It shows the answer is D but I want to know how to work out the problem. ) 0.010

Question

It shows the answer is D but I want to know how to work out the problem.

) 0.010 moes of HCIO2 (chlorous acid, a weak monoprotic acid) is added to 1.000 L of each of the following solutions. For which solution will the percent ionization of the chlorous acid be largest? a) A 1.0 x 103 M solution of HNO2 (nitrous acid, a weak acid) b) A 1.0 x 103 M solution of HBr (hydrobromic acid, a strong acid) c) A 1.0x 103 M solution of NH3 (ammonia, a weak base) d) A 1.0 x 103 M solution of KOH (potassium hydroxide, a strong base) e) Pure water D

Explanation / Answer

Ans. # Option A and B. Being weak acid, HClO2 will not dissolve in any stronger acid.

Le Chatelier’s principle states “if a dynamic equilibrium is disturbed by changing the conditions (Concentration, Volume, Pressure, temperature, etc.), the position of equilibrium shifts to counteract the change to reestablish an equilibrium”.

HClO2(aq) <-------------> ClO2-(aq) + H+(aq) + H+(from other strong or weak acid)

Following Le Chatelier’s principle, presence of H+ ions in the solution from another weak or strong acid would shift the equilibrium to the left. So, the solubility and % dissociation of HClO2 in HNO2 and HBr would be lesser than that pure water.

# Option C. HClO2(aq) <-------------> ClO2-(aq) + H+(aq)

            NH3 (aq) + H+(aq) <-----------> NH4+ (aq)

Note that NH3(weak base) accepts the protons from HClO2. So, the equilibrium of HClO2 dissociation shifts to the right in ammonia solution. Since NH3 is a weak base, only a small fraction of NH3 actually accepts protons from HClO2.

Therefore, % dissociation of HClO2 in NH3 solution is greater than that of in HNO2 and HBr solution.

# Option D. HClO2(aq) <-------------> ClO2-(aq) + H+(aq)

            KOH (aq) + H+(aq) <-----------> H2O(aq) + K+

Note that KOH (strong base) accepts the protons from HClO2. So, the equilibrium of HClO2 dissociation shifts to the right in KOH solution.

Being strong base, KOH undergoes complete dissociations. In turn, it would cause highest [OH-] in the solution that would in turn neutralize highest amount of H+ from HClO2.

Therefore, HClO2 would undergo maximum dissociation in KOH solution due to shifting of equilibrium to the right to greatest extent.

# So, correct option is- D.

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