NCERT Textbook: Acids, Bases & Salts | Science & Technology for UPSC CSE PDF Download

 Page 1


Acids, Bases
and Salts
2 CHAPTER
Y
ou have learnt in your previous classes that the sour and bitter
tastes of food are due to acids and bases, respectively, present in them.
If someone in the family is suffering from a problem of acidity after
overeating, which of the following would you suggest as a remedy– lemon
juice, vinegar or baking soda solution?
n Which property did you think of while choosing the remedy?
Surely you must have used your knowledge about the ability of
acids and bases to nullify each other’s effect.
n Recall how we tested sour and bitter substances without tasting
them.
You already know that acids are sour in taste and change the colour
of blue litmus to red, whereas, bases are bitter and change the colour of
the red litmus to blue. Litmus is a natural indicator, turmeric is another
such indicator. Have you noticed that a stain of curry on a white cloth
becomes reddish-brown when soap, which is basic in nature, is scrubbed
on it? It turns yellow again when the cloth is washed with plenty of
water. You can also use synthetic indicators such as methyl orange and
phenolphthalein to test for acids and bases.
In this Chapter, we will study the reactions of acids and bases, how
acids and bases cancel out each other’s effects and many more interesting
things that we use and see in our day-to-day life.
Do You Know?
Litmus solution is a purple dye, which is extracted from lichen, a plant belonging to
the division Thallophyta, and is commonly used as an indicator. When the litmus
solution is neither acidic nor basic, its colour is purple. There are many other natural
materials like red cabbage leaves, turmeric, coloured petals of some flowers such as
Hydrangea, Petunia and Geranium, which indicate the presence of acid or base in a
solution. These are called acid-base indicators or sometimes simply indicators.
2024-25
Page 2


Acids, Bases
and Salts
2 CHAPTER
Y
ou have learnt in your previous classes that the sour and bitter
tastes of food are due to acids and bases, respectively, present in them.
If someone in the family is suffering from a problem of acidity after
overeating, which of the following would you suggest as a remedy– lemon
juice, vinegar or baking soda solution?
n Which property did you think of while choosing the remedy?
Surely you must have used your knowledge about the ability of
acids and bases to nullify each other’s effect.
n Recall how we tested sour and bitter substances without tasting
them.
You already know that acids are sour in taste and change the colour
of blue litmus to red, whereas, bases are bitter and change the colour of
the red litmus to blue. Litmus is a natural indicator, turmeric is another
such indicator. Have you noticed that a stain of curry on a white cloth
becomes reddish-brown when soap, which is basic in nature, is scrubbed
on it? It turns yellow again when the cloth is washed with plenty of
water. You can also use synthetic indicators such as methyl orange and
phenolphthalein to test for acids and bases.
In this Chapter, we will study the reactions of acids and bases, how
acids and bases cancel out each other’s effects and many more interesting
things that we use and see in our day-to-day life.
Do You Know?
Litmus solution is a purple dye, which is extracted from lichen, a plant belonging to
the division Thallophyta, and is commonly used as an indicator. When the litmus
solution is neither acidic nor basic, its colour is purple. There are many other natural
materials like red cabbage leaves, turmeric, coloured petals of some flowers such as
Hydrangea, Petunia and Geranium, which indicate the presence of acid or base in a
solution. These are called acid-base indicators or sometimes simply indicators.
2024-25
Science
18
2.1 2.1 2.1 2.1 2.1 UNDERST UNDERST UNDERST UNDERST UNDERSTANDING THE CHEMIC ANDING THE CHEMIC ANDING THE CHEMIC ANDING THE CHEMIC ANDING THE CHEMICAL PROPERTIES OF AL PROPERTIES OF AL PROPERTIES OF AL PROPERTIES OF AL PROPERTIES OF
ACIDS AND BASES ACIDS AND BASES ACIDS AND BASES ACIDS AND BASES ACIDS AND BASES
2.1.1 Acids and Bases in the Laboratory
Activity 2.1 Activity 2.1 Activity 2.1 Activity 2.1 Activity 2.1
These indicators tell us whether a substance is acidic or basic by
change in colour. There are some substances whose odour changes in
acidic or basic media. These are called olfactory indicators. Let us try
out some of these indicators.
