Activity 2.9 Class 10 Science

Acids show their characteristics such as a sour taste, conduct electricity, ability to turn blue litmus red because they release H+ ions. This activity explains whether acids produce ions only in aqueous solutions.

 

Do Acids Produce Ions in Aqueous Solutions?

 

 

 Aim of the activity

To find the acidic property of hydrochloric acid

 

Materials used in the activity

 

S.N.	Materials
1	NaCl
2	Conc. H2SO4
3	Test tube
4	Delivery tube
5	Dry blue litmus paper
6	Wet blue litmus paper
7	Clamp/tongue
8	CaCl2

 

Procedure

We take about 1g solid NaCI in a clean and dry test tube and set up the apparatus. Now we add some concentrated sulphuric acid to the test tube.

We observe the production of a gas. We  test the gas evolved successively with dry and wet blue litmus paper and observe the change in colour of the litmus paper in both cases.

Note to teachers

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

 

 

Observation

    1. A colourless gas is evolved.

    2. There is no colour change in dry blue litmus paper.

    3. Wet blue litmus paper turns red. 

 

Explanation

When sodium chloride reacts with concentrated acid, hydrogen chloride gas is produced

NaCl + H₂SO₄ → NaHSO₄ + 2HCl_(g)  

 

This is dry `HCl` gas, and it is not ionised. So when `HCl` gas comes in contact with dry blue litmus paper, there is no change in colour.

When HCl gas comes in contact with wet or moist blue litmus paper, it gets ionised and releases hydrogen ions, so the colour of blue litmus paper changes to red.

 

Conclusion

We can conclude –

    1.  Dry `HCl` gas does not release `H^+`  ions.

  2. `HCl` gas shows acidic characteristics only in the presence of water.

             

      `HCl  + H_2O  →H_3O^+ + Cl^-`

Multiple Choice Questions

 1. Which gas is evolved when `NaCl` reacts with `H_2SO_4`?

    a) Chlorine gas

    b)   Hydrogen gas

    c) Hydrogen chloride gas

    d)    Sulphur dioxide gas

Correct answer – (c) Hydrogen chloride gas

    2. What happens when dry `HCl` gas comes in contact with dry blue litmus paper?

    a) It turns red

    b)    It turns black

    c)  No change

    d)    It turns yellow

Correct answer – (c) No change

    3. What does this activity 2.9 prove?

    a)  Acids are liquid

    b)    Acids produce hydrogen in water

    c)  Acids are sour

    d)    All of the above

Correct answer – (b) Acids produce hydrogen in water

  4. What happens when `HCl` gas comes in contact with wet blue litmus paper?

    a) Turns red

    b)  Turns yellow

    c)  No change

    d)   Turns green

Correct answer- (a) Turns red

    5. Why do we use `CaCl_2` in this activity?

    a) It is an activator

    b)   It is a drying agent

    c) It is a catalyst

    d)     None of the above

Correct answer -  (b) It is a drying agent