What happens when chlorine gas is bubbled through water?

When chlorine gas is bubbled into an aqueous solution of potassium iodide, some of the iodide ions are oxidized to iodine. The iodine molecules combine with iodide ions to form brown triiodide ion, I3-. In this demonstration, the aqueous solution is above a layer of carbon tetrachloride, in which iodine is quite soluble. The beautiful violet color of iodine can be seen as the iodine dissolves in the carbon tetrachloride layer.

With excess chlorine, iodine reacts to form iodine monochloride, ICl, which is ruby red. The iodine monochloride reacts further to form iodine trichloride, ICl3, which is much lighter in color, causing the solution to be decolorized.

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Keywords

combination reaction, covalent bonding/structure/properties, descriptive chemistry, evidence of chemical reaction, halogens/halides/hydrohalic acids, redox reaction, single exchange/replacement reaction

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Multimedia

Play movie (QuickTime 3.0 Sorenson, duration 84 seconds, size 5.7 MB)

A test tube contains a layer of potassium iodide solution over a denser layer of carbon tetrachloride. Chlorine is bubbled through the potassium iodide layer. The chlorine reacts with the iodide to form iodine. In the aqueous layer the brown triiodide ion is formed by the reaction of iodine with iodide. In the carbon tetrachloride layer, iodine forms a purple solution. The iodine in the aqueous layer reacts further with chlorine to form iodine monochloride. As more chlorine is added, the iodine reacts with the excess chlorine to form iodine trichloride and the solution decolorizes. Some iodine remains in the carbon tetrachloride layer.

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Discussion

This demonstration illustrates that chlorine is a stronger oxidizing agent than iodine, since iodide is oxidized by chlorine to iodine. However, it also illustrates the properties of two interhalogen compounds, ICl and ICl3. ICl is a ruby-red solid that melts at 27 oC. Its properties are intermediate between those of iodine and chlorine, which makes it similar to bromine. The color at the end of the video is probably due to ICl in the carbon tetrachloride layer, because it is redder than iodine's violet. ICl3 forms a bright yellow solid that consists of I2Cl6 molecules. It decomposes readily to ICl and Cl2, but this is not seen in the video. The color of ICl3 is much lighter than that of ICl or I2, and when it forms the aqueous layer is decolorized.

When chlorine gas is bubbled into an aqueous solution of potassium bromide, some of the bromide ions are oxidized to bromine. Some of the bromine molecules combine with bromide ions to form tribromide ion, Br3-. In this demonstration, the aqueous solution is above a layer of carbon tetrachloride, in which bromine is quite soluble. The red-brown color of bromine can be seen as the bromine dissolves in the carbon tetrachloride layer.

When enough chlorine has bubbled through the solution, the bromine either dissolves in the carbon tetrachloride or is swept out of the liquid into the gas phase, causing the solution to decolorize.

(168 )

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Keywords

combination reaction, descriptive chemistry, evidence of chemical reaction, halogens/halides/hydrohalic acids, redox reaction, single exchange/replacement reaction

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Multimedia

Play movie (QuickTime 3.0 Sorenson, duration 71 seconds, size 4.9 MB)

A test tube contains a layer of potassium bromide solution over a denser layer of carbon tetrachloride. Chlorine is bubbled through the potassium bromide layer. The chlorine reacts with the bromide to form bromine. The aqueous layer contains a mixture of bromine, bromide ion and tribromide ion. Bromine is also dissolved in the carbon tetrachloride layer to form a reddish solution. The bromide and tribromide ions do not dissolve in the carbon tetrachloride and remain in the aqueous layer. Some bromine gas can be seen above the aqueous layer. After some time the stream of chlorine has swept all of the bromine from the aqueous solution into the gas phase. Some bromine remains in the carbon tetrachloride layer.

Additional still images for this movie

Discussion

This demonstration illustrates that chlorine is a stronger oxidizing agent than bromine, since bromide is oxidized by chlorine to bromine. Only one interhalogen compound of bromine and chlorine can be formed, namely BrCl. It is a red-brown gas. Decolorization of the solution probably occurs when all of the bromine and bromine monochloride have been swept out of the solution by the steam of chlorine.

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