Reaction of Chlorine with Hydrogen
Hydrogen gas from a storage tank is ignited in air. When the hydrogen flame is lowered into chlorine gas in a glass cylinder, the flame becomes larger and brighter, indicating that the hydrogen is now being oxidized by chlorine instead of oxygen. The product of the reaction of hydrogen and chlorine is hydrogen chloride. The presence of hydrogen chloride is demonstrated by bringing the stopper from a bottle of aqueous ammonia above the glass cylinder. A smoke of ammonium chloride forms.
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Keywords
descriptive chemistry, enthalpy/heat, evidence of chemical reaction, exothermic process, fire/flammability, halogens/halides/hydrohalic acids, hydrogen, redox reaction
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(QuickTime 3.0 Sorenson, duration 39 seconds, size 2.7 MB)
Hydrogen gas flowing from a capillary is ignited. The watch glass covering a glass cylinder of chlorine is removed and the hydrogen flame lowered into the chlorine. The reaction between hydrogen and air is replaced by the reaction between hydrogen and chlorine, which produces hydrogen chloride. As the flame burns the level of chlorine gas in the container decreases. When a stopper from a bottle of aqueous ammonia is brought near the flame, white fumes of ammonium chloride are produced indicating the presence of hydrogen chloride.
 Hydrogen gas is ignited. |
 The reaction between hydrogen and air is replaced... |
 ... by the reaction between hydrogen and chlorine |
 When aqueous ammonia is brought near the flame, ammonium chloride is produced. |
Additional still images for this movie
Discussion
Hydrogen gas and chlorine do not react at room temperature, just as hydrogen gas and air do not react. If the hydrogen is ignited in air, the increase in temperature due to the exothermic reaction between hydrogen and oxygen allows the reaction to proceed at a fast rate and a flame appears. The hydrogen flame in air is nearly invisible. Once ignited in air the hydrogen flame can be moved to an atmosphere that consists of mainly chlorine. Then the chlorine takes over as the oxidizing agent. The flame becomes much more visible and appears larger. A chemical reaction continues, but the flame temperature and reaction products are different.
Demonstration Notes, Warnings, Safety Information, etc.
Exam and Quiz Questions
1. What observable evidence indicates that a chemical reaction is taking place?
2. Classify the reactions shown in the video as combination, decomposition, exchange, acid-base, combustion, or redox. (There is more than one reaction, and each reaction may fall within more than one of these categories.)
3. Are the reactions shown exothermic or endothermic? Cite observations that justify your choice.
4. When the hydrogen flame is lowered from air into the container of chlorine, the color of the flame changes. Explain why the color of the flame changes. Base your explanation on the theory of spectra of atoms and molecules.