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Activity 2.9 Explanation: HCL H + CL

The document discusses what happens when an acid or base is added to water. It describes an experiment where hydrochloric acid gas is produced from sodium chloride and sulfuric acid. Dry HCl gas does not affect litmus paper, but the presence of water allows HCl to act as an acid and turn litmus red due to hydrogen ions.

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10K views2 pages

Activity 2.9 Explanation: HCL H + CL

The document discusses what happens when an acid or base is added to water. It describes an experiment where hydrochloric acid gas is produced from sodium chloride and sulfuric acid. Dry HCl gas does not affect litmus paper, but the presence of water allows HCl to act as an acid and turn litmus red due to hydrogen ions.

Uploaded by

sciencee2009
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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What Happens to an Acid or a Base in a Water Solution?

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) + H2O(l) → H3O+ +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)
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.

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