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Hydrogen — Chemistry STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceChemistryHydrogen1 Mark
MCQ
In which of the following reactions $H_2O$ acts only as a Bronsted acid?
  • ✓
    $\text{H}_2\text{O}(\text{l})+\text{NH}_3(\text{aq})\rightleftharpoons\text{OH}^-(\text{aq})+\text{NH}^+_4(\text{aq})$
  • B
    $\text{H}_2\text{O}(\text{l})+\text{H}_2\text{S}(\text{aq})\rightleftharpoons\text{H}_3\text{O}^+(\text{aq})+\text{HS}^-(\text{aq})$
  • C
    $\text{H}_2\text{O}(\text{l})+\text{H}_2\text{O}(\text{l})\rightleftharpoons\text{H}_3\text{O}^+(\text{aq})+\text{O}\overline{\text{H}}(\text{aq})$
  • D
    None of the above.
✓

Answer

Correct option: A.
$\text{H}_2\text{O}(\text{l})+\text{NH}_3(\text{aq})\rightleftharpoons\text{OH}^-(\text{aq})+\text{NH}^+_4(\text{aq})$
  1. $\text{H}_2\text{O}(\text{l})+\text{NH}_3(\text{aq})\rightleftharpoons\text{OH}^-(\text{aq})+\text{NH}^+_4(\text{aq})$
Explanation:
$H_2O$ has the ability to act as an acid as well as base, i.e. it behaves as an amphoteric substance. In Bronsted concept, it acts as an acid with $NH_3$ and a base with $H_2S$.
$\text{H}_2\text{O}(\text{l})+\text{NH}_3(\text{aq})\rightleftharpoons\text{OH}^-(\text{aq})+\text{NH}^+_4(\text{aq})$
$\text{H}_2\text{O}(\text{l})+\text{H}_2\text{S}(\text{aq})\rightleftharpoons\text{H}_3\text{O}^+(\text{aq})+\text{HS}^-(\text{aq})$

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