1. The Chemical Properties of Acids and Bases

Indicators: Indicators are substances which indicate the acidic or basic nature of the solution by the colour change.

Types of Indicator:  Some common types of indicators are:

1. Natural Indicators: Indicators obtained from natural sources are called Natural Indicators. Litmus, turmeric, red cabbage, China rose, etc., are some common natural indicators used widely to show the acidic or basic character of substances.

Turmeric: Turmeric is another natural indicator. Turmeric is yellow in colour. Turmeric solution or paper turns reddish brown with base. Turmeric does not change colour with acid.

Red Cabbage: The juice of red cabbage is originally purple in colour.

2. Olfactory Indicator: Substances which change their smell when mixed with acid or base are known as Olfactory Indicators. For example; Onion, vanilla etc.

Onion: Paste or juice of onion loses its smell when added with base. It does not change its smell with acid.

Vanilla: The smell of vanilla vanishes with base, but its smell does not vanish with an acid.

3. Synthetic Indicator: Indicators that are synthesized in the laboratory are known as Synthetic Indicators. For example; Phenolphthalein, methyl orange, etc.

Phenolphthalein is a colour less liquid. It remains colour less with acid but turns into pink with a base.

Methyl orange is originally orange in colour. It turns into the red with acid and turns into yellow with base.

Acids, Bases and Salts

Classification of matter

On the basis of

a) composition –  elements, compounds and mixtures

b) state – solids, liquids and gases

c) solubility – suspensions, colloids and solutions

Types of mixtures – homogeneous and heterogeneous

Types of compounds – covalent and ionic

an Acid and a Base?

Ionisable and non-ionisable compounds

An ionisable compound when dissolved in water or in its molten state, dissociates into ions almost entirely. Example: NaCl, HCl, KOH, etc.

A non-ionisable compound does not dissociate into ions when dissolved in water or in its molten state. Example: glucose, acetone, etc.

Arrhenius theory of acids and bases

Acids: Acids are sour in taste, turn blue litmus red, and dissolve in water to release H+ ions.

Properties of Acids:

Acids have a sour taste.

Turns blue litmus red.

Acid solution conducts electricity.

Release H+ ions in aqueous solution.

Types of Acids: Acids are divided into two types on the basis of their occurrence i.e., Natural acids and Mineral acids.

(i) Natural Acids: Acids which are obtained from natural sources are called Natural Acids or Organic Acids.


Methanoic acid (HCOOH)

Acetic acid (CH3COOH)

Oxalic acid (C2H2O4) etc.

(ii) Mineral Acids: Acids that are prepared from minerals are known as Mineral Acids Example; Inorganic acids, man-made acids or synthetic acid are also known as Mineral Acids.


Nitric acid (HNO3)

Carbonic acid (H2CO3)

Phosphoric acid (H3PO4) etc.

Chemical Properties of Acid:

(i) Reaction of acids with metal: Acids give hydrogen gas along with respective salt when they react with a metal.

Metal + Acid → Salt + Hydrogen

Test For Hydrogen Gas: The gas evolved after reaction of acid with metal can be tested by bringing a lighted candle near it. If the gas bums with a pop sound, then it confirms the evolution of hydrogen gas.

(ii) Reaction of acids with metal carbonate: Acids give carbon dioxide gas and respective salts along with water when they react with metal carbonates.

Metal carbonate + Acid → Salt + Carbon dioxide + Water

 (iii) Reaction of acid with hydrogen carbonates (bicarbonates): Acids give carbon dioxide gas, respective salt and water when they react with metal hydrogen carbonate.


Test For Evolution of Carbon Dioxide Gas: Carbon dioxide turns lime water milky when passed through it. This is the characteristic test for carbon dioxide gas.

The gas evolved because of reaction of the acid with metal carbonate or metal hydrogen carbonate turns lime water milky. This shows that the gas is carbon dioxide gas.


  • Strong Acids

An acid which is completely ionised in water and produces (H+) is called Strong Acid.

