Concept - Acids, Bases & Salts Class 10 Notes | EduRev

Class 10 : Concept - Acids, Bases & Salts Class 10 Notes | EduRev

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Class X: Chemistry  
Chapter 2: Acids, Bases and Salts 
Top Concepts 
1. Definition of acids , bases and salts: 
 
Acids Bases Salts 
Sour in taste 
Bitter in taste & 
soapy to touch 
Acid + Base ? Salt 
+ Water 
Give H
+
 or H
3
O
+
 
ions in aqueous 
solutions 
Give OH
-
 ions in 
aqueous solutions 
 
 
2. On the basis of origin, acids are classified as: 
a. Organic acids: Acids derived from living organisms like plants and 
animals are called organic acids. They are weak acids and are not 
harmful for living organisms. For example: citric acid is present in 
fruits, acetic acid present in vinegar, oxalic acid present in 
tomato, tartaric acid present in tamarind, lactic acid present in 
sour milk and curd. 
b. Mineral acids: They are also called inorganic acids. They are 
dangerous and corrosive. Special precautions have to be taken 
while handling them. For example: sulphuric acid (H
2
SO
4
), 
hydrochloric acid (HCl) etc. 
 
3. On the basis of their strength, acids are classified as: 
a. Strong acids: Strong acids are those acids which completely 
dissociate into its ions in aqueous solutions. Example: nitric acid 
(HNO
3
), sulphuric acid (H
2
SO
4
), hydrochloric acid (HCl).  
b. Weak acids: Weak acids are those acids which do not completely 
dissociate into its ions in aqueous solutions. For example: 
carbonic acid (H
2
CO
3
), acetic acid (CH
3
COOH).  
 
4. On the basis of their concentration, acids are classified as:  
a. Dilute acids: Have a low concentration of acids in aqueous 
solutions.  
b. Concentrated acids: Have a high concentration of acids in 
aqueous solutions. 
 
5. Alkalies: Water soluble bases are called alkalies. For example: Sodium 
hydroxide (NaOH), potassium hydroxide (KOH).  
 
6. On the basis of their strength, bases are classified as: 
a. Strong bases: Strong bases are those bases which completely 
dissociate into its ions in aqueous solutions. Example: sodium 
hydroxide (NaOH), potassium hydroxide (KOH).  
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Class X: Chemistry  
Chapter 2: Acids, Bases and Salts 
Top Concepts 
1. Definition of acids , bases and salts: 
 
Acids Bases Salts 
Sour in taste 
Bitter in taste & 
soapy to touch 
Acid + Base ? Salt 
+ Water 
Give H
+
 or H
3
O
+
 
ions in aqueous 
solutions 
Give OH
-
 ions in 
aqueous solutions 
 
 
2. On the basis of origin, acids are classified as: 
a. Organic acids: Acids derived from living organisms like plants and 
animals are called organic acids. They are weak acids and are not 
harmful for living organisms. For example: citric acid is present in 
fruits, acetic acid present in vinegar, oxalic acid present in 
tomato, tartaric acid present in tamarind, lactic acid present in 
sour milk and curd. 
b. Mineral acids: They are also called inorganic acids. They are 
dangerous and corrosive. Special precautions have to be taken 
while handling them. For example: sulphuric acid (H
2
SO
4
), 
hydrochloric acid (HCl) etc. 
 
3. On the basis of their strength, acids are classified as: 
a. Strong acids: Strong acids are those acids which completely 
dissociate into its ions in aqueous solutions. Example: nitric acid 
(HNO
3
), sulphuric acid (H
2
SO
4
), hydrochloric acid (HCl).  
b. Weak acids: Weak acids are those acids which do not completely 
dissociate into its ions in aqueous solutions. For example: 
carbonic acid (H
2
CO
3
), acetic acid (CH
3
COOH).  
 
4. On the basis of their concentration, acids are classified as:  
a. Dilute acids: Have a low concentration of acids in aqueous 
solutions.  
b. Concentrated acids: Have a high concentration of acids in 
aqueous solutions. 
 
5. Alkalies: Water soluble bases are called alkalies. For example: Sodium 
hydroxide (NaOH), potassium hydroxide (KOH).  
 
6. On the basis of their strength, bases are classified as: 
a. Strong bases: Strong bases are those bases which completely 
dissociate into its ions in aqueous solutions. Example: sodium 
hydroxide (NaOH), potassium hydroxide (KOH).  
 
