Question

(a) Which element is common to all acids?
(b) Compounds such as alcohol and glucose also contain hydrogen but are not categorised as acids. Describe an activity to prove it.

Answer 1

(a) All acids have hydrogen as a common element in them.
Examples: Hydrochloric acid (HCl), sulphuric acid (H₂SO₄), nitric acid (HNO₃).

(b) Activity to show that alcohol and glucose also contain hydrogen but are not acids:
Procedure:
i) Take samples of alcohol, glucose and hydrochloric acid.
ii) Take a 100 ml beaker. Take a cork and fix two nails on it.
iii) Place the cork inside the beaker as shown in the figure.
iv) Connect the nails to two terminals of a 6-volt battery through a bulb and a switch.
v) Now pour some dilute hydrochloric acid in the beaker so that the nails and the cork are immersed in it.
vi) Switch on the current flow.
vii) Repeat the same with alcohol and glucose.


Observation :

The bulb starts glowing in the case of acid, whereas it does not glow in the case of glucose and alcohol solutions. Glowing of the bulb signifies that there is a flow of electric current through the solution. The electric current is carried through the solution by ions.

Conclusion:
Acids dissociate in aqueous solutions to give H⁺(aq) ions, which determine their acidic property. Glucose and alcohol do not dissociate and do not furnish H⁺ ions in aqueous solutions even though they contain hydrogen atoms. Hence, HCl shows acidic character in aqueous solutions, whereas solutions of compounds such as C₆H₁₂O₆ (glucose) and C₂H₅OH (alcohol) do not show acidic character.