The chemical reaction of an acid with a metal is specific to these classes of compounds. In its course, the hydrogen proton is restored and, in conjunction with the acid anion, is replaced by a metal cation. This is an example of a s alt-forming reaction, although there are several types of interactions that do not follow this principle. They proceed as redox and are not accompanied by hydrogen evolution.
Principles of reactions of acids with metals
All reactions of an inorganic acid with a metal lead to the formation of s alts. The only exception is, perhaps, the reaction of the noble metal with aqua regia, a mixture of hydrochloric and nitric acid. Any other interaction of acids with metals leads to the formation of a s alt. If the acid is neither concentrated sulfuric nor nitric, then molecular hydrogen is split off as a product.
But when concentrated sulfuric acid reacts, the interaction with metals proceeds according to the principle of a redox process. Therefore, two types of interactions were experimentally distinguished, typicalmetals and strong inorganic acids:
- reaction of metals with dilute acids;
- interaction with concentrated acid.
Reactions of the first type proceed with any acid. The only exceptions are concentrated sulfuric acid and nitric acid of any concentration. They react according to the second type and lead to the formation of s alts and products of reduction of sulfur and nitrogen.
Typical reactions of acids with metals
Metals located to the left of hydrogen in the standard electrochemical series react with dilute sulfuric acid and other acids of various concentrations, with the exception of nitric acid, to form a s alt and release molecular hydrogen. Metals located to the right of hydrogen in the electronegativity series cannot 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 a typical interaction of acids with metals.
Reactions of metals with concentrated sulfuric acid
When the content of sulfuric acid in the solution is more than 68%, it is considered concentrated and interacts with metals to the left and to the right of hydrogen. The principle of the reaction with metals of various activity is shown in the photo below. Here, the oxidizing agent is the sulfur atom in the sulfate anion. It is reduced to hydrogen sulfide, 4-valent oxide or to molecular sulfur.
Reactions with dilute nitric acid
Dilutednitric acid reacts with metals located to the left and to the right of hydrogen. During the reaction with active metals, ammonia is formed, which immediately dissolves and interacts with the nitrate anion, forming another s alt. With metals of medium activity, the acid reacts with the release of molecular nitrogen. With inactive, the reaction proceeds with the release of dinitric oxide. Most often, several sulfur reduction products are formed in one reaction. Examples of reactions are suggested in the graphical application below.
Reactions with concentrated nitric acid
In this case, nitrogen also acts as an oxidizing agent. All reactions end with the formation of s alt and the release of nitric oxide. Schemes of the course of redox reactions are proposed in the graphical application. At the same time, the reaction of aqua regia with low-active elements deserves special attention. Such interaction of acids with metals is nonspecific.
Reactivity of metals
Metals react quite readily with acids, although there are a few 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's called the electronegativity series. If the metal is located to the left of hydrogen in it, then it is able to react with a dilute acid.
There is only one exception: iron andaluminum due to the formation of 3-valent oxides on their surface cannot react with acid without heating. If the mixture is heated, then initially the oxide film of the metal enters into the reaction, and then it dissolves in the acid itself. Metals located to the right of hydrogen in the electrochemical series of activity cannot react with inorganic acid, including dilute sulfuric acid. There are two exceptions to the rule: these metals dissolve in concentrated and dilute nitric acid and aqua regia. Only rhodium, ruthenium, iridium and osmium cannot be dissolved in the latter.
