Acids , Bases and Salts : Notes, Class 10 Science PDF Download

 Page 1


 
 
ACIDS, BASES AND SALTS
 
In our day-to-day life we use and see many things like lemon 
juice, vinegar, chilly, baking soda, soap and detergent, milk, 
orange, caustic soda etc. . Some of these things taste sour and 
some bitter. This taste of the things is due to the presence of 
acids or bases respectively in them. If someone in the family is 
suffering from the problem of acidity due to overeating, we 
suggest that person to have baking soda solution. This is 
because baking soda is basic in nature and therefore it will 
neutralize the effect of an acid giving relief to that person. 
 
Indicators 
An indicator is a substance which tells us whether the other 
substance is an acid or a base by changing their colour and 
smell. 
 
Types Of Indicators 
1. Indicators showing different colours in acidic and basic 
media. (Colour indicators) 
2. Indicators giving different ordour in acidic or basic media. 
(Olfactory indicators) 
 
Colour Indicators 
(i) Natural Indicators 
 Litmus Solution 
It is a purple coloured dye extracted from lichen plant. 
Two types of litmus solutions are used as indicators they 
are blue litmus which is obtained by acidifying the purple 
litmus and red litmus which is obtained by making the 
purple dye alkaline. 
Acids turn blue litmus to red whereas bases turn red 
 litmus to blue. 
(ii) Synthetic Indicators 
They are methyl orange and phenolphthalein. These are 
manufactured in the industry. 
Acids turn phenolphthalein colourless whereas bases turn 
it pink. 
Acids turn methyl orange pink whereas bases turn it 
yellow. 
Olfactory Indicators 
(i) Onion 
(ii) Vanilla essence 
(iii) Clove oil 
The ordour of these substances change when acid or base 
is added. 
 
Acids 
General Properties Of Acids 
(i) Acids are sour in taste. 
(ii) Acids turn blue litmus to red and methyl orange pink. 
(iii) Acid are oily liquids. 
(iv) Acids are drying and dehydrating in nature. 
(v) Acids can conduct electricity in their aqueous solutions. 
 
Chemical Properties Of Acids 
(i) Reaction With Metals 
Acids react with metals to form salts and hydrogen gas is 
released. 
Metal  +  Acid  ??? Salt  + Hydrogen gas 
Zn  + 2HCl  ???  ZnCl
2
  + H
2
 
 
Zn  + H
2
SO
4
  ???  ZnSO
4
  +  H
2
 
2 K  +  2HCl  ???  2KCl  +  H
2
 
2 K  +  H
2
SO
4
  ???  K
2
SO
4
  +  H
2 
The above reactions are also called displacement reactions. 
Note 
Metals present in reactivity series below hydrogen do not react 
with dilute acids. 
 
(ii) Reaction With Metal Carbonates And Metal 
Bicarbonates 
 Acids react with metal carbonates and metal bicarbonates 
to give out carbon dioxide with effervescence (bubbles) 
and forming the corresponding salt and water. 
 Metal carbonate +  Acid  ???  Metal salt  +  CO
2
  + 
and bicarbonate          H
2
O 
 K
2
CO
3
  +  HCl  ???  KCl  + H
2
O  +  CO
2
 
 KHCO
3
  HCl  ???  KCl  +  H
2
O  +  CO
2
 
 CaCO
3
  +  H
2
SO
4
  ???  CaSO
4
  +  H
2
O  +  CO
2
 
 2 Ca(HCO
3
)
2
 + 2  H
2
SO
4
 ???2 CaSO
4
 + 4 H
2
O + 4 
CO
2
 
 
(iii) Reaction With Bases 
 Acids react with bases to form salt and water. These types 
of reactions are called neutralization reactions. 
 Acid  +  Base  ???  Salt  +  Water 
 HCl  +  NaOH  ???  NaCl  +  H
2
O  
 
(iv) Reaction With Metallic Oxides 
As metallic oxides are also basic in nature therefore the 
acids react with metallic oxides to form salt and water.  
 Metallic Oxide  +  Acid  ???  Salt  +  Water 
 CuO  +  2  HCl  ???  CuCl
2
  +  H
2
O 
  
Bases 
General Properties Of Bases 
(i) Bases are bitter in taste. 
(ii) Bases turn red litmus to blue and methyl orange to yellow. 
(iii) Bases are slippery or soapy to touch. 
(iv) Some bases are also corrosive in nature; they cause 
burning sensation like caustic soda. 
(v) Bases conduct electricity in their aqueous solutions. 
 
Chemical Properties Of Bases 
(i) Reaction With Metals 
Some bases (strong) like sodium hydroxide and potassium 
hydroxide react with strong active metals like aluminium 
and zinc to form corresponding salt and water. 
Base  +  Metal  ???  Salt  +  Hydrogen Gas 
2 NaOH  +  Zn  ???  Na
2
ZnO
2
  +  H
2 
2 NaOH  +  Al  + 2H
2
O  ???  2NaAlO
2
  +  3H
2 
 
(ii) Reaction With Acids 
Bases react with acids to form salt and water. This 
reaction is also called neutralization reaction. 
Base  +  Acid  ???  Salt  +  Water 
Page 2


 
 
ACIDS, BASES AND SALTS
 
In our day-to-day life we use and see many things like lemon 
juice, vinegar, chilly, baking soda, soap and detergent, milk, 
orange, caustic soda etc. . Some of these things taste sour and 
some bitter. This taste of the things is due to the presence of 
acids or bases respectively in them. If someone in the family is 
suffering from the problem of acidity due to overeating, we 
suggest that person to have baking soda solution. This is 
because baking soda is basic in nature and therefore it will 
neutralize the effect of an acid giving relief to that person. 
 
Indicators 
An indicator is a substance which tells us whether the other 
substance is an acid or a base by changing their colour and 
smell. 
 
Types Of Indicators 
1. Indicators showing different colours in acidic and basic 
media. (Colour indicators) 
2. Indicators giving different ordour in acidic or basic media. 
(Olfactory indicators) 
 
Colour Indicators 
(i) Natural Indicators 
 Litmus Solution 
It is a purple coloured dye extracted from lichen plant. 
Two types of litmus solutions are used as indicators they 
are blue litmus which is obtained by acidifying the purple 
litmus and red litmus which is obtained by making the 
purple dye alkaline. 
Acids turn blue litmus to red whereas bases turn red 
 litmus to blue. 
(ii) Synthetic Indicators 
They are methyl orange and phenolphthalein. These are 
manufactured in the industry. 
Acids turn phenolphthalein colourless whereas bases turn 
it pink. 
Acids turn methyl orange pink whereas bases turn it 
yellow. 
Olfactory Indicators 
(i) Onion 
(ii) Vanilla essence 
(iii) Clove oil 
The ordour of these substances change when acid or base 
is added. 
 
Acids 
General Properties Of Acids 
(i) Acids are sour in taste. 
(ii) Acids turn blue litmus to red and methyl orange pink. 
(iii) Acid are oily liquids. 
(iv) Acids are drying and dehydrating in nature. 
(v) Acids can conduct electricity in their aqueous solutions. 
 
Chemical Properties Of Acids 
(i) Reaction With Metals 
Acids react with metals to form salts and hydrogen gas is 
released. 
Metal  +  Acid  ??? Salt  + Hydrogen gas 
Zn  + 2HCl  ???  ZnCl
2
  + H
2
 
 
Zn  + H
2
SO
4
  ???  ZnSO
4
  +  H
2
 
2 K  +  2HCl  ???  2KCl  +  H
2
 
2 K  +  H
2
SO
4
  ???  K
2
SO
4
  +  H
2 
The above reactions are also called displacement reactions. 
Note 
Metals present in reactivity series below hydrogen do not react 
with dilute acids. 
 
(ii) Reaction With Metal Carbonates And Metal 
Bicarbonates 
 Acids react with metal carbonates and metal bicarbonates 
to give out carbon dioxide with effervescence (bubbles) 
and forming the corresponding salt and water. 
 Metal carbonate +  Acid  ???  Metal salt  +  CO
2
  + 
and bicarbonate          H
2
O 
 K
2
CO
3
  +  HCl  ???  KCl  + H
2
O  +  CO
2
 
 KHCO
3
  HCl  ???  KCl  +  H
2
O  +  CO
2
 
 CaCO
3
  +  H
2
SO
4
  ???  CaSO
4
  +  H
2
O  +  CO
2
 
 2 Ca(HCO
3
)
2
 + 2  H
2
SO
4
 ???2 CaSO
4
 + 4 H
2
O + 4 
CO
2
 
 
(iii) Reaction With Bases 
 Acids react with bases to form salt and water. These types 
of reactions are called neutralization reactions. 
 Acid  +  Base  ???  Salt  +  Water 
 HCl  +  NaOH  ???  NaCl  +  H
2
O  
 
(iv) Reaction With Metallic Oxides 
As metallic oxides are also basic in nature therefore the 
acids react with metallic oxides to form salt and water.  
 Metallic Oxide  +  Acid  ???  Salt  +  Water 
 CuO  +  2  HCl  ???  CuCl
2
  +  H
2
O 
  
Bases 
General Properties Of Bases 
(i) Bases are bitter in taste. 
(ii) Bases turn red litmus to blue and methyl orange to yellow. 
(iii) Bases are slippery or soapy to touch. 
(iv) Some bases are also corrosive in nature; they cause 
burning sensation like caustic soda. 
(v) Bases conduct electricity in their aqueous solutions. 
 
