Electrolyte A substance that produces ions

According to the Arrhenius concept, a base is a substance that produces OH-ions in aqueous solution. According to the Bronsted-Lowry definition, a base is a proton acceptor. The bases sodium hydroxide (NaOH) and potassium hydroxide (KOH) fulfill both criteria. They contain OH- ions in the solid lattice and behave as strong electrolytes, dissociating completely when dissolving in water ... 

Many reactions, particularly those that involve ionic compounds, take place in aqueous solution. Substances whose aqueous solutions contain ions and therefore conduct electricity are called electrolytes. Ionic compounds, such as NaCl, and molecular compounds that dissociate substantially into ions when dissolved in water are strong electrolytes. Substances that dissociate to only a small extent are weak electrolytes, and substances that do not produce ions in aqueous solution are nonelectrolytes. Acids dissociate in aqueous solutions to yield an anion and a hydronium ion, H30 +. Those acids that dissociate to a large extent are strong acids those acids that dissociate to a small extent are weak acids. 

When each unit of a substance that dissolves in water produces separated ions, the substance is called a strong electrolyte. Barium nitrate is a strong electrolyte in water, because each Ba(N03)2 unit... 

Weak electrolytes are substances that exhibit a small degree of ionization in water. That is, they produce relatively few ions when dissolved in water, as shown in Fig. 4.4(b). The most common weak electrolytes are weak acids and weak bases. 

Strong electrolyte (3.3) A substance that ionizes or dissociates completely in water to produce an aqueous solution in which only the constituent ions, and not intact molecules, are present. 

Acid-base models. You can indicate that in the 17 century Boyle described acids as substances with a sour taste and bases ( alkahs ) as substances that have the ability to neutralise them. At the end of the 19 century Arrhenius used his work on electrolytic dissociation to revise this model by defining acids and bases as substances that produce LL ions (acids) or OH" ions (bases) in an aqueous solution. In the 1920s a more general model was introduced by Bronsted (and also by Lowry) who defined acids and bases as particles that donate protons (acids) or accept protons (bases). Their model exceeds the acid-base model to solvents other than water such as ammonia. In the same period of time this model was extended by Lewis who defined acids as electron pair acceptors and bases as electron pair donors. This extension also comprises of reactions that do not involve ions. 

In 1887, the Swedish chemist Svante Arrhenius was the first to describe acids as substances that produce hydrogen ions (H ) when they dissolve in water. Because acids produce ions in water, they are also electrolytes. For example, hydrogen chloride ionizes completely in water to give hydrogen ions, H, and chloride ions, CF. It is the hydrogen ions that give acids a sour taste, change blue litmus indicator to red, and corrode some metals. 

The effects of solutes on colligative properties depend upon the actual concentration of solute particles. For nonelectrolytes, the solute particle concentration is the same as the solute concentration. This is because nonelectrolytes, such as sucrose, do not ionize in solution. Electrolytes are substances that ionize or that dissociate into ions. Thus, electrolytes produce particle concentrations higher than those of the original substance. For example, sodium chloride, NaCl, dissociates almost completely into separate sodium ions and chloride ions, so a Im NaCl solution is actually nearly 2m in particles. 

Whether or not an aqueous solution is a conductor of electricity depends on the nature of the solute(s). Pure water contains so few ions that it does not conduct electric current. However, some solutes produce ions in solution, thereby making the solution an electrical conductor. Solutes that provide ions when dissolved in water are called electrolytes. Solutes that that do not provide ions in water are called nonelectrolytes. All electrolytes provide ions in water but not all electrolytes are equal in their tendencies for providing ions. A strong electrolyte is a substance that is essentially completely ionized in aqueous solution essentially all of the dissolved solute exists as ions. A weak electrolyte is only partially ionized in aqueous solution only some of the dissolved solute is converted into ions. One scheme for classifying solutes is summarized in Figure 5-3. 

Apart from the two classifications described above, electrolytes may also be classified according to the number and valence of the ions produced. Thus, sodium chloride and copper sulfate may both be termed binary electrolytes since one molecule of each of these chemical substances is capable of producing two ions. In the case of sodium chloride, both the ions produced are univalent so that this substance may also be called a uni-univalent electrolyte. Copper sulfate, however, yields two bivalent ions and so may be called a bibivalent electrolyte. The valences of the ions are quoted in the positive-negative sequence. Calcium chloride and potassium sulfate are both ternary electrolytes since one molecule of each yields three ions the former is bi-univalent, whilst the latter is uni-bivalent. 