QUESTION
?
1. You have been provided with three test tubes. One of them contains
distilled water and the other two contain an acidic solution and a basic
solution, respectively. If you are given only red litmus paper, how will
you identify the contents of each test tube?
n Collect the following solutions from the science laboratory–
hydrochloric acid (HCl),  sulphuric acid (H
2
SO
4
), nitric acid (HNO
3
),
acetic acid (CH
3
COOH), sodium hydroxide (NaOH), calcium
hydroxide [Ca(OH)
2
], potassium hydroxide (KOH), magnesium
hydroxide [Mg(OH)
2
], and ammonium hydroxide (NH
4
OH).
n Put a drop of each of the above solutions on a watch-glass one by
one and test with a drop of the indicators shown in Table 2.1.
n What change in colour did you observe with red litmus, blue litmus,
phenolphthalein and methyl orange solutions for each of the
solutions taken?
n Tabulate your observations in Table 2.1.
Table 2.1
Sample Red Blue Phenolph- Methyl
solution litmus litmus -thalein     orange
solution solution solution solution
Activity 2.2 Activity 2.2 Activity 2.2 Activity 2.2 Activity 2.2
n Take some finely chopped onions in a plastic bag along with some
strips of clean cloth. Tie up the bag tightly and leave overnight in
the fridge. The cloth strips can now be used to test for acids and
bases.
n Take two of these cloth strips and check their odour.
n Keep them on a clean surface and put a few drops of dilute HCl
solution on one strip and a few drops of dilute NaOH solution on
the other.
2024-25
Page 3


Acids, Bases
and Salts
2 CHAPTER
Y
ou have learnt in your previous classes that the sour and bitter
tastes of food are due to acids and bases, respectively, present in them.
If someone in the family is suffering from a problem of acidity after
overeating, which of the following would you suggest as a remedy– lemon
juice, vinegar or baking soda solution?
n Which property did you think of while choosing the remedy?
Surely you must have used your knowledge about the ability of
acids and bases to nullify each other’s effect.
n Recall how we tested sour and bitter substances without tasting
them.
You already know that acids are sour in taste and change the colour
of blue litmus to red, whereas, bases are bitter and change the colour of
the red litmus to blue. Litmus is a natural indicator, turmeric is another
such indicator. Have you noticed that a stain of curry on a white cloth
becomes reddish-brown when soap, which is basic in nature, is scrubbed
on it? It turns yellow again when the cloth is washed with plenty of
water. You can also use synthetic indicators such as methyl orange and
phenolphthalein to test for acids and bases.
In this Chapter, we will study the reactions of acids and bases, how
acids and bases cancel out each other’s effects and many more interesting
things that we use and see in our day-to-day life.
Do You Know?
Litmus solution is a purple dye, which is extracted from lichen, a plant belonging to
the division Thallophyta, and is commonly used as an indicator. When the litmus
solution is neither acidic nor basic, its colour is purple. There are many other natural
materials like red cabbage leaves, turmeric, coloured petals of some flowers such as
Hydrangea, Petunia and Geranium, which indicate the presence of acid or base in a
solution. These are called acid-base indicators or sometimes simply indicators.
2024-25
Science
18
2.1 2.1 2.1 2.1 2.1 UNDERST UNDERST UNDERST UNDERST UNDERSTANDING THE CHEMIC ANDING THE CHEMIC ANDING THE CHEMIC ANDING THE CHEMIC ANDING THE CHEMICAL PROPERTIES OF AL PROPERTIES OF AL PROPERTIES OF AL PROPERTIES OF AL PROPERTIES OF
ACIDS AND BASES ACIDS AND BASES ACIDS AND BASES ACIDS AND BASES ACIDS AND BASES
2.1.1 Acids and Bases in the Laboratory
Activity 2.1 Activity 2.1 Activity 2.1 Activity 2.1 Activity 2.1
These indicators tell us whether a substance is acidic or basic by
change in colour. There are some substances whose odour changes in
acidic or basic media. These are called olfactory indicators. Let us try
out some of these indicators.
QUESTION
?