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b. Weak bases: Weak bases are those bases which do not 
completely dissociate into its ions in aqueous solutions. For 
example: ammonium hydroxide (NH
4
OH).  
 
7. On the basis of their concentration, bases are classified as:  
a. Dilute bases: Have a low concentration of alkali in aqueous 
solutions.  
b. Concentrated bases: Have a high concentration of alkali in 
aqueous solutions. 
 
8. Acids and bases conduct electricity because they produce ions in 
water. There is a flow of electric current through the solution by ions. 
 
9. Indicators are those chemical substances which behave differently in 
acidic and basic medium and help in determining the chemical nature 
of the substance. Acid base indicators indicate the presence of an acid 
or a base by a change in their colour or smell.  
 
10. Indicators can be natural or synthetic.   
 
11. Olfactory indicators: These are those indicators whose odour changes 
in acidic or basic medium. Example: onion 
 
 
12. Onion: Smell of onion diminishes in a base and remains as it is in an 
acid.  
 
13. Vanilla essence: The odour of vanilla essence disappears when it is 
added to a base. The odour of vanilla essence persists when it is added 
to an acid.  
 
 
14. Turmeric: In acids, yellow colour of turmeric remains yellow. In bases, 
yellow colour of turmeric turns red. 
 
15. Litmus: Litmus is a natural indicator. Litmus solution is a purple dye 
which is extracted from lichen. Acids turn blue litmus red. Bases turn 
red litmus blue. Water is essential for acids and bases to change the 
colour of litmus paper. Remember that litmus paper will act as an 
indicator only if either the litmus paper is moist or the acid or base is 
in the form of aqueous solution. This is because acids and bases 
release H
+
 and OH
-
 ions respectively in aqueous solutions. 
 
16. Phenolphthalein: Phenolphthalein remains colourless in acids but turn 
pink in bases. 
 
17. Methyl orange: Methyl orange turns pink in acids and becomes yellow 
in bases. 
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Class X: Chemistry  
Chapter 2: Acids, Bases and Salts 
Top Concepts 
1. Definition of acids , bases and salts: 
 
Acids Bases Salts 
Sour in taste 
Bitter in taste & 
soapy to touch 
Acid + Base ? Salt 
+ Water 
Give H
+
 or H
3
O
+
 
ions in aqueous 
solutions 
Give OH
-
 ions in 
aqueous solutions 
 
 
2. On the basis of origin, acids are classified as: 
a. Organic acids: Acids derived from living organisms like plants and 
animals are called organic acids. They are weak acids and are not 
harmful for living organisms. For example: citric acid is present in 
fruits, acetic acid present in vinegar, oxalic acid present in 
tomato, tartaric acid present in tamarind, lactic acid present in 
sour milk and curd. 
b. Mineral acids: They are also called inorganic acids. They are 
dangerous and corrosive. Special precautions have to be taken 
while handling them. For example: sulphuric acid (H
2
SO
4
), 
hydrochloric acid (HCl) etc. 
 
3. On the basis of their strength, acids are classified as: 
a. Strong acids: Strong acids are those acids which completely 
dissociate into its ions in aqueous solutions. Example: nitric acid 
(HNO
3
), sulphuric acid (H
2
SO
4
), hydrochloric acid (HCl).  
b. Weak acids: Weak acids are those acids which do not completely 
dissociate into its ions in aqueous solutions. For example: 
carbonic acid (H
2
CO
3
), acetic acid (CH
3
COOH).  
 
4. On the basis of their concentration, acids are classified as:  
a. Dilute acids: Have a low concentration of acids in aqueous 
solutions.  
b. Concentrated acids: Have a high concentration of acids in 
aqueous solutions. 
 
5. Alkalies: Water soluble bases are called alkalies. For example: Sodium 
hydroxide (NaOH), potassium hydroxide (KOH).  
 
6. On the basis of their strength, bases are classified as: 
a. Strong bases: Strong bases are those bases which completely 
dissociate into its ions in aqueous solutions. Example: sodium 
hydroxide (NaOH), potassium hydroxide (KOH).  
 
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b. Weak bases: Weak bases are those bases which do not 
completely dissociate into its ions in aqueous solutions. For 
example: ammonium hydroxide (NH
4
OH).  
 