The quantitative laws of electrochemistry were discovered by Michael Faraday of England. His 1834 paper on electrolysis introduced many of the terms that you have seen throughout this book, including ion, cation, anion, electrode, cathode, anode, and electrolyte. He found that the mass of a substance produced by a redox reaction at an electrode is proportional to the quantity of electrical charge that has passed through the electrochemical cell. For elements with different oxidation numbers, the same quantity of electricity produces fewer moles of the element with higher oxidation number. 

Solutions of non-electrolytes contain neutral molecules or atoms and are nonconductors. Solutions of electrolytes are good conductors due to the presence of anions and cations. The study of electrolytic solutions has shown that electrolytes may be divided into two classes ionophores and ionogens [134]. lonophores (like alkali halides) are ionic in the crystalline state and they exist only as ions in the fused state as well as in dilute solutions. Ionogens (like hydrogen halides) are substances with molecular crystal lattices which form ions in solution only if a suitable reaction occurs with the solvent. Therefore, according to Eq. (2-13), a clear distinction must be made between the ionization step, which produces ion pairs by heterolysis of a covalent bond in ionogens, and the dissociation process, which produces free ions from associated ions [137, 397, 398]. 

In the lemon battery shown in Figure 17.9, a different chemical reaction occurs at each of the metal-strip electrodes. The electrode made of the metal that is more easily oxidized becomes the anode—the electrode at which the oxidation reaction occurs. The second electrode becomes the cathode, and a reduction reaction proceeds at its surface. The substance in a lemon that is most easily reduced is the abundant hydrogen ion of the electrolyte. When these two reactions occur together, in the same cell, they combine to produce a spontaneous redox reaction. This type of reaction is represented by the equation below, where M is the metal that is oxidized. 

There are two kinds of electrochemical cells, voltaic (galvanic) and electrolytic. In voltaic cells, a chemical reaction spontaneously occurs to produce electrical energy. The lead storage battery and the ordinary flashlight battery are common examples of voltaic cells. In electrolytic cells, on the other hand, electrical energy is used to force a nonspontaneous chemical reaction to occur, that is, to go in the reverse direction it would in a voltaic cell. An example is the electrolysis of water. In both types of these cells, the electrode at which oxidation occurs is the anode, and that at which reduction occurs is the cathode. Voltaic cells wOl be of importance in our discussions in the next two chapters, dealing with potentiometry. Electrolytic cells are important in electrochemical methods such as voltammetry, in which electroactive substances like metal ions are reduced at an electrode to produce a measurable current by applying an appropriate potential to get the nonspontaneous reaction to occur (Cha]pter 15). The current that results from the forced electrolysis is proportional to the concentration of the electroactive substance. 

Discussion When two samples of material have the same characteristic properties, the fact is summarized by saying that they are the same substance. Likewise if two mixtures exhibit a number of characteristic properties in common, it is concluded that they each contain some of the same substance. Such mixtures, Avith similar properties, are common in certain classes of solutions, as for example in solutions of acids, where similarity in taste, action with indicators, with metals, etc., have been noted. It appears, then, that all acid solutions are mixtures containing some of the same substance, but since these solutions were made from different acids, different substances, they must have reacted to form some of the same neAV substance in every case. By no type of reaction previously studied could the facts be so well explained as by the assumption that every acid in solution breaks up into two electrically charged substances one of which is always hydrogen and that this is the substance which gives the similar properties to all acid solutions. This particular kind of reaction which produces electrically charged substances in solution is termed electrolytic dissociation and the charged substances are called ions. 

The importance of molar conductivity is that it gives us information about the conductivity of ions produced in solution by 1 mol of a substance. Studies of the variation of molar conductivity have revealed important results, such as those shown schematically in Figure 6.2. In all cases, molar conductivity diminishes as the concentration is raised, but two patterns of behavior can be distinguished. The magnitudes of conductivities suggest that there are two extreme classes of electrolytes the strong, which produce many ions, and the weak, which produce few. 

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