Chemical Properties Of Bases 
(i) Reaction With Metals 
Some bases (strong) like sodium hydroxide and potassium 
hydroxide react with strong active metals like aluminium 
and zinc to form corresponding salt and water. 
Base  +  Metal  ???  Salt  +  Hydrogen Gas 
2 NaOH  +  Zn  ???  Na
2
ZnO
2
  +  H
2 
2 NaOH  +  Al  + 2H
2
O  ???  2NaAlO
2
  +  3H
2 
 
(ii) Reaction With Acids 
Bases react with acids to form salt and water. This 
reaction is also called neutralization reaction. 
Base  +  Acid  ???  Salt  +  Water 
 
NaOH  +  HCl  ???  NaCl  +  H
2
O 
(iii) Reaction With Non Metallic Oxides 
As non metallic oxides are acidic in nature, bases react 
with them to form salt and water. 
Ca(OH)
2
  +  CO
2
  ???  CaCO
3
  +  H
2
O 
On passing excess of carbon dioxide the following reaction 
takes place 
CaCO
3
  +  H
2
O  +  CO
2
  ???  Ca(HCO
3
)
2 
  
More About Acids And Bases 
 
Chemical Nature Of Acids 
Acids are the substances which contain hydrogen ions 
(protons). These hydrogen ions in the form of hydrogen gas 
are released out when acids react with active metals. 
 
Conduction Of Electricity By Acids Or Bases 
Acids in their aqueous solution conduct electricity. There are 
many substances which have hydrogen in them but all of them 
do not conduct electricity. It is because hydrogen is not 
present in ionic form and these substances do not dissociate in 
their aqueous solutions.  
Example 
Alcohol, Sugar 
Acids release H
+
 ions only in the presence of water. 
 
Experiment To Illustrate Conduction Of Electricity By 
An Acid 
(i) Take a rubber cork. 
(ii) Fix two nails in it. 
(iii) Place this cork in a 100 ml beaker. 
(iv) Connect the nails to a 6 V battery with the help of wires. 
(v) Connect a small torch bulb or an ammeter into the circuit. 
(vi) Now add dilute sulphuric acid into the beaker so that the 
nails are completely immersed. 
(vii) Switch on the battery. 
 
Observation 
It is observed that the bulb starts glowing or the needle of the 
ammeter shows deflection. This shows that dilute acids 
conduct electricity. 
 
Dilution Of Concentrated Acid 
Mixing of an acid with water is called dilution of an acid. It is 
an exothermic process. 
To dilute an acid it is added to water slowly and is continuously 
stirred. It is because dilution of concentrated acid is a highly 
exothermic reaction. If water will be added to acid the heat 
produced will be so large that the solution may splash out or 
the glass beaker may break due to excessive heat. Hence for 
dilution, the acid is always added to water and not water into 
acid. 
 
Effect Of Dilution On H
+
 Ion Concentration Of An Acid  
When an acid is diluted, the concentration of H
+
 ions per unit 
volume decreases and the solution becomes less acidic. 
 
Chemical Nature Of Base 
Bases are oxides and hydroxides of metals. A base is a 
substance which when dissolved in water gives hydroxide ions 
(OH
-
) in the solution. Bases which are soluble in water are 
called alkalis. 
All alkalis are bases whereas all bases are not alkalis. 
Because all bases do not dissolve in water therefore they do 
not release OH
-
 ions in their aqueous solutions. 
Examples Of Some Bases 
CaO, MgO, CuO, NaOH, Mg(OH)
2
, Ca(OH)
2
, NH
4
OH. 
 
Conduction Of Electricity By Bases 
Bases in their aqueous solution conduct electricity. 
Note 
The compound C
2
H
5
OH (ethanol) contains –OH group. But it 
does not ionize in the aqueous solution to give OH
-
 ions. Hence 
it is not a base. 
 
Dilution OF Concentrated Bases 
Just as dilution of concentrated acid is an exothermic process, 
similarly if we dissolve bases like NaOH or KOH in water the 
solution is found to be hotter. Therefore it is also an 
exothermic process. 
 
Effect Of Dilution On OH
-
 Ion Concentration Of A Base 
When a base is diluted, the concentration of OH
-
 ions per unit 
volume decreases and the solution becomes less basic. 
 
How Strong Are The Acid Or Base Solutions 
The strength of acid or base solutions depends upon the 
presence of more and more numbers of H
+
 and OH
-
 ions 
respectively. The method to judge the strength of an acid or a 
base is as follows: - 
(i) By using universal indicator which is a mixture of several 
indicators. It shows different colours at different 
concentrations of H ions in the solution. 
(ii) By using pH scale where ‘p’ stands for ‘potenz’ in German 
meaning power. 
 
pH Scale 
A scale for measuring hydrogen ion concentration is called pH 
scale. On the scale we can measure pH from zero (very acidic) 
to 14 (very basic). Higher is the H
+
 ion concentration, lower is 
the pH value. The pH of a neutral solution is 7. Value less than 
7 represents that the solution is acidic, values more than 7 
represents that the solution is basic. 
 
 pH  =  - log [H
+
] 
The pH of a solution is defined as the negative log of its 
hydrogen ion concentration. 
 
Strong And Weak Acids And Bases 
Strength of an acid or a base depends upon the number of 
ions produced in the solution. Greater is the dissociation i.e., 
greater is the amount of H
+
 or OH
-
 ions produced in the 
solution, stronger is the acid or base. 
 
Strong Acids 
Acids which completely dissociate into ions, are called strong 
acids. For example HCl, H
2
SO
4
 and HNO
3
 are strong acids 
HCl  +  H
2
O  ???  H
+
  +  Cl
- 
HNO
3
  +  H
2
O  ???  H
+
  +  NO
3
-
 
Page 3


 
 
ACIDS, BASES AND SALTS
 
In our day-to-day life we use and see many things like lemon 
juice, vinegar, chilly, baking soda, soap and detergent, milk, 
orange, caustic soda etc. . Some of these things taste sour and 
some bitter. This taste of the things is due to the presence of 
acids or bases respectively in them. If someone in the family is 
suffering from the problem of acidity due to overeating, we 
suggest that person to have baking soda solution. This is 
because baking soda is basic in nature and therefore it will 
neutralize the effect of an acid giving relief to that person. 
 
Indicators 
An indicator is a substance which tells us whether the other 
substance is an acid or a base by changing their colour and 
smell. 
 
Types Of Indicators 
1. Indicators showing different colours in acidic and basic 
media. (Colour indicators) 
2. Indicators giving different ordour in acidic or basic media. 
(Olfactory indicators) 
 
Colour Indicators 
(i) Natural Indicators 
 Litmus Solution 
It is a purple coloured dye extracted from lichen plant. 
Two types of litmus solutions are used as indicators they 
are blue litmus which is obtained by acidifying the purple 
litmus and red litmus which is obtained by making the 
purple dye alkaline. 
Acids turn blue litmus to red whereas bases turn red 
 litmus to blue. 
(ii) Synthetic Indicators 
They are methyl orange and phenolphthalein. These are 
manufactured in the industry. 
Acids turn phenolphthalein colourless whereas bases turn 
it pink. 
Acids turn methyl orange pink whereas bases turn it 
yellow. 
Olfactory Indicators 
(i) Onion 
(ii) Vanilla essence 
(iii) Clove oil 
The ordour of these substances change when acid or base 
is added. 
 
Acids 
General Properties Of Acids 
(i) Acids are sour in taste. 
(ii) Acids turn blue litmus to red and methyl orange pink. 
(iii) Acid are oily liquids. 
(iv) Acids are drying and dehydrating in nature. 
(v) Acids can conduct electricity in their aqueous solutions. 
 
Chemical Properties Of Acids 
(i) Reaction With Metals 
Acids react with metals to form salts and hydrogen gas is 
released. 
Metal  +  Acid  ??? Salt  + Hydrogen gas 
Zn  + 2HCl  ???  ZnCl
2
  + H
2
 
 
Zn  + H
2
SO
4
  ???  ZnSO
4
  +  H
2
 
2 K  +  2HCl  ???  2KCl  +  H
2
 
2 K  +  H
2
SO
4
  ???  K
2
SO
4
  +  H
2 
The above reactions are also called displacement reactions. 
Note 
Metals present in reactivity series below hydrogen do not react 
with dilute acids. 
 
(ii) Reaction With Metal Carbonates And Metal 
Bicarbonates 
 Acids react with metal carbonates and metal bicarbonates 
to give out carbon dioxide with effervescence (bubbles) 
and forming the corresponding salt and water. 
 Metal carbonate +  Acid  ???  Metal salt  +  CO
2
  + 
and bicarbonate          H
2
O 
 K
2
CO
3
  +  HCl  ???  KCl  + H
2
O  +  CO
2
 
 KHCO
3
  HCl  ???  KCl  +  H
2
O  +  CO
2
 
 CaCO
3
  +  H
2
SO
4
  ???  CaSO
4
  +  H
2
O  +  CO
2
 
 2 Ca(HCO
3
)
2
 + 2  H
2
SO
4
 ???2 CaSO
4
 + 4 H
2
O + 4 
CO
2
 
 
(iii) Reaction With Bases 
 Acids react with bases to form salt and water. These types 
of reactions are called neutralization reactions. 
 Acid  +  Base  ???  Salt  +  Water 
 HCl  +  NaOH  ???  NaCl  +  H
2
O  
 
(iv) Reaction With Metallic Oxides 
As metallic oxides are also basic in nature therefore the 
acids react with metallic oxides to form salt and water.  
 Metallic Oxide  +  Acid  ???  Salt  +  Water 
 CuO  +  2  HCl  ???  CuCl
2
  +  H
2
O 
  
Bases 
General Properties Of Bases 
(i) Bases are bitter in taste. 
(ii) Bases turn red litmus to blue and methyl orange to yellow. 
(iii) Bases are slippery or soapy to touch. 
(iv) Some bases are also corrosive in nature; they cause 
burning sensation like caustic soda. 
(v) Bases conduct electricity in their aqueous solutions. 
 
