ACIDS

CONTENT
⦁ Definition of Acid
⦁ Strength of an Acid
⦁ Basicity of an Acid
⦁ Characteristics of Acid (Physical Properties)
⦁ Preparation of Acids
⦁ Reaction of Acids (Chemical Properties)
⦁ Uses of Acids

Definition of Acid
Acids are associated with the sour taste we feel when we take fruits such as lemon, lime and oranges especially when they are not ripe. Palm wine left open in the air becomes sour because of the formation of an acid.
An acid is a substance which produces hydrogen ions (or protons) as the only positive ion when dissolved in water. For example, hydrochloric acid (HCl) dissolves in water to form hydrogen ion (H+) and hydroxyl ion (OH–). This process is known as ionization. There are two main classes of acids: Organic acids and mineral or inorganic acids. The former occur as natural products in plants or animal materials while the later can be prepared from mineral elements or inorganic matter. Acids can also be grouped into Strong acids (ionizes completely) and Weak acids (ionizes partially).
Some Organic and Inorganic Acids

Organic acids Source Inorganic acids Constituents
Ethanoic acids Vinegar Hydrochloric acid Hydrogen, Chlorine
Citric acids Lime, Lemon Tetraoxosulphate
(vi) acid Hydrogen ,Chlorine,
Sulphur, Oxygen
Fatty acids Fats and Oil Trioxonitrate
(v) acid Hydrogen, Nitrogen,
Oxygen

Strength of an Acid
Strength of an acid is defined as the degree or the extent to which an acid ionizes in water. Based on this fact, acids can be weak or strong.
Strong acids are those that ionize completely in water. Examples of strong acids are H2SO4, HCl, HNO3, HBr, HI etc. For example HCl ionizes completely according to the equation below:
HCl → H+  + Cl–  (100% ionization)
Strong acids are also strong electrolytes i.e. they have high electrical conductivity.
Weak acids are those that ionize partially in water. Examples are organic acids, such as (Ethanoic acids, Citric acids, amino acids)  and  some inorganic acids such as HNO2,H2CO3,H3PO4,HF etc. For example ethanoic acid, CH3COOH, ionizes partially in water according to the equation below:
CH3COOH ⇋ CH3COO–  +  H+
Weak acids are also weak electrolyte because they are poor conductor of electricity.

Basicity of an Acid
All acids in an aqueous solution yield hydrogen ions which can be replaced by metallic ion.
The basicity of an acid is the number of replaceable hydrogen ions, H+, in one molecule of the acid.

Acids Basicity
HCl 1
H2SO4 2
H3PO4 3
H2CO3 2
CH3COOH 1

Characteristics of Acids (Physical Properties)
⦁ Acids turn blue litmus paper red.
⦁ They have sour taste; e.g. sour taste of unripe fruits.
⦁ Strong acids are corrosive in concentrated form; e.g. HCl, H2SO4
EVALUATION
⦁ Define an acid and give two examples each of organic acid and inorganic acid
⦁ Differentiate between a strong acid and a weak acid. Give two examples of each.
⦁ (a) What is basicity of an acid? (b). Mention four physical properties of an acid.
⦁ Compare and contrast the electrical conductivity of HCl and CH3COOH

Preparation of Acids
1. Dissolving non-metallic oxide (acid anhydride) in water.
Carbon (iv) oxide dissolves in water to form weak acid, trioxocarbonate (iv) acid.
CO2(g) +  H2O(l)   →    H2CO3(aq)

2. Direct combination of constituent elements.
Hydrogen reacts directly with Halogens in the presence of catalyst to form halogen acids gas which dissolves readily in water to form acid.

activated charcoal
H2(g) + Cl2(g) → 2HCl(g)
heat

3. Heating Hydrogen gas and bromine vapour, in the presence of platinum as the catalyst, produces hydrogen bromide gas, which dissolves readily in water to form hydrobromic acid.

Platinum
H2(g) + Br2(g) → 2HBr(g)
heat

4. Displacement of weak or volatile acid from its salt by a strong acid.
Concentrated H2SO4 is stronger but less volatile than HCl and, H2SO4 can therefore be used to displace the weaker HCl acid from its salt (NaCl).
NaCl(s)   +  H2SO4(aq)   →    NaHSO4(aq)  +  HCl(g)
The hydrogen chloride gas formed dissolved in water readily to produce hydrogen chloride acid.
EVALUATION
Mention the methods of preparing acids

Reaction of Acids (Chemical Properties)
1. Reaction of Acid with Metals
Acid react with some metals to liberate hydrogen gas.
Zn(s)+ 2HCl (aq)    →     ZnCl2(aq) + H2(g)
Mg(s)   +  H2SO4 (aq)   →     MgSO4+  H2(g)
NOTE: Dilute HNO3 does not react with metals to produce hydrogen gas.
2. Reaction of Acids with Base and Alkalis
Dilute acids react with bases and alkalis to form salts and water (known as neutralization reaction)
HCl (aq) + NaOH (aq)     →     NaCl (aq) +  H2O(l)
H2SO4(aq)  +  CaO(aq)    →      CaSO4(aq)  +  H2O(l)
3. Reaction of Acids with Trioxocarbonate (iv) and Hydrogen trioxocarbonate (iv).
Acid reacts with CO32-  or  HCO3– to liberate carbon (iv) oxide (CO2).
NaCO3(s) +  2HCl(aq)    →    2NaCl(aq)  +  H2O(l)  +  CO2(g)
NaHCO3  +  HCl(aq)    →      NaHCll(aq)  +  H2O(l)  +  CO2(g)

EVALUATION
⦁ What is neutralization?
⦁ State three chemical properties of acids.

Uses of Acids

S/N Name Uses
1 Hydrochloric acid (i) In industries to make chemicals
(ii) To remove rust
2 Tetraoxosulphate (vi) acid (i) To make chemicals
(ii) As drying and dehydrating agent
(ii) As drying and dehydrating agent
(iii) As electrolyte in lead-acid accumulators
3 Trioxonitrate (v) acid (i) For making fertilizers, explosives, etc.
4 Acetic acid (ethanoic) (i) In preserving food
(ii) In dyeing silk and other textiles
5 Tartaric (i) In making baking soda, soft drinks and
health salt
6 Citric acid (i) in making fruit juice
7 Fatty acids
(e.g. palmitic and
stearic acids) (i) In manufacturing soap.
(A process known as Saponification)

EVALUATION
⦁ Give three (3) uses of each of the following acids: HCl, H2SO4, HNO3, Citric acid
⦁ Give three physical properties of an acid.
⦁ Write an equation for the reaction between iron fillings and tetraoxosulphate(vi) acid.
⦁ State how hydrogen chloride gas can be obtained from tetraoxosulphate (vi) acid
⦁ (a) What is basicity? (b) State the basicity of the following acids: (i) HNO3 (ii)  H2SO4 (iii) CH3COOH.
⦁ State the natural source of (i) ethanoic acid (ii) Citric acid (iii) Amino acid
⦁ (a) Why is ethanoic acid regarded as weak acid? (b) Hydrochloric acid is regarded as a strong acid. Why?