NCERT Class 10 Science Activity 2.9 Explanation

In this post, you will find NCERT Class 10 Science Activity 2.9 Explanation in detail. This activity is based on Chapter 2 Acids, Bases, and Salts of Class 10 Science.

NCERT Class 10 Science Activity 2.9 Explanation

 

Activity -Take about 1g solid NaCI in a clean and dry test tube and set up the apparatus as shown in ahead fig.

·      Add some concentrated sulphuric acid to the test tube.

·      What do you observe? Is there gas coming out of the delivery tube?

·      Test the gas evolved successively with dry and wet blue litmus paper.

·      In which case does the litmus paper change colour?

·      On the basis of the above activity, what do you infer about the acidic character of:

(i)           dry HCI gas.

(ii)        HCI solution.

Note to teachers - If the climate is very humid, you will have to pass the gas produced through a guard tube (drying tube) containing calcium chloride to dry the gas.

 

Production of HCl gas

Observation 

Sulphuric acid reacts with sodium chloride to produce HCl gas and sodium sulphate.

2NaCl + H₂SO₄ →2HCl + Na₂SO₄

When we bring dry blue litmus paper near the opening of the calcium chloride tube, the colour of the litmus paper remains unchanged.

On bringing a moistened blue litmus paper near the mouth of the delivery tube, the blue litmus changes to red.

 

 Explanation

Acids are substances that can release protons (H⁺ ions) when dissolved in water.

 

Hydrochloric acid (HCl)gas produces hydrogen ions (H⁺) and chloride ions (Cl⁻) in the case of wet blue litmus paper.

 

 `HCl →H^+ + Cl^-`

 

Hydrogen ions react with water molecules and form hydronium ions.

 `HCI(g)+ H_2O(l)     →     H_3O^+ + CI^-`

 

(H⁺) ions show an acidic character.

Conclusion

Dry HCl gas has no effect on blue litmus paper. But in the presence of moisture, hydrogen chloride gas turns blue litmus to red. Thus HCI gas shows its acidic character only in the presence of water.

 

 HCI(g)+ H₂O(I)     →     H₃O⁺ + CI^-

 

Similarly, bases in the presence of water produce OH^- (aq) ions.

NH₃(g) + H₂O(I)     →     NH₄(aq) + OH-(aq) 

Watch Video to understand the activity 2.9

Questions based on Activity 2.9 

1. What is the formula of sulphuric acid?

Ans-  H₂SO₄

2. Write the reaction between NaCl and sulphuric acid.

Ans - 2NaCl + H₂SO₄ →2HCl + Na₂SO₄

 

3. Which gas evolve during the activity 2.9 Class 10 Science?

Ans -  HCl gas

4. What is the use of a calcium chloride (CaCl2) guard tube?

Ans - Calcium chloride is a drying agent and a tube containing CaCl₂ makes the HCl gas dry in activity 2.9.

5. Which ion is responsible for the acidic character?

Ans- Hydrogen ions are responsible for acidic character. 

Related Topics -

1.  Activity 2.10

2.  Activity 2.8

2. Solutions of Chapter 2 

3. MCQ Questions of Chapter 2

4. Extra Questions of Chapter 2