Chemical Properties Of Bases 
(i) Reaction With Metals 
Some bases (strong) like sodium hydroxide and potassium 
hydroxide react with strong active metals like aluminium 
and zinc to form corresponding salt and water. 
Base  +  Metal  ???  Salt  +  Hydrogen Gas 
2 NaOH  +  Zn  ???  Na
2
ZnO
2
  +  H
2 
2 NaOH  +  Al  + 2H
2
O  ???  2NaAlO
2
  +  3H
2 
 
(ii) Reaction With Acids 
Bases react with acids to form salt and water. This 
reaction is also called neutralization reaction. 
Base  +  Acid  ???  Salt  +  Water 
 
NaOH  +  HCl  ???  NaCl  +  H
2
O 
(iii) Reaction With Non Metallic Oxides 
As non metallic oxides are acidic in nature, bases react 
with them to form salt and water. 
Ca(OH)
2
  +  CO
2
  ???  CaCO
3
  +  H
2
O 
On passing excess of carbon dioxide the following reaction 
takes place 
CaCO
3
  +  H
2
O  +  CO
2
  ???  Ca(HCO
3
)
2 
  
More About Acids And Bases 
 
Chemical Nature Of Acids 
Acids are the substances which contain hydrogen ions 
(protons). These hydrogen ions in the form of hydrogen gas 
are released out when acids react with active metals. 
 
Conduction Of Electricity By Acids Or Bases 
Acids in their aqueous solution conduct electricity. There are 
many substances which have hydrogen in them but all of them 
do not conduct electricity. It is because hydrogen is not 
present in ionic form and these substances do not dissociate in 
their aqueous solutions.  
Example 
Alcohol, Sugar 
Acids release H
+
 ions only in the presence of water. 
 
Experiment To Illustrate Conduction Of Electricity By 
An Acid 
(i) Take a rubber cork. 
(ii) Fix two nails in it. 
(iii) Place this cork in a 100 ml beaker. 
(iv) Connect the nails to a 6 V battery with the help of wires. 
(v) Connect a small torch bulb or an ammeter into the circuit. 
(vi) Now add dilute sulphuric acid into the beaker so that the 
nails are completely immersed. 
(vii) Switch on the battery. 
 
Observation 
It is observed that the bulb starts glowing or the needle of the 
ammeter shows deflection. This shows that dilute acids 
conduct electricity. 
 
Dilution Of Concentrated Acid 
Mixing of an acid with water is called dilution of an acid. It is 
an exothermic process. 
To dilute an acid it is added to water slowly and is continuously 
stirred. It is because dilution of concentrated acid is a highly 
exothermic reaction. If water will be added to acid the heat 
produced will be so large that the solution may splash out or 
the glass beaker may break due to excessive heat. Hence for 
dilution, the acid is always added to water and not water into 
acid. 
 
Effect Of Dilution On H
+
 Ion Concentration Of An Acid  
When an acid is diluted, the concentration of H
+
 ions per unit 
volume decreases and the solution becomes less acidic. 
 
Chemical Nature Of Base 
Bases are oxides and hydroxides of metals. A base is a 
substance which when dissolved in water gives hydroxide ions 
(OH
-
) in the solution. Bases which are soluble in water are 
called alkalis. 
All alkalis are bases whereas all bases are not alkalis. 
Because all bases do not dissolve in water therefore they do 
not release OH
-
 ions in their aqueous solutions. 
Examples Of Some Bases 
CaO, MgO, CuO, NaOH, Mg(OH)
2
, Ca(OH)
2
, NH
4
OH. 
 
Conduction Of Electricity By Bases 
Bases in their aqueous solution conduct electricity. 
Note 
The compound C
2
H
5
OH (ethanol) contains –OH group. But it 
does not ionize in the aqueous solution to give OH
-
 ions. Hence 
it is not a base. 
 
Dilution OF Concentrated Bases 
Just as dilution of concentrated acid is an exothermic process, 
similarly if we dissolve bases like NaOH or KOH in water the 
solution is found to be hotter. Therefore it is also an 
exothermic process. 
 
Effect Of Dilution On OH
-
 Ion Concentration Of A Base 
When a base is diluted, the concentration of OH
-
 ions per unit 
volume decreases and the solution becomes less basic. 
 
How Strong Are The Acid Or Base Solutions 
The strength of acid or base solutions depends upon the 
presence of more and more numbers of H
+
 and OH
-
 ions 
respectively. The method to judge the strength of an acid or a 
base is as follows: - 
(i) By using universal indicator which is a mixture of several 
indicators. It shows different colours at different 
concentrations of H ions in the solution. 
(ii) By using pH scale where ‘p’ stands for ‘potenz’ in German 
meaning power. 
 
pH Scale 
A scale for measuring hydrogen ion concentration is called pH 
scale. On the scale we can measure pH from zero (very acidic) 
to 14 (very basic). Higher is the H
+
 ion concentration, lower is 
the pH value. The pH of a neutral solution is 7. Value less than 
7 represents that the solution is acidic, values more than 7 
represents that the solution is basic. 
 
 pH  =  - log [H
+
] 
The pH of a solution is defined as the negative log of its 
hydrogen ion concentration. 
 
Strong And Weak Acids And Bases 
Strength of an acid or a base depends upon the number of 
ions produced in the solution. Greater is the dissociation i.e., 
greater is the amount of H
+
 or OH
-
 ions produced in the 
solution, stronger is the acid or base. 
 
Strong Acids 
Acids which completely dissociate into ions, are called strong 
acids. For example HCl, H
2
SO
4
 and HNO
3
 are strong acids 
HCl  +  H
2
O  ???  H
+
  +  Cl
- 
HNO
3
  +  H
2
O  ???  H
+
  +  NO
3
-
 
 
H
2
SO
4
  +  H
2
O  ???  2 H
+
  +  SO
4
2-
 
The dissociation of strong acids is represented by putting 
single arrow ( ??? ) towards the ions produced. 
 
Weak Acids 
Acids which partially dissociate into ions in their aqueous 
solutions are called weak acids. For example Acetic acid, 
(CH
3
COOH), Carbonic acid (H
2
CO
3
), Phosphoric acid (H
3
PO
4
) 
etc. are called weak acids. 
CH
3
COOH    CH
3
COO
-
  +  H
+
   
H
2
CO
3
     2H
+
  +  CO
3
2-
  
H
3
PO
4
     3H
+
  +  PO
4
3-
  
The dissociation of weak acids is represented by putting a 
double arrow ( ) one pointing towards the ions 
produced and the other pointing towards the undissociated 
ions. 
 
Strong Bases 
Bases which completely dissociate into their ions are called 
strong bases. For example NaOH, KOH. 
KOH  ???  K
+
  +  OH
- 
NaOH  ???  Na
+
  +  OH
- 
 
Weak Bases 
The bases which partially dissociate into their ions are called 
weak bases. For example Ca(OH)
2
, NH
4
OH. 
Ca(OH)
2
     Ca
2+
  +  2OH
-
  
NH
4
OH    NH
4+
  +  OH
-
 
 
Importance Of pH In Every Day Life 
 
Are Plants And Animals pH Sensitive? 
Our body works within pH range of 7.0 to 7.8. Living 
organisms can survive in only a narrow range of pH change. 
When pH of rain water is less than 5.6, it is called acid rain. 
When this acid rain mixes with river water, it makes the water 
acidic due to which the survival of the aquatic animals 
becomes difficult. 
 
pH Of Soil 
Plants require a specific pH range for their healthy growth. To 
maintain their good health the ph of soil should be maintained 
according to the plant’s requirements. 
 
pH In Our Digestive System 
As our stomach secretes hydrochloric acid, the ph of our 
stomach is acidic. This acid helps in the proper digestion of 
food without harming the stomach. During indigestion the 
stomach produces too much acid and it causes pain and 
irritation. To get rid of the pain the people use bases called 
antacids. These antacids neutralize the excess acids. 
 
pH Change As The Cause Of Tooth Decay 
Tooth decay starts when the ph of the mouth is lower than 
5.5. Tooth enamel made up of calcium phosphate is the 
hardest substance in the body. It does not dissolve in water, 
but it is corroded in acidic medium that is pH below 5.5. 
Bacteria present in the mouth produce acids by degradation of 
sugar and food particles remaining in the mouth after eating. 
The best way to prevent this is to clean the mouth after 
eating. Toothpastes which are basic can also help to prevent 
tooth decay. 
 
Self Defense By Animals And Plants Through Chemical 
Warfare 
Bee sting leaves an acid which causes pain and irritation. Use 
of a mild base like baking soda on the stung area gives relief. 
Stinging hair of nettle leaves inject methanoic acid which 
causes burning pain. 
 
