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Zorluk: OrtaHalogens: Chlorine, Hydrogen Chloride, and Oxoacids

Chlorine gas dissolves in water to produce a pale greenish-yellow mixture known as chlorine water. When this solution is left exposed to bright sunlight for a prolonged period, the solution loses its color and gas bubbles are observed escaping from the container. Which gas is evolved, and which specific component of chlorine water decomposes to produce it?

  1. Oxygen gas (O2\text{O}_2), produced by the light-catalyzed decomposition of hypochlorous acid (HClO\text{HClO})Cevap
  2. B
    Hydrogen gas (H2\text{H}_2), produced by the thermal decomposition of hydrochloric acid (HCl\text{HCl})
  3. C
    Chlorine gas (Cl2\text{Cl}_2), produced by the volatilization of dissolved chloride ions
  4. D
    Oxygen gas (O2\text{O}_2), produced by the direct decomposition of hydrochloric acid (HCl\text{HCl})

Cevap

Oxygen gas (O2\text{O}_2), produced by the light-catalyzed decomposition of hypochlorous acid (HClO\text{HClO})
When chlorine dissolves in water, it undergoes a reversible reaction to form hydrochloric acid (HCl\text{HCl}) and hypochlorous acid (HClO\text{HClO}). Hypochlorous acid is a weak, unstable oxoacid that decomposes in the presence of sunlight to yield additional hydrochloric acid and oxygen gas (2HClO→2HCl+O22\text{HClO} \rightarrow 2\text{HCl} + \text{O}_2). The release of oxygen gas bubbles accounts for the observed gas evolution, while the removal of green Cl2\text{Cl}_2 shifts the initial equilibrium until the pale color disappears completely.

Adım Adım Çözüm

1
Identify the equilibrium products of chlorine gas dissolved in water.
Chlorine reacts reversibly with water to form hydrochloric acid (HCl\text{HCl}) and hypochlorous acid (HClO\text{HClO}): Cl2(g)+H2O(l)⇌HCl(aq)+HClO(aq)\text{Cl}_2\text{(g)} + \text{H}_2\text{O(l)} \rightleftharpoons \text{HCl(aq)} + \text{HClO(aq)}.
Chlorine water is an equilibrium mixture containing both acids.
2
Determine the photochemical behavior of the oxoacid component in sunlight.
Hypochlorous acid (HClO\text{HClO}) is photochemically unstable and decomposes under bright sunlight: 2HClO(aq)→sunlight2HCl(aq)+O2(g)2\text{HClO(aq)} \xrightarrow{\text{sunlight}} 2\text{HCl(aq)} + \text{O}_2\text{(g)}.
The weak O-Cl\text{O-Cl} bond in hypochlorous acid readily breaks upon absorption of ultraviolet/visible light energy.
3
Conclude the identity of the evolved gas and the decomposing species.
The evolved gas is oxygen (O2\text{O}_2), and the decomposing species is hypochlorous acid (HClO\text{HClO}).
Hydrochloric acid remains in solution, causing the overall solution to become gradually more acidic as hypochlorous acid decomposes.

Anahtar Kavram

Photochemical decomposition of hypochlorous acid in chlorine water
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Konular

Halogens: Chlorine, Hydrogen Chloride, and Oxoacids

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