What you see in this reaction are the steamy fumes of hydrogen bromide contaminated with the brown colour of bromine vapour. Note: If you aren't confident about redox reactions, electron-half equations, and oxidation states you really ought to follow this link before you go any further. You can combine these two half-equations to give the overall ionic equation for the reaction: This is a decrease of oxidation state of the sulphur from +6 in the sulphuric acid to +4 in the sulphur dioxide. The bromide ions reduce the sulphuric acid to sulphur dioxide gas. In the process the bromide ions are oxidised to bromine. The bromide ions are strong enough reducing agents to reduce the concentrated sulphuric acid. That isn't true, though, with bromides and iodides. Whichever way you look at it, all you get is the hydrogen halide! The fluoride and chloride ions aren't strong enough reducing agents to reduce the sulphuric acid. You can look at this another way - from the point of view of the halide ions. In those cases, all you get produced are the steamy fumes of the hydrogen halide - hydrogen fluoride or hydrogen chloride. If you want to read a bit more about them, follow this link and use the BACK button on your browser to return to this page.Ĭoncentrated sulphuric acid acting as an oxidising agentĬoncentrated sulphuric acid isn't a strong enough oxidising agent to oxidise fluoride or chloride ions. Note: These reactions to make the hydrogen halides are dealt with on a separate page. If the hydrogen halide is exposed to moist air, you see it as steamy fumes.Īs an example, concentrated sulphuric acid reacts with solid sodium chloride in the cold to produce hydrogen chloride and sodium hydrogensulphate.Īll of the halide ions (fluoride, chloride, bromide and iodide) behave similarly. Because this is a gas, it immediately escapes from the system. The concentrated sulphuric acid gives a hydrogen ion to the halide ion to produce a hydrogen halide. The concentrated sulphuric acid can act both as an acid and as an oxidising agent.Ĭoncentrated sulphuric acid acting as an acid There are two different types of reaction which might go on when concentrated sulphuric acid is added to a solid ionic halide like sodium fluoride, chloride, bromide or iodide. It uses these reactions to discuss the trend in reducing ability of the ions as you go from fluoride to chloride to bromide to iodide. This page describes and explains the redox reactions involving halide ions and concentrated sulphuric acid. THE REDOX REACTIONS BETWEEN HALIDE IONS AND CONCENTRATED SULPHURIC ACID Redox reactions involving halide ions and sulphuric acid
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