7. On the basis of their concentration, bases are classified as:  
a. Dilute bases: Have a low concentration of alkali in aqueous 
solutions.  
b. Concentrated bases: Have a high concentration of alkali in 
aqueous solutions. 
 
8. Acids and bases conduct electricity because they produce ions in 
water. There is a flow of electric current through the solution by ions. 
 
9. Indicators are those chemical substances which behave differently in 
acidic and basic medium and help in determining the chemical nature 
of the substance. Acid base indicators indicate the presence of an acid 
or a base by a change in their colour or smell.  
 
10. Indicators can be natural or synthetic.   
 
11. Olfactory indicators: These are those indicators whose odour changes 
in acidic or basic medium. Example: onion 
 
 
12. Onion: Smell of onion diminishes in a base and remains as it is in an 
acid.  
 
13. Vanilla essence: The odour of vanilla essence disappears when it is 
added to a base. The odour of vanilla essence persists when it is added 
to an acid.  
 
 
14. Turmeric: In acids, yellow colour of turmeric remains yellow. In bases, 
yellow colour of turmeric turns red. 
 
15. Litmus: Litmus is a natural indicator. Litmus solution is a purple dye 
which is extracted from lichen. Acids turn blue litmus red. Bases turn 
red litmus blue. Water is essential for acids and bases to change the 
colour of litmus paper. Remember that litmus paper will act as an 
indicator only if either the litmus paper is moist or the acid or base is 
in the form of aqueous solution. This is because acids and bases 
release H
+
 and OH
-
 ions respectively in aqueous solutions. 
 
16. Phenolphthalein: Phenolphthalein remains colourless in acids but turn 
pink in bases. 
 
17. Methyl orange: Methyl orange turns pink in acids and becomes yellow 
in bases. 
 
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18. Reaction of acids and bases with water: 
Acids Bases 
Release H
+
 or H
3
O
+
 ions in water Release OH
-
 ions in water 
HCl + H
2
O ? H
3
O
+
 + Cl
-
 
2
H O
NaOH(s) Na (aq) OH (aq)
+ -
??? ? + 
 
19. Reaction of acids and bases with metals:  
Metals displace hydrogen from the acids and form salt and hydrogen 
gas. This is a displacement reaction. So, acids react with only those 
metals which are placed above hydrogen in the reactivity series so that 
metals can displace hydrogen from acids. 
Zn + H
2
SO
4
 ? ZnSO
4
 + H
2
 
Metal  Acid        Salt     Hydrogen gas 
 
Bases react with some metals to form salt and hydrogen gas.  
Zn + 2 NaOH ?  Na
2
ZnO
2
 + H
2 
Metal   Base          Sodium   Hydrogen gas 
                            zincate 
                             (salt) 
Bases do not react with all the metals to form salt and water. 
 
20. Reaction of acids and bases with metal carbonates:  
Acids react with metal carbonate to form salt, water and release 
carbon dioxide. 
2 3 2 2
Na CO 2HCl 2 NaCl CO H O + ? + + 
Bases do not react with metal carbonates. 
 
21. Reaction of acids and bases with metal bicarbonates:  
Acids react with metal bicarbonate to form salt, water and release 
carbon dioxide. 
3 2 2
NaHCO HCl NaCl CO H O + ? + + 
Bases do not react with metal bicarbonates. 
 
22. Reaction of acids with bases: Neutralisation reaction: 
Acids react with bases to form salt and water. 
HCl + NaOH ? NaCl + H
2
O 
                  or 
      H
+
 +OH
-
 ? H
2
O 
 
23. Reaction of acids with metallic oxides: 
Metallic oxides are basic. Therefore, acids react with metallic oxides to 
form salt and water. 
HCl + CuO ? CuCl
2
 + H
2
O 
 
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1 
Class X: Chemistry  
Chapter 2: Acids, Bases and Salts 
Top Concepts 
1. Definition of acids , bases and salts: 
 
Acids Bases Salts 
Sour in taste 
Bitter in taste & 
soapy to touch 
Acid + Base ? Salt 
+ Water 
Give H
+
 or H
3
O
+
 
ions in aqueous 
solutions 
Give OH
-
 ions in 
aqueous solutions 
 
 
2. On the basis of origin, acids are classified as: 
a. Organic acids: Acids derived from living organisms like plants and 
animals are called organic acids. They are weak acids and are not 
harmful for living organisms. For example: citric acid is present in 
fruits, acetic acid present in vinegar, oxalic acid present in 
tomato, tartaric acid present in tamarind, lactic acid present in 
sour milk and curd. 
b. Mineral acids: They are also called inorganic acids. They are 
dangerous and corrosive. Special precautions have to be taken 
while handling them. For example: sulphuric acid (H
2
SO
4
), 
hydrochloric acid (HCl) etc. 
 
