Definition of acids
An acid is an agent capable of donating a proton (hydrogen ion H+) or alternatively, capable of forming a covalent bond with an electron pair.
Acids are classified into two types,
- The acids which are capable of donating a proton are called Bronsted–Lowry acids or Arrhenius Acids. Example: Hydro Chloric Acid(HCL), Sulphuric Acid (H2SO4), Acetic Acid( CH3COOH) etc.
- The acids which are capable of forming a covalent bond with an electron pair are called Lewis acid. Ex: Boron tri fluoride (BF3), Aluminum fluoride (AlF3) etc.
Characteristic of acids
- They release hydrogen ions when added to water.
- They react with base and certain metals to form Salts.
- They form aqueous solution and with a sour taste.
- They turn blue litmus to red.
The pH is the scale that is used to represent the level of acidity in a solution. pH is defined as the decimal logarithm of the reciprocal of the hydrogen ion activity in a solution. A lower pH means higher acidity.
- A solution with a pH of 7 is neutral
- A solution with a pH of below 7 is an acid
- A solution with a pH of above 7 is a base
Definition of a strong and weak acid
Acids may be identified as either strong or weak based on how completely they dissociate into their ions in water.
- A strong acid, such as hydrochloric acid and Sulphuric acid, completely dissociates into its ions in water.
- A weak acid, such as Acetic acid only partly dissociates into its ions, so the solution contains water, ions, and the acid.
Definition of basicity of the acid
Basicity of an acid is the number of replaceable hydrogen atoms present in a molecule of that acid. It can be further classified into several types. Ie. Monobasic, Dibasic , Tribasic etc.
- The molecule of an acid which contains one replaceable hydrogen atom is called monobasic acid and it’s basicity is 1. Example : HCL, HNO3.
- The molecule of an acid which contains two replaceable hydrogen atom is called dibasic acid and it’s basicity is 2. Example : H2SO4.
- The molecule of an acid which contains three replaceable hydrogen atom is called tribasic acid and it’s basicity is 3. Example : H3PO4.
Equivalent Mass of acids
Equivalent mass of an acid is a number which shows how many parts by mass of the acid contain one part by mass of replaceable hydrogen.
Example 1: Acetic acid (CH3COOH)
Molecular Mass of Acetic acid= 12+(1×3)+12+16+16+1=60
Example 1: Sulphuric acid (H2SO4)
Molecular Mass of Sulphuric acid= (1×2)+32+(16×4)=98
Example 1: Sulphuric acid (H3PO4)
Molecular Mass of Phosphoric acid= (1×3)+31+(16×4)=98
Definition of bases
Bases are those substances which releases hydroxide ions (OH-) in aqueous solution. Example: Sodium Hydroxide (NaOH), Calcium Hydroxide ( Ca(OH)2 ) etc.
Characteristic of bases
- Base reacts with acid to form Salt.
- They turn red litmus to blue.
- Accept protons from any proton donor.
- Taste bitter and slippery to the touch.
Base can be thought of as the chemical opposite of acids. So a reaction between a base and an acid is known as neutralisation reaction. One of the products of a neutralisation reaction must be a salt.
Definition of acidity of the base
- Acidity of the base can be defined as the number of replaceable hydroxyl group (OH) present in one molecule of the base. For example,
- Acidity of Sodium Hydroxide ( NaOH ) is 1. It has One OH group.
- Acidity of Calcium Hydroxide ( Ca(OH)2 ) is 2. It has Two OH group.
- The number of moles of monobasic acid which can completely neutralize one mole of the base determines the acidity of the base. For example,
Na2CO3+2HCl = 2NaCl+CO2+H2O
Here 2 moles of HCl is required to neutralise 1 mole of Na2CO3
So the Acidity of Na2CO3 is 2.
Equivalent Mass of bases
The equivalent mass of a base is a number that shows how many parts by mass of a base can just be neutralized by one equivalent mass of an acid.
Example 1: Sodium Hydroxide – NaOH
Molecular Mass of Sodium Hydroxide = 23+16+1=40
Example 2: Calcium Hydroxide – Ca(OH)2
Molecular Mass of Calcium Hydroxide = 40+(16+1)x2=74
Example 3: Aluminium Hydroxide – Al(OH)3
Molecular Mass of Aluminum Hydroxide= 27+(16+1)x3=78
Definition of salt
A salt is a chemical compound consisting of an ionic assembly of Cations and Anions. Salts are composed of related numbers of cations and anions so that the product is electrically neutral.
For example: Sodium Chloride (NaCl), Barium Chloride (BaCl2) etc.
Definition of ion, cation & anion
An Ion is an atom or molecule that has a net electrical charge. In an ion total number of electrons is unequal with the total number of protons.
If the total number of protons is more than the total number of electrons in an ion then it is called Cation. So cations are positively(+) charged ions.
If the total number of protons is less than the total number of electrons in an ion then it is called Anion. So anions are negatively(-) charged ions.
Characteristic of salts
- Salts dissociate in solution into anionic and cationic components
- Salts are characteristically insulators. But Solutions of salts conduct electricity.
- The name of a salt starts with the name of the cation followed by the name of the anion present in that salt. Ex: Sodium Chloride (NaCl). Here Sodium is cation and Chloride is anion.
- Salts characteristically have high melting points. Example: Sodium Chloride melts at 8010C.
- Salts can be classified into various types
- Alkali salts (Produce hydroxide ions when dissolved in water )
- Acid salts (Produce acidic solutions)
- Neutral salts (Neither acidic nor Base)
Equivalent Mass of Salts
Equivalent mass of salt is a number which shows how many parts by mass of the salts contain one part by mass of hydrogen equivalent of an active element of a positive group.
Or Equivalent mass of a salt is a number of parts by mass of the salt that is produced by the neutralization of one equivalent of an acid by a base.
Example 1: Sodium Sulphate – Na2SO4
Molecular Mass = (23×2)+32+(16×4)=142
Equivalent Mass = 142/2=71 (Here Valency of Na = 2)
Example 2: Ferric chloride – FeCl3
Molecular Mass = 56+(35.45×3)=162.35
Equivalent Mass = 162.35/3=54.11 (Here Valency of Fe = 3)
Example 3: Aluminium chloride – AlCl3
Molecular Mass = 27+(35.45×3)=133.5
Equivalent Mass = 133.5/3=44.5 (Here Valency of Al= 3)
Gram Equivalent Mass
Equivalent mass expressed in grams is called gram-equivalent mass and written as gram-equivalent.
For Example : Equivalent mass of H2SO4 = 49
Hence 1 gram-equivalent of H2SO4 = 49 gram