1. You have been provided with three test tubes. One of them contains
distilled water and the other two contain an acidic solution and a basic
solution, respectively. If you are given only red litmus paper, how will
you identify the contents of each test tube?
n Collect the following solutions from the science laboratory–
hydrochloric acid (HCl),  sulphuric acid (H
2
SO
4
), nitric acid (HNO
3
),
acetic acid (CH
3
COOH), sodium hydroxide (NaOH), calcium
hydroxide [Ca(OH)
2
], potassium hydroxide (KOH), magnesium
hydroxide [Mg(OH)
2
], and ammonium hydroxide (NH
4
OH).
n Put a drop of each of the above solutions on a watch-glass one by
one and test with a drop of the indicators shown in Table 2.1.
n What change in colour did you observe with red litmus, blue litmus,
phenolphthalein and methyl orange solutions for each of the
solutions taken?
n Tabulate your observations in Table 2.1.
Table 2.1
Sample Red Blue Phenolph- Methyl
solution litmus litmus -thalein     orange
solution solution solution solution
Activity 2.2 Activity 2.2 Activity 2.2 Activity 2.2 Activity 2.2
n Take some finely chopped onions in a plastic bag along with some
strips of clean cloth. Tie up the bag tightly and leave overnight in
the fridge. The cloth strips can now be used to test for acids and
bases.
n Take two of these cloth strips and check their odour.
n Keep them on a clean surface and put a few drops of dilute HCl
solution on one strip and a few drops of dilute NaOH solution on
the other.
2024-25
Acids, Bases and Salts 19
Which of these – vanilla, onion and clove, can be used as olfactory
indicators on the basis of your observations?
Let us do some more activities to understand the chemical properties
of acids and bases.
2.1.2 How do Acids and Bases React with Metals?
n Rinse both cloth strips with water and again check their odour.
n Note your observations.
n Now take some dilute vanilla essence and clove oil and check their
odour.
n Take some dilute HCl solution in one test tube and dilute NaOH
solution in another. Add a few drops of dilute vanilla essence to
both test tubes and shake well. Check the odour once again and
record changes in odour, if any.
n Similarly, test the change in the odour of clove oil with dilute HCl
and dilute NaOH solutions and record your observations.
Activity 2.3 Activity 2.3 Activity 2.3 Activity 2.3 Activity 2.3
CAUTION: This activity needs the teacher’s assistance.
n Set the apparatus as shown in Fig. 2.1.
n Take about 5 mL of dilute sulphuric acid in a test tube and add a
few pieces of zinc granules to it.
n What do you observe on the surface of zinc granules?
n Pass the gas being evolved through the soap solution.
n Why are bubbles  formed in the soap solution?
n Take a burning candle near a gas filled bubble.
n What do you observe?
n Repeat this Activity with some more acids like HCl, HNO
3
 and
CH
3
COOH.
n Are the observations in all the cases the same or different?
Figure 2.1 Figure 2.1 Figure 2.1 Figure 2.1 Figure 2.1 Reaction of zinc granules with dilute sulphuric acid and testing hydrogen
gas by burning
2024-25
Page 4


Acids, Bases
and Salts
2 CHAPTER
Y
ou have learnt in your previous classes that the sour and bitter
tastes of food are due to acids and bases, respectively, present in them.
If someone in the family is suffering from a problem of acidity after
overeating, which of the following would you suggest as a remedy– lemon
juice, vinegar or baking soda solution?
n Which property did you think of while choosing the remedy?
Surely you must have used your knowledge about the ability of
acids and bases to nullify each other’s effect.
n Recall how we tested sour and bitter substances without tasting
them.
You already know that acids are sour in taste and change the colour
of blue litmus to red, whereas, bases are bitter and change the colour of
the red litmus to blue. Litmus is a natural indicator, turmeric is another
such indicator. Have you noticed that a stain of curry on a white cloth
becomes reddish-brown when soap, which is basic in nature, is scrubbed
on it? It turns yellow again when the cloth is washed with plenty of
water. You can also use synthetic indicators such as methyl orange and
phenolphthalein to test for acids and bases.
In this Chapter, we will study the reactions of acids and bases, how
acids and bases cancel out each other’s effects and many more interesting
things that we use and see in our day-to-day life.
