Electrolytes and Nonelectrolytes

You have probably heard of electrolytes in the context of sports drinks such as Gatorade. Electrolytes in body fluids are necessary for the transmission of electrical impulses, which are critical to physiological processes such as nerve impulses and muscle contractions. In general, an electrolyte is a substance that dissolves in water to yield a solution that conducts electricity. By contrast, a nonelectrolyte is a substance that dissolves in water to yield a solution that does not conduct electricity. Every water-soluble substance fits into one of these two categories. 

The difference between an aqueous solution that conducts electricity and one that does not is the presence or absence of ions. As an illustration, consider solutions of sugar and salt. The physical processes of sugar (sucrose, C12H22O11) dissolving in water and salt (sodium chloride, NaCl) dissolving in water can be represented with the following chemical equations  

Note that while the sucrose molecules remain intact upon dissolving, becoming aqueous sucrose molecules, the sodium chloride dissociates, producing aqueous sodium ions and aqueous chloride ions. Dissociation is the process by which an ionic compound, upon dissolution, breaks apart into its constituent ions. It is the presence of ions that allows the solution of sodium chloride to conduct electricity. Thus, sodium chloride is an electrolyte and sucrose is a nonelectrolyte. 

Like sucrose, which is a molecular compound (W Section 2.6], many water-soluble molecular compounds are nonelectrolytes. Some molecular compounds are electrolytes, however, because they ionize on dissolution. Ionization is the process by which a molecular compound forms ions when it dissolves. Recall from Chapter 2 that acids are compounds that dissolve in water to produce hydrogen ions (H ) [W Section 2.6]. HCl, for example, ionizes to produce H ions and Cl ions. 

Acids constitute one of two important classes of molecular compounds that are electrolytes. Molecular bases constitute the other one. A base is a compound that dissolves in water to produce hydroxide ions (OH ). Ammonia (NH3), for example, ionizes in water to produce ammonium (NH4) and hydroxide (OH ) ions. 

An electrolyte is a substance that, when dissolved in a solvent or melted conducts an electrical current. A nonelectrolyte does not conduct a current when dissolved. The conduction of the electrical current is usually determined using a light bulb connected to a power source and two electrodes. The electrodes are placed in the aqueous solution or melt, and if a conducting medium is present, such as ions, the light bulb will light, indicating the substance is an electrolyte. 

The ions that conduct the electrical current can result from a couple of sources. They may result from the dissociation of an ionically bonded substance (a salt). If sodium chloride (NaCl) is dissolved in water, it dissociates into the sodium cation (Na+) and the chloride anion (CL). But certain covalently bonded substances may also produce ions if dissolved in water, a process called ionization. For example, acids, both inorganic and organic, will produce ions when dissolved in water. Some acids, such as hydrochloric acid (HC1), will essentially completely ionize. Others, such as acetic acid (CH3COOH), will only partially ionize. They establish an equilibrium with the ions and the unionized species (see Chapter 13 for more on chemical equilibrium). 

Species such as HCl that completely ionize in water are called strong electrolytes, and those that only partially ionize are called weak electrolytes. Most soluble salts also fall into the strong electrolyte category. 

Some of the properties of solutions depend on the chemical and physical nature of the individual solute. The blue color of a copper(II) sulfate solution and the sweetness of a sucrose 

If a liquid is placed in a sealed container, molecules will evaporate from the surface of the liquid and eventually establish a gas phase over the liquid that is in equilibrium with the liquid phase. The pressure generated by this gas is the vapor pressure of the liquid. Vapor pressure is temperature-dependent the higher the temperature, the higher the vapor pressure. If the liquid is made a solvent by adding a nonvolatile solute, the vapor pressure of the resulting solution is always less than that of the pure liquid. The vapor pressure has been lowered by the addition of the solute the amount of lowering is proportional to the number of solute particles added and is thus a colligative property. 

Solutes can be classified by their ability to conduct an electrical current. When electrolytes dissolve in water, the process of dissociation separates them into ions forming solutions that conduct electricity. When nonelectrolytes dissolve in water, they do not separate into ions and their solutions do not conduct electricity. 

To test solutions for the presence of ions, we can use an apparatus that consists of a battery and a pair of electrodes connected by wires to a light bulb. The light bulb glows when electricity flows, which can only happen when electrolytes provide ions that move between electrodes to complete the circuit. 

