Chemical reactions metal displacement

Seven chemical reactions were identified from the chemistry syllabus. These chemical reactions were selected because they were frequently encountered during the 2-year chemistiy course and based on their importance in understanding concepts associated with three topics, namely, acids, bases and salts, metal reactivity series and inorganic chemistry qualitative analysis. The seven types of chemical reactions were combustion of reactive metals in air, chemical reactions between dilute acids and reactive metals, neutralisation reactions between strong acids and strong alkalis, neutralisation reactions between dilute acids and metal oxides, chemical reactions between dilute acids and metal carbonates, ionic precipitation reactions and metal ion displacement reactions. Although two of the chemical reactions involved oxidation and reduction, it was decided not to include the concept of redox in this study as students had only recently been introduced to ion-electron... 

The metallic impurities present in an impure metal can be broadly divided into two groups those nobler (less electronegative) and those less noble or baser (more electronegative) as compared to the metal to be purified. Purification with respect to these two classes of impurities occurs due to the chemical and the electrochemical reactions that take place at the anode and at the cathode. At the anode, the impurities which are baser than the metal to be purified would go into solution by chemical displacement and by electrochemical reactions whereas the nobler impurities would remain behind as sludges. At the cathode, the baser impurities would not get electrolytically deposited because of the unfavorable electrode potential and the concentration of these impurities would build up in the electrolyte. If, however, the baser impurities enter the cell via the electrolyte or from the construction materials of the cell, there would be no accumulation or build up because these would readily co-deposit at the cathode and contaminate the metal. It is for this reason that it is extremely important to select the electrolyte and the construction materials of the cell carefully. In actual practice, some of the baser impurities do get transferred to the cathode due to chemical reactions. As an example, let the case of the electrorefining of vanadium in a molten electrolyte composed of sodium chloride-potassium chloride-vanadium dichloride be considered. Aluminum and iron are typically considered as baser and nobler impurities in the metal. When the impure metal is brought into contact with the molten electrolyte, the following reaction occurs... 

When you place a piece of zinc metal into a solution of CuS04, you expect a chemical reaction because the more active zinc displaces the less active copper from its compound (Sec. 7.3). We learned in Chap. 13 that this is an oxidation-reduction reaction, involving transfer of electrons from the zinc to the copper. 

After the apparatus has again reached room temperature, bring the pressure in it to atmospheric. Measure the volume of the water displaced from the apparatus by the evolved hydrogen. Write the equation of the chemical reaction. Calculate the equivalent of the metal taken. Compare the value of the found equivalent of magnesium with its true value, and enter the results in your laboratory notebook, using Form 5. 

These reactions are part of a larger category of reactions known as redox reactions (redox is short for oxidation-reduction). Sometimes these are called displacement reactions. These are chemical reactions in which atoms of one element replace the atoms of a second element in a compound. A general equation for a single-replacement reaction involving a metal (A), replacing a metallic cation in solution (B) is ... 

This is presented schematically in Fig. 6.3, which also shows that the kinetics of these processes is described by the transport rate of A from the wall to the adjacent media. Using Fig. 6.3, we can establish that two elementary processes are presented in this system. The first is the flow induced by the concentration gradient and the second is the mass transfer sustained by the processes on the surface (a chemical reaction in the case of the metal placket immersed in a specifically formulated liquid and the transport through the porosity in the case of the drying wall). The case presented here corresponds to the situation when, in respect of the bulk density, the fluid density begins to decrease near the wall. This generates the displacement of the media and the specific ascension force, which is equivalent to the density difference. This phenomenon depends on the concentration difference in fluid A Aca=(cap - c ). From Fig. 6.3 we can write a list of process variables ... 

As with any other chemical reaction, the formation of a metal complex from a metal ion and a set of proligands can be described by an equilibrium constant. In its simplest form, a complexation reaction might involve the reaction of unsolvated metal ions in the gas phase with gas phase proligands to form a complex. In practice it is difficult to study such reactions in the gas phase and complex formation is normally studied in solution, often in water. This introduces the complication that the solvent can also function as a ligand, so that complex formation will involve the displacement of solvent from the metal coordination sphere by the proligand. 

The alkaline earth metals form a host of unique monovalent free radicals. Most of these molecules can be formed by the laser-driven chemical reactions of metal vapors with a wide variety of organic and inorganic molecules. This photochemical production of new molecules has led to an extensive gas-phase inorganic chemistry and spectroscopy of alkaline earth derivatives. In recent years, the Broida oven source has been displaced by the pulsed molecular beam spectrometer. The chemical dynamics and photochemistry of these new molecules are still at a very early stage of investigation. 

Thinking it Through Each of the three experiments gives some information about the relative ability of the element to displace an ion in a single-replacement chemical reaction. When a free metallic element reacts with a compound, the free element will replace the metallic ion in the compound, but only if the free element is more reactive than the element it replaces. Here are the two possibilities represented symbolically. 

Figure 4 shows the schematic principle for displacement plating. In this case, you don t need any external electron source to make the metal ions in the solution precipitate onto the work. Instead, the metal component of the work would dissolve to give the metal ions in the solution electrons. The chemical reactions can be written in the following way schematically. Eq. 1 is the cathode reaction for the precipitation and plating film formation, while Eq. 2 is the anode reaction to give the plating metal electrons. 

Helmont s chemical theory was also a curious blend of the archaic and the advanced. Many of his day accepted the dissolution of metals in acid as evidence of transmutation, and transmutation was also used to explain the reaction (called displacement in modem terminology) wherein an iron horseshoe left in a stream naturally rich in copper salts eventually becomes coated with a copper layer. Helmont was able to discern the difference and denied that either of these reactions was transmutation, but this did not stop him from believing in the possibility. He gave an account of what he sincerely believed to be a transmutation of 8 ounces of mercury into gold achieved by a quarter of a grain of a yellow powder given to him by a stranger. 

A common chemical reaction is the displacement of hydrogen from water or acids (shown in 1 and 2 above). This reaction is a good illustration of the relative reactivity of metals and the use of the activity series. For example,... 

A related phenomenon is the common occurrence of secondary deposition in molten salts. Thus, a metal may be deposited as a result of a chemical reaction between a metallic ion in the melt and another preferentially-deposited, reactive metal corresponding to the solvent cation(s). (Notably, there is still discussion as to whether sodium or aluminum is the primarily deposited metal during operation of the Hall-Heroult cell. " ) Such occurrences can be rationalized in theoretical terms if the primary deposition of the solute metal is precluded by an observed limiting current exceeding that predicted, or if its deposition potential is displaced in a cathodic direction by activation overpotential. Some authors have preferred an explanation which involves underpotential deposition (vide infra). 

Many similarities exist between metallabenzenes and conventional arenes. Among these similarities are structural features such as ring planarity and the absence of bond length alternation, spectroscopic features such as downfield chemical shifts for ring protons, and chemical reactions such as electrophilic aromatic substitution and arene displacement from (arene)Mo(CO)3. All of these features, taken together, strongly support the thesis that metallabenzenes represent a new class of aromatic compounds, one in which metal d orbitals participate fully with carbon p orbitals in the formation of ring 7r-bonds. 

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