Electrolysis of Ionic Compounds
Electrolysis of ionic compounds involves the breaking down of the compound into its constituent elements using an electric current. This process occurs in an electrolytic cell, where positive ions migrate to the negative electrode (cathode) and negative ions migrate to the positive electrode (anode). At the electrodes, the ions gain or lose electrons, resulting in the formation of new substances.
6 Key excerpts on "Electrolysis of Ionic Compounds"
eBook - ePubElectrical Engineering
Fundamentals
- Viktor Hacker, Christof Sumereder(Authors)
- 2020(Publication Date)
- De Gruyter Oldenbourg(Publisher)
...Inside the cell, the charged ions migrate to the respective oppositely charged electrode through an electrolyte with ion conduction. A current flow is generated (ion current). 6.2 Electrolysis Electrolysis is a redox reaction provoked by electric current (inversion of processes of a galvanic cell); reduction and oxidation happen spatially separated. The electric current (direction of movement of positive charge carriers) is fed in through the anode 63 (positive pole) and is discharged at the cathode (negative pole). Between the two electrodes an electric field and ionic migration occurs. The negatively charged ions (anions) migrate to the anode where they are oxidised. During this process, electrons are emitted. The positive ions (cations) migrate towards the cathode where they are reduced. During this process, electrons are absorbed. Electrolysis is used to produce hydrogen and extract (pure) metals, among others. 6.2.1 Electrolysis of water During the electrolysis of water, hydrogen (H 2) is produced at the cathode and oxygen (O 2) is produced at the anode. Through the addition of e.g. caustic potash solution, sulphuric acid or sodium chloride water becomes an electrolyte with ion conductivity. H 3 O + and OH - ions are created (also through autoprotolysis). The positive ions (H 3 O +, cations) move towards the cathode (negative) where they absorb an electron, producing H 2. The negative ions (OH -, anions) move towards the anode (positive) where they emit an electron, producing O 2. The total electric charges of the protons and electrons amount to zero (in the closed system). The complete partial reactions are as. follows: A u t o p r o t o l y s i s : 2 H 2 O → H 3 O + O H − A n o d e : 2 O H − → 1 2 O 2 + H 2 O + 2 e − o r 3 H 2 O → 1 2 O 2 + 2 H 3 O + + 2 e − C a t h o d e : 2 H 2[--=PL. GO-SEPARATOR=--]O + 2 e − → H 2 + 2 O H − o r H 3 O + + e − → 1 2 H 2 + H 2 O O v e r a l l r e a c t i o n : H 2 O → H 2 + 1 2 O 2 In the fuel cell (e.g...
eBook - ePubExtractive Metallurgy 1
Basic Thermodynamics and Kinetics
- Alain Vignes(Author)
- 2013(Publication Date)
- Wiley-ISTE(Publisher)
...Chapter 8 Electrochemical Reactions 8.1. Overview of electrochemical processes A chemical reaction is a reaction where only chemical species (neutral molecules and positively or negatively charged ions) are involved. An electrochemical reaction is a reaction where chemical species and free electrons are involved. The two elementary electrochemical reactions are: – oxidation : liberation of electrons. For a metal (in the solid state) immersed in an electrolytic solution, the reaction is a dissolution, which gives a metallic ion in solution (corrosion): [8.1.1] – reduction : absorption of electrons. For a metallic ion in an aqueous solution (heterogeneous precipitation, see Chapter 5, section 5.6.1): [8.1.2] Various overall reactions are the result of elementary electrochemical reactions: – redox chemical reactions resulting from two simultaneous elementary electrochemical reactions where the electrons are directly transferred between the reactants...
eBook - ePub- Orjan G. Martinsen, Sverre Grimnes(Authors)
- 2014(Publication Date)
- Academic Press(Publisher)
...Chapter 2 Electrolytics Abstract The basic electrolytic processes are described in this chapter. Concepts such as ionization and molecular bonds are explained as well as the mechanisms of electrical conductance and semiconductor properties. An overview of electrokinetic effects is also given. Keywords Electrokinetics; Electrolysis; Ionization; Molecular bonds 2.1. Ionic and Electronic DC Conduction An electrolyte is a substance with ionic DC conductivity. Intracellular and extracellular liquids contain ions free to migrate. In pure electrolytes, the charge carriers are ions, and there is no separate flow of electrons—they are all bound to their respective atoms. Therefore, tissue DC currents are ionic currents, in contrast to the electronic current in metals. This is not contradictory to a possible local electronic conductance due to free electrons (e.g., in the intracellular DNA molecules). New solid materials such as organic polymers and glasses may contain an appreciable amount of free ions with considerable mobility; therefore, the materials of an electrolytic measuring cell are not limited to liquid media. Some of these solid media show a mixture of ionic and electronic conductivity. Two current-carrying electrodes in an electrolyte are the source and sink of electrons—from electrons of the metal to ions or uncharged species of the electrolyte. The electrode is the site of a charge carrier shift, or a charge exchange between electrons and ions. In a metal, the conductance electrons are free to move; they are similar to an electron gas not linked to particular metal atoms, but with a probability of being at a certain location at a certain time. The metal atoms can be considered bound but ionized; they have lost electrons. Electron transport in a metal involves no transport of metal ions and not even a transport of electrons all of the way. When we supply an electron into a wire end, “another” electron is coming out of the other end...
