Do acids produce ions only in aqueous solution? Let us test this.
Activity 8
- Take about 1.0g of solid NaCl in a clean and dry test tube.
- Add some concentrated sulphuric acid to the test tube.
• What do you observe? Is there a gas coming out of the delivery tube?
Let us write chemical equation for the above reaction.
2NaCl
(s) + H2SO4(l)
--> 2HCl
(g) ↑ + Na2SO4(s)
Test the gas evolved successively with dry and wet blue litmus paper. In
which case does the litmus paper change colour?
• What do you infer from the above observation?
You can conclude that dry HCl gas (Hydrogen chloride) is not an acid
because you have noticed that there is no change in colour of dry litmus
paper but HCl aqueous solution is an acid because wet blue litmus paper
turned into red.
Note to teachers: If the climate is very humid, pass the gas produced
through a guard tube (drying tube) containing calcium chloride to dry the gas.
• Can you write the chemical equation for the reaction takes place at the
mouth of delivery tube?
Laboratory precaution : Observe the following pictures. Did you find
any problems with this? When ever you work with concentrated solutions
it is very important to use test tube holder. It is very dangerous to work
with bare hands in the laboratory.
fig-4: preparation of HCL gas
The HCl gas evolvated delivery tube is sociates source in presensence of water to produce ions . in the absence of water d is s of HCl molecules do not occur.