Distilled water: electrical conductivity

The electrolysis of water can be seen by taking a 9 V battery and placing it in enough distilled water to cover the entire battery. Make sure the electrodes are several centimeters below the water s surface. After placing the battery in the distilled water, note any evidence of a reaction. There are not enough free ions in distilled water to conduct electricity and no evidence of a reaction should be observed. Now add a teaspoon of vinegar to the water and note what happens at the battery terminals. Bubbles form around the terminals and then a steady stream of tiny bubbles emerge from both terminals of the cell. 

Specific Conductance. The specific conductance depends on the total concentration of the dissolved ioni2ed substances, ie, the ionic strength of a water sample. It is an expression of the abiUty of the water to conduct an electric current. Freshly distilled water has a conductance of 0.5—2 ]lS/cm, whereas that of potable water generally is 50—1500 ]lS/cm. The conductivity of a water sample is measured by means of an a-c Wheatstone-bridge circuit with a null indicator and a conductance cell. Each cell has an associated constant which, when multiphed by the conductance, yields the specific conductance. 

Pour 50 ml of a 0.1 aqueous or ethanol solution of potassium hydroxide or potassium nitrate into four 100-ml heakers (use two of them for each solvent). Using a stationary setnp for determining the electrical conductance (Fig. 50), check whether these solutions conduct an electric current. For this purpose, immerse the carhon electrodes into a heaker with the relevant solution and observe the reading of the ammeter. See that the electrodes are always immersed to the same depth. When transferring the electrodes from one solution into another one, wash them with distilled water. 

Additional checks were made using a dialysis procedure in which zeolite samples which had been isotopically equilibrated with a 22Na O.OlAf NaCl solution were dialyzed against distilled water. After repeated washings, the sodium loss from NaX reached a steady value of 2.8 ( 0.1) ions/ unit cell at a zeolite content of 0.44 gram/liter, i.e. a value which is nearly identical to the data in Table I for a 10 NaCl concentration. Under similar conditions, the sodium loss from NaY is much less and corresponds to 1.5 ( 0.1) ions/unit cell. These results were confirmed by electrical conductivity measurements on the respective dialysates the conductivity for NaX is about twice as large (7.5 X 10 6 mhos/cm) as for NaY (3.9 X 10 6 mhos/cm). 

The electrical conductivity of water at 18°C is 0.04 x 10 reciprocal ohms (measurements of Kohlraush and IfeydweiUer, 1902) of pure water in equilibrium with air, 0.8 x 10-6 of ordinary distilled water, about 5 x 10- . 

UMEs used in our laboratory were constructed by sealing of carbon fibre into low viscosity epoxy resin (see Fig. 32.4) [118]. This method is simple, rapid and no specialised instrumentation is required. Firstly, the fibres are cleaned with this aim. They are immersed in dilute nitric acid (10%), rinsed with distilled water, soaked in acetone, rinsed again with distilled water and dried in an oven at 70°C. A single fibre is then inserted into a 100- iL standard micropipette tip to a distance of 2 cm. A small drop of low-viscosity epoxy resin (A. R. Spurr, California) is carefully applied to the tip of the micropipette. Capillary action pulls the epoxy resin, producing an adequate sealing. The assembly is placed horizontally in a rack and cured at 70°C for 8h to ensure complete polymerization of the resin. After that, the electric contact between the carbon fibre and a metallic wire or rod is made by back-filling the pipette with mercury or conductive epoxy resin. Finally, the micropipette tip is totally filled with epoxy resin to avoid the mobility of the external connection. Then, the carbon fibre UME is ready. An optional protective sheath can be incorporated to prevent electrode damage. 

Electrical Conductivity, (a) Pure Substances. Note that the lamp does not glow when air fills the space between the electrodes. Then raise successively between electrodes B distilled water, alcohol, pure acetic acid (labeled glacial acetic acid ), and place in contact with electrodes A lumps of any two dry salts found in the laboratory, for example, common salt, NaCl, and blue vitriol, CuS04 5H20. 

