Electrical conductivity of ionic solutions

Figure 4.3 The electrical conductivity of ionic solutions. A, When electrodes connected to a power source are placed in distilled water, no current flows and the bulb is unlit. B, A solid ionic compound, such as KBr, conducts no current because the ions are bound tightly together. C, When KBr dissolves in H2O, the ions separate and move through the solution toward the oppositely charged electrodes, thereby conducting a current.

Most of the students were able to distinguish between the eleetrieal eonductivity of metals and the electrical conductivity of ionic solutions and between the characteristics of copper as a metal and copper chloride as an ionie solution. 

The electrical conductance of a solution is a measure of its current-carrying capacity and is therefore determined by the total ionic strength. It is a nonspecific property and for this reason direct conductance measurements are of little use unless the solution contains only the electrolyte to be determined or the concentrations of other ionic species in the solution are known. Conductometric titrations, in which the species of interest are converted to non-ionic forms by neutralization, precipitation, etc. are of more value. The equivalence point may be located graphically by plotting the change in conductance as a function of the volume of titrant added. 

In ionic solids, electrons are held in place around the ions so they don t conduct electricity. However, in aqueous solution and molten state, they do conduct electricity. Electrical conductance of ionic compounds is not due to movement of electrons but to the movement of ions. 

If the reaction system has a ionic species and if there is a change in number and/or nature of the ionic species during the reaction, the electrical conductance of the solution can be measured as a function of time. Let us consider the hydrolysis of an ester in presence of NaOH... 

When the relative permittivity of the organic solvent or solvent mixture is e < 10, then ionic dissociation can generally be entirely neglected, and potential electrolytes behave as if they were nonelectrolytes. This is most clearly demonstrated experimentally by the negligible electrical conductivity of the solution, which is about as small as that of the pure organic solvent. The interactions between solute and solvent in such solutions have been discussed in section 2.3, and the concern here is with solute-solute interactions only. These take place mainly by dipole-dipole interactions, hydrogen bonding, or adduct formation. 

Conductometric titration — A -> titration method in which the electrical conductivity of a solution is measured as a function of the volume of -> titrant added. The method is based on replacing an ionic species of the - analyte with another species, corresponding to the titrant or the product of significantly different conductance. Thus, a - linear titration curve is plotted to obtain the - end point. This method can be used for deeply colored or turbid solutions. It does not require knowing the actual specific conductance of the solution, and only few data points far from the end point are necessary. This is to avoid effects such as hydrolysis or appreciable solubility of the reaction product that give rise to curvature in the vicinity of the end point [i]. 

The conversation shows that the teacher does not clarify the student s position and the misconception is thereby produced or even cemented by the lecture. The student thinks therefore that the electric conductivity of a solution confirms an ionic bonding, whereas for the teacher, it confirms the existence of free moveable ions in the solution. This leads to the student not being able to differentiate between ions and ionic bonding, that students think the conductivity of a solution is equal to that of an ionic bonding they are not capable of separating ionic bonding from the existence of free moving ions. 

Acetic anhydride is a neutral molecule and therefore does not form ions. However, as the reaction progresses, ionic species are produced tty the hydrolysis of the anhydride to form acetic acid, an ionizable molecule. As a result, the electrical conductivity of the solution will change with the concentration of the acetic acid formed (i.e. with the conversion of the anhydride), but not directly. The reason for this complication is that the acetic acid produced does not dissociate completely but forms an equilibrium with its ions ... 

Electrical conductivity of aqueous solutions. The result of this experiment is strong evidence that ionic compounds dissolved in water exist in the form of separated ions. 

As with decreasing of the cation average ionic radius the electrical conductivity of solid solution samples on the basis of Zr02 increases and stability of solid solution deceases [4] and one of the most important demands that are made to the solid electrolytes is a combination of high electrical conductivity with the ageing stability (R /Ro), the ageing of investigated solid electrolytes was studied in the present work. 

Because acid-base and precipitation reactions discussed in this chapter all involve ionic species, their progress can be monitored by measuring the electrical conductance of the solution. Match the following reactions with the diagrams shown here. The electrical conductance is shown in arbitrary units. 

The British scientist Henry Cavendish (1731-1810) reported that the electric conductivity of water is greatly increased by dissolving salt in it. In 1884 the young Swedish scientist Svante Arrhenius (1859-1927) published his doctor s dissertation, which included measurements of the electric conductivity of salt solutions and his ideas as to their interpretation. These ideas were rather vague, but he later made them more precise and then published a detailed paper on ionic dissociation in 1887. Arrhenius assumed that in a solution of sodium chloride in water there are present sodium ions, Na, and chloride ions, Cl . When electrodes are put into such a solution the sodium ions are attracted toward the cathode and move in that direction, and the chloride ions are attracted toward the anode and move in the direction of the anode. The motion of these ions through the solution, in opposite directions, provides the mechanism of conduction of the current of electricity by the solution. 