Electrolytes can be further classihed as strong electrolytes and weak electrolytes. For a strong electrolyte, such as sodium chloride (NaCl), there is 100% dissociation of the solute into ions. When the electrodes from the light bulb apparatus are placed in the NaCl solution, the light bulb is very bright. 

In an equation for dissociation, the charges must balance. For example, magnesium nitrate dissociates to give one magnesium ion for every two nitrate ions. However, only the ionic bonds between Mg + and NO3 are broken the covalent bonds within the polyatomic ion are retained. The dissociation for Mg(N03)2 is written as follows  

A weak electrolyte is a compound that dissolves in water mostly as undissociated molecules. Only a few of the dissolved solute molecules separate, producing a small number of ions in solution. Thus, solutions of weak electrolytes do not conduct electrical current as well as solutions of strong electrolytes. When the electrodes are placed in a solution of a weak electrolyte, the glow of the light bulb is very dim. For example, an aqueous solution of the weak electrolyte HF contains mostly HF molecules and only a few and F ions. As more H+ and F ions form, some recombine to give HF molecules. These forward and reverse reactions of molecules to ions and back again are indicated by two arrows between the reactants and products that point in opposite directions  

At a young age we learn not to bring electrical devices into the bathtub so as not to electrocute ourselves. That is a useful lesson because most of the water we encounter in daily life is electrically conducting. Pure water, however, is a very poor conductor of electricity. The conductivity of bathwater originates from the substances dissolved in the water, not from the water itself. 

Pure water does not conduct electricity. An nonelectrolyte solution does not conduct electricity / An electrolyte solution conducts electricity.  

A substance (such as NaCl) whose aqueous solutions contain ions is called an electrolyte. A substance (such as C12H22O11) that does not form ions in solution is called a nonelectrolyte. The different classifications of NaCl and C12H22O11 arise largely because NaCl is an ionic compound, whereas C12H22O11 is a molecular compound. 

We can usually predict the nature of the ions in a solution of an ionic compound from the chemical name of the substance. Sodium sulfate (Na2S04), for example, dissociates into sodium ions (Na ) and sulfate ions (S04 ). You must remember the formulas and charges of common ions (Tables 2.4 and 2.5) to understand the forms in which ionic compounds exist in aqueous solution. 

Which solution, NaCKag) or CHsOHCaqf), conducts electricity  

A conductivity apparatus shows the difference in conductivity of solutions. 

H2S04 HC2H3O2 C12H22O11 (sugar) CH3OH (methyl alcohol) 

---

Sec. 7.4.1), a large range of acid-base properties, and often a better solubility for many materials, electrolytes and nonelectrolytes, better compatibility with electrode materials, and increased chemical stability of the solution. Their drawbacks are lower conductivity, higher costs, flammability, and environmental problems. 

To distinguish between strong electrolytes, weak electrolytes and nonelectrolytes, prepare equimolar aqueous solutions of the compounds and test their electrical conductivity. If a compound s solution conducts electricity well, it is a strong electrolyte if its solution conducts electricity poorly, it is a weak electrolyte. A solution of a nonelectrolyte does not conduct electricity at all. 

In this chapter, you learned about solutions and how to use molarity to express the concentration of solutions. You also learned about electrolytes and nonelectrolytes. Using a set of solubility rules allows you to predict whether or not precipitation will occur if two solutions are mixed. You examined the properties of acids and bases and the neutralization reactions that occur between them. You then learned about redox reactions and how to use an activity table to predict redox reactions. You learned about writing net ionic equations. Finally, you learned how to use the technique of titrations to determine the concentration of an acid or base solution. 

We will follow the same procedure as in the naphthalene/benzene example above. You may wish to look over these examples in parallel to see exactly where the difference between an electrolyte and nonelectrolyte manifests itself. We will again begin by calculating the freezing point, ATf. The problem gives us the value of Kf. In solution, the strong electrolyte, sodium sulfate, ionizes as ... 

One area not discussed so far is the problem of thermodynamic properties of mixtures containing both electrolyte and nonelectrolyte components. It is the belief of the author that this problem will not be completely resolved until equations of state are developed to handle these systems. We will only make progress in this direction when we recognize this as a problem and work toward solving the problem. Anything short of this also falls short in solving the ultimate problems of these mixtures. 

