Metals reactions with hydrochloric acid

Aqueous hydrazine solutions, materials compatibility for, 13 587t Aqueous hydrazine specifications, 13 586t Aqueous hydrochloric acid reaction with metals, 13 826 thermodynamic functions of, 13 816t uses for, 13 834-835... 

Hydrochloric acid reacts with metals such as zinc, magnesium, and aluminmn. A colorless gas escapes, and the metal seems to disappear. What happens to the atoms of the metals in these reactions Are they destroyed If not, where do they go ... 

Hydrochloric acid is a strong monobasic acid, dissolving metals to form salt and evolving hydrogen. The reaction may be slow if the chloride formed is insoluble (for example lead and silver are attacked very slowly). The rate of attack on a metal also depends on concentration thus aluminium is attacked most rapidly by 9 M hydrochloric acid, while with other metals such as zinc or iron, more dilute acid is best. 

Oxides and hydroxides react with HCl to form a salt and water as in a simple acid—base reaction. However, reactions with low solubiHty or insoluble oxides and hydroxides is complex and the rate is dependent on many factors similar to those for reactions with metals. Oxidizing agents such as H2O2, H2SeO, and V2O3 react with aqueous hydrochloric acid, forming water and chlorine. 

The determination of tin in metals containing over 75 wt % tin (eg, ingot tin) requites a special procedure (17). A 5-g sample is dissolved in hydrochloric acid, reduced with nickel, and cooled in CO2. A calculated weight of pure potassium iodate (dried at 100°C) and an excess of potassium iodide (1 3) are dissolved in water and added to the reduced solution to oxidize 96—98 wt % of the stannous chloride present. The reaction is completed by titration with 0.1 Af KIO —KI solution to a blue color using starch as the indicator. 

Chemical Reactivity - Reactivity with Water Forms hydrogen chloride (hydrochloric acid). Reaction not very vigorous in cold water Reactivity with Common Materials Slow corrosion of metals Stability During Transport Stable Neutralizing Agents for Acids and Caustics Flush with and rinse with sodium bicarbonate or lime solution Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

It has already been indicated that titanium is not particularly resistant to corrosion in hot, strong acids of the type that usually generate hydrogen upon reaction with metals —acids such as sulphuric or hydrochloric. In contact with such acids, corroding titanium assumes a negative electrical potential (approximately -0-7 V, S.C.E.). 

Hydrochloric acid is thought to give dangerous reactions with metal carbides. There are no further details regarding risks. The dangers may be linked to the acetylene produced. 

The metal is attacked by mineral acids. Reactions with sulfuric and hydrochloric acids produce hydrogen. With nitric acid, no hydrogen is evolved but the pentavalent nitrogen is reduced to nitrogen at lower valence states. 

Test the reaction of a 3 % hydrochloric acid solution with the metal sulphides, taking a small amount of them. Explain the different reaction of hydrochloric acid with metal sulphides. 

There are two series of compounds of tin and the halogens those related to stannous oxide, SnO, in which the metal has a valence of 2 (stannous salts), and those related to stannic oxide, Sn02, in which it has a valence of 4 (stannic salts). The compounds with lower valence are usually prepared by the action of the halogen acids on the metal. Stannous chloride, for example, is formed when hydrochloric acid reacts with tin. Stannic salts, on the other hand, are prepared by the reaction of tin and the free halogen. In this preparation stannic bromide results from the reaction of bromine and tin. The reaction between the two ele-... 

The characteristic colours and solubilities of many metallic sulphides have already been discussed in connection with the reactions of the cations in Chapter III. The sulphides of iron, manganese, zinc, and the alkali metals are decomposed by dilute hydrochloric acid with the evolution of hydrogen sulphide those of lead, cadmium, nickel, cobalt, antimony, and tin(IV) require concentrated hydrochloric acid for decomposition others, such as mercury(II) sulphide, are insoluble in concentrated hydrochloric acid, but dissolve in aqua regia with the separation of sulphur. The presence of sulphide in insoluble sulphides may be detected by reduction with nascent hydrogen (derived from zinc or tin and hydrochloric acid) to the metal and hydrogen sulphide, the latter being identified with lead acetate paper (see reaction 1 below). An alternative method is to fuse the sulphide with anhydrous sodium carbonate, extract the mass with water, and to treat the filtered solution with freshly prepared sodium nitroprusside solution, when a purple colour will be obtained the sodium carbonate solution may also be treated with lead nitrate solution when black lead sulphide is precipitated. 

Calculate the number of moles of hydrogen gas that can be produced by reaction of 0.750 mol of hydrochloric acid, HCl, with calcium metal. 

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