Conductivity, electrical hydrochloric acid

The electrical conductivity.—The electrical conductivity of hydrochloric acid has been very frequently measured.27 The eq. conductivities, A, of W-soln. of hydrochloric acid at different temp., by A. A. Noyes, are indicated in Table XII. For more cone, soln., of normality N, at 18°, the molecular conductivity is ... 

Values of/x = Ac/A may be calculated from Kohlrausch s measurements of electrical conductivity of hydrochloric acid solutions. /h and fci can be evaluated from the potentiometric measurements on hydrochloric acid solutions performed by Scatchaed. These data are very reliable since the concentration chain was so arranged as to eliminate diffusion potentials. In this way, ScATCHARD determined the mean activity coefficient V/h/ci instead of the individual ion activities. If we assume that in a potassium chloride solution/ = /ci— which is plausible when we recall that both ions have the same structure—and that fci is the same in hydrochloric acid solutions and potassium chloride solutions of the same concentration, then we can calculate/h and fci in hydrochloric acid solutions. Naturally these values are not strictly correct since the effect of the potassium ions on the activity of the chloride ions probably is different from that of the hydrogen ions at the same ionic strength. In the succeeding table are given values of /x, /h, and fci calculated by the above method. 

Ash is a measure of residual sodium acetate. A simple method consists of dissolving the PVA in water, diluting to a known concentration of about 0.5 wt %, and measuring the electrical conductivity of the solution at 30°C. The amount of sodium acetate is estabUshed by comparing the result to a cahbration curve. A more lengthy method involves the extraction of the PVA with methanol using a Soxhlet extractor. The methanol is evaporated and water is added. The solution is titrated using hydrochloric acid in order to determine the amount of sodium acetate. 

We have contrasted the electrical conductivities of 0.1 M aqueous solutions of hydrochloric acid... 

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). 

The order of the electrical conductivities runs parallel with the order of the affinities of these acids. The dielectric constant of soln. of hydrochloric acid are usually greater than that of water for example, for O OOl V-soln., the dielectric constant is 0 990 (water unity) for 0 002V-soln., 1033 and for O OlV-soln., 1 126. The dielectric constants are not proportional to the conductivities of the soln. 

The alloys of tin and arsenic are very hard and readily crystallise.11 When the arsenic is not present in excess they are white, sonorous and brittle, and attacked by hydrochloric acid with liberation of arsine. When heated strongly, arsenic volatilises. The electrical conductivity of thin rods, of composition Sn Asg, SnAs and Sn3As2, has been measured12 between -81° and 400° C. In each case it passes through a maximum, at 25°, 0° and - 25° C. respectively. 

A solute may be present as ions or as molecules. We can identify the form of the solute by noting whether the solution conducts an electric current. Because a current is a flow of electric charge, only solutions that contain ions conduct electricity. There is such a tiny concentration of ions in pure water (about 10-7 m) that water alone does not conduct electricity. A substance that dissolves to give a solution that conducts electricity is called an electrolyte. Electrolyte solutions (solutions of electrolytes), which conduct electricity because they contain ions, include aqueous solutions of ionic compounds, such as sodium chloride and potassium nitrate. The ions are not formed when an ionic solid dissolves they exist as separate ions in the solid but become free to move apart in the presence of water (Fig. 1.1). Acids also are electrolytes. Unlike salts, they are molecular compounds in the pure state but form ions when they dissolve. One example is hydrogen chloride, which exists as gaseous HC1 molecules. In solution, however, HCl is called hydrochloric acid and is present as hydrogen ions and chloride ions. 

W. Traube described the formation of what he called sulphimide, along with ammonia and imidosulphonic acid, when sulphamide is heated at 200°-210°. The solid product is treated with water, the soln. mixed with silver nitrate, and the precipitated silver sulphimide, purified by recrystallization, is decomposed with dil. hydrochloric acid. The aq. soln. decomposes when the attempt is made to isolate the solid, for when the soln. is evaporated below 40°, only ammonium hydrosulphate remains. A. Hantzsch and A. Holl found the soln. in ethyl acetate has properties in accord with the trimolecular formula sulphucyl trumide, or trisulphimide, (S02.NH)3—e.g. ebulliscopic determinations of the mol. wt. and the electrical conductivities of the aq. soln. of trisulphimide and its salts. They were able to isolate a crystalline solid by crystallization from ethyl alcohol which they considered to be trisulphimide itself. A. Hantzsch and B. C. Stuer, however, showed that the alleged compound is extremely unstable, and that the soln. obtained by W. Traube, and the solid obtained by A. Hantzsch and A. Holl, was really sulphuryl imidodiamide, only indications of the transient formation of trisulphimide in non-aqueous solvents were obtained. Trisulphimide acts as an acid, and a few salts have been reported. A. Hantzsch and B. C. Stuer consider that the compound has tautomeric forms—a true imide and an acid ... 

Experimental evidence of the existence of aci-forms has soon been provided. In 1895 Holleman [51] found that m- nitrophenylnitromethane yielded a yellow salt, which under the influence of hydrochloric acid was converted initially into a yellow substance having a high electrical conductivity. After some time, the product changed into a colourless substance, showing no electrical conductivity. The aci-structure was assigned to the yellow substance, and that of a pseudoacid to the colourless one. 

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