Salts 
Salts are the ionic compounds formed by the following 
methods: - 
(i) Neutralization of acids and bases 
(ii) Action of metals on acids 
(iii) Action of metals on carbonates and bicarbonates 
(iv) Action of metals on alkalies 
 
Example 
NaOH  +  HCl  ???  NaCl  +  H
2
O 
Zn  +  H
2
SO
4
  ???  ZnSO
4
  +  H
2
 
CaCO
3
  +  HCl  ???  CaCl
2
  +  H
2
O  +  CO
2
 
NaHCO
3
  +  HCl  ???  NaCl  +  H
2
O  +  CO
2
 
NaOH  +  Zn  ???  Na
2
ZnO
2
  +  H
2
 
 
pH Of Salt Solution 
Depending upon the nature of the acid and the base reacting 
to form the salt, the salts can be classified as follows: - 
(i) Acidic Salts 
(ii) Basic Salts 
(iii) Neutral Salts 
 
Acidic Salts 
A salt of strong acid and weak base is called acidic salt. 
 
Example 
NH
4
Cl, CuSO
4
, AlCl
3
, ZnSO
4
, Ca(NO
3
)
2
 
NH
4
OH  +  HCl  ???  NH
4
Cl  +  H
2
O 
 
Basic Salts 
A salt of strong acid and a weak base is called basic salt. 
 
Example 
Na
2
CO
3
, NaHCO
3
, CH
3
COONa 
NaOH  +  Na
2
CO
3
  ???  Na
2
CO
3
  +  H
2
O 
 
Neutral Salts 
A salt of strong acid and a strong base is called neutral salt. 
 
Example 
NaCl, NaNO
3
, KCl, KNO
3
 
KOH  +  HNO
3
  ???  KNO
3
  +  H
2
O 
 
A salt of weak acid and a weak base is also called neutral salt 
with pH nearly 7. 
 
Example 
CH
3
COONH
4
 
CH
3
COOH  +  NH
4
OH  ???  CH
3
COONH
4
  +  H
2
O 
 
Common Salt 
Chemically common salt is sodium chloride (NaCl). Common 
salt is a mixture of sodium chloride (main constituent), 
magnesium chloride, potassium iodide. 
 
Sources From Where Common Salt Is Obtained 
(i)  Sea Water 
Sea water mostly contains sodium chloride. To extract the 
salt from sea water, it is kept to evaporate in shallow 
tanks. The salt obtained contains impurities of magnesium 
Page 4


 
 
ACIDS, BASES AND SALTS
 
In our day-to-day life we use and see many things like lemon 
juice, vinegar, chilly, baking soda, soap and detergent, milk, 
orange, caustic soda etc. . Some of these things taste sour and 
some bitter. This taste of the things is due to the presence of 
acids or bases respectively in them. If someone in the family is 
suffering from the problem of acidity due to overeating, we 
suggest that person to have baking soda solution. This is 
because baking soda is basic in nature and therefore it will 
neutralize the effect of an acid giving relief to that person. 
 
Indicators 
An indicator is a substance which tells us whether the other 
substance is an acid or a base by changing their colour and 
smell. 
 
Types Of Indicators 
1. Indicators showing different colours in acidic and basic 
media. (Colour indicators) 
2. Indicators giving different ordour in acidic or basic media. 
(Olfactory indicators) 
 
Colour Indicators 
(i) Natural Indicators 
 Litmus Solution 
It is a purple coloured dye extracted from lichen plant. 
Two types of litmus solutions are used as indicators they 
are blue litmus which is obtained by acidifying the purple 
litmus and red litmus which is obtained by making the 
purple dye alkaline. 
Acids turn blue litmus to red whereas bases turn red 
 litmus to blue. 
(ii) Synthetic Indicators 
They are methyl orange and phenolphthalein. These are 
manufactured in the industry. 
Acids turn phenolphthalein colourless whereas bases turn 
it pink. 
Acids turn methyl orange pink whereas bases turn it 
yellow. 
Olfactory Indicators 
(i) Onion 
(ii) Vanilla essence 
(iii) Clove oil 
The ordour of these substances change when acid or base 
is added. 
 
Acids 
General Properties Of Acids 
(i) Acids are sour in taste. 
(ii) Acids turn blue litmus to red and methyl orange pink. 
(iii) Acid are oily liquids. 
(iv) Acids are drying and dehydrating in nature. 
(v) Acids can conduct electricity in their aqueous solutions. 
 
Chemical Properties Of Acids 
(i) Reaction With Metals 
Acids react with metals to form salts and hydrogen gas is 
released. 
Metal  +  Acid  ??? Salt  + Hydrogen gas 
Zn  + 2HCl  ???  ZnCl
2
  + H
2
 
 
Zn  + H
2
SO
4
  ???  ZnSO
4
  +  H
2
 
2 K  +  2HCl  ???  2KCl  +  H
2
 
2 K  +  H
2
SO
4
  ???  K
2
SO
4
  +  H
2 
The above reactions are also called displacement reactions. 
Note 
Metals present in reactivity series below hydrogen do not react 
with dilute acids. 
 
(ii) Reaction With Metal Carbonates And Metal 
Bicarbonates 
 Acids react with metal carbonates and metal bicarbonates 
to give out carbon dioxide with effervescence (bubbles) 
and forming the corresponding salt and water. 
 Metal carbonate +  Acid  ???  Metal salt  +  CO
2
  + 
and bicarbonate          H
2
O 
 K
2
CO
3
  +  HCl  ???  KCl  + H
2
O  +  CO
2
 
 KHCO
3
  HCl  ???  KCl  +  H
2
O  +  CO
2
 
 CaCO
3
  +  H
2
SO
4
  ???  CaSO
4
  +  H
2
O  +  CO
2
 
 2 Ca(HCO
3
)
2
 + 2  H
2
SO
4
 ???2 CaSO
4
 + 4 H
2
O + 4 
CO
2
 
 
(iii) Reaction With Bases 
 Acids react with bases to form salt and water. These types 
of reactions are called neutralization reactions. 
 Acid  +  Base  ???  Salt  +  Water 
 HCl  +  NaOH  ???  NaCl  +  H
2
O  
 
(iv) Reaction With Metallic Oxides 
As metallic oxides are also basic in nature therefore the 
acids react with metallic oxides to form salt and water.  
 Metallic Oxide  +  Acid  ???  Salt  +  Water 
 CuO  +  2  HCl  ???  CuCl
2
  +  H
2
O 
  
Bases 
General Properties Of Bases 
(i) Bases are bitter in taste. 
(ii) Bases turn red litmus to blue and methyl orange to yellow. 
(iii) Bases are slippery or soapy to touch. 
(iv) Some bases are also corrosive in nature; they cause 
burning sensation like caustic soda. 
(v) Bases conduct electricity in their aqueous solutions. 
 
Chemical Properties Of Bases 
(i) Reaction With Metals 
Some bases (strong) like sodium hydroxide and potassium 
hydroxide react with strong active metals like aluminium 
and zinc to form corresponding salt and water. 
Base  +  Metal  ???  Salt  +  Hydrogen Gas 
2 NaOH  +  Zn  ???  Na
2
ZnO
2
  +  H
2 
2 NaOH  +  Al  + 2H
2
O  ???  2NaAlO
2
  +  3H
2 
 
(ii) Reaction With Acids 
Bases react with acids to form salt and water. This 
reaction is also called neutralization reaction. 
Base  +  Acid  ???  Salt  +  Water 
 
NaOH  +  HCl  ???  NaCl  +  H
2
O 
(iii) Reaction With Non Metallic Oxides 
As non metallic oxides are acidic in nature, bases react 
with them to form salt and water. 
Ca(OH)
2
  +  CO
2
  ???  CaCO
3
  +  H
2
O 
On passing excess of carbon dioxide the following reaction 
takes place 
CaCO
3
  +  H
2
O  +  CO
2
  ???  Ca(HCO
3
)
2 
  
More About Acids And Bases 
 
Chemical Nature Of Acids 
Acids are the substances which contain hydrogen ions 
(protons). These hydrogen ions in the form of hydrogen gas 
are released out when acids react with active metals. 
 
Conduction Of Electricity By Acids Or Bases 
Acids in their aqueous solution conduct electricity. There are 
many substances which have hydrogen in them but all of them 
do not conduct electricity. It is because hydrogen is not 
present in ionic form and these substances do not dissociate in 
their aqueous solutions.  
Example 
Alcohol, Sugar 
Acids release H
+
 ions only in the presence of water. 
 
Experiment To Illustrate Conduction Of Electricity By 
An Acid 
(i) Take a rubber cork. 
(ii) Fix two nails in it. 
(iii) Place this cork in a 100 ml beaker. 
(iv) Connect the nails to a 6 V battery with the help of wires. 
(v) Connect a small torch bulb or an ammeter into the circuit. 
(vi) Now add dilute sulphuric acid into the beaker so that the 
nails are completely immersed. 
(vii) Switch on the battery. 
 
Observation 
It is observed that the bulb starts glowing or the needle of the 
ammeter shows deflection. This shows that dilute acids 
conduct electricity. 
 
Dilution Of Concentrated Acid 
Mixing of an acid with water is called dilution of an acid. It is 
an exothermic process. 
To dilute an acid it is added to water slowly and is continuously 
stirred. It is because dilution of concentrated acid is a highly 
exothermic reaction. If water will be added to acid the heat 
produced will be so large that the solution may splash out or 
the glass beaker may break due to excessive heat. Hence for 
dilution, the acid is always added to water and not water into 
acid. 
 