Examples: Hydrochloric acid (HCl), Sulphuric acid (H2SO4), Nitric acid (HNO3)

  • Weak Acids

An acid which is partially ionised in water and thus produces a small amount of hydrogen ions (H+) is called a Weak Acid.

Example: Acetic acid (CH3COOH), Carbonic acid (H2CO3) , When a concentrated solution of acid is diluted by mixing water, then the concentration of Hydrogen ions (H+) or hydronium ion (H3O–) per unit volume decreases.

Bases: Bases are bitter in taste, have soapy touch, turn red litmus blue and give hydroxide ions (OH–) in aqueous solution.

Examples: Sodium hydroxide (caustic soda) – NaOH

Calcium hydroxide – Ca(OH)2

Potassium hydroxide (caustic potash) – (KOH)

Properties of Bases:

1.Have a bitter taste.

2.Turns red litmus blue.

3.Conducts electricity in solution.

4.Release OH– ions in Aqueous Solution

Types of bases: Bases can be divided in two types – Water soluble and Water-insoluble.

The hydroxide of alkali and alkaline earth metals are soluble in water. These are also known as alkali.

For example; sodium hydroxide, magnesium hydroxide, calcium hydroxide, etc.

Chemical properties of bases:

(i) Reaction of Base with Metals: When alkali (base) reacts with metal, it produces salt and hydrogen gas.

Alkali + Metal → Salt + Hydrogen

(ii) Reaction of Base with Oxides of Non-metals: Non-metal oxides are acidic in nature. For example; carbon dioxide is a non-metal oxide. When carbon dioxide is dissolved in water it produces carbonic acid.

Therefore, when a base reacts with non-metal oxide, both neutralize each other resulting respective salt and water.

Base + Non-metal oxide → Salt + Water

(iii) Neutralisation Reaction: An acid neutralizes a base when they react with each other and respective salt and water are formed.

Acid + Base → Salt + Water

(iv) Reaction of Acid with Metal Oxides: Metal oxides are basic in nature. Thus, when an acid reacts with a metal oxide both neutralize each other. In this reaction, the respective salt and water are formed.

Acid + Metal Oxide → Salt + Water

Common in all bases: A base dissociates hydroxide ion in water, which is responsible for the basic behaviour of a compound.

Example: When sodium hydroxide is dissolved in water, it dissociates hydroxide ion and sodium ion.

Neutralisation Reaction: When an acid reacts with a base, the hydrogen ion of acid combines with the hydroxide ion of base and forms water

Dilution of Acid and Base: The hydrogen ion in an acid and hydroxide ion in a base, per unit volume, shows the concentration of acid or base.By mixing of acid to water, the concentration of hydrogen ion per unit volume decreases. Similarly, by addition of base to water, the concentration of hydroxide ion per unit volume decreases. This process of addition of acid or base to water is called Dilution and the acid or base is called Diluted.The dilution of acid or base is exothermic. Thus, acid or base is always added to water and water is never added to acid or base. If water is added to a concentrated acid or base, a lot of heat is generated, which may cause splashing out of acid or base and may cause severe damage as concentrated acid and base are highly corrosive



1.Hydrochloric acid (HCl)

2.Sulphuric acid  (H2SO4)

3.Nitric acid (HNO3)


1.Sodium hydroxide (NaOH)

2.Potassium hydroxide (KOH)

3.Calcium hydroxide (Ca(OH)2)

Bronsted Lowry theory

1.A Bronsted acid is an H+ (aq) ion donor.

2.A Bronsted base is an H+ (aq) ion acceptor.


In the reaction: HCl (aq) + NH3 (aq) → NH+4(aq) + Cl− (aq)

HCl – Bronsted acid and Cl− : its conjugate acid

NH3 – Bronsted base and NH+4 : its conjugate acid

Physical test

Given are two possible physical tests to identify an acid or a base.

a. Taste

An acid tastes sour whereas a base tastes bitter.

