SS1 Chemistry Lesson Note on Definition and Characteristics of Acid

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TOPIC: ACIDS, BASES AND SALTS

CONTENTS:    

  ACIDS

1. DEFINITION AND CHARACTERISTICS OF ACIDS
2. PREPARATION OF ACIDS
3. REACTIONS OF ACIDS
4. USES OF ACIDS

PERIOD 1: DEFINITION AND CHARACTERISTICS 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.

• Definition of 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 occurs 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

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