Effect Of Dilution On H
+
 Ion Concentration Of An Acid  
When an acid is diluted, the concentration of H
+
 ions per unit 
volume decreases and the solution becomes less acidic. 
 
Chemical Nature Of Base 
Bases are oxides and hydroxides of metals. A base is a 
substance which when dissolved in water gives hydroxide ions 
(OH
-
) in the solution. Bases which are soluble in water are 
called alkalis. 
All alkalis are bases whereas all bases are not alkalis. 
Because all bases do not dissolve in water therefore they do 
not release OH
-
 ions in their aqueous solutions. 
Examples Of Some Bases 
CaO, MgO, CuO, NaOH, Mg(OH)
2
, Ca(OH)
2
, NH
4
OH. 
 
Conduction Of Electricity By Bases 
Bases in their aqueous solution conduct electricity. 
Note 
The compound C
2
H
5
OH (ethanol) contains –OH group. But it 
does not ionize in the aqueous solution to give OH
-
 ions. Hence 
it is not a base. 
 
Dilution OF Concentrated Bases 
Just as dilution of concentrated acid is an exothermic process, 
similarly if we dissolve bases like NaOH or KOH in water the 
solution is found to be hotter. Therefore it is also an 
exothermic process. 
 
Effect Of Dilution On OH
-
 Ion Concentration Of A Base 
When a base is diluted, the concentration of OH
-
 ions per unit 
volume decreases and the solution becomes less basic. 
 
How Strong Are The Acid Or Base Solutions 
The strength of acid or base solutions depends upon the 
presence of more and more numbers of H
+
 and OH
-
 ions 
respectively. The method to judge the strength of an acid or a 
base is as follows: - 
(i) By using universal indicator which is a mixture of several 
indicators. It shows different colours at different 
concentrations of H ions in the solution. 
(ii) By using pH scale where ‘p’ stands for ‘potenz’ in German 
meaning power. 
 
pH Scale 
A scale for measuring hydrogen ion concentration is called pH 
scale. On the scale we can measure pH from zero (very acidic) 
to 14 (very basic). Higher is the H
+
 ion concentration, lower is 
the pH value. The pH of a neutral solution is 7. Value less than 
7 represents that the solution is acidic, values more than 7 
represents that the solution is basic. 
 
 pH  =  - log [H
+
] 
The pH of a solution is defined as the negative log of its 
hydrogen ion concentration. 
 
Strong And Weak Acids And Bases 
Strength of an acid or a base depends upon the number of 
ions produced in the solution. Greater is the dissociation i.e., 
greater is the amount of H
+
 or OH
-
 ions produced in the 
solution, stronger is the acid or base. 
 
Strong Acids 
Acids which completely dissociate into ions, are called strong 
acids. For example HCl, H
2
SO
4
 and HNO
3
 are strong acids 
HCl  +  H
2
O  ???  H
+
  +  Cl
- 
HNO
3
  +  H
2
O  ???  H
+
  +  NO
3
-
 
 
H
2
SO
4
  +  H
2
O  ???  2 H
+
  +  SO
4
2-
 
The dissociation of strong acids is represented by putting 
single arrow ( ??? ) towards the ions produced. 
 
Weak Acids 
Acids which partially dissociate into ions in their aqueous 
solutions are called weak acids. For example Acetic acid, 
(CH
3
COOH), Carbonic acid (H
2
CO
3
), Phosphoric acid (H
3
PO
4
) 
etc. are called weak acids. 
CH
3
COOH    CH
3
COO
-
  +  H
+
   
H
2
CO
3
     2H
+
  +  CO
3
2-
  
H
3
PO
4
     3H
+
  +  PO
4
3-
  
The dissociation of weak acids is represented by putting a 
double arrow ( ) one pointing towards the ions 
produced and the other pointing towards the undissociated 
ions. 
 
Strong Bases 
Bases which completely dissociate into their ions are called 
strong bases. For example NaOH, KOH. 
KOH  ???  K
+
  +  OH
- 
NaOH  ???  Na
+
  +  OH
- 
 
Weak Bases 
The bases which partially dissociate into their ions are called 
weak bases. For example Ca(OH)
2
, NH
4
OH. 
Ca(OH)
2
     Ca
2+
  +  2OH
-
  
NH
4
OH    NH
4+
  +  OH
-
 
 
Importance Of pH In Every Day Life 
 
Are Plants And Animals pH Sensitive? 
Our body works within pH range of 7.0 to 7.8. Living 
organisms can survive in only a narrow range of pH change. 
When pH of rain water is less than 5.6, it is called acid rain. 
When this acid rain mixes with river water, it makes the water 
acidic due to which the survival of the aquatic animals 
becomes difficult. 
 
pH Of Soil 
Plants require a specific pH range for their healthy growth. To 
maintain their good health the ph of soil should be maintained 
according to the plant’s requirements. 
 
pH In Our Digestive System 
As our stomach secretes hydrochloric acid, the ph of our 
stomach is acidic. This acid helps in the proper digestion of 
food without harming the stomach. During indigestion the 
stomach produces too much acid and it causes pain and 
irritation. To get rid of the pain the people use bases called 
antacids. These antacids neutralize the excess acids. 
 
pH Change As The Cause Of Tooth Decay 
Tooth decay starts when the ph of the mouth is lower than 
5.5. Tooth enamel made up of calcium phosphate is the 
hardest substance in the body. It does not dissolve in water, 
but it is corroded in acidic medium that is pH below 5.5. 
Bacteria present in the mouth produce acids by degradation of 
sugar and food particles remaining in the mouth after eating. 
The best way to prevent this is to clean the mouth after 
eating. Toothpastes which are basic can also help to prevent 
tooth decay. 
 
Self Defense By Animals And Plants Through Chemical 
Warfare 
Bee sting leaves an acid which causes pain and irritation. Use 
of a mild base like baking soda on the stung area gives relief. 
Stinging hair of nettle leaves inject methanoic acid which 
causes burning pain. 
 
Salts 
Salts are the ionic compounds formed by the following 
methods: - 
(i) Neutralization of acids and bases 
(ii) Action of metals on acids 
(iii) Action of metals on carbonates and bicarbonates 
(iv) Action of metals on alkalies 
 
Example 
NaOH  +  HCl  ???  NaCl  +  H
2
O 
Zn  +  H
2
SO
4
  ???  ZnSO
4
  +  H
2
 
CaCO
3
  +  HCl  ???  CaCl
2
  +  H
2
O  +  CO
2
 
NaHCO
3
  +  HCl  ???  NaCl  +  H
2
O  +  CO
2
 
NaOH  +  Zn  ???  Na
2
ZnO
2
  +  H
2
 
 
pH Of Salt Solution 
Depending upon the nature of the acid and the base reacting 
to form the salt, the salts can be classified as follows: - 
(i) Acidic Salts 
(ii) Basic Salts 
(iii) Neutral Salts 
 
Acidic Salts 
A salt of strong acid and weak base is called acidic salt. 
 
Example 
NH
4
Cl, CuSO
4
, AlCl
3
, ZnSO
4
, Ca(NO
3
)
2
 
NH
4
OH  +  HCl  ???  NH
4
Cl  +  H
2
O 
 
Basic Salts 
A salt of strong acid and a weak base is called basic salt. 
 
Example 
Na
2
CO
3
, NaHCO
3
, CH
3
COONa 
NaOH  +  Na
2
CO
3
  ???  Na
2
CO
3
  +  H
2
O 
 
Neutral Salts 
A salt of strong acid and a strong base is called neutral salt. 
 
Example 
NaCl, NaNO
3
, KCl, KNO
3
 
KOH  +  HNO
3
  ???  KNO
3
  +  H
2
O 
 
A salt of weak acid and a weak base is also called neutral salt 
with pH nearly 7. 
 
Example 
CH
3
COONH
4
 
CH
3
COOH  +  NH
4
OH  ???  CH
3
COONH
4
  +  H
2
O 
 
Common Salt 
Chemically common salt is sodium chloride (NaCl). Common 
salt is a mixture of sodium chloride (main constituent), 
magnesium chloride, potassium iodide. 
 
Sources From Where Common Salt Is Obtained 
(i)  Sea Water 
Sea water mostly contains sodium chloride. To extract the 
salt from sea water, it is kept to evaporate in shallow 
tanks. The salt obtained contains impurities of magnesium 
 
chloride, magnesium sulphate. The salt is therefore 
purified. 
(ii) Rock Salt 
Beds of rock salt have been formed as a result of drying 
up of seas.  
(iii) Inland Lakes 
Large quantities of salts are obtained by the natural 
evaporation of water of the inland lakes. 
            
Physical Properties Of Common Salt 
(i) It is a crystalline colourless solid. 
(ii) It is soluble in water. 
(iii) It is hygroscopic in nature due to the presence of 
magnesium and calcium chloride in it. 
(iv) It has a melting point of 820
0
C. 
 
Note 
Common salt is an important raw material for the 
manufacturing of a number of other chemicals such as sodium 
chloride, hydrochloric acid, sodium hydroxide, washing soda, 
baking soda, bleaching powder and many others. 
 
Caustic Soda  
Chemical Name: - Sodium Hydroxide 
Chemical Formula : - NaOH 
Manufacturing Process : - Chlor Alkali Process 
 
Process 
Caustic soda is manufactured by the electrolysis of an aqueous 
solution of sodium chloride called brine. 
       