All solutions were prepared using background solution KC1 10-4 M and three-distilled water with electrical conductivity 10-6 Q-1 cm-1 and pH 6.5 to avoid problems connected with conformational and surface charge changes with increasing of salt concentration and pH. 

Many processes in soil are controlled by colloid flocculation or dispersion. One such process is hydraulic conductivity. The data in Figure 10.3 show that for a Mg2+-saturated soil containing a solution of 3.16 x 10 2 M MgCl2, its hydraulic conductivity decreased by 35% after 5 hr of leaching with distilled water (Quirk and Schofield, 1955). This demonstrates that as solution ionic strength approaches zero, soil hydraulic conductivity decreases significantly owing to soil dispersion induced by a decompressed electric double layer. 

The purity of distilled water is usually specified on the basis of low electrical conductivity rather than organic contaminants. In distilled water systems, it is therefore common practice to use a variety of plastics or rubber materials, but from the previous experience it was apparent that these materials should be eliminated. When it is necessary to use similar material such as in gaskets, it has been found that Teflon, a fluorocarbon resin, is satisfactory. 

Preparation of Solvent Conductance Water.—Distilled water is a poor conductor of electricity, but owing to the presence of impurities such as ammonia, carbon dioxide and traces of dissolved substances derived from containing vessels, air and dust, it has a conductance sufficiently large to have an appreciable effect on the results in accurate work. This source of error is of greatest importance with dilute solutions or weak electrolytes, because the conductance of the water is then of the same order as that of the electrolyte itself. If the conductance of the solvent were merely superimposed on that of the electrolyte the correction would be a comparatively simple matter. The conductance of the electrolyte would then be obtained by subtracting that of the solvent from the total this is possible, however, for a limited number of solutes. In most cases the impurities in the water can influence the ionization of the electrolyte, or vice versa, or chemical reaction may occur, and the observed conductance of the solution is not the sum of the values of the constituents. It is desirable, therefore, to use water which is as free as possible from impurities such water is called conductance water, or conductivity water. 

Even very pure distilled water will still just conduct electricity, so water must contain ions, it is said to dissociate into ions. The conductivity of pure water is very low, so there cannot be many ions in a given volume the dissociation is said to be partial or incomplete. 

Aniline yields thecompound, Me3SnI.2PhNH2, soluble in alcohol or boiling water, and which may be distilled without decomposition. Crystalline compounds are also obtained with isoamylamine and pyridine, the latter melting at -17° C. The iodide forms the complexes (Me3Sn.OH)2. MegSnl and Me Sn.OH.MegSnl.HgO, M.jDt. 221° C. with decomposition. The electrical conductivity of the iodide in various solvents has been determined. ... 

If you collect rainwater in a relatively unpolluted area, you will discover that the rainwater is essentially a nonconductor of electricity. A small concentration of carbonic acid from the carbon dioxide in the air added to the rainwater causes the rain water to be a weak conductor. Pure rainwater conducts almost as poorly as distilled water. However, most of the water we use comes from wells, lakes, or rivers. This water has been in contact with soil and rocks, which contain ionic compounds that dissolve in the water. Consequently, tap water conducts electricity. The conduction is not high, but the water can conduct enough current to stop a person s heart. So, for example, a person should not use an electrical appliance when in the bathtub or shower. 

Why does tap water conduct electricity, whereas distilled water does not ... 

Insight into the conductivity is provided by measuring the electrical conductivity of aqueous ionic solutions (Fig. 22.20 this topic is referred to in Chapters 11 and 15). The conductivity of pure water, multiply distilled to remove all impurities, is about 0.043 X lO (O cm) h Exposed to the air, pure water dissolves CO2, which forms carbonic acid, H2CO3 dissociation produces H30 and HCO3, which increase the conductivity to about 1 X 10 (O cm) . As ionic solutes are added to water, the conductivity increases rapidly a 1.0-M solution in NaOH has conductivity of about 0.180 (El cm) at 25°C. The conductivity depends strongly on both concentration and ionic species. The concentration dependence is summarized by the molar... 

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