Do You Know?
Litmus solution is a purple dye, which is extracted from lichen, a plant belonging to
the division Thallophyta, and is commonly used as an indicator. When the litmus
solution is neither acidic nor basic, its colour is purple. There are many other natural
materials like red cabbage leaves, turmeric, coloured petals of some flowers such as
Hydrangea, Petunia and Geranium, which indicate the presence of acid or base in a
solution. These are called acid-base indicators or sometimes simply indicators.
2024-25
Science
18
2.1 2.1 2.1 2.1 2.1 UNDERST UNDERST UNDERST UNDERST UNDERSTANDING THE CHEMIC ANDING THE CHEMIC ANDING THE CHEMIC ANDING THE CHEMIC ANDING THE CHEMICAL PROPERTIES OF AL PROPERTIES OF AL PROPERTIES OF AL PROPERTIES OF AL PROPERTIES OF
ACIDS AND BASES ACIDS AND BASES ACIDS AND BASES ACIDS AND BASES ACIDS AND BASES
2.1.1 Acids and Bases in the Laboratory
Activity 2.1 Activity 2.1 Activity 2.1 Activity 2.1 Activity 2.1
These indicators tell us whether a substance is acidic or basic by
change in colour. There are some substances whose odour changes in
acidic or basic media. These are called olfactory indicators. Let us try
out some of these indicators.
QUESTION
?
1. You have been provided with three test tubes. One of them contains
distilled water and the other two contain an acidic solution and a basic
solution, respectively. If you are given only red litmus paper, how will
you identify the contents of each test tube?
n Collect the following solutions from the science laboratory–
hydrochloric acid (HCl),  sulphuric acid (H
2
SO
4
), nitric acid (HNO
3
),
acetic acid (CH
3
COOH), sodium hydroxide (NaOH), calcium
hydroxide [Ca(OH)
2
], potassium hydroxide (KOH), magnesium
hydroxide [Mg(OH)
2
], and ammonium hydroxide (NH
4
OH).
n Put a drop of each of the above solutions on a watch-glass one by
one and test with a drop of the indicators shown in Table 2.1.
n What change in colour did you observe with red litmus, blue litmus,
phenolphthalein and methyl orange solutions for each of the
solutions taken?
n Tabulate your observations in Table 2.1.
Table 2.1
Sample Red Blue Phenolph- Methyl
solution litmus litmus -thalein     orange
solution solution solution solution
Activity 2.2 Activity 2.2 Activity 2.2 Activity 2.2 Activity 2.2
n Take some finely chopped onions in a plastic bag along with some
strips of clean cloth. Tie up the bag tightly and leave overnight in
the fridge. The cloth strips can now be used to test for acids and
bases.
n Take two of these cloth strips and check their odour.
n Keep them on a clean surface and put a few drops of dilute HCl
solution on one strip and a few drops of dilute NaOH solution on
the other.
2024-25
Acids, Bases and Salts 19
Which of these – vanilla, onion and clove, can be used as olfactory
indicators on the basis of your observations?
Let us do some more activities to understand the chemical properties
of acids and bases.
2.1.2 How do Acids and Bases React with Metals?
n Rinse both cloth strips with water and again check their odour.
n Note your observations.
n Now take some dilute vanilla essence and clove oil and check their
odour.
n Take some dilute HCl solution in one test tube and dilute NaOH
solution in another. Add a few drops of dilute vanilla essence to
both test tubes and shake well. Check the odour once again and
record changes in odour, if any.
n Similarly, test the change in the odour of clove oil with dilute HCl
and dilute NaOH solutions and record your observations.
Activity 2.3 Activity 2.3 Activity 2.3 Activity 2.3 Activity 2.3
CAUTION: This activity needs the teacher’s assistance.
n Set the apparatus as shown in Fig. 2.1.
n Take about 5 mL of dilute sulphuric acid in a test tube and add a
few pieces of zinc granules to it.
n What do you observe on the surface of zinc granules?
n Pass the gas being evolved through the soap solution.
n Why are bubbles  formed in the soap solution?
n Take a burning candle near a gas filled bubble.
n What do you observe?
n Repeat this Activity with some more acids like HCl, HNO
3
 and
CH
3
COOH.
n Are the observations in all the cases the same or different?
