solvents.
c) As preservatives.
d) For refining gasoline and lubricating oils.
e) In dissolving metals.
Definition illustrations and preparation:
A base is stated as a compound that generates OH- as the only negative ion in the aqueous solution. A more common definition is that a base neutralizes an acid to form only salt and water. A soluble base is termed as an alkali.
By the above statement CaO, NaOH and Ca(OH)2 are bases.
Bases are made up of by the listed methods.
i) Burning of metallic elements in the oxygen:
4Na + O2 → 2Na2O
2Mg + O2 → 2MgO
ii) Decomposition of the carbonates:
CaCO3 → CaO + CO2
CuCO3 → CuO + CO2
iii) Alkaline solutions are made by dissolving metallic oxides in the water:
Na2O + H2O → NaOH (aq)
CaO + H2O → Ca(OH)2 (aq)
iv) Direct reaction of the electropositive metals by water:
2Na + 2H2O → 2NaOH + H2
Ca + 2H2O → Ca(OH)2 + H2
Common properties of bases:
Bases encompass bitter taste and appear slippery or soapy to touch. Their solutions will turn red litmus blue. Bases release ammonia gas whenever warmed by an ammonium salt.
NH4Cl + NaOH → NaCl + NH3 + H2O
(NH4)2SO4 + 2 KOH → K2SO4 + 2NH3 + 2H2O
Uses of bases:
i) In the manufacture of dyes, paper, soap and so on.
ii) A few are employed as drying agents.
iii) Calcium hydroxide is employed for making mortar, plaster of paris (POP) and cement. This is as well employed in sugar refining and neutralization of soil acidity.
iv) Milk of magnesia is the suspension of magnesium hydroxide in water. This is employed as a mild laxative and antacid in tooth pastes to neutralize the acidity in the mouth.
Definition, illustrations and preparation:
A salt is made up of whenever a base is neutralized through an acid. A salt comprises of a metallic and acidic radicals.
Illustrations are NaCl, NaNO3, Na2SO4, KCl and so on.
Salts are made up of by the listed processes.
i) Neutralization of a base through an acid.
ii) Reaction of the acid through a reactive metal
Zn + H2SO4 → ZnSO4 + H2
iii) Reaction of an acid by a trioxocabonate (iv)
Na2CO3 + 2HCl → 2Nacl + H2O + CO2
iv) Reaction of soluble salts to generate an insoluble salt.
AgNO3 (aq) + NaCl (aq) → AgCl (s) + NaNO3 (aq)
BaCl2 (aq) + Na2SO4 (aq) → BaSO4 (s) + 2NaCl (aq)
v) Direct combination of the gas by metal
2Na (s) + Cl2 → 2NaCl
2Fe + 3Cl2 → FeCl3
Types of salts:
a) Normal Salt: This is the salt made up of whenever all the replaceable hydrogen in the acid has been fully substituted through a metal.
Example: NaCl, Na2SO4, Ca (NO3)2
b) Acid salts: These are made whenever the replaceable hydrogen in the acid are partly substituted through a metal. They are generated through partial neutralization of acids by more than one replaceable hydrogen.
They are acidic to litmus example: NaHSO4, NaHCO3 is alkaline to litmus due to hydrolysis.
c) Basic salts: They are made whenever there is partial substitution of the hydroxyl ions in a metallic hydroxide via an acid. They are made up as an outcome of partial neutralization of a base.
Zn (OH)2 + HCl → Zn OH Cl + H2O
Ba (OH)2 + HCl → Ba OH Cl + H2O
They are alkaline to litmus.
d) Double salts:
Double salts are made up of whenever two salts crystallize from the solution in definite proportion via mass.
Example: K2SO4 . Al2(SO4)3 .24 H2O
From K2SO4 and Al2(SO4)3. They join the chemical properties of the two salts.
e) Complex salts:
These are the salts of complex ions.
Example: K3Fe(CN)6, Cu(NH3)4SO4
Remember that the complex ions are made up by coordinate covalent bonding of metal ions having covalent molecules which can donate lone pair of electrons for binding. Such covalent molecules are known as the ligands.
(f) Hydrated salts:
These are the salts which have water of crystallization example: Na2CO3. 10H2O. CuSO4. 5H2O. The water of crystallization is chemically bonded to the salt. On heating or on exposure, a few hydrated salts lose their water of crystallization.
Common Characteristics of Acids, Bases and Salts:
Acids, bases and salts ionize in the aqueous solution to generate ions. They are all electrolytes. Acids and bases that are fully ionized in solution generally water are strong acids or bases example: HNO3, HCl, NaOH, KOH and H2SO4. Weak acids and bases are partially ionized in solution example: NH4OH. The extent of ionization is produced by the acid or base dissociation constant.
Strong acids and bases are strong electrolytes and weak acids and bases are weak electrolytes. Extremely soluble salts ionize readily in solution and are strong electrolytes however sparingly soluble salts are weak electrolytes.
As acids ionize and raise the IP concentration in water, the pH of acid solutions is less than 7. Bases which dissociate in water raise the hydroxide ion concentration in water. The pH of base solutions is more than 7. Salts solutions are usually neutral to litmus. A few though exhibit acidic or basic behavior due to hydrolysis.
It is a phenomenon whereby substances absorb moisture and form solution. Substances which exhibit this behavior are known as deliquescent compounds.
Example: NaOH, KOH, NaCl, MgCl2 and CaCl2
They encompass great affinity for water and are at times employed as drying agents, example: fused calcium II chloride.
Hygroscopic compounds absorb moisture devoid of forming solution whenever exposed to the atmosphere. They encompass very strong affinity for water and are employed as drying agents.
Example: CuO, CaO, and concentrated H2SO4. They are at times termed as dessiccants.
Efflorescence is the phenomenon whereby a hydrated salt loses all or portion of its water of crystallization whenever exposed to the atmosphere. An illustration is Na2CO3.10H2O. This salt loses nine molecules of water of crystallization whenever exposed and is transformed to the mono hydrate.
Na2CO3 . 10 H2O → Na2CO3 H2O + 9H2O
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