The method of taste is not advised as an acid or a base could be contaminated or corrosive.

b. Effect on indicators by acids and bases

An indicator is a chemical substance which shows a change in its physical properties, mainly colour or odour when brought in contact with an acid or a base.

Below mentioned are commonly used indicators and the different colours they exhibit:

a) Litmus

In a neutral solution – purple

In acidic solution – red

In basic solution – blue

b) Methyl orange

In a neutral solution – orange

In acidic solution – red

In basic solution – yellow

c) Phenolphthalein

In a neutral solution – colorless

In acidic solution – remains colorless

In basic solution – pink

Acid-Base Reactions & Reactions of acids and bases

a) Reaction of acids and bases with metals

Acid + active metal →  salt + hydrogen + heat

2HCl + Mg → MgCl2 + H2 (↑)

2NaOH + Zn → Na2ZnO2 + H2 (↑)

b) Reaction of acids with metal carbonates and bicarbonates

Acid + metal carbonate or bicarbonate →  salt + water + carbon dioxide.

2HCl + CaCO3 → CaCl2 + H2O + CO2

H2SO4 + Mg (HCO3)2 → MgSO4 + 2H2O + 2CO2

c) Neutralisation reaction

1. Reaction of metal oxides and hydroxides with acids

Metal oxides or metal hydroxides are basic in nature.

Acid + base → salt + water + heat

 H2SO4 + MgO → MgSO4 + H2O

2HCl + Mg (OH) 2 → MgCl2 + 2H2O

2. Reaction of non-metal oxides with bases

Non-metal oxides are acidic in nature

Base + Nonmetal oxide →  salt + water + heat

2NaOH + CO2→ Na2CO3 + H2O


Bases undergo neutralisation reaction with acids.

They are comprised of metal oxides, metal hydroxides, metal carbonates and metal bicarbonates.

Most of them are insoluble in water.

1. The Chemical Properties of Acids and Bases



These are the substances which have sour taste

  • They turn blue litmus solution  red
  • They give H+ ions in aqueous solution

Type  of acids are as follows

  1. Strong Acid :  Hcl , H2SO4
  2. Weak Acid : CH3COOH, HCOOH
  3. Concentrated Acid : which have more amount of acid and less amount of water.
  4. Dilute Acid : which have more amount of water and less amount of acid


* These are the substances which have bitter taste and soapy in touch .

  • They turn red litmus solution blue
  • They give OH- ions in aqueous solution.

Type of bases are as follows :-

  1. Strong Bases :-  NaOH, KOH
  3. ALKALI :- These are the bases which are soluble in water (like NaOH,KOH)

SALTS :-  A salts is a substance produced from the reaction of an acid and a base.


INDICATORS :- The substances that change their colour/ smell when they are added to acidic or alkaline solutions.

Types of Indicators.

  1. Natural Indicators :- Litmus , turmeric
  2. Synthetic Indicators :-  Phenolphthalein, Mythyl
  3. Olfactory Indicators:- Onion, vanilla essence.


(i)  Reaction of Metal with :-     

(a)  ACIDS 

Acid   +  Metal                 Salt +    Hydrogen  gas                      

For Example,

2Hcl           +          Zn                    ZnCl2      +    H2

(Hydrochloric acid) (zinc)       (zinc chloride ) (hydrogen)

(b)  Bases  Base + metal        salt + hydrogen gas

For example,

2NsoH         +          Zn           Na3ZnO2        +        H2  

(sodium hydroxide )  ( zinc)  ( sodium zincate)  ( hydrogen gas )

 Hydrogen gas released can be tested by bringing burning candle near gas bubbles , it burst with pop sound.

(ii)    REACTION OF METAL CARBONATES / Metal Hydrogen carbonates with 

(a)  Acids :- 

(b) Acid   +   metal carbonate/ metal hydrogen carbonate     salt + carbon dioxide + water.

