Gas reducing agent

Chromium(IJ) chloride, chromous chloride, CrCl2- White solid (Cr plus HCl gas) dissolving to give a blue solution. Forms hydrates, widely used as a reducing agent. 

Sulphur dioxide, SO2, m.p. — 72-7°C, b.p. — I0"C. Colourless gas with characteristic smell. Formed by burning S, metal sulphides, H2S in air or acid on a sulphite or hydrogen sulphite. Powerful reducing agent, particularly in water. Dissolves in water to give a gas hydrate the solution behaves as an acid - see sulphurous acid. Used in the production of SO3 for sulphuric acid. 

It is a colourless gas which decomposes on heating above 420 K to give metallic tin, often deposited as a mirror, and hydrogen. It is a reducing agent and will reduce silver ions to silver and mercury(II) ions to mercury. SnSn bonding is unknown in hydrides but does exist in alkyl and aryl compounds, for example (CH3)3Sn-Sn(CH3)3. 

Ammonia as a reducing agent. Ammonia gas will not burn in air but it does burn in oxygen with a yellowish flame after ignition. A convenient apparatus is shown in Figure 9.3. By reversing the gas supplies it can easily be shown that oxygen will also burn in ammonia. 

Reduction products vary depending on the reducing agent, for example dinitrogen oxide is obtained with sulphurous acid, nitrogen is obtained when the gas is passed over heated metals (e.g. copper and iron) and ammonia is produced when the gas reacts with aqueous chromiumfll) salts. 

Although sulphur dioxide, as a gas, is a reducing agent in the sense that it unites with oxygen, free or combined (for example in dioxides or peroxides) most of its reducing reactions in aqueous solution are better regarded as reactions of sulphurous acid (in acid solution), or the sulphite ion (in alkaline solution). 

The special reducing agent (a solution containing cupro-ammonia ions) is first prepared. Dissolve 63 g. of crystallised copper sulphate in 250 ml. of water in a 1-Utre heaker, add 100 ml. of concentrated ammonium hydroxide solution (sp. gr. 0-88), and cool the solution to 10°. Dissolve 17 8 g. of hydroxylammonium chloride or 21 g. of hydroxylammonium sulphate in 60 ml. of water, cool to 10°, and add 42 -5 ml. of QN sodium hydroxide solution if the resulting solution of tydroxylamine is not clear, filter it at the pump. Without delay add the hydroxylamine solution, with stirring, to the ammoniacal cupric sulphate solution. Reduction occurs at once, a gas is evolved, and the solution assumes a pale blue colour. Protect the reducing agent from the air if it is not used immediately. 

SO2 absorbed from gas with Mg(OH)2 slurry, giving MgSO —MgSO sohds which are calcined with coke or other reducing agent, regenerating MgO and releasing SO2. 

Zinc dust is used in the sherardizing process where work pieces are tumbled with zinc dust in rotating steel dmms which are heated electrically or by gas to 370—420°C (149). The steel parts are uniformly coated with zinc. In the chemical and metallurgical industries, zinc dust is used as a reducing agent, in the manufacture of hydrosulfite compounds for the textile and paper industries, and to enhance the physical properties of plastics and lubricants (2). 

Stibiae may be inadvertentiy formed by acidified reducing agents reacting with antimony-containing materials. It is an extremely poisonous gas which causes blood destmction and damage to the fiver and kidneys (2). 

Chloride Reductant. Processes prior to 1945 used hydrochloric acid as both the acid and reducing agent. Hydrochloric acid is oxidized to chlorine gas and chlorate is reduced to chlorine dioxide. The overall stoichiometry produces a 2 1 molar ratio of chlorine dioxide to chlorine. Sodium chloride is a by-product ... 

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