Since ionic surfactants carry a charge with an accompanying counterion, these will contribute to the electrical conductivity of aqueous solutions. Thus, by measuring the electrical conductivity, the adsorption of ionic surfactants can then be determined. 

The series of REM complexes containing germanium and mercury atoms has been obtained from the reactions of metallic lanthanoids with [(QF5)3Ge]2Hg [3, 17, 21]. A primary supposition on the structure of these compounds as adducts of the [( 6 5)3-Ge]3Ln-Hg[Ge(QF5)3]2 type has not been confirmed. The electrical conductivity of die solution, the infrared spectroscopy data and their chemical behaviour show the ionic nature of the products. Their synthesis can be described by the equations... 

Electric conductivity of electrolyte solutions strongly depends on temperature. To a certain point, typically the conductance is increasing due to decreasing viscosity of solvent. There are, however, counteracting factors. In aqueous solution, e.g. above 90 °C, the conductance is decreasing due to decreasing dielectric constant of the solvent [37]. The solvent shell is reduced, and ionic interactions tend to affect the mobility of ions more and more. 

ConductiTity.— The electrical conductivity of the solution is determined by the nature and concentration of the solute particles. Solutions of non-ionised molecules or dipolar ions have minimal conductivity and are termed non-electrolytes solutions containing ions have a conductivity depending on the ionic concentration, and are termed electrolytes. 

Electrical conductivity of aqueous solutions, (a) Pure water does not conduct an electric current. The lamp does not light, (b) When an ionic compound is dissolved in water, current flows and the lamp lights. The result of this experiment is strong evidence that ionic compounds dissolved in water exist in the form of separated ions. 

Vila, J. Gines, P. Rilo, E. Cabeza, O. Varela, L.M. (2006a). Great increase of the electrical conductivity of ionic liquids in aqueous solutions. Fluid Phase Equilib. 247, 1-2 (September 2006) 32-39. 

Despite its initial successes, there were apparent deficiencies in Arrhenius s theory. The electrical conductivities of concentrated solutions of strong electrolytes are not as great as expected, and values of the van t Hoff factor i depend on the solution concentrations, as shown in Table 14.4. For strong electrolytes that exist completely in ionic form in aqueous solutions, we would expect i = 2 for NaCl, i = 3 for MgCl2, and so on, regardless of the solution concentration. 

Bismuth Trichloride. Bismuth(III) chloride is a colodess, crystalline, dehquescent soHd made up of pyramidal molecules (19). The nearest intermolecular Bi—Cl distances are 0.3216 nm and 0.3450 nm. The density of the soHd is 4.75 g/mL and that of the Hquid at 254°C is 3.851 g/mL. The vapor density corresponds to that of the monomeric species. The compound is monomeric in dilute ether solutions, but association occurs at concentrations greater than 0.1 Af. The electrical conductivity of molten BiCl is of the same order of magnitude as that found for ionic substances. 

When an ionic solution contains neutral molecules, their presence may be inferred from the osmotic and thermodynamic properties of the solution. In addition there are two important effects that disclose the presence of neutral molecules (1) in many cases the absorption spectrum for visible or ultraviolet light is different for a neutral molecule in solution and for the ions into which it dissociates (2) historically, it has been mainly the electrical conductivity of solutions that has been studied to elucidate the relation between weak and strong electrolytes. For each ionic solution the conductivity problem may be stated as follows in this solution is it true that at any moment every ion responds to the applied field as a free ion, or must we say that a certain fraction of the solute fails to respond to the field as free ions, either because it consists of neutral undissociated molecules, or for some other reason ... 

A distinguishing property of ionic solutions is electrical conductivity, just as it is a distinguishing property for metals, but the current-carrying mechanism differs. Electric charge moves through a metal wire, we believe, by means of... 

The electrical conduction in a solution, which is expressed in terms of the electric charge passing across a certain section of the solution per second, depends on (i) the number of ions in the solution (ii) the charge on each ion (which is a multiple of the electronic charge) and (iii) the velocity of the ions under the applied field. When equivalent conductances are considered at infinite dilution, the effects of the first and second factors become equal for all solutions. However, the velocities of the ions, which depend on their size and the viscosity of the solution, may be different. For each ion, the ionic conductance has a constant value at a fixed temperature and is the same no matter of which electrolytes it constitutes a part. It is expressed in ohnT1 cm-2 and is directly proportional to the mobilities or speeds of the ions. If for a uni-univalent electrolyte the ionic mobilities of the cations and anions are denoted, respectively, by U+ and U, the following relationships hold ... 

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