The solubility of copper in water and acids

The chemical properties of most elements are based on their ability to dissolve in aqueous media and acids. The study of the characteristics of copper is associated with a low-activity in normal conditions. A peculiarity of its chemical processes is the formation of compounds with ammonia, mercury, nitric and sulfuric acids. Low copper solubility in water is not capable of causing corrosion processes. It has special chemical properties that make it possible to use the compound in various industries.

Item Description

Copper is considered to be the oldest metal that people learned to mine before our era. This substance is obtained from natural sources in the form of ore. Copper is called an element of the chemical table with the Latin name cuprum, the ordinal number of which is 29. In the periodic system it is located in the fourth period and belongs to the first group.

The natural substance is a pink-red heavy metal with a soft and forging structure. The temperature of its boiling and melting is more than 1000 ° С. It is considered a good conductor.

Chemical structure and properties

If you study the electronic formula of a copper atom, you can find that it has 4 levels. On the valence 4s-orbitals there is only one electron. During chemical reactions, from 1 to 3 negatively charged particles can be split off from the atom, then copper compounds with an oxidation state of +3, +2, +1 are obtained. Its bivalent derivatives possess the greatest stability.

In chemical reactions, it acts as a low-activity metal. Under normal conditions, the solubility of copper in water is absent. In dry air, corrosion is not observed, but when heated, the metal surface is covered with a black coating of bivalent oxide. The chemical stability of copper is manifested by the action of anhydrous gases, carbon, a number of organic compounds, phenolic resins and alcohols. It is characterized by complexation reactions with the release of colored compounds. Copper has a slight similarity with the metals of the alkali group, associated with the formation of derivatives of the monovalent series.

What is solubility?

This is the process of formation of homogeneous systems in the form of solutions in the interaction of one compound with other substances. Their components are individual molecules, atoms, ions and other particles. The degree of solubility is determined by the concentration of the substance, which was dissolved in the preparation of a saturated solution.

The unit of measurement is most often percentages, volumetric or weight fractions. The solubility of copper in water, as well as of other compounds of a solid type, is subject only to changes in temperature conditions. This dependence is expressed by means of curves. If the indicator is very small, then the substance is considered insoluble.

The solubility of copper in an aqueous medium

The metal exhibits corrosion resistance under the influence of sea water. This proves its inertness under ordinary conditions. The solubility of copper in water (fresh) is practically not observed. But in a humid environment and under the influence of carbon dioxide on the metal surface, a green film forms, which is the main carbonate:

Cu + Cu + O ₂ + H ₂ O + CO ₂ → Cu (OH) ₂ · CuCO ₂ .

If we consider its monovalent compounds in the form of a salt, then their insignificant dissolution is observed. Such substances are susceptible to rapid oxidation. As a result, copper compounds are divalent. These salts have good solubility in an aqueous medium. There is a complete dissociation into ions.

Solubility in acids

The usual conditions for the reaction of copper with weak or dilute acids do not contribute to their interaction. There is no chemical process of metal with alkalis. The solubility of copper in acids is possible if they are strong oxidants. Only in this case there is interaction.

The solubility of copper in nitric acid

Such a reaction is possible in view of the fact that a process of oxidation of the metal with a strong reagent takes place. Nitric acid in dilute and concentrated form shows oxidative properties with copper dissolution.

In the first variant, during the reaction, copper nitrate and nitrogen bivalent oxide are obtained in a ratio of 75% to 25%. The process with dilute nitric acid can be described by the following equation:

8HNO ₃ + 3Cu → 3Cu (NO ₃ ) ₂ + NO + NO + 4H ₂ O.

In the second case, copper nitrate and nitrogen are obtained, divalent and tetravalent oxides, the ratio of which is 1 to 1. In this process, 1 mole of metal and 3 moles of acid are concentrated. When copper dissolves, the solution warms up strongly, as a result of which thermal decomposition of the oxidizer and the release of an additional volume of nitrogen oxides are observed:

4HNO ₃ + Cu → Cu (NO ₃ ) ₂ + NO ₂ + NO ₂ + 2H ₂ O.

The reaction is used in low-tonnage production, related to the processing of scrap or the removal of coating from waste. However, such a method of dissolving copper has a number of disadvantages associated with the release of a large amount of nitrogen oxides. For their capture or neutralization, special equipment is necessary. These processes are very expensive.

Dissolution of copper is considered complete, when there is a complete cessation of the production of volatile nitrogen oxides. The reaction temperature ranges from 60 to 70 ° C. The next step is to release the solution from the chemical reactor. On its bottom are small pieces of metal, which has not reacted. Water was added to the resulting liquid and filtration was carried out.

Solubility in sulfuric acid

In the normal state, this reaction does not occur. The factor determining the dissolution of copper in sulfuric acid is its strong concentration. Diluted media can not oxidize the metal. Dissolution of copper in concentrated sulfuric acid proceeds with the liberation of sulphate.

The process is expressed by the following equation:

Cu + H ₂ SO ₄ + H ₂ SO ₄ → CuSO ₄ + 2H ₂ O + SO ₂ .