  For example :-

  1. 2 Hcl + Na2CO3                  2NaCl +  CO2    +   H2O
  2. HCl +  NaHCO3                  NaCl +  CO2  +H2O
  3. Ca(OH)2   +   CO2     →         CaCO3 H2O

                ( Line Water)                   ( White precipitate )

On passing CO Through lime water , lime water turns milky and in this way CO2 can be tested.

And when excess CO2 is passed , milkiness disappers and the following reaction take place.

Passing carbon dioxide gas through calcium hydroxide.

CaCo3    +    CO2     +     H2O        Ca (HCO3)

(iii)     Reaction of acids and bases with each other  

Acid     +       base               Salt   +    H2O

Neutralisation Reaction :-   The reaction between an aid and a base to give a salt and water is known as neutralization reaction.

  For Example :-    

HCl (aq)   + NaOH (aq)    →  NaCl(aq) + H2O(l)

(iV)  Reaction of Metallic Oxides with Acids  :-

Metallic oxide +  acid          salt   +  water

 Metallic oxides are basic in nature

For Example :- 

CaO  + 2HCl       CaCl2   +    H2O

(v) Reaction of Non- metallic Oxide with base :-

Non- metallic oxide + base    →        salt   +    H2

Non- metallic oxide are acidic in nature.

For Example :-

CO2   +   Ca(OH)2       CaCO3  +    H2O

2. Common Things in All Acids and Bases

Hydronium ion

Hydronium ion is formed when a hydrogen ion accepts a lone pair of electrons from the oxygen atom of a water molecule, forming a coordinate covalent bond.


Dilution is the process of reducing the concentration of a solution by adding more solvent (usually water) to it.

It is a highly exothermic process. Strong acid or base: When all molecules of a given amount of an acid or a base dissociate completely in water to furnish their respective ions, H+(aq) for acid and OH−(aq) for base).

Weak acid or base: When only a few of the molecules of a given amount of an acid or a base dissociate in water to furnish their respective ions, H+(aq) for acid and OH−(aq) for base).

Dilute acid: contains less number of H+(aq) ions per unit volume.

Concentrated acid: contains more number of H+(aq) ions per unit volume

2. Common Things in All Acids and Bases

Common Things in All Acids and Bases:-

All acids have H+ ios in common

All bases have OH- ions in common

 Acids produce H+ ions which  ar responsible for their acidic properties.

Acids solution in water conducts electricity.

An Acid or a Base in water solution:-

  • Acids produce H+Ions in presence of water.
  • H+ ions cannot exist alone , they exist as H3O+ ions.

H+   +   H2O      H3O+

HCl  +  H2O     H3O+ +  Cl-

Bases when dissolved in water gives  Oh-  ions.

For Example:- 


Bases soluble in water are called alkali.

 It is recommended that the acid / base should be added to water and not water. Is added to acid/ base, the heat generated may cause the mixture to splash out and cause burns and the glass

conatiner may also break due to exessing  heating.

  Mixing an acid or base with water results in decrease of concentration of ions per unit volume. Such a process is called dilution.

3. Strongness about Acids or Bases

Universal indicator

A universal indicator has a pH range from 0 to 14 that indicates the acidity or alkalinity of a solution.

A neutral solution has pH=7


In pure water, [H+]=[OH]=10−7 mol/L. Hence, the pH of pure water is 7.
The pH scale ranges from 0 to 14.
If pH < 7 
acidic solution
If pH > 7
basic solution

Importance of pH in everyday life

1. pH sensitivity of plants and animals

Plants and animals are sensitive to pH. Crucial life processes such as digestion of food, functions of enzymes and hormones happen at a certain pH value.

2. pH of a soil

The pH of a soil optimal for the growth of plants or crops is 6.5 to 7.0.

3. pH in the digestive system

The process of digestion happens at a specific pH in our stomach which is 1.5 to 4.
The pH of the interaction of enzymes, while food is being digested, is influenced by HCl in our stomach.

4. pH in tooth decay

Tooth decay happens when the teeth are exposed to an acidic environment of pH 5.5 and below.

