Question #79236

1 Answer
Sep 12, 2015

Here's how the half-reactions look like.


Chlorinegas can react with water to form hypochlorous acid, #"HClO"#, and hydrochloric acid, #"HCl"#.

This reaction is actually a disproportionation reaction because chlorine is being oxidized and reduced at the same time.

The balanced chemical equation - with oxidation numbers included- looks like this

#stackrel(color(blue)(0))("Cl"_2) + stackrel(color(blue)(+1))("H"_2) stackrel(color(blue)(-2))("O") -> stackrel(color(blue)(+1))("H") stackrel(color(blue)(+1))"Cl" stackrel(color(blue)(-2)) ("O") + stackrel(color(blue)(+1)) ("H") stackrel(color(blue)(-1)) ("Cl")#

Notice that chlorine is being oxidized to a +1 oxidation state in hypochlorous acid and reduced to a -1 oxidation state in hydrochloric acid.

The half-reactions will be

  • reduction half-reaction

#stackrel(color(blue)(0))("Cl"_2) + 2e^(-) -> 2"H"stackrel(color(blue)(-1))("Cl")#

Use protons to balance the hydrogen atoms

#2"H"^(+) + stackrel(color(blue)(0))("Cl"_2) + 2e^(-) -> 2"H"stackrel(color(blue)(-1))("Cl")#

  • reduction half-reaction

#stackrel(color(blue)(0))("Cl"_2) -> 2"H"stackrel(color(blue)(+1))("Cl")"O" + 2e^(-)#

Balance the oxygen atoms by adding water molecules and the hydrogen atoms by adding protons

#2"H"_2"O" + stackrel(color(blue)(0))("Cl"_2) -> 2"H"stackrel(color(blue)(+1))("Cl")"O" + 2e^(-) + 2"H"^(+)#

The number of electrons lost in the oxidation half-reaction is equal to the number of electrons gained in the reduction half-reaction, which means that you can add these two half-reactions to get

#2"H"^(+) + "Cl"_2 + 2e^(-) + 2"H"_2"O" + "Cl"_2 -> 2"HCl" + 2e^(-) + "2HClO" + 2"H"^(+)#

This is reduced to

#color(red)(cancel(color(black)(2"H"^(+)))) + "Cl"_2 + color(red)(cancel(color(black)(2e^(-)))) + 2"H"_2"O" + "Cl"_2 -> 2"HCl" + 2"HClO" + color(red)(cancel(color(black)(2e^(-)))) + color(red)(cancel(color(black)(2"H"^(+))))#

#2"Cl"_2 + 2"H"_2"O" -> 2"HClO" + 2"HCl"#

Finally, you have

#"Cl"_(2(aq)) + "H"_2"O"_text((l]) -> "HClO"_text((aq]) + "HCl"_text((aq])#