In aqueous solution, sodium chloride dissociates 
NaCl (aq)  ???  Na
+
  +  Cl
-
 
 
Water also dissociates to a small extent 
H
2
O  ???  H
+
  +   OH
-
 
 
At Cathode the following reaction takes place 
H
+
  +  e
-
  ???  H 
H  +  H  ???  H
2
 
 
At Anode the following reaction takes place 
Cl
-
  ???  Cl  +  e
-
 
Cl  +  Cl  ???  Cl
2
 
 
Na
+
 and OH
-
 ions left in the solution combine with each other 
to form sodium hydroxide. 
Na
+
  +  OH
-
  ???  NaOH 
The sodium hydroxide solution is formed near the cathode. 
 
Uses Of Caustic Soda 
(i) It is used in the manufacturing of soaps and detergents. 
(ii) It is used for degreasing metals. 
(iii) It is used in the paper industry. 
(iv) It is used in the manufacturing of dyes. 
(v) Used in petroleum refining. 
(vi) It is used for making cotton unshrinkable. 
(vii) It is used as a laboratory reagent. 
 
Bleaching Powder 
Chemical Name: - Calcium Oxychloride 
Chemical Formula: - CaOCl
2
 or Ca(OCl)Cl 
Manufacturing Process: - Hasenclever Plant 
 
Manufacture Of Bleaching Powder 
Bleaching powder is manufactured by passing chlorine gas 
over dry slaked lime. 
 
 
2 2
Cl ) OH ( Ca + ? ? ?   O H CaOCl
2 2
+ 
 Slaked        Chlorine         Bleaching      Water 
 Lime         Gas          Powder 
The manufacture of bleaching powder is carried out by two 
methods. 
1. Hasenclever Method 
2. Bachmann’s Method 
Hasenclever Method 
Hasenclever plant consists of a number of cast iron cylinders 
each provided with a rotating shaft fitted with blades and 
arranged horizontally one above the other. 
 
Steps For The Manufacturing 
1. Slaked Lime is introduced through the hopper at the top. 
2. Chlorine gas is introduced from the lower most cylinder. 
3. The slaked lime is pushed onwards by the rotating shaft 
until it falls into the next lower cylinder. 
4. The down going lime and upcoming chlorine come in 
contact with each other and the reaction take place. By 
the time slaked lime reaches the lowest cylinder it has 
been completely saturated with chlorine gas and is 
converted into bleaching powder. The bleaching powder is 
collected in a vessel placed underneath by an outlet in the 
lowest cylinder. The waste gases escape through an 
outlet at the top. 
 
Physical Properties 
1. It is yellowish white in colour. 
2. It is a powdered solid. 
3. It strongly smells of chlorine. 
4. It is soluble in cold water. The small insoluble portion is 
always left behind as the lime present in it. 
 
Chemical Properties 
1. Reaction With Carbon Dioxide 
When exposed to air bleaching powder decomposes  
gradually due to its reaction with carbon dioxide present 
in the atmosphere giving off chlorine. 
 
2
CaOCl 
+ 
2
CO 
? ? ? 
Calcium oxychloride  Carbon dioxide  
(Bleaching powder)  (From air)  
 
Page 5


 
 
ACIDS, BASES AND SALTS
 
In our day-to-day life we use and see many things like lemon 
juice, vinegar, chilly, baking soda, soap and detergent, milk, 
orange, caustic soda etc. . Some of these things taste sour and 
some bitter. This taste of the things is due to the presence of 
acids or bases respectively in them. If someone in the family is 
suffering from the problem of acidity due to overeating, we 
suggest that person to have baking soda solution. This is 
because baking soda is basic in nature and therefore it will 
neutralize the effect of an acid giving relief to that person. 
 
Indicators 
An indicator is a substance which tells us whether the other 
substance is an acid or a base by changing their colour and 
smell. 
 
Types Of Indicators 
1. Indicators showing different colours in acidic and basic 
media. (Colour indicators) 
2. Indicators giving different ordour in acidic or basic media. 
(Olfactory indicators) 
 
Colour Indicators 
(i) Natural Indicators 
 Litmus Solution 
It is a purple coloured dye extracted from lichen plant. 
Two types of litmus solutions are used as indicators they 
are blue litmus which is obtained by acidifying the purple 
litmus and red litmus which is obtained by making the 
purple dye alkaline. 
Acids turn blue litmus to red whereas bases turn red 
 litmus to blue. 
(ii) Synthetic Indicators 
They are methyl orange and phenolphthalein. These are 
manufactured in the industry. 
Acids turn phenolphthalein colourless whereas bases turn 
it pink. 
Acids turn methyl orange pink whereas bases turn it 
yellow. 
Olfactory Indicators 
(i) Onion 
(ii) Vanilla essence 
(iii) Clove oil 
The ordour of these substances change when acid or base 
is added. 
 
Acids 
General Properties Of Acids 
(i) Acids are sour in taste. 
(ii) Acids turn blue litmus to red and methyl orange pink. 
(iii) Acid are oily liquids. 
(iv) Acids are drying and dehydrating in nature. 
(v) Acids can conduct electricity in their aqueous solutions. 
 
Chemical Properties Of Acids 
(i) Reaction With Metals 
Acids react with metals to form salts and hydrogen gas is 
released. 
Metal  +  Acid  ??? Salt  + Hydrogen gas 
Zn  + 2HCl  ???  ZnCl
2
  + H
2
 
 
Zn  + H
2
SO
4
  ???  ZnSO
4
  +  H
2
 
2 K  +  2HCl  ???  2KCl  +  H
2
 
2 K  +  H
2
SO
4
  ???  K
2
SO
4
  +  H
2 
The above reactions are also called displacement reactions. 
Note 
Metals present in reactivity series below hydrogen do not react 
with dilute acids. 
 
(ii) Reaction With Metal Carbonates And Metal 
Bicarbonates 
 Acids react with metal carbonates and metal bicarbonates 
to give out carbon dioxide with effervescence (bubbles) 
and forming the corresponding salt and water. 
 Metal carbonate +  Acid  ???  Metal salt  +  CO
2
  + 
and bicarbonate          H
2
O 
 K
2
CO
3
  +  HCl  ???  KCl  + H
2
O  +  CO
2
 
 KHCO
3
  HCl  ???  KCl  +  H
2
O  +  CO
2
 
 CaCO
3
  +  H
2
SO
4
  ???  CaSO
4
  +  H
2
O  +  CO
2
 
 2 Ca(HCO
3
)
2
 + 2  H
2
SO
4
 ???2 CaSO
4
 + 4 H
2
O + 4 
CO
2
 
 
(iii) Reaction With Bases 
 Acids react with bases to form salt and water. These types 
of reactions are called neutralization reactions. 
 Acid  +  Base  ???  Salt  +  Water 
 HCl  +  NaOH  ???  NaCl  +  H
2
O  
 
(iv) Reaction With Metallic Oxides 
As metallic oxides are also basic in nature therefore the 
acids react with metallic oxides to form salt and water.  
 Metallic Oxide  +  Acid  ???  Salt  +  Water 
 CuO  +  2  HCl  ???  CuCl
2
  +  H
2
O 
  
Bases 
General Properties Of Bases 
(i) Bases are bitter in taste. 
(ii) Bases turn red litmus to blue and methyl orange to yellow. 
(iii) Bases are slippery or soapy to touch. 
(iv) Some bases are also corrosive in nature; they cause 
burning sensation like caustic soda. 
(v) Bases conduct electricity in their aqueous solutions. 
 
Chemical Properties Of Bases 
(i) Reaction With Metals 
Some bases (strong) like sodium hydroxide and potassium 
hydroxide react with strong active metals like aluminium 
and zinc to form corresponding salt and water. 
Base  +  Metal  ???  Salt  +  Hydrogen Gas 
2 NaOH  +  Zn  ???  Na
2
ZnO
2
  +  H
2 
2 NaOH  +  Al  + 2H
2
O  ???  2NaAlO
2
  +  3H
2 
 
(ii) Reaction With Acids 
Bases react with acids to form salt and water. This 
reaction is also called neutralization reaction. 
Base  +  Acid  ???  Salt  +  Water 
 
NaOH  +  HCl  ???  NaCl  +  H
2
O 
(iii) Reaction With Non Metallic Oxides 
As non metallic oxides are acidic in nature, bases react 
with them to form salt and water. 
Ca(OH)
2
  +  CO
2
  ???  CaCO
3
  +  H
2
O 
On passing excess of carbon dioxide the following reaction 
takes place 
CaCO
3
  +  H
2
O  +  CO
2
  ???  Ca(HCO
3
)
2 
  
More About Acids And Bases 
 
Chemical Nature Of Acids 
Acids are the substances which contain hydrogen ions 
(protons). These hydrogen ions in the form of hydrogen gas 
are released out when acids react with active metals. 
 
Conduction Of Electricity By Acids Or Bases 
Acids in their aqueous solution conduct electricity. There are 
many substances which have hydrogen in them but all of them 
do not conduct electricity. It is because hydrogen is not 
present in ionic form and these substances do not dissociate in 
their aqueous solutions.  
Example 
Alcohol, Sugar 
Acids release H
+
 ions only in the presence of water. 
 