We can recognize four main periods in the history of the study of aqueous solutions. Each period starts with one or more basic discoveries or advances in theoretical understanding. The first period, from about 1800 to 1890, was triggered by the discovery of the electrolysis of water followed by the investigation of other electrolysis reactions and electrochemical cells. Developments during this period are associated with names such as Davy, Faraday, Gay-Lussac, Hittorf, Ostwald, and Kohlrausch. The distinction between electrolytes and nonelectrolytes was made, the laws of electrolysis were quantitatively formulated, the electrical conductivity of electrolyte solutions was studied, and the concept of independent ions in solutions was proposed. 

The prevalence of water in many industrial processes has led to the accumulation of a large body of experimental data on aqueous solutions of both electrolytes and nonelectrolytes. 

All binding processes in real-life systems occur in some solvent. The solvent is, in general, a mixture of many components, including water electrolytes and nonelectrolytes. At present, it is impossible to account for all possible solvent effects, even when the solvent is pure water. Yet, the solvent, whether a single or multi-component, cannot be ignored. Any serious molecular theory of cooperativity must deal with solvent effects. We shall see in this chapter that this is not an easy task even when the solvent is inert, such as argon, or a simple hydrocarbon liquid. ... 

This expression is analogous to Eiq. (2.3), in that (1 — (p) expresses the contribution of the solvent and In y+ that of the electrolyte to the excess Gibbs energy of the solution. The calculation of the mean ionic activity coefficient of an electrolyte in solution is required for its activity and the effects of the latter in solvent extraction systems to be estimated. The osmotic coefficient or the activity of the water is also an important quantity related to the ability of the solution to dissolve other electrolytes and nonelectrolytes. 

PLASMA. The portion of the blood remaining after removal of the white and red cells and the platelets it differs from serum in that it contains fibrinogen, which induces clotting by conversion into fibrin by activity of the enzyme thrombin. Plasma is made up of more than 40 proteins and also contains acids, lipids, and metal ions. It is an amber, opalescent solution in which the proteins are in colloidal suspension and the solutes (electrolytes and nonelectrolytes) are either emulsified or in true solution. The proteins can be separated from each other and from the other solutes by nltrafiltration, nltracentrifugation, electrophoresis, and immuno-chemical techniques. See also Blood. 

An understanding of equilibrium phenomena in naturally occurring aqueous systems must, in the final analysis, involve understanding the interaction between solutes and water, both in bulk and in interfacial systems. To achieve this goal, it is reasonable to attempt to describe the structure of water, and when and if this can be achieved, to proceed to the problems of water structure in aqueous solutions and solvent-solute interactions for both electrolytes and nonelectrolytes. This paper is particularly concerned with two aspects of these problems—current views of the structure of water and solute-solvent interactions (primarily ion hydration). It is not possible here to give an exhaustive account of all the current structural models of water instead, we shall describe only those which may concern the nature of some reported thermal anomalies in the properties of water and aqueous solutions. Hence, the discussion begins with a brief presentation of these anomalies, followed by a review of current water structure models, and a discussion of some properties of aqueous electrolyte solutions. Finally, solute-solvent interactions in such solutions are discussed in terms of our present understanding of the structural properties of water. 

In several previous papers, the possible existence of thermal anomalies was suggested on the basis of such properties as the density of water, specific heat, viscosity, dielectric constant, transverse proton spin relaxation time, index of refraction, infrared absorption, and others. Furthermore, based on other published data, we have suggested the existence of kinks in the properties of many aqueous solutions of both electrolytes and nonelectrolytes. Thus, solubility anomalies have been demonstrated repeatedly as have anomalies in such diverse properties as partial molal volumes of the alkali halides, in specific optical rotation for a number of reducing sugars, and in some kinetic data. Anomalies have also been demonstrated in a surface and interfacial properties of aqueous systems ranging from the surface tension of pure water to interfacial tensions (such as between n-hexane or n-decane and water) and in the surface tension and surface potentials of aqueous solutions. Further, anomalies have been observed in solid-water interface properties, such as the zeta potential and other interfacial parameters. 