Properties of copper sulfate

Salt dibasic is also called sulfuric acid, it is designated as CuSO ₄ . It is a substance without a characteristic odor, not showing volatility. In anhydrous form, the salt has no color, it is opaque and has a high hygroscopicity. Copper (sulfate) solubility is good. Molecules of water, joining the salt, can form crystalline hydrate compounds. An example is copper sulfate, which is a blue pentahydrate. Its formula: CuSO ₄ · 5H ₂ O.

Crystal hydrates have a transparent structure of a bluish hue, they exhibit a bitter, metallic taste. Their molecules are able in time to lose bound water. In nature, they occur in the form of minerals, which include chalcantite and butyl.

Copper sulfate is exposed to copper. Solubility is an exothermic reaction. During the hydration of salt, a significant amount of heat is released.

The solubility of copper in iron

As a result of this process, pseudoalloys from Fe and Cu are formed. For metallic iron and copper, limited mutual solubility is possible. Its maximum values are observed at a temperature of 1099.85 ° C. The degree of solubility of copper in the solid form of iron is 8.5%. These are small indicators. The dissolution of metallic iron in the solid form of copper is about 4.2%.

Reducing the temperature to room values makes mutual processes insignificant. When melting metallic copper, it is able to wet the iron well in a solid form. When preparing pseudoalloys Fe and Cu, special blanks are used. They are created by pressing or baking an iron powder in a pure or alloyed form. Such blanks are impregnated with liquid copper, forming pseudoalloys.

Dissolution in ammonia

The process often occurs when NH _{3 is} passed in gaseous form over the molten metal. The result is the dissolution of copper in ammonia, the release of Cu ₃ N. This compound is called a monovalent nitride.

Its salts are exposed to a solution of ammonia. Addition of such a reagent to copper chloride leads to the precipitation of a precipitate in the form of a hydroxide:

CuCl ₂ + NH ₃ + NH ₃ + 2H ₂ O → 2NH ₄ Cl + Cu (OH) ₂ ↓.

Ammonium excess promotes the formation of a compound of a complex type having a dark blue color:

Cu (OH) ₂ ↓ + 4NH ₃ → [Cu (NH ₃ ) ₄ ] (OH) ₂ .

This process is used to determine the ions of bivalent copper.

Solubility in cast iron

In the structure of malleable pearlitic iron, in addition to the main components, there is an additional element in the form of ordinary copper. It increases the graphitization of carbon atoms, contributes to the increase in fluidity, strength and hardness of alloys. Metal positively affects the level of perlite in the final product. The solubility of copper in cast iron is used to dope the original composition. The main purpose of this process is to obtain a malleable alloy. It will have increased mechanical and corrosive properties, but embrittlement is reduced.

If the content of copper in cast iron is about 1%, then the tensile strength is equal to 40%, and the yield increases to 50%. This significantly changes the characteristics of the alloy. An increase in the amount of metal alloying up to 2% leads to a change in strength to a value of 65%, and the yield value becomes 70%. With a higher copper content in the composition of cast iron, spherical graphite is more difficult to form. Introduction to the structure of the alloying element does not change the technology of formation of a viscous and soft alloy. The time that is set aside for annealing coincides with the duration of such a reaction in the production of cast iron without a copper impurity. It is about 10 hours.

The use of copper for making cast iron with a high concentration of silicon is not capable of completely eliminating the so-called ferruginization of the mixture during annealing. As a result, a product with a low elasticity is obtained.

Solubility in mercury

When mixing mercury with the metals of other elements, amalgams are obtained. This process can take place at room temperature, because in such conditions Pb is a liquid. The solubility of copper in mercury passes only during heating. Metal must be crushed beforehand. When wet copper mercury is wetted, there is a mutual penetration of one substance into another or a process of diffusion. The solubility value is expressed as a percentage and is 7.4 * 10 ^-3 . During the reaction, a solid, simple amalgam, similar to cement, is obtained. If it is slightly heated, then it softens. As a result, this mixture is used to repair products from porcelain. There are also complex amalgams with the optimal content of metals in it. For example, in the dental alloy there are elements of silver, tin, copper and zinc. Their percentage in percent refers to as 65: 27: 6: 2. Amalgam with this composition is called silver. Each component of the alloy fulfills a certain function, which makes it possible to obtain a high quality seal.

Another example is an amalgam alloy, in which a high copper content is observed. It is also called copper alloy. In the amalgam composition, from 10 to 30% Cu is present. The high content of copper prevents the interaction of tin with mercury, which does not allow the formation of a very weak and corrosive phase of the alloy. In addition, a decrease in the amount of silver filling leads to a reduction in price. For the preparation of amalgams it is desirable to use an inert atmosphere or a protective fluid that forms a film. Metals that make up the alloy can be rapidly oxidized by air. The process of heating the amalgam of cuprum to the presence of hydrogen leads to the distillation of mercury, which makes it possible to separate elementary copper. As you can see, this topic is easy to learn. Now you know how copper interacts not only with water, but also with acids and other elements.