3. On the basis of their strength, acids are classified as: 
a. Strong acids: Strong acids are those acids which completely 
dissociate into its ions in aqueous solutions. Example: nitric acid 
(HNO
3
), sulphuric acid (H
2
SO
4
), hydrochloric acid (HCl).  
b. Weak acids: Weak acids are those acids which do not completely 
dissociate into its ions in aqueous solutions. For example: 
carbonic acid (H
2
CO
3
), acetic acid (CH
3
COOH).  
 
4. On the basis of their concentration, acids are classified as:  
a. Dilute acids: Have a low concentration of acids in aqueous 
solutions.  
b. Concentrated acids: Have a high concentration of acids in 
aqueous solutions. 
 
5. Alkalies: Water soluble bases are called alkalies. For example: Sodium 
hydroxide (NaOH), potassium hydroxide (KOH).  
 
6. On the basis of their strength, bases are classified as: 
a. Strong bases: Strong bases are those bases which completely 
dissociate into its ions in aqueous solutions. Example: sodium 
hydroxide (NaOH), potassium hydroxide (KOH).  
 
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b. Weak bases: Weak bases are those bases which do not 
completely dissociate into its ions in aqueous solutions. For 
example: ammonium hydroxide (NH
4
OH).  
 
7. On the basis of their concentration, bases are classified as:  
a. Dilute bases: Have a low concentration of alkali in aqueous 
solutions.  
b. Concentrated bases: Have a high concentration of alkali in 
aqueous solutions. 
 
8. Acids and bases conduct electricity because they produce ions in 
water. There is a flow of electric current through the solution by ions. 
 
9. Indicators are those chemical substances which behave differently in 
acidic and basic medium and help in determining the chemical nature 
of the substance. Acid base indicators indicate the presence of an acid 
or a base by a change in their colour or smell.  
 
10. Indicators can be natural or synthetic.   
 
11. Olfactory indicators: These are those indicators whose odour changes 
in acidic or basic medium. Example: onion 
 
 
12. Onion: Smell of onion diminishes in a base and remains as it is in an 
acid.  
 
13. Vanilla essence: The odour of vanilla essence disappears when it is 
added to a base. The odour of vanilla essence persists when it is added 
to an acid.  
 
 
14. Turmeric: In acids, yellow colour of turmeric remains yellow. In bases, 
yellow colour of turmeric turns red. 
 
15. Litmus: Litmus is a natural indicator. Litmus solution is a purple dye 
which is extracted from lichen. Acids turn blue litmus red. Bases turn 
red litmus blue. Water is essential for acids and bases to change the 
colour of litmus paper. Remember that litmus paper will act as an 
indicator only if either the litmus paper is moist or the acid or base is 
in the form of aqueous solution. This is because acids and bases 
release H
+
 and OH
-
 ions respectively in aqueous solutions. 
 
16. Phenolphthalein: Phenolphthalein remains colourless in acids but turn 
pink in bases. 
 
17. Methyl orange: Methyl orange turns pink in acids and becomes yellow 
in bases. 
 
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18. Reaction of acids and bases with water: 
Acids Bases 
Release H
+
 or H
3
O
+
 ions in water Release OH
-
 ions in water 
HCl + H
2
O ? H
3
O
+
 + Cl
-
 
2
H O
NaOH(s) Na (aq) OH (aq)
+ -
??? ? + 
 
19. Reaction of acids and bases with metals:  
Metals displace hydrogen from the acids and form salt and hydrogen 
gas. This is a displacement reaction. So, acids react with only those 
metals which are placed above hydrogen in the reactivity series so that 
metals can displace hydrogen from acids. 
Zn + H
2
SO
4
 ? ZnSO
4
 + H
2
 
Metal  Acid        Salt     Hydrogen gas 
 
Bases react with some metals to form salt and hydrogen gas.  
Zn + 2 NaOH ?  Na
2
ZnO
2
 + H
2 
Metal   Base          Sodium   Hydrogen gas 
                            zincate 
                             (salt) 
Bases do not react with all the metals to form salt and water. 
 