In the following sections we discuss some aspects of solute-solvent interactions. This discussion is not a complete, current survey but rather an attempt to bring together some divergent experimental facets of water-solute interactions which often are not discussed by either theoreticians or experimentalists. For more detailed, general information see Refs. 18, 19, 20, and 73. The two essential points we wish to make are (1) even in moderately concentrated solutions, there is evidence for the persistence of structural elements of the type found in pure water and especially in dilute solutions (2) there is evidence for what appears to be discrete changes with concentration in the behavior of some aqueous solutions of both electrolytes and nonelectrolytes, and for nonelectrolytes this may be caused by the existence of discrete sites available to the solute molecules. Unfortunately, we shall be able to discuss only electrolyte-water interactions to any extent the often more interesting nonelectrolyte-water interactions will be discussed in a later paper. This is all the more... 

It is apparent that introducing the inert gas does induce a local structural change in the water. At the same time lines are still observed in these solutions, characteristic of pure water. Recall again our claim that the temperatures of the kinks are largely unaffected by the presence of solute even in a moderately high concentration (of both electrolytes and nonelectrolytes.)... 

Mikhailov draws attention to the fact that Persianova and Tarasov have studied compressibility of aqueous solutions of nonelectrolytes and found it necessary also to postulate the filling of cavities in a quasicrystalline lattice of water. This again agrees with our claim that solutes —both electrolytes and nonelectrolytes—do not significantly influence the temperature at which the kinks are observed and that this must be explained by assuming that there exists in such solutions elements of water structure which are unaffected by the presence of the solute. It is possible (to be discussed elsewhere) that the structured units responsible for the kinks merely possess a latent existence in pure water and that it is indeed the presence of the solute which induces the stabilization and thus furthers rather than disrupts the original structuredness of the water. 

Zavitsas AA. 2001. Properties of water solutions of electrolytes and nonelectrolytes. J Phys Chem B 105 7805-7817. 

Combinations of Electrolytes and Nonelectrolytes. Combinations of nonelectrolytes and electrolytes were often found to be superior to either alone at improving percutaneous absorption of DIL and DSCG. In particular, the bioavailability of DIL was increased remarkably by BL-9EX/TLP-4, Vifpant N/TLP-4, urea/TLP-4, urea/sacrosinate LN and urea/dehydrocholic acid. It is... 

The shrinkage temperature of collagen is very much affected by interaction with various small molecules, including electrolytes and nonelectrolytes, acids and bases, tanning agents, etc., and much interesting ex-... 

The major important organic electrolytes and nonelectrolytes transported by epithelial cells include sugars, amino acids, nucleosides, organic cations, and organic anions. Transport systems have significant implications for the absorption, distribution, elimination, and pharmacokinetic properties of many clinically important drugs. The major epithelial tissues... 

Chapter 7 of our landmark reference [6] discusses various aspects of the adsorption of weak electrolytes and nonelectrolytes from aqueous solution. In particular an attempt is made to elucidate the mechanism of adsorption of undissociated aromatic compounds from dilute aqueous solutions. As discussed in detail in Section VI, the authors concluded that the aromatic ring of the adsorbate inter-... 

State is the ionic medium (i.e., infinitely diluted with respect to HCl only). In such a medium /hci (solid line, right ordinate) is very nearly constant, that is,/Hci = 1- Both activity coefficients are thermodynamically equally meaningful. (Adapted from P. Schindler.) (b) A comparison of activity coefficients (infinite dilution scale) of electrolytes and nonelectrolytes as a function of concentration (mole fraction of solute) m = moles of solute per kg of solvent (molality) = number of moles of ions formed from 1 mol of electrolyte 1 kg solvent contains 55.5 mol of water. (From Robinson and Stokes, 1959. Reproduced with permission from Butterworths, Inc., London.)... 

In fact, for quick practical calculations, the formula of Wilke and Chang (W8) is often sufficient. It has been verified with many systems, both electrolyte and nonelectrolyte. For water at 10°-60°C, Shrier (S26) has... 

Topic Electrolytes and Nonelectrolytes Sci Links code HW4047... 

Summarize the electrical properties of strong electrolytes, weak electrolytes, and nonelectrolytes. 

J. J. Kosinski and A. Anderko, Equation of State for High-Temperature Aqueous Electrolyte and Nonelectrolyte Systems, Fluid Phase Equilib., 183-184, 75-86 (2001). 

---