5. pH of self-defence by animals and plants

Acidic substances are used by animals and plants as a self-defence mechanism. For example, bee and plants like nettle secrete a highly acidic substance for self-defence. These secreted acidic substances have a specific pH.

3. Strongness about Acids or Bases

Strongness  about  Acids or Bases 

Strength of acid and base can be determined by universal indicator.

concentrations of H+ ions in the solution.

pH scale :-  A scale for measuring hydrogen ion concentration in a solution called PH scale.

pH = 7                           Neutral Solution

pH Less than 7             Acidic  Solution

pH more than 7           Basic solution

pH of some common substances shown on a pH paper.

Importance of  pH in everyday life :-

1 ,  Plants and animals are Ph sensitive.

  • Our body works within the pH range of  7- 7.8 .
  • When pH of rain water is less than 5.6, it is called acid rain.
  • When acid rain flows into the rivers ,it lower the pH of river water and makes the survival  of aquatic life difficult.

2, pH of the soil

  • Plants require a specific pH range for their healthy growth.

3,  pH in our digestive system.

  • Our stomach produce hydrogenchloric acid which helps in digestion without harming the stomach.
  • During indigestion, stomach produces more acid and cause pain and irritation.
  • To get rid of pain ,prople use mild bases called antacid to neutralize the excess acid. Magnesium hydroxide ( Milk of magnesia) is an antacid.

  4,  Ph changes as the cause of tooth decay.

  • Tooth decay starts when pH of mouth is lower than 5.5
  • Tooth enamel is made up of calcium phosphate ( hardest substance in body) .it does not dissolve in water but carodes when pHis low than 5.5
  • Using basic toothpaste , tooth decay can be prevented    

5, self defence by animals and plants through chemical warfare.

  • Bee sting leaves an acid which cause pain and irritation. Bakig soda (mild base) gives relief by rubbing it on stung area.
  • Stinging hair of nettle leaves inject  methanoic  acid causing  buring or pain rubbing this with leaf of dock plant give relief.

4. About Salts


A salt is a combination of an anion of an acid and a cation of a base.

Examples – KCl, NaNO3 ,CaSO4, etc.

Salts are usually prepared by the neutralisation reaction of an acid and a base.

Common salt

Sodium Chloride (NaCl) is referred to as common salt because it’s used all over the world for cooking. Sodium chloride (NaCl) is also known as Common or Table Salt. It is formed after the reaction between sodium hydroxide and hydrochloric acid. It is a neutral salt. The pH value of sodium chloride is about 7. Sodium chloride is used to enhance the taste of food. Sodium chloride is used in the manufacturing of many chemicals.

Family of salts

Salts having the same cation or anion belong to the same family. For example, NaCl, KCl, LiCl.

pH of salts

A salt of a strong acid and a strong base will be neutral in nature. pH = 7 (approx.).

A salt of a weak acid and a strong base will be basic in nature. pH > 7.

A salt of a strong acid and a weak base will be acidic in nature. pH < 7.

The pH of a salt of a weak acid and a weak base is determined by conducting a pH test.

Preparation of Sodium hydroxide

Chemical formula – NaOH

Also known as – caustic soda

Preparation (Chlor-alkali process):

Electrolysis of brine (solution of common salt, NaCl) is carried out.

At anode: Cl2 is released

At cathode: H2 is released

Sodium hydroxide remains in the solution.

Bleaching powder

Chemical formula – Ca(OCl)Cl or CaOCl2

Preparation – Ca(OH)2(aq)+Cl2(g)→CaOCl2(aq)+H2O(l)

On interaction with water – bleaching powder releases chlorine which is responsible for bleaching action.

