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

Unveiling the Science Behind Washing Powders: Insights from a Chemist

Unveiling the Science Behind Washing Powders: Insights from a Chemist Introduction: In our everyday lives, we encounter numerous challenges, and one that most of us can relate to is laundry. The quest for cleaner, fresher, and more vibrant clothes has led to the development of various laundry detergents, including the ever-popular washing powders. As a chemist, I find the science behind these powders fascinating. In this blog, we will delve into the intricate world of washing powders, exploring their composition, working mechanisms, and the chemical reactions that make them effective . 1. Composition of Washing Powders: Washing powders are complex mixtures of chemicals carefully formulated to remove dirt, stains, and odors from fabrics. The composition of washing powders typically includes the following key components:  a. Surfactants:  These are the primary cleansing agents in washing powders. Surfactants contain both hydrophilic (water-attracting) and lipophilic (oil-attract...
Post a Comment
Read more

NEET 2025, negative marking, exam tips, study strategies, NEET preparation, medical entrance exam, NEET coaching

Navigating NEET 2025: Strategies to Minimize Negative Marking The National Eligibility cum Entrance Test (NEET) is a highly competitive exam for aspiring medical professionals. Conducted by the National Testing Agency (NTA), it is crucial to secure a good rank to gain admission to prestigious medical colleges in India. One significant factor that can significantly impact your NEET score is negative marking. For every incorrect answer, a portion of the marks allotted to that question is deducted from your total score. Understanding the Impact of Negative Marking Reduced Total Score : Each incorrect answer directly lowers your overall score. Lowered Qualifying Marks : A lower total score might not meet the minimum qualifying marks for various medical colleges. Wasted Potential : Incorrect answers can negate the positive impact of correct ones, diminishing your hard work. Key Strategies to Minimize Negative Marking Thorough Understanding of Concepts: Master the Basics : Ensure a strong fo...
Post a Comment
Read more

IUPAC NOMENCLATURE part 3

IUPAC NOMENCLATURE part 1 IUPAC NOMENCLATURE  part 2 IUPAC NOMENCLATURE   IUPAC NOMENCLATURE OF ALICYCLIC COMPOUNDS : ( 1 ) The names of alicylic compounds are obtained by adding the prefix "cyclo". (2) The numbering of the carbon atoms in the ring is done in such a way that the substituent which comes first in the alphabetical order is given the lowest possible number provided it does not violate the lowest set of locants rule.  Example : (3)When the ring contains more or equal number of carbon atoms than the alkyl group attached to it, then it is named as a derivative of cycloalkane and the alkyl group is treated as substituent. Example : (4)The alkane chain contains greater number of carbon atoms than present in the ring, the compound is considered as the derivative of alkane and the ring is designated as substituent.  Example : (5)If ring has unsaturation and side chain is saturated then ring is selected as parent chain.  If side chain has unsatura...
Post a Comment
Read more