Figure 2.1 Figure 2.1 Figure 2.1 Figure 2.1 Figure 2.1 Reaction of zinc granules with dilute sulphuric acid and testing hydrogen
gas by burning
2024-25
Science
20
 Note that the metal in the above reactions displaces hydrogen atoms
from the acids as hydrogen gas and forms a compound called a salt.
Thus, the reaction of a metal with an acid can be summarised as –
Acid + Metal ? Salt + Hydrogen gas
Can you now write the equations for the reactions you have observed?
Activity 2.4 Activity 2.4 Activity 2.4 Activity 2.4 Activity 2.4
The reactions occurring in the above Activity are written as –
Test tube A: Na CO HCl(aq) Cl(aq) H O(l) + CO
2 3 2 2
(s) Na (g) + ? + 2 2
Test tube B: NaHCO HCl(aq) Cl(aq) H O(l) + CO
3 2 2
(s) Na (g) + ? +
On passing the carbon dioxide gas evolved through lime water,
Ca(OH) CO H O(l)
2 2 2
(aq) (g) CaCO s
3
+ ? + ( )
(Lime water) (White precipitate)
n Place a few pieces of granulated zinc metal in a test tube.
n Add 2 mL of sodium hydroxide solution and warm the contents
of the test tube.
n Repeat the rest of the steps as in Activity 2.3 and record your
observations.
The reaction that takes place can be written as follows.
2NaOH(aq) + Zn(s) ? Na
2
ZnO
2
(s) + H
2
(g)
      (Sodium zincate)
You find again that hydrogen is formed in the reaction. However,
such reactions are not possible with all metals.
2.1.3 How do Metal Carbonates and Metal
Hydrogencarbonates React with Acids?
Activity 2.5 Activity 2.5 Activity 2.5 Activity 2.5 Activity 2.5
n Take two test tubes, label them as A
and B.
n Take about 0.5 g of sodium carbonate
(Na
2
CO
3
) in test tube A and about
0.5 g of sodium hydrogencarbonate
(NaHCO
3
) in test tube B.
n Add about 2 mL of dilute HCl to both
the test tubes.
n What do you observe?
n Pass the gas produced in each case
through lime water (calcium
hydroxide solution) as shown in
Fig. 2.2 and record your observations.
Figure 2.2 Figure 2.2 Figure 2.2 Figure 2.2 Figure 2.2
Passing carbon dioxide gas
through calcium hydroxide
solution
2024-25
Page 5


Acids, Bases
and Salts
2 CHAPTER
Y
ou have learnt in your previous classes that the sour and bitter
tastes of food are due to acids and bases, respectively, present in them.
If someone in the family is suffering from a problem of acidity after
overeating, which of the following would you suggest as a remedy– lemon
juice, vinegar or baking soda solution?
n Which property did you think of while choosing the remedy?
Surely you must have used your knowledge about the ability of
acids and bases to nullify each other’s effect.
n Recall how we tested sour and bitter substances without tasting
them.
You already know that acids are sour in taste and change the colour
of blue litmus to red, whereas, bases are bitter and change the colour of
the red litmus to blue. Litmus is a natural indicator, turmeric is another
such indicator. Have you noticed that a stain of curry on a white cloth
becomes reddish-brown when soap, which is basic in nature, is scrubbed
on it? It turns yellow again when the cloth is washed with plenty of
water. You can also use synthetic indicators such as methyl orange and
phenolphthalein to test for acids and bases.
In this Chapter, we will study the reactions of acids and bases, how
acids and bases cancel out each other’s effects and many more interesting
things that we use and see in our day-to-day life.
Do You Know?
Litmus solution is a purple dye, which is extracted from lichen, a plant belonging to
the division Thallophyta, and is commonly used as an indicator. When the litmus
solution is neither acidic nor basic, its colour is purple. There are many other natural
materials like red cabbage leaves, turmeric, coloured petals of some flowers such as
Hydrangea, Petunia and Geranium, which indicate the presence of acid or base in a
solution. These are called acid-base indicators or sometimes simply indicators.