20. Reaction of acids and bases with metal carbonates:  
Acids react with metal carbonate to form salt, water and release 
carbon dioxide. 
2 3 2 2
Na CO 2HCl 2 NaCl CO H O + ? + + 
Bases do not react with metal carbonates. 
 
21. Reaction of acids and bases with metal bicarbonates:  
Acids react with metal bicarbonate to form salt, water and release 
carbon dioxide. 
3 2 2
NaHCO HCl NaCl CO H O + ? + + 
Bases do not react with metal bicarbonates. 
 
22. Reaction of acids with bases: Neutralisation reaction: 
Acids react with bases to form salt and water. 
HCl + NaOH ? NaCl + H
2
O 
                  or 
      H
+
 +OH
-
 ? H
2
O 
 
23. Reaction of acids with metallic oxides: 
Metallic oxides are basic. Therefore, acids react with metallic oxides to 
form salt and water. 
HCl + CuO ? CuCl
2
 + H
2
O 
 
 
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24. Reaction of bases with non-metallic oxides: Non – metallic oxides are 
acidic in nature. Bases react with non- metallic oxides to form salt and 
water. Example: CO
2
 
Ca(OH)
2
 + CO
2 
? CaCO
3 
+ H
2
O 
 
25. Amphoteric oxides: Oxides which show acidic as well as basic 
properties. For example: ZnO, Al
2
O
3
 
HCl + ZnO ? ZnCl
2
 + H
2
O 
Zn + 2 NaOH ? Na
2
ZnO
2
 + H
2
O 
 
26. Neutral oxides: Oxides which are neither acidic nor basic are called 
neutral oxides. Example: CO 
 
27. pH: It is used to find out the strength of acids and bases i.e., how 
strong or weak the acid or a base is. p in pH stands for ‘potenz’ in 
German. The strength of acids and bases depends on the number of 
H
+
 ions and OH
-
 ions produced respectively. 
 
28. pH scale: A scale for measuring hydrogen ion concentration in a 
solution is called pH scale. 
 
29. On pH scale, we measure pH from 0 to 14.  
pH value: 
pH Type of solution 
Less than 7 Acidic 
Equal to 7 Neutral 
More than 7 Basic 
 
30. More the hydrogen ion (or hydronium ion) concentration, lower is the 
pH value. 
 
31. More the hydroxyl ion concentration, higher is the pH value. 
 
 
32. Variation in pH: 
 
 
 
33. Acids which produce more hydrogen ions are said to be strong acids 
and acids which produce less hydrogen ions are said to be weak acids. 
In other words, strong acids have a lower pH value than weak acids. 
 
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Class X: Chemistry  
Chapter 2: Acids, Bases and Salts 
Top Concepts 
1. Definition of acids , bases and salts: 
 
Acids Bases Salts 
Sour in taste 
Bitter in taste & 
soapy to touch 
Acid + Base ? Salt 
+ Water 
Give H
+
 or H
3
O
+
 
ions in aqueous 
solutions 
Give OH
-
 ions in 
aqueous solutions 
 
 
2. On the basis of origin, acids are classified as: 
a. Organic acids: Acids derived from living organisms like plants and 
animals are called organic acids. They are weak acids and are not 
harmful for living organisms. For example: citric acid is present in 
fruits, acetic acid present in vinegar, oxalic acid present in 
tomato, tartaric acid present in tamarind, lactic acid present in 
sour milk and curd. 
b. Mineral acids: They are also called inorganic acids. They are 
dangerous and corrosive. Special precautions have to be taken 
while handling them. For example: sulphuric acid (H
2
SO
4
), 
hydrochloric acid (HCl) etc. 
 
3. On the basis of their strength, acids are classified as: 
a. Strong acids: Strong acids are those acids which completely 
dissociate into its ions in aqueous solutions. Example: nitric acid 
(HNO
3
), sulphuric acid (H
2
SO
4
), hydrochloric acid (HCl).  
b. Weak acids: Weak acids are those acids which do not completely 
dissociate into its ions in aqueous solutions. For example: 
carbonic acid (H
2
CO
3
), acetic acid (CH
3
COOH).  
 
