Interaction of acids with metals. Interaction of sulfuric acid with metals

The chemical reaction of an acid with a metal is specific for these classes of compounds. In its course, the hydrogen proton is reduced and, in conjunction with the acid anion, is replaced by a metal cation. This is an example of the reaction with the formation of salt, although there are several types of interactions that do not obey this principle. They proceed as oxidation-reduction and are not accompanied by the evolution of hydrogen.

Principles of reactions of acids with metals

All reactions of inorganic acid with metal lead to the formation of salts. The exception is, perhaps, only the reaction of a noble metal with royal vodka, a mixture of hydrochloric and nitric acid. Any other interaction of acids with metals leads to the formation of salt. In the case where the acid is neither sulfuric nor nitrogenous, then the product is cleaved molecular hydrogen.

But when concentrated sulfuric acid enters the reaction, the interaction with metals proceeds according to the principle of the oxidation-reduction process. Therefore, experimentally, two types of interactions of typical metals and strong inorganic acids were isolated:

• Interaction of metals with dilute acids;
• Interaction with concentrated acid.

The reactions of the first type proceed with any acid. The exception is only concentrated sulfuric acid and nitric acid of any concentration. They react according to the second type and lead to the formation of salts and products of sulfur and nitrogen reduction.

Typical interactions of acids with metals

Metals located to the left of hydrogen in a standard electrochemical series react with dilute sulfuric acid and other acids of various concentrations except for nitric acid to form a salt and liberate molecular hydrogen. Metals located to the right of hydrogen in the series of electronegativity can not react with the above acids and interact only with nitric acid, regardless of its concentration, with concentrated sulfuric acid and with aqua regia. This is the typical interaction of acids with metals.

Reactions of metals with concentrated sulfuric acid

If the content of sulfuric acid in the solution is more than 68%, it is considered to be concentrated and interacts with the metals to the left and right of hydrogen. The principle of the reaction with metals of different activities is shown in the photo below. Here, the oxidant is a sulfur atom in the sulfate anion. It is reduced to hydrogen sulfide, 4-valent oxide or to molecular sulfur.

Reactions with dilute nitric acid

Diluted nitric acid reacts with metals located to the left and right of hydrogen. During the reaction with the active metals, ammonia is formed, which immediately dissolves and reacts with the nitrate anion, forming another salt. With metals of medium activity, the acid reacts with the release of molecular nitrogen. With low reactivity, the reaction proceeds with the liberation of 2-valent nitrogen oxide. Most often, several sulfur reduction products are formed in one reaction. Examples of reactions are suggested in the graphical annex below.

Reactions with concentrated nitric acid

In this case, the oxidant is also nitrogen. All reactions result in the formation of salt and the release of nitric oxide. Flow patterns of oxidation-reduction reactions are proposed in the graphical annex. At the same time, special attention deserves the reaction of royal vodka with low-active elements. Such interaction of acids with metals is not specific.

Reactivity of metals

Metals react with acids quite readily, although there are several inert substances. These are noble metals and elements that have a high standard electrochemical potential. There are a number of metals that are built on the basis of this indicator. It is called the electronegativity series. If the metal is in it to the left of hydrogen, then it is able to react with dilute acid.

There is only one exception: iron and aluminum due to the formation of 3-valence oxides on their surface can not react with acid without heating. If the mixture is heated, then initially an oxide film of metal enters the reaction, and then it dissolves itself in the acid itself. Metals located to the right of hydrogen in the electrochemical activity series can not react with inorganic acid, including dilute sulfuric acid. There are two exceptions to the rules: these metals dissolve in concentrated and diluted nitric acid and royal vodka. In the latter, only rhodium, ruthenium, iridium and osmium can not be dissolved.