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 under ordinary conditions. A feature of its chemical processes is the formation of compounds with ammonia, mercury, nitric and sulfuric acids. The low solubility of copper in water is not able to cause corrosion processes. It has special chemical properties that allow the use of the compound in various industries.
Item Description
Copper is considered the oldest of the metals that people learned to mine even before our era. This substance is obtained from natural sources in the form of ore. Copper is an element of a chemical table with the Latin name cuprum, whose serial number 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 ° C. 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 orbital 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. The most stable are its divalent derivatives.
In chemical reactions, it acts as a low-activity metal. Under normal conditions, there is no solubility of copper in water. Corrosion is not observed in dry air, but when heated, the metal surface is covered with a black coating of divalent 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 little resemblance to alkali metals associated with the formation of monovalent derivatives.
What is solubility?
This is the process of formation of homogeneous systems in the form of solutions during 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 upon receipt of a saturated solution.
The unit of measurement is most often percent, volume or weight fractions. The solubility of copper in water, as well as other solid compounds, is subject only to changes in temperature conditions. This dependence is expressed using curves. If the indicator is very small, then the substance is considered insoluble.
The solubility of copper in the aquatic environment
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 a 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 salt, then their slight dissolution is observed. Such substances are subject to rapid oxidation. The result is divalent copper compounds. These salts have good solubility in an aqueous medium. Their complete dissociation into ions occurs.
Acid solubility
The usual conditions for reactions of copper with weak or dilute acids do not facilitate their interaction. The chemical process of the metal with alkalis is not observed. The solubility of copper in acids is possible if they are strong oxidizing agents. Only in this case the interaction proceeds.
Solubility of copper in nitric acid
Such a reaction is possible due to the fact that the process of metal oxidation by a strong reagent occurs. Nitric acid in diluted and concentrated form exhibits oxidizing properties with the dissolution of copper.
In the first embodiment, during the reaction, copper nitrate and nitrogen divalent 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. 1 mol of metal and 3 moles of concentrated nitric acid are involved in this process. When copper is dissolved, a strong heating of the solution occurs, resulting in the thermal decomposition of the oxidizing agent and the release of an additional volume of nitric oxides:
4HNO 3 + Cu → Cu (NO 3 ) 2 + NO 2 + NO 2 + 2H 2 O.
The reaction is used in small-scale production associated with the processing of scrap or removal of coating from waste. However, this method of dissolving copper has several disadvantages associated with the release of a large amount of nitric oxides. For their capture or neutralization requires special equipment. These processes are very expensive.
The dissolution of copper is considered complete when there is a complete cessation of the production of volatile nitrous oxides. The reaction temperature ranges from 60 to 70 ° C. The next step is to drain the solution from the chemical reactor. At the bottom of it are small pieces of metal that have not reacted. Water was added to the obtained liquid and filtration was carried out.
Solubility in sulfuric acid
In the normal state, such a reaction does not proceed. A factor determining the dissolution of copper in sulfuric acid is its strong concentration. The diluted medium cannot oxidize the metal. The dissolution of copper in concentrated sulfuric acid proceeds with the release of sulfate.
The process is expressed by the following equation:
Cu + H 2 SO 4 + H 2 SO 4 → CuSO 4 + 2H 2 O + SO 2 .
Copper Sulfate Properties
The dibasic salt is also called sulfate, designate it like this: CuSO 4 . It is a substance without a characteristic odor that does not exhibit volatility. In an anhydrous form, the salt has no color, it is opaque, with high hygroscopicity. In copper (sulfate), solubility is good. Water molecules, 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 are characterized by a transparent structure of a bluish tint, they exhibit a bitter, metallic taste. Their molecules are capable of losing bound water over time. In nature, they are found in the form of minerals, which include chalcanthite and butite.
Exposed to copper sulfate. Solubility is an exothermic reaction. In the process of salt hydration, a significant amount of heat is released.