4. On the basis of their concentration, acids are classified as:  
a. Dilute acids: Have a low concentration of acids in aqueous 
solutions.  
b. Concentrated acids: Have a high concentration of acids in 
aqueous solutions. 
 
5. Alkalies: Water soluble bases are called alkalies. For example: Sodium 
hydroxide (NaOH), potassium hydroxide (KOH).  
 
6. On the basis of their strength, bases are classified as: 
a. Strong bases: Strong bases are those bases which completely 
dissociate into its ions in aqueous solutions. Example: sodium 
hydroxide (NaOH), potassium hydroxide (KOH).  
 
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b. Weak bases: Weak bases are those bases which do not 
completely dissociate into its ions in aqueous solutions. For 
example: ammonium hydroxide (NH
4
OH).  
 
7. On the basis of their concentration, bases are classified as:  
a. Dilute bases: Have a low concentration of alkali in aqueous 
solutions.  
b. Concentrated bases: Have a high concentration of alkali in 
aqueous solutions. 
 
8. Acids and bases conduct electricity because they produce ions in 
water. There is a flow of electric current through the solution by ions. 
 
9. Indicators are those chemical substances which behave differently in 
acidic and basic medium and help in determining the chemical nature 
of the substance. Acid base indicators indicate the presence of an acid 
or a base by a change in their colour or smell.  
 
10. Indicators can be natural or synthetic.   
 
11. Olfactory indicators: These are those indicators whose odour changes 
in acidic or basic medium. Example: onion 
 
 
12. Onion: Smell of onion diminishes in a base and remains as it is in an 
acid.  
 
13. Vanilla essence: The odour of vanilla essence disappears when it is 
added to a base. The odour of vanilla essence persists when it is added 
to an acid.  
 
 
14. Turmeric: In acids, yellow colour of turmeric remains yellow. In bases, 
yellow colour of turmeric turns red. 
 
15. Litmus: Litmus is a natural indicator. Litmus solution is a purple dye 
which is extracted from lichen. Acids turn blue litmus red. Bases turn 
red litmus blue. Water is essential for acids and bases to change the 
colour of litmus paper. Remember that litmus paper will act as an 
indicator only if either the litmus paper is moist or the acid or base is 
in the form of aqueous solution. This is because acids and bases 
release H
+
 and OH
-
 ions respectively in aqueous solutions. 
 
16. Phenolphthalein: Phenolphthalein remains colourless in acids but turn 
pink in bases. 
 
17. Methyl orange: Methyl orange turns pink in acids and becomes yellow 
in bases. 
 
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18. Reaction of acids and bases with water: 
Acids Bases 
Release H
+
 or H
3
O
+
 ions in water Release OH
-
 ions in water 
HCl + H
2
O ? H
3
O
+
 + Cl
-
 
2
H O
NaOH(s) Na (aq) OH (aq)
+ -
??? ? + 
 
19. Reaction of acids and bases with metals:  
Metals displace hydrogen from the acids and form salt and hydrogen 
gas. This is a displacement reaction. So, acids react with only those 
metals which are placed above hydrogen in the reactivity series so that 
metals can displace hydrogen from acids. 
Zn + H
2
SO
4
 ? ZnSO
4
 + H
2
 
Metal  Acid        Salt     Hydrogen gas 
 
Bases react with some metals to form salt and hydrogen gas.  
Zn + 2 NaOH ?  Na
2
ZnO
2
 + H
2 
Metal   Base          Sodium   Hydrogen gas 
                            zincate 
                             (salt) 
Bases do not react with all the metals to form salt and water. 
 
20. Reaction of acids and bases with metal carbonates:  
Acids react with metal carbonate to form salt, water and release 
carbon dioxide. 
2 3 2 2
Na CO 2HCl 2 NaCl CO H O + ? + + 
Bases do not react with metal carbonates. 
 
21. Reaction of acids and bases with metal bicarbonates:  
Acids react with metal bicarbonate to form salt, water and release 
carbon dioxide. 
3 2 2
NaHCO HCl NaCl CO H O + ? + + 
Bases do not react with metal bicarbonates. 
 