Experiment To Illustrate Conduction Of Electricity By 
An Acid 
(i) Take a rubber cork. 
(ii) Fix two nails in it. 
(iii) Place this cork in a 100 ml beaker. 
(iv) Connect the nails to a 6 V battery with the help of wires. 
(v) Connect a small torch bulb or an ammeter into the circuit. 
(vi) Now add dilute sulphuric acid into the beaker so that the 
nails are completely immersed. 
(vii) Switch on the battery. 
 
Observation 
It is observed that the bulb starts glowing or the needle of the 
ammeter shows deflection. This shows that dilute acids 
conduct electricity. 
 
Dilution Of Concentrated Acid 
Mixing of an acid with water is called dilution of an acid. It is 
an exothermic process. 
To dilute an acid it is added to water slowly and is continuously 
stirred. It is because dilution of concentrated acid is a highly 
exothermic reaction. If water will be added to acid the heat 
produced will be so large that the solution may splash out or 
the glass beaker may break due to excessive heat. Hence for 
dilution, the acid is always added to water and not water into 
acid. 
 
Effect Of Dilution On H
+
 Ion Concentration Of An Acid  
When an acid is diluted, the concentration of H
+
 ions per unit 
volume decreases and the solution becomes less acidic. 
 
Chemical Nature Of Base 
Bases are oxides and hydroxides of metals. A base is a 
substance which when dissolved in water gives hydroxide ions 
(OH
-
) in the solution. Bases which are soluble in water are 
called alkalis. 
All alkalis are bases whereas all bases are not alkalis. 
Because all bases do not dissolve in water therefore they do 
not release OH
-
 ions in their aqueous solutions. 
Examples Of Some Bases 
CaO, MgO, CuO, NaOH, Mg(OH)
2
, Ca(OH)
2
, NH
4
OH. 
 
Conduction Of Electricity By Bases 
Bases in their aqueous solution conduct electricity. 
Note 
The compound C
2
H
5
OH (ethanol) contains –OH group. But it 
does not ionize in the aqueous solution to give OH
-
 ions. Hence 
it is not a base. 
 
Dilution OF Concentrated Bases 
Just as dilution of concentrated acid is an exothermic process, 
similarly if we dissolve bases like NaOH or KOH in water the 
solution is found to be hotter. Therefore it is also an 
exothermic process. 
 
Effect Of Dilution On OH
-
 Ion Concentration Of A Base 
When a base is diluted, the concentration of OH
-
 ions per unit 
volume decreases and the solution becomes less basic. 
 
How Strong Are The Acid Or Base Solutions 
The strength of acid or base solutions depends upon the 
presence of more and more numbers of H
+
 and OH
-
 ions 
respectively. The method to judge the strength of an acid or a 
base is as follows: - 
(i) By using universal indicator which is a mixture of several 
indicators. It shows different colours at different 
concentrations of H ions in the solution. 
(ii) By using pH scale where ‘p’ stands for ‘potenz’ in German 
meaning power. 
 
pH Scale 
A scale for measuring hydrogen ion concentration is called pH 
scale. On the scale we can measure pH from zero (very acidic) 
to 14 (very basic). Higher is the H
+
 ion concentration, lower is 
the pH value. The pH of a neutral solution is 7. Value less than 
7 represents that the solution is acidic, values more than 7 
represents that the solution is basic. 
 
 pH  =  - log [H
+
] 
The pH of a solution is defined as the negative log of its 
hydrogen ion concentration. 
 
Strong And Weak Acids And Bases 
Strength of an acid or a base depends upon the number of 
ions produced in the solution. Greater is the dissociation i.e., 
greater is the amount of H
+
 or OH
-
 ions produced in the 
solution, stronger is the acid or base. 
 
Strong Acids 
Acids which completely dissociate into ions, are called strong 
acids. For example HCl, H
2
SO
4
 and HNO
3
 are strong acids 
HCl  +  H
2
O  ???  H
+
  +  Cl
- 
HNO
3
  +  H
2
O  ???  H
+
  +  NO
3
-
 
 
H
2
SO
4
  +  H
2
O  ???  2 H
+
  +  SO
4
2-
 
The dissociation of strong acids is represented by putting 
single arrow ( ??? ) towards the ions produced. 
 
Weak Acids 
Acids which partially dissociate into ions in their aqueous 
solutions are called weak acids. For example Acetic acid, 
(CH
3
COOH), Carbonic acid (H
2
CO
3
), Phosphoric acid (H
3
PO
4
) 
etc. are called weak acids. 
CH
3
COOH    CH
3
COO
-
  +  H
+
   
H
2
CO
3
     2H
+
  +  CO
3
2-
  
H
3
PO
4
     3H
+
  +  PO
4
3-
  
The dissociation of weak acids is represented by putting a 
double arrow ( ) one pointing towards the ions 
produced and the other pointing towards the undissociated 
ions. 
 
Strong Bases 
Bases which completely dissociate into their ions are called 
strong bases. For example NaOH, KOH. 
KOH  ???  K
+
  +  OH
- 
NaOH  ???  Na
+
  +  OH
- 
 
Weak Bases 
The bases which partially dissociate into their ions are called 
weak bases. For example Ca(OH)
2
, NH
4
OH. 
Ca(OH)
2
     Ca
2+
  +  2OH
-
  
NH
4
OH    NH
4+
  +  OH
-
 
 
Importance Of pH In Every Day Life 
 
Are Plants And Animals pH Sensitive? 
Our body works within pH range of 7.0 to 7.8. Living 
organisms can survive in only a narrow range of pH change. 
When pH of rain water is less than 5.6, it is called acid rain. 
When this acid rain mixes with river water, it makes the water 
acidic due to which the survival of the aquatic animals 
becomes difficult. 
 
pH Of Soil 
Plants require a specific pH range for their healthy growth. To 
maintain their good health the ph of soil should be maintained 
according to the plant’s requirements. 
 
pH In Our Digestive System 
As our stomach secretes hydrochloric acid, the ph of our 
stomach is acidic. This acid helps in the proper digestion of 
food without harming the stomach. During indigestion the 
stomach produces too much acid and it causes pain and 
irritation. To get rid of the pain the people use bases called 
antacids. These antacids neutralize the excess acids. 
 
pH Change As The Cause Of Tooth Decay 
Tooth decay starts when the ph of the mouth is lower than 
5.5. Tooth enamel made up of calcium phosphate is the 
hardest substance in the body. It does not dissolve in water, 
but it is corroded in acidic medium that is pH below 5.5. 
Bacteria present in the mouth produce acids by degradation of 
sugar and food particles remaining in the mouth after eating. 
The best way to prevent this is to clean the mouth after 
eating. Toothpastes which are basic can also help to prevent 
tooth decay. 
 
Self Defense By Animals And Plants Through Chemical 
Warfare 
Bee sting leaves an acid which causes pain and irritation. Use 
of a mild base like baking soda on the stung area gives relief. 
Stinging hair of nettle leaves inject methanoic acid which 
causes burning pain. 
 
Salts 
Salts are the ionic compounds formed by the following 
methods: - 
(i) Neutralization of acids and bases 
(ii) Action of metals on acids 
(iii) Action of metals on carbonates and bicarbonates 
(iv) Action of metals on alkalies 
 
Example 
NaOH  +  HCl  ???  NaCl  +  H
2
O 
Zn  +  H
2
SO
4
  ???  ZnSO
4
  +  H
2
 
CaCO
3
  +  HCl  ???  CaCl
2
  +  H
2
O  +  CO
2
 
NaHCO
3
  +  HCl  ???  NaCl  +  H
2
O  +  CO
2
 
NaOH  +  Zn  ???  Na
2
ZnO
2
  +  H
2
 
 
pH Of Salt Solution 
Depending upon the nature of the acid and the base reacting 
to form the salt, the salts can be classified as follows: - 
(i) Acidic Salts 
(ii) Basic Salts 
(iii) Neutral Salts 
 
Acidic Salts 
A salt of strong acid and weak base is called acidic salt. 
 
Example 
NH
4
Cl, CuSO
4
, AlCl
3
, ZnSO
4
, Ca(NO
3
)
2
 
NH
4
OH  +  HCl  ???  NH
4
Cl  +  H
2
O 
 
Basic Salts 
A salt of strong acid and a weak base is called basic salt. 
 
Example 
Na
2
CO
3
, NaHCO
3
, CH
3
COONa 
NaOH  +  Na
2
CO
3
  ???  Na
2
CO
3
  +  H
2
O 
 
Neutral Salts 
A salt of strong acid and a strong base is called neutral salt. 
 
Example 
NaCl, NaNO
3
, KCl, KNO
3
 
KOH  +  HNO
3
  ???  KNO
3
  +  H
2
O 
 
A salt of weak acid and a weak base is also called neutral salt 
with pH nearly 7. 
 
Example 
CH
3
COONH
4
 
CH
3
COOH  +  NH
4
OH  ???  CH
3
COONH
4
  +  H
2
O 
 
Common Salt 
Chemically common salt is sodium chloride (NaCl). Common 
salt is a mixture of sodium chloride (main constituent), 
magnesium chloride, potassium iodide. 
 
Sources From Where Common Salt Is Obtained 
(i)  Sea Water 
Sea water mostly contains sodium chloride. To extract the 
salt from sea water, it is kept to evaporate in shallow 
tanks. The salt obtained contains impurities of magnesium 
 
chloride, magnesium sulphate. The salt is therefore 
purified. 
(ii) Rock Salt 
Beds of rock salt have been formed as a result of drying 
up of seas.  
(iii) Inland Lakes 
Large quantities of salts are obtained by the natural 
evaporation of water of the inland lakes. 
            
