Define acid base and salt with example

In our daily life, we use many substances, including food items like lemon, orange, curd, milk, table salt, etc. These can be classified into acids, bases, and salts.

We will discuss acid base and salt definitions in detail with some examples.

Table of Content

1. Definition of acid-base and  salt

2. Arrhenius theory of acid and base

   3.  Bronsted -Lowry concept of acids and bases

   4.  Lewis concept of acids and bases

   5. Acid  bases and salt important questions

   6. FAQs

 What is the definition of acid-base and salt?

 

Acid

The term acid comes from the Latin term ‘acere’ or ‘acidus’ which means “sour’.

So, acids-

i.              Taste sour

ii.           Are corrosive

iii.        Change blue litmus to red

Base

The substances which have the following characteristics are classified in base.

Bases are also called ‘alkali’ which means ‘ash of plant’

·     Alkali – The bases which dissolve in water are called such as NaOH, KOH. So, all bases are not alkali.

Bases-

i.              Has a bitter taste

ii.           Have a soapy feeling

iii.        Change red litmus to blue

Salt

Salts are basically ionic compounds that have anion and cation and are formed when acids and bases react with each other. The reaction is called the neutralization reaction. 

       Acid + base = salt + water

Salts –

i.              Have a high melting point

ii.           Are generally found in crystal form

 

These are the basic definitions of acids, bases, and salts but some other definitions of acids, bases, and salts are following –

   1.  Arrhenius theory of acid and base

   2.  Bronsted -Lowry concept of acids and bases

   3.  Lewis concept of acids and bases

   1. Arrhenius theory of acid and base

According to the Arrhenius theory, an acid is a substance that gives hydrogen ion (`H^+`) when decomposes in water and the substances that decompose in water and give hydroxyl ion OH- are called bases.

`HCl_{(aq)} \rightarrow  H^+  + Cl^-`

`HNO_{3(aq)}\rightarrow  H^+   +  NO3^-`

`H_2SO_{4(aq)}\rightarrow  H^+  + SO_4^(-2)`

`CH_3COOH_{(aq)}\rightarrow  H^+  + CH_3COO^-`

`H_2CO_{3(aq)}  \rightarrow  H^+  + CO_3^-`

All above are acids because they give `H^+` ions in an aqueous solution. But some acids get completely ionized, they are strong acids and some acids do not ionize completely, they are called weak acids.

`KOH_{(aq)} \rightarrow K^+ + OH^-`

`NaOH_{(aq)} \rightarrow Na^+   + OH^-`

`Ca(OH)_{2(aq)} \rightarrow Ca^(+2)  + 2OH^-`

`NH_4OH_{(aq)}  \rightarrow  NH4^+  + OH^-`

All above are bases because they give hydroxyl ions in an aqueous solution. Those bases which get completely ionized are called strong bases and the other bases which get partially ionized are called weak bases

Limitations of Arrhenius theory

Arrhenius theory of acids and bases is only useful for that substances that have hydrogen and hydroxyl ions. But the substances without hydrogen and hydroxyl ions can not be determined by this theory.

   2. Bronsted Lowry concept of acids and bases

 According to Bronsted Lowry, acids are proton donors and bases are proton acceptors. This concept describes conjugate acids and conjugate bases.

`HA   +  B \rightarrow    A^-     +    HB^+`

Acid    base     conjugate       conjugate 

                       base                   acid

(`HA-A^-`) is called acid -conjugate base pair and (`B-HB^+`) is called base- conjugate acid pair.

`H_2O + NH_3 ⇌ NH_4^+  + OH^-` 

 In the above reaction, water is a proton donor, so it is an acid. It gives proton and changes into corresponding base OH- called conjugate base and ammonia is a proton acceptor so it is a base and it accepts proton and changes into NH4+ which is conjugate acid.

So,(` NH_4^+ -NH_3`) and( `H_2O-OH^-`) are conjugate acid-base pairs.

Limitations of Bronsted Lowry theory  

This theory is not applicable to aprotic acids and bases like `SO_2`, `BF_3`,` CO_2`, etc.

   

   3. Lewis concept of acids and bases

       

    Acids are the substances that accept electron pair and bases are the substances that donate electron pair.

So electron pair acceptors are acids and electron pair donors are bases.

According to the theory, the electron-deficient compound works like acid and is called Lewis acid

Compounds whose octet is incomplete and cations are Lewis acids.

Examples of Lewis acids 

`AlCl_3`, `BF_3`, `Mg^2+`, `Na^+`

Electron rich compound work like base and is called Lewis base

Examples of Lewis bases

`H_2O`, `NH_3`, `OH^-`,`Cl^-`

 Limitations  of Lewis concept of acids and bases

1.  This theory is only applicable to those substances that form coordination compounds but HCl, `H_2SO_4` do not form coordination compounds.

2.  It does not include the relative strength of acids and bases.

 

Acid  bases and salt important questions

Q1. What is the amphoteric nature of water?

Ans. – Water has the ability to act as both an acid and a base so it amphoteric in nature. In chemistry, substances are classified into acidic, basic, and natural nature.

Q2. Why does the water show amphoteric nature?

Ans.  On the basis of Bronsted Lowry's concept  water is amphoteric due to its ability to donate or accept protons (H+ ions), water shows both properties

Water can donate a proton to the other substance and acts as an acid.

`H_2O + NH_3\rightarrow NH_4^+  + OH^-`

(acid)

On the other hand, water accepts a proton and acts as a base

`H_2O + HCl → H_3O^+ + Cl^-`

(base)

That’s why water is amphoteric in nature.

Q3. Is salt made when an acid and bases are mixed?

Ans. – Yes, salt and water are produced when an acid and base are mixed.

Q4. How did Arrhenius define an acid and a base

Ans. - Arrhenius defined an acid as a hydrogen ion producer and a base as a hydroxyl ion producer in an aqueous solution.

FAQs

1.  When an acid and a base react what is produced?

 Ans. – Salt and water are produced when an acid and a base react.

2.  Do acid-base reactions always produce water?

Ans. – Yes, Generally acid-base reactions produce water.

3.  What do bases produce in a reaction?

 Ans.

4.  Do bases react with metals?

Ans. – Yes, bases can react with metals in the reaction.

5.  When Arrhenius theory was introduced?

Ans. – Arrhenius theory was introduced in 1887