2024-25
Science
18
2.1 2.1 2.1 2.1 2.1 UNDERST UNDERST UNDERST UNDERST UNDERSTANDING THE CHEMIC ANDING THE CHEMIC ANDING THE CHEMIC ANDING THE CHEMIC ANDING THE CHEMICAL PROPERTIES OF AL PROPERTIES OF AL PROPERTIES OF AL PROPERTIES OF AL PROPERTIES OF
ACIDS AND BASES ACIDS AND BASES ACIDS AND BASES ACIDS AND BASES ACIDS AND BASES
2.1.1 Acids and Bases in the Laboratory
Activity 2.1 Activity 2.1 Activity 2.1 Activity 2.1 Activity 2.1
These indicators tell us whether a substance is acidic or basic by
change in colour. There are some substances whose odour changes in
acidic or basic media. These are called olfactory indicators. Let us try
out some of these indicators.
QUESTION
?
1. You have been provided with three test tubes. One of them contains
distilled water and the other two contain an acidic solution and a basic
solution, respectively. If you are given only red litmus paper, how will
you identify the contents of each test tube?
n Collect the following solutions from the science laboratory–
hydrochloric acid (HCl),  sulphuric acid (H
2
SO
4
), nitric acid (HNO
3
),
acetic acid (CH
3
COOH), sodium hydroxide (NaOH), calcium
hydroxide [Ca(OH)
2
], potassium hydroxide (KOH), magnesium
hydroxide [Mg(OH)
2
], and ammonium hydroxide (NH
4
OH).
n Put a drop of each of the above solutions on a watch-glass one by
one and test with a drop of the indicators shown in Table 2.1.
n What change in colour did you observe with red litmus, blue litmus,
phenolphthalein and methyl orange solutions for each of the
solutions taken?
n Tabulate your observations in Table 2.1.
Table 2.1
Sample Red Blue Phenolph- Methyl
solution litmus litmus -thalein     orange
solution solution solution solution
Activity 2.2 Activity 2.2 Activity 2.2 Activity 2.2 Activity 2.2
n Take some finely chopped onions in a plastic bag along with some
strips of clean cloth. Tie up the bag tightly and leave overnight in
the fridge. The cloth strips can now be used to test for acids and
bases.
n Take two of these cloth strips and check their odour.
n Keep them on a clean surface and put a few drops of dilute HCl
solution on one strip and a few drops of dilute NaOH solution on
the other.
2024-25
Acids, Bases and Salts 19
Which of these – vanilla, onion and clove, can be used as olfactory
indicators on the basis of your observations?
Let us do some more activities to understand the chemical properties
of acids and bases.
2.1.2 How do Acids and Bases React with Metals?
n Rinse both cloth strips with water and again check their odour.
n Note your observations.
n Now take some dilute vanilla essence and clove oil and check their
odour.
n Take some dilute HCl solution in one test tube and dilute NaOH
solution in another. Add a few drops of dilute vanilla essence to
both test tubes and shake well. Check the odour once again and
record changes in odour, if any.
n Similarly, test the change in the odour of clove oil with dilute HCl
and dilute NaOH solutions and record your observations.
Activity 2.3 Activity 2.3 Activity 2.3 Activity 2.3 Activity 2.3
CAUTION: This activity needs the teacher’s assistance.
n Set the apparatus as shown in Fig. 2.1.
n Take about 5 mL of dilute sulphuric acid in a test tube and add a
few pieces of zinc granules to it.
n What do you observe on the surface of zinc granules?
n Pass the gas being evolved through the soap solution.
n Why are bubbles  formed in the soap solution?
n Take a burning candle near a gas filled bubble.
n What do you observe?
n Repeat this Activity with some more acids like HCl, HNO
3
 and
CH
3
COOH.
n Are the observations in all the cases the same or different?
Figure 2.1 Figure 2.1 Figure 2.1 Figure 2.1 Figure 2.1 Reaction of zinc granules with dilute sulphuric acid and testing hydrogen
gas by burning
2024-25
Science
20
 Note that the metal in the above reactions displaces hydrogen atoms
from the acids as hydrogen gas and forms a compound called a salt.