Solubility of Copper in Iron
As a result of this process, pseudo-alloys of Fe and Cu are formed. For metallic iron and copper, limited mutual solubility is possible. Its maximum values are observed at a temperature indicator of 1099.85 ° C. The 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%.
Lowering the temperature to room values makes the mutual processes insignificant. When melting metallic copper, it is able to wet the solid well in solid form. In the preparation of Fe and Cu pseudo-alloys, special preforms are used. They are created by pressing or baking iron powder, which is in pure or alloyed form. Such preforms are impregnated with liquid copper, forming pseudo-alloys.
Dissolution in ammonia
The process often proceeds when NH 3 is passed in gaseous form over a hot metal. The result is the dissolution of copper in ammonia, the release of Cu 3 N. This compound is called monovalent nitride.
Its salts are exposed to an ammonia solution. The addition of such a reagent to copper chloride leads to the precipitation in the form of hydroxide:
CuCl 2 + NH 3 + NH 3 + 2H 2 O → 2NH 4 Cl + Cu (OH) 2 ↓.
Ammonia excess contributes to the formation of compounds of the complex type, having a dark blue color:
Cu (OH) 2 ↓ + 4NH 3 → [Cu (NH 3 ) 4 ] (OH) 2 .
This process is used to determine divalent copper ions.
Solubility in Cast Iron
In the structure of malleable pearlite cast iron, in addition to the main components, there is an additional element in the form of ordinary copper. It is it that increases the graphitization of carbon atoms, helps to increase the fluidity, strength and hardness of the alloys. Metal has a positive effect on the level of perlite in the final product. The solubility of copper in cast iron is used to alloy the initial composition. The main goal of this process is to obtain a malleable alloy. It will have increased mechanical and corrosive properties, but embrittlement is reduced.
If the copper content in cast iron is about 1%, then the tensile strength during stretching is equal to 40%, and the yield strength increases to 50%. This significantly changes the characteristics of the alloy. An increase in the amount of metal alloying to 2% leads to a change in strength to 65%, and the yield index 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 allotted for annealing coincides with the duration of such a reaction in the production of cast iron without copper impurities. It is about 10 hours.
The use of copper for the manufacture of cast iron with a high concentration of silicon is not able to completely eliminate the so-called ironization of the mixture during annealing. The result is a product with low elasticity.
Solubility in mercury
When mercury is mixed with metals of other elements, amalgams are obtained. This process can take place at room temperature, because under such conditions Pb is a liquid. The solubility of copper in mercury only occurs during heating. The metal must first be crushed. When solid copper is wetted with liquid mercury, a mutual penetration of one substance into another or a diffusion process occurs. The solubility value is expressed as a percentage and is 7.4 * 10 -3 . The reaction process produces a solid, simple amalgam similar to cement. If it is slightly heated, then it softens. As a result, such a mixture is used to repair porcelain products. There are also complex amalgams with an optimal content of metals in it. For example, in a dental alloy there are elements of silver, tin, copper and zinc. Their percentage percentage refers to 65: 27: 6: 2. An amalgam with such a composition is called silver. Each component of the alloy performs a specific function, which allows you to get a high-quality seal.
Another example is an amalgam alloy, in which a high copper content is observed. It is also called copper alloy. Amalgam contains from 10 to 30% Cu. The high copper content prevents the interaction of tin with mercury, which prevents the formation of a very weak and corrosive phase of the alloy. In addition, a decrease in the amount of silver in a seal leads to a reduction in price. To prepare the amalgam, it is advisable to use an inert atmosphere or a protective liquid that forms a film. The metals that make up the alloy are able to oxidize quickly with air. The process of heating the cuprum amalgam in the presence of hydrogen leads to the distillation of mercury, which allows the separation of elemental copper. As you can see, this topic is not difficult to study. Now you know how copper interacts not only with water, but also with acids and other elements.