Physical Properties Of Common Salt 
(i) It is a crystalline colourless solid. 
(ii) It is soluble in water. 
(iii) It is hygroscopic in nature due to the presence of 
magnesium and calcium chloride in it. 
(iv) It has a melting point of 820
0
C. 
 
Note 
Common salt is an important raw material for the 
manufacturing of a number of other chemicals such as sodium 
chloride, hydrochloric acid, sodium hydroxide, washing soda, 
baking soda, bleaching powder and many others. 
 
Caustic Soda  
Chemical Name: - Sodium Hydroxide 
Chemical Formula : - NaOH 
Manufacturing Process : - Chlor Alkali Process 
 
Process 
Caustic soda is manufactured by the electrolysis of an aqueous 
solution of sodium chloride called brine. 
       
In aqueous solution, sodium chloride dissociates 
NaCl (aq)  ???  Na
+
  +  Cl
-
 
 
Water also dissociates to a small extent 
H
2
O  ???  H
+
  +   OH
-
 
 
At Cathode the following reaction takes place 
H
+
  +  e
-
  ???  H 
H  +  H  ???  H
2
 
 
At Anode the following reaction takes place 
Cl
-
  ???  Cl  +  e
-
 
Cl  +  Cl  ???  Cl
2
 
 
Na
+
 and OH
-
 ions left in the solution combine with each other 
to form sodium hydroxide. 
Na
+
  +  OH
-
  ???  NaOH 
The sodium hydroxide solution is formed near the cathode. 
 
Uses Of Caustic Soda 
(i) It is used in the manufacturing of soaps and detergents. 
(ii) It is used for degreasing metals. 
(iii) It is used in the paper industry. 
(iv) It is used in the manufacturing of dyes. 
(v) Used in petroleum refining. 
(vi) It is used for making cotton unshrinkable. 
(vii) It is used as a laboratory reagent. 
 
Bleaching Powder 
Chemical Name: - Calcium Oxychloride 
Chemical Formula: - CaOCl
2
 or Ca(OCl)Cl 
Manufacturing Process: - Hasenclever Plant 
 
Manufacture Of Bleaching Powder 
Bleaching powder is manufactured by passing chlorine gas 
over dry slaked lime. 
 
 
2 2
Cl ) OH ( Ca + ? ? ?   O H CaOCl
2 2
+ 
 Slaked        Chlorine         Bleaching      Water 
 Lime         Gas          Powder 
The manufacture of bleaching powder is carried out by two 
methods. 
1. Hasenclever Method 
2. Bachmann’s Method 
Hasenclever Method 
Hasenclever plant consists of a number of cast iron cylinders 
each provided with a rotating shaft fitted with blades and 
arranged horizontally one above the other. 
 
Steps For The Manufacturing 
1. Slaked Lime is introduced through the hopper at the top. 
2. Chlorine gas is introduced from the lower most cylinder. 
3. The slaked lime is pushed onwards by the rotating shaft 
until it falls into the next lower cylinder. 
4. The down going lime and upcoming chlorine come in 
contact with each other and the reaction take place. By 
the time slaked lime reaches the lowest cylinder it has 
been completely saturated with chlorine gas and is 
converted into bleaching powder. The bleaching powder is 
collected in a vessel placed underneath by an outlet in the 
lowest cylinder. The waste gases escape through an 
outlet at the top. 
 
Physical Properties 
1. It is yellowish white in colour. 
2. It is a powdered solid. 
3. It strongly smells of chlorine. 
4. It is soluble in cold water. The small insoluble portion is 
always left behind as the lime present in it. 
 
Chemical Properties 
1. Reaction With Carbon Dioxide 
When exposed to air bleaching powder decomposes  
gradually due to its reaction with carbon dioxide present 
in the atmosphere giving off chlorine. 
 
2
CaOCl 
+ 
2
CO 
? ? ? 
Calcium oxychloride  Carbon dioxide  
(Bleaching powder)  (From air)  
 
 
3
CaCO 
+ 
2
Cl 
Calcium carbonate  Chlorine 
Bleaching powder always smells of chlorine because the 
carbon dioxide present in air decomposes it slowly to 
produce chlorine gas. 
 
2. Reaction With Acids 
  
 (i) Reaction With Dilute Sulphuric Acid  
When bleaching powder is treated with an excess of 
dilute sulphuric acid, then all the chlorine present in it 
is liberated. 
 
2
CaOCl 
+ 
4 2
SO H 
? ? ? 
Calcium oxychloride  Sulphuric acid  
(Bleaching powder)  (Dilute)  
  
4
CaSO 
+ 
2
Cl 
+ 
O H
2
 
Calcium sulphate  
Chlorine 
Gas 
 Water 
 
 Available Chlorine 
The amount of chlorine which is liberated during reaction 
of bleaching powder with acid is called available chlorine. 
Greater the amount of available chlorine more superior 
the bleaching powder would be. A good sample of 
bleaching powder contains 35 to 38 percent of available 
chlorine. 
 
2. Reaction With Dilute Hydrochloric Acid 
When bleaching powder is treated with an excess of dilute 
hydrochloric acid, all the chlorine present in it is liberated. 
 
2
CaOCl 
+ HCl 
? ? ? 
Calcium oxychloride  Hydrochloric acid  
(Bleaching powder)  (Dilute)  
 
2
CaCl 
+ 
2
Cl 
+ 
O H
2
 
Calcium Chloride  Chlorine Gas  Water 
Uses Of Bleaching Powder 
1. Bleaching powder is used for bleaching cotton and linen in 
textile industry and for bleaching wood pulp in paper 
industry. It is also used for bleaching clothes in laundry.  
2. It is used for the manufacture of Chloroform (CHCl
3
) 
3. Bleaching powder is used for making wool unshrinkable. 
4. It is used as an oxidizing agent in many chemical 
industries. 
5. It is used for disinfecting lavatories, drainages and 
ditches. 
6. It is used as disinfectant and germicide in sterilization of 
water. 
 
Plaster Of Paris (POP) 
Chemical Name: - Calcium Sulphate Hemi hydrate 
Chemical Formula: - CaSO
4 
.
 
2
1
 H
2
O 
Preparation Of Plaster Of Paris 
It is prepared from Gypsum ( O H 2 . CaSO
2 4
) at 100
0
C (373 K) 
in a kiln. At 100
0
C gypsum looses three fourth of its water of 
crystallization and forms plaster of paris. 
 
O H 2 . CaSO
2 4
 
Gypsum 
) K 373 (
C 100 to Heat
? ? ? ? ? ? ?
o
 
O H
2
1
. CaSO
2 4
 
+ 
? O H
2
1
1
2
 
Plaster Of Paris  Water 
Heating of Gypsum should be controlled carefully. The 
temperature should not be allowed to go beyond 100
0
C 
because above 100
0
C all water of crystallization is eliminated 
and anhydrous calcium sulphate called dead burnt plaster 
(CaSO
4
) is formed. It does not have the properties of plaster 
of paris. 
 
Physical Properties 
1. It is a white powder 
2. It can settle into hard mass. 
 
Chemical Properties 
1. Reaction With Water 
When water is added to plaster of Paris it set into a hard 
mass in about half an hour due to dehydration. 
O H
2
1
. CaSO
2 4
 
 
Plaster Of Paris 
 
+ 
O H
2
1
1
2
 
 Water 
 
? ? ?
 
 
O H 2 . CaSO
2 4
 
 
Gypsum 
(sets as hard mass) 
The process is known as setting of plaster of Paris. It is an 
exothermic reaction. 
 
Uses Of Plaster Of Paris 
1. It is used in making cast of statues, toys, models, and 
decorative articles. 
2. It is used for making fire proof materials. 
3. It is used for making chalks for writing on the blackboard. 
4. It is used for setting fractured bones. 
5. It is used in dental surgery for making casts of denture. 
6. It is used for sealing air gaps. 
 
Baking Soda 
Chemical Name: - Sodium Hydrogen Carbonate  Or 
        Sodium Bicarbonate 
Chemical Formula: - NaHCO
3
 
 
Preparation Of Sodium Hydrogen Carbonate 
In the laboratory and on a small scale baking soda is prepared 
by passing carbon dioxide gas through a cold saturated 
solution of sodium carbonate. Being less soluble, sodium 
bicarbonate settles down as white crystals. 
3 2 2 3 2
NaHCO 2 CO O H CO Na ? ? ? ? + + 
      Sodium Bicarbonate  
 
Manufacture Of Sodium Hydrogen Carbonate (Baking 
Soda) 
Raw Materials 
1. Concentrated Solution Of Sodium Chloride (NaCl) 
Common Salt (Brine). 
2. Ammonia Gas (NH
3
) 
3. Carbon Dioxide (Obtained By Heating Limestone CaCO
3
) 
 
On large scale sodium hydrogen carbonate is obtained as an 
intermediate product in the Solvay process of manufacture 
of washing soda by passing carbon dioxide through brine 
solution saturated with ammonia. The reaction for the 
preparation of baking soda can also be written as: - 
Carbonation Of Ammoniacle Brine 
NaCl + 
3
NH 
+ 
O H
2
 
+ 
2
CO 
Sodium  Ammonia  Water  Carbon 
chloride      Dioxide 
 
    Ammoniacal brine