Thus, the reaction of a metal with an acid can be summarised as –
Acid + Metal ? Salt + Hydrogen gas
Can you now write the equations for the reactions you have observed?
Activity 2.4 Activity 2.4 Activity 2.4 Activity 2.4 Activity 2.4
The reactions occurring in the above Activity are written as –
Test tube A: Na CO HCl(aq) Cl(aq) H O(l) + CO
2 3 2 2
(s) Na (g) + ? + 2 2
Test tube B: NaHCO HCl(aq) Cl(aq) H O(l) + CO
3 2 2
(s) Na (g) + ? +
On passing the carbon dioxide gas evolved through lime water,
Ca(OH) CO H O(l)
2 2 2
(aq) (g) CaCO s
3
+ ? + ( )
(Lime water) (White precipitate)
n Place a few pieces of granulated zinc metal in a test tube.
n Add 2 mL of sodium hydroxide solution and warm the contents
of the test tube.
n Repeat the rest of the steps as in Activity 2.3 and record your
observations.
The reaction that takes place can be written as follows.
2NaOH(aq) + Zn(s) ? Na
2
ZnO
2
(s) + H
2
(g)
      (Sodium zincate)
You find again that hydrogen is formed in the reaction. However,
such reactions are not possible with all metals.
2.1.3 How do Metal Carbonates and Metal
Hydrogencarbonates React with Acids?
Activity 2.5 Activity 2.5 Activity 2.5 Activity 2.5 Activity 2.5
n Take two test tubes, label them as A
and B.
n Take about 0.5 g of sodium carbonate
(Na
2
CO
3
) in test tube A and about
0.5 g of sodium hydrogencarbonate
(NaHCO
3
) in test tube B.
n Add about 2 mL of dilute HCl to both
the test tubes.
n What do you observe?
n Pass the gas produced in each case
through lime water (calcium
hydroxide solution) as shown in
Fig. 2.2 and record your observations.
Figure 2.2 Figure 2.2 Figure 2.2 Figure 2.2 Figure 2.2
Passing carbon dioxide gas
through calcium hydroxide
solution
2024-25
Acids, Bases and Salts 21
Activity 2.6 Activity 2.6 Activity 2.6 Activity 2.6 Activity 2.6
n Take about 2 mL of dilute NaOH solution in a test tube and add
two drops of phenolphthalein solution.
n What is the colour of the solution?
n Add dilute HCl solution to the above solution drop by drop.
n Is there any colour change for the reaction mixture?
n Why did the colour of phenolphthalein change after the addition
of an acid?
n Now add a few drops of NaOH to the above mixture.
n Does the pink colour of phenolphthalein reappear?
n Why do you think this has happened?
On passing excess carbon dioxide the following reaction takes place:
CaCO s Ca(HCO aq
3 3
( ) ) ( ) + ? H O(l)+ CO (g) 
2 2 2
(Soluble in water)
Limestone, chalk and marble are different forms of calcium carbonate.
All metal carbonates and hydrogencarbonates react with acids to give a
corresponding salt, carbon dioxide and water.
Thus, the reaction can be summarised as –
In the above Activity, we have observed that the effect of a base is
nullified by an acid and vice-versa. The reaction taking place is written as –
NaOH(aq) + HCl(aq) ? NaCl(aq) + H
2
O(l)
The reaction between an acid and a base to give a salt and water is
known as a neutralisation reaction. In general, a neutralisation reaction
can be written as –
Base + Acid ? Salt + Water
2.1.5 Reaction of Metallic Oxides with Acids
Activity 2.7 Activity 2.7 Activity 2.7 Activity 2.7 Activity 2.7
n Take a small amount of copper oxide in a beaker and add dilute
hydrochloric acid slowly while stirring.
n Note the colour of the solution. What has happened to the copper
oxide?
You will notice that the colour of the solution becomes blue-green
and the copper oxide dissolves. The blue-green colour of the solution is
due to the formation of copper(II) chloride in the reaction. The general
reaction between a metal oxide and an acid can be written as –
Metal oxide + Acid ? Salt + Water
Metal carbonate/Metal hydrogencarbonate + Acid ? Salt + Carbon dioxide + Water
2.1.4 How do Acids and Bases React with each other?
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