Skip to main content

ACIDS AND BASES

ACIDS AND BASES   

For thousands of years, people have known that vinegar, lemon juice, amla, tamarind and many other food items taste sour. However, only a few hundred years ago it was proposed that these things taste sour because they  contain 'acids'. The term acid comes from Latin term 'accre' which means sour . It was first used in the seventeenth century by robert boyle to label substance as acids and bases according to the following characteristics.  

While Robert Boyle was sussessful in characterising acids and bases he could not explain their behaviour on the basis of their chemical structure.This was accomplished by Swedish scientist  Svante Arrhenius in the late nineteenth century. He proposed thaton dissolving in water , manycompounds dissociate and form ions and their properties are mainly the properties of the ions they form. Governed by this, he identified the ions furnished by acids and bases responsible for thier characteristics behaviour and gave their definitions.

Arrhenius concept of acids and bases: The Arrhenius definition of acids says that they are compounds that give off H+ ions in water and that bases are compounds that give off OH- ions in water. Thus, according to this theory only protic acids are allowed and only hydroxide bases are allowed to be classified as an acid or a base.

Brοnsted-Lowry definition: The Bronsted-Lowry definition of acids is that acids are compounds that give off H+ ions when they react with another compound. Likewise, this definition says that bases are compounds that accept H+ ions from other compounds. Furthermore, it also brings a new concept of conjugate acids and conjugate bases. Since an acid after donating its proton is technically a base according to this definition and is referred to as a conjugate acid. So every acid has its conjugate base and vice versa. Also, the stronger is an acid, the weaker is its conjugate base and vice versa. 

Lewis concept of acids and bases: Acids are electron pair acceptors while bases are electron pair donors. Thus, electron deficient species like BF3 are Lewis acids while electron rich species such as tertiary amines are Lewis bases. Lewis acids may combine with Lewis bases to generate a salt. 

pH and pOH 

The basic criterion for distinguishing acids and bases in aqueous solutions  is the concetration of hydrogen and hydroxide ions. 

              solution , pH , pOH , and ion concetrations 

Solution

pH

pOH

[H+]

[OH-]

Neutral

7

7

1.0×10-7              

1.0×10-7

 Acid 

<7 

 >7

>1.0×10-7

<1.0×10-7

 Base 

 >7

<7

<1.0×10-7 

>1.0×10-7 






     ACIDS

  SOME EXAMPLES OF ACIDS ARE: 

1. Hydrochloric acid (HCL)  in gastric acid.

2. Ascorbic acid (vitamin c) in lemon and many fruits. 

3.Citric acid in orange and lemons.

4. Acetic acid in vinegar.

5. tannic acid in tea.

Properties of acids

BASES 

The term alkali is often used for water soluble bases.  

SOME EXAMPLES OF BASES ARE : 

1. sodium hydroxide (NaOH) or caustic soda used in washing soaps.

2. potassium hydroxide (KOH) or potash used in bathing soaps.

3. ammonium hydroxide use in hair dyes.




Labels:

Comments

Post a Comment

Popular posts from this blog

PERIODIC TABLE

 Modern Periodic table Modern Periodic Law :  The recent work has established that the fundamental property of an atom is atomic number and not atomic weight. Therefore, atomic number is taken as the basis of the classification of the elements. The modern periodic law was given by Moseley, it may be stated as : ''The properties of elements are periodic functions of their atomic number". Modern periodic table is also called long form of the periodic table or Bohr’s table. In this table, the elements are arranged in order of their increasing atomic number. It consists of 4 blocks (s, p, d and f), 18 groups numbered from 1 to 18 and 7 periods numbered from 1 to 7. Short tricks to learn periodic table  Blocks : The periodic table is divided into four main blocks (s, p, d and f) depending upon the subshell to which the valence electron enters into.  (1) Elements of group 1 and 2 constitute s-Block.   (2) Elements of group 13, 14, 15, 16, 17, 18 constitut...
Post a Comment
Read more

COMPOUNDS OF ALKALI METALS

 COMPOUNDS OF ALKALI METALS  1. Sodium (Na) , Natrium  Extraction of sodium  : Down's Process  By Electrolysis of fused NaCl + CaCl 2 + NaF  At cathode (Iron Vessel) : Na+ +e– ⟶  Na(s)  At Anode (Graphite) : 2Cl–   →    Cl 2 + 2e–  (i) (CaCl 2 + NaF) is used to lower Melting point (8000 C) of NaCl to about 6000 C.  (ii) Aqueous sodium chloride cannot be used for preparing sodium by electrolysis. Because instead of metallic sodium, hydrogen gas will be liberated at cathode. Properties sodium , Natrium (i) sodium is a crystalline soft metal.  (ii) Highly reactive, so kept in kerosene.  (iii) Na dissolves in liquid NH3 to give blue solution.  Uses of sodium , natrium  (i) In the preparation of sodium amalgam (used as reducing agent)  (ii) In sodium vapour lamp, which emits monochromatic yellow light.  (iii) As heat transfer medium in nuclear reactors. 2. Sodium chloride NaCl Occ...
Post a Comment
Read more

Molar : Understanding the Concept and Its Significance

Demystifying Molar: Understanding the Concept and Its Significance Introduction: In the field of chemistry, the concept of the mole, often referred to as "molar," serves as a fundamental unit of measurement. The molar is a crucial concept that allows scientists to quantify and understand the relationships between atoms, molecules, and reactions. In this blog, we will delve into the fascinating world of moles, exploring their definition, significance, and applications in various aspects of chemistry. What is a Molar? Simply put, a molar is a unit of measurement used in chemistry to quantify the amount of a substance. It provides a bridge between the microscopic world of atoms and molecules and the macroscopic world of everyday measurements. The molar is defined as the amount of a substance that contains as many entities (atoms, molecules, ions, etc.) as there are atoms in exactly 12 grams of carbon-12. This definition is based on Avogadro's number, which is approximately 6...
Post a Comment
Read more