22. Reaction of acids with bases: Neutralisation reaction: 
Acids react with bases to form salt and water. 
HCl + NaOH ? NaCl + H
2
O 
                  or 
      H
+
 +OH
-
 ? H
2
O 
 
23. Reaction of acids with metallic oxides: 
Metallic oxides are basic. Therefore, acids react with metallic oxides to 
form salt and water. 
HCl + CuO ? CuCl
2
 + H
2
O 
 
 
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24. Reaction of bases with non-metallic oxides: Non – metallic oxides are 
acidic in nature. Bases react with non- metallic oxides to form salt and 
water. Example: CO
2
 
Ca(OH)
2
 + CO
2 
? CaCO
3 
+ H
2
O 
 
25. Amphoteric oxides: Oxides which show acidic as well as basic 
properties. For example: ZnO, Al
2
O
3
 
HCl + ZnO ? ZnCl
2
 + H
2
O 
Zn + 2 NaOH ? Na
2
ZnO
2
 + H
2
O 
 
26. Neutral oxides: Oxides which are neither acidic nor basic are called 
neutral oxides. Example: CO 
 
27. pH: It is used to find out the strength of acids and bases i.e., how 
strong or weak the acid or a base is. p in pH stands for ‘potenz’ in 
German. The strength of acids and bases depends on the number of 
H
+
 ions and OH
-
 ions produced respectively. 
 
28. pH scale: A scale for measuring hydrogen ion concentration in a 
solution is called pH scale. 
 
29. On pH scale, we measure pH from 0 to 14.  
pH value: 
pH Type of solution 
Less than 7 Acidic 
Equal to 7 Neutral 
More than 7 Basic 
 
30. More the hydrogen ion (or hydronium ion) concentration, lower is the 
pH value. 
 
31. More the hydroxyl ion concentration, higher is the pH value. 
 
 
32. Variation in pH: 
 
 
 
33. Acids which produce more hydrogen ions are said to be strong acids 
and acids which produce less hydrogen ions are said to be weak acids. 
In other words, strong acids have a lower pH value than weak acids. 
 
 
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34. Bases which produce more hydroxyl ions are said to be strong bases 
and bases which produce less hydroxyl ions are said to be weak bases. 
In other words, strong bases have a higher pH value than weak bases. 
 
35. Living organisms are pH sensitive. Human body works within a pH 
range of 7.0 to 7.8.  
 
36. Rain water with a pH less than 5.6 is called acid rain. This acid rain if it 
flows into river water makes the survival of aquatic life difficult. 
 
37. Plants also require a specific pH range of soil for their healthy growth. 
 
38. pH of our digestive system: Our stomach produces hydrochloric acid 
for digestion of food. But during indigestion, excess of acid is produced 
in the stomach and therefore, the pH decreases. This causes pain and 
irritation. So, to neutralise this excess acid, a mild base is used. This 
mild base works as an antacid.  An antacid is any substance, generally 
a base or basic salt, which counteracts stomach acidity. 
 
39. Tooth decay: Tooth decay starts when the pH of the mouth is lower 
than 5.5. Tooth enamel is made up of calcium phosphate which is the 
hardest substance in the body. It does not dissolve in water, but is 
corroded when the pH in the mouth is below 5.5. If food particles 
remain in the mouth after eating, bacteria present in our mouth 
produce acid by degradation of sugar. This decreases the pH of mouth 
and hence tooth decay occurs. The best way to prevent this is to clean 
the mouth after eating food. Using toothpastes, which are generally 
basic, for cleaning the teeth can neutralise the excess acid and prevent 
tooth decay. 
 
40. pH is also significant as it is used in self defence by animals and 
plants. Bees use acids in their sting. To neutralise the effect a mild 
base like baking soda can be used. 
 
41. Sodium hydroxide (NaOH) 
Preparation: 
Chlor Alkali process: 
       In this process, electricity is passed through an aqueous solution of 
Sodium chloride (called brine). Sodium chloride decomposes to form 
sodium hydroxide. Chlorine gas is formed at the anode, and hydrogen 
gas at the cathode. Sodium hydroxide solution is formed near the 
cathode. 
                   2NaCl(aq) + 2 H
2
O (l) ? 2NaOH(aq) + Cl
2
(g) + H
2
(g) 
 
42. Bleaching powder: Bleaching powder is represented as CaOCl
2
, though 
the actual composition is quite complex. 
       Preparation: Bleaching powder is produced by the action of chlorine on 
dry slaked lime. 
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