- Kevin Reel, Derrick C. Wood, Scott A. Best(Authors)
- 2014(Publication Date)
- Research & Education Association(Publisher)
...Similar to before, reduction still takes place at the cathode and oxidation at the anode. Electrolysis of a Molten Salt Figure 13.3 shows an electrolytic cell used to separate the components of a molten salt: NaCl. You will notice that unlike the voltaic cells from before, there is an external source of electricity (a battery). Figure 13.3. Electrolysis of a Molten Salt Based on the preceding half reactions, you will note that there are negative voltages for both reactions. Since there is no such thing as a negative voltage, the negative sign simply means it is a nonspontaneous process and 4.07 V must be supplied for the reaction to take place. Electrolysis of Aqueous Salts The electrolysis of aqueous solutions also introduces the possibility of the oxidation and reduction of water in addition to the cation and anion of the salt. The following equations demonstrate the electrolysis of water: In order to determine which oxidation or reduction reaction occurs, you must compare the oxidation and reduction cell potentials. The cell potential that is the largest will be the half reaction that occurs. EXAMPLE: What is produced at the anode and cathode with the electrolysis of CuF 2(aq) ? SOLUTION: Anode • The oxidation of water occurs at the anode because the oxidation potential for water is larger (less negative). Cathode • The reduction of copper will occur at the cathode because its reduction potential is larger. The overall reaction would be as follows: • The negative sign simply means it is a nonspontaneous process and 0.89 V must be supplied for the reaction to take place. Electrolysis Stoichiometry The amount of substance reduced or oxidized in an electrolytic cell can be computed through stoichiometry...
eBook - ePubExtractive Metallurgy 3
Processing Operations and Routes
- Alain Vignes(Author)
- 2013(Publication Date)
- Wiley-ISTE(Publisher)
...Chapter 9 Molten Salt Electrolysis Operations 9.1. Overview of molten salt electrolysis operations The extraction of metals by aqueous salt electrolysis is limited by the discharge of H+ ions. The standard electrode potentials EM/M z+ in aqueous solutions (see [VIG 11a], Chapter 8, section 8.2.2.2 and Table 8.2.1) of aluminum −1.66 V, titanium −1.75 V, magnesium −2.03 and sodium −2.71 V prevent their electrolysis in an aqueous medium. The production of metals by electrolysis of their salts (chlorides) or oxides in molten salt solution requires major problems to be overcome. For instance, the solubility of the metal in the electrolyte can be substantial with the possibility of reoxidation at the anode, leading to low yields. The electrolyte has to have the following characteristics: – Thermal characteristics : the electrolyte has to melt at a relatively low temperature but higher than the melting point of the metal in order to collect it as a liquid. A mixture of salts is used to lower the melting point by using a composition close to the eutectic. – Electro-chemical characteristics : the salt making up the electrolyte has to be more stable than that to be electrolyzed. The decomposition voltage (standard potential) of the salts (see [VIG 11b], Chapter 2, section 2.2.5) making up the electrolyte has to be significantly higher than that of the salt or the oxide of the metal to be deposited (see the Ellingham diagrams of the chlorides in [VIG 11a] Chapter 2, Figure 2.4.3). We then have to use alkaline or alkaline earth salts (see [VIG 11b], Figure 9.1.1). Figure 9.1.1. Reversible decomposition voltage of sulfides, oxides, chlorides and fluorides at 1,000 K The electrolytes in the electrolysis of chlorides and oxides are therefore a mixture of halides (chlorides and fluorides) of alkaline and alkaline-earth metals (see [VIG 11a], Chapter 4, section 4.3). Industrially, only lithium, sodium, calcium and magnesium are extracted by electrolysis of their chlorides...
eBook - ePub- John Kenkel(Author)
- 2020(Publication Date)
- CRC Press(Publisher)
...C HAPTER 11 E LECTROANALYTICAL M ETHODS 11.1 INTRODUCTION The subject of electroanalytical chemistry encompasses all analytical techniques which are based on electrode potential and current measurements at the surfaces of electrodes immersed in the solution tested. Either an electrical current flowing between a pair of immersed electrodes or an electrical potential developed between a pair of immersed electrodes is measured and related to the concentration of some dissolved species. Electroanalytical techniques are an extension of classical oxidation-reduction chemistry, and indeed oxidation and reduction processes occur at or within the two electrodes, oxidation at one and reduction at the other. Electrons are consumed by the reduction process at one electrode and generated by the oxidation process at the other. The complete system is often called a “cell,” the individual electrodes “half-cells,” and the individual oxidation and reduction reactions are the “half-reactions.” Electrons flow on a conductor between the half-cells, and this flow constitutes the electrical current that is often measured. A “galvanic” cell is one in which this current flows spontaneously because of the strong tendency for the chemical species involved to give and take electrons. A battery that has its positive and negative poles externally connected is an example of a such a cell. An “electrolytic” cell is one in which the current is not a spontaneous current, but rather is the result of connecting an external power source, such as a battery, to the system. A rechargeable battery, when it is positioned in the recharging unit, would be an example of such a cell (see Figure 11.1). Electroanalytical techniques utilize both general types of cells. FIGURE 11.1 (a) A battery with its negative and positive poles connected is a galvanic cell...