Baking soda

Chemical name – Sodium hydrogen carbonate

Chemical formula – NaHCO3

Preparation (Solvay process):

a. Limestone is heated: CaCO3→CaO+CO2

b. CO2 is passed through a concentrated solution of sodium chloride and ammonia:



1. Textile industry

2. Paper industry

3. Disinfectant

Washing soda

Chemical name – Sodium hydrogen carbonate

Chemical formula – NaHCO3

Preparation (Solvay process) – 

a. Limestone is heated: CaCO3 → CaO + CO2

b. CO2 is passed through a concentrated solution of sodium chloride and ammonia:

NaCl(aq) + NH3(g) + CO2(g) + H2O(l) → NaHCO3(aq) + NH4Cl(aq)


1. In glass, soap and paper industries

2. Softening of water

3. Domestic cleaner

Crystals of salts

Certain salts form crystals by combining with a definite proportion of water. The water that combines with the salt is called water of crystallisation.

Plaster of paris

Gypsum, CaSO4.2H2O (s) on heating at 100°C (373K) gives CaSO4. ½ H2O and 3/2 H2O

CaSO4. ½ H2O is plaster of paris.

CaSO4. ½ H2O means two formula units of CaSO4 share one molecule of water.

Uses – cast for healing fractures.

4. About Salts

About  salts

  1. Strong acid  +  strong base       neutral salt :  pH = 7
  2. Salt of strong   +  weak base      Acidic salt :    pH <7
  3. Salt of strong base + weak acid  Basic salt  :  pH  >7

Chemical from common salt

1;  sodium hydroxide  ( NaOH)

  When electricity is passed through an aqueous solution of NaCl (called brine) it decomposes to form NaOH.

This process is called chlor- alkali process.

2NaCl  +   2H2O              2NaOH + Cl2    + H2

 At cathode  :     H2    gas

 At anode :    Cl2 gas

Near cathode :   NaOH solution is formed


  1. Cl2 :   Water treatment , PVC , pesticides.
  2. H2 :      Fuels,  margarine.
  3. Hcl :       Medicines, cleaning steels.
  4.  NaOH :   De- greasing metals, soaps and paper making.

(2) Bleaching powder  ( CaOCl2)

   Bleaching powder is produced by the action of chlorine on dry slaked lime   ( Ca(OH)2).

 Cl2  +  Ca(OH)2        CaOCl2  +   H2O

 USES :   * Bleaching cotton and linen in textile industry

  • Bleaching washed clothes in laundry .
  • Oxidising in chemical industries.
  •  Make drinking water free from germs

(3)   Baking Soda ( NaHCO3)

 The chemical name of the compound is sodium hydrogen carbonate.

NaCl+H2O+CO2+NH3      NH4Cl  +  NaHCO3

                                     (Ammonium Chloride) (Sodium hydrogen carbonate)

  • IT is a mild non- corrosive base.
  • When it is heated during cooking.

2 NaHCO3      Na2CO3  +   H2O  +  CO2


  1. For making baking powder, which is a mixture of baking soda ( sodium hydrogen carbonate ) and tartaric acid. Following reaction takes place.

 NaHCO3   +  H+         CO2  H2O + Sodium salt of acid

  1. Sodium hydrogen carbonate is an ingredient in antacids.
  2. Used in soda-acid , fire extinguisher

 (4)  Washing Soda  :-   ( Na2 CO3IOH2O)

  Recrystallisation of sodium carbonate gives washing sod. It is a basic salt.

  Na2CO3 + IOH2O     →    Na2CO3. IOH2O


  1. In glass , soap and paper industries.
  2. Manufacture of borax
  3. Cleaning agent for domestic purpose.
  4. For removing permanent hardness of water.

 (5)  Plaster of paris CaSO4 .2H2 O. 

On heating gypsum ( CaSo4.2H2O) at 373k, ut loses water molecules and becomes plaster of paris (POP) .

It is a white powder and on mixing with waater it changes to gypsum.

 Removing water of crystallization.


It is a fixed number of water molecules present in one formula unit of a salt.

For Example; 

  • CuSO4.5H2O   has 5 water molecules.
  • Na2CO3.10H2  has 10 water molecules.
  •  CaSO4.2H2O  has 2 water molecules.