NCERT Solution for Class Tenth Science Chapter 2
Acids, Bases and Salts
Intext Questions
Page No-6
Questions No-1
Why do HCl, HNO3, etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?
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The dissociation of HCl or HNO3 to form hydrogen ions always occurs in the presence of water. Hydrogen ions (H⁺) combine with H2O to form hydronium ions (H3O⁺).
The reaction is as follows:
HCl + Water → H ⁺ + Cl –
H ⁺+ H₂O → H₃O +
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The dissociation of HCl or HNO3 to form hydrogen ions always occurs in the presence of water. Hydrogen ions (H⁺) combine with H2O to form hydronium ions (H3O⁺).
The reaction is as follows:
HCl + Water → H ⁺ + Cl –
H ⁺+ H₂O → H₃O +
Although aqueous solutions of glucose and alcohol contain hydrogen, these cannot dissociate in water to form hydrogen ions. Hence, they do not show acidic character.
HCl or HNO3 shows acidic character on aqueous solution because hydrogen ions dissociation always occurs in the presence of water. Hydrogen ions (H+) when combined with H2O to form hydronium ions (H3O+).
The reaction is as follows:
HCL(aq) → H+ + CL–
H+ + H2O → H3O+
Whereas aqueous solutions of glucose and alcohol contain hydrogen, these cannot dissociate in water to form hydrogen ions. Therefore they do not show acidic character.
The acidic or basic properties of a substance in aqueous solution are related to its ability to donate or accept protons (H⁺ ions). Let’s look at the examples you mentioned:
1. Hydrochloric Acid (HCl):
» In aqueous solution, HCl dissociates into H⁺ ions and Cl⁻ ions.
» HCl → H+ + Cl⁻
» The presence of H⁺ ions in solution makes it acidic.
2. Nitric Acid (HNO₃):
» In aqueous solution, HNO₃ dissociates into H⁺ ions and NO₃⁻ ions.
» HNO₃ → H+ + NO₃⁻
» Again, the presence of H⁺ ions in solution makes it acidic.
Substances like alcohols (e.g., ethanol) and glucose do not exhibit acidic behavior in aqueous solution. This is because they do not readily release protons (H⁺ ions) into the solution. For example, ethanol does undergo partial ionization in water, but it doesn’t release as many H⁺ ions as strong acids do:
C₂H₅OH ⇌ C₂H₅O⁻ + H⁺
However, the extent of ionization for alcohols and glucose is much lower compared to strong acids like HCl or HNO₃. As a result, the concentration of H⁺ ions in the solution is not high enough to cause a significant change in pH, and the solution is not classified as acidic.