Conductivity solution

For the electrospinning process to be initiated, the solution must gain sufficient charges such that the repulsive forces within the solution are able to overcome the surface tension of the solution. Subsequent stretching or drawing of the electrospinning jet is also dependent on the ability of the solution to carry charges. 

and dissolved carbon dioxide may increase the conductivity of the solvent. The solvent conductivity can be increased remarkably by mixing chemically inert components. Substances, such as mineral salts, mineral acids, carboxylic acids, some complexes of acids with amines, stannous chloride, and some tetraalkylammonium salts, are added to the solvent to increase its conductivity. For organic acid solvents, small amount of water addition will significantly increase their conductivity due to ionization of the solvent molecules. This increase in the conductivity can help production of headless fibers just because stretching of the solution has increased, and to some degree a fiber diameter decrease can be observed. 

Electrospun polymer nanofibres with the lowest fibre diameter were obtained at tbe highest electrical conductivity, so the drop in fibre size may be possibly explained by 

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Ash and Inorganic Constituents. Ash may be measured gravimetdcaHy by incineration in the presence of sulfudc acid or, more conveniendy, by conductivity measurement. The gravimetric result is called the sulfated ash. The older carbonate ash method is no longer in use. Ash content of sugar and sugar products is approximated by solution conductivity measurements using standardized procedures and conversion factors. 

Conductometric Analysis Solutions of elec trolytes in ionizing solvents (e.g., water) conduct current when an electrical potential is applied across electrodes immersed in the solution. Conductance is a function of ion concentration, ionic charge, and ion mobility. Conductance measurements are ideally suited tor measurement of the concentration of a single strong elec trolyte in dilute solutions. At higher concentrations, conduc tance becomes a complex, nonlinear func tion of concentration requiring suitable calibration for quantitative measurements. 

When an ionic solid such as NaCl dissolves in water the solution formed contains Na+ and Cl- ions. Since ions are charged particles, the solution conducts an electric current (Figure 2.12) and we say that NaCl is a strong electrolyte. In contrast, a water solution of sugar, which is a molecular solid, does not conduct electricity. Sugar and other molecular solutes are nonelectrolytes. 

Thus we find great variation among solutions. Iodine dissolves in ethyl alcohol, coloring the liquid brown, but does not dissolve readily in water. Sodium chloride does not dissolve readily in ethyl alcohol but does dissolve in water, forming a solution that conducts electric current. Sugar dissolves readily both in ethyl alcohol and in water, but neither solution conducts electric current. These differences are very important to the chemist, and variations in electrical conductivity are among the most important. We shall investigate electrical conductivity further but, first, we need to explore the electrical nature of matter. 

Water is a very poor conductor of electricity. Yet when sodium chloride dissolves in water, the solution conducts readily. The dissolved sodium chloride must be responsible. How does the dissolved salt permit charge to move through the liquid One possibility is that when salt dissolves in water, particles with electric charge are produced. The movement of these charged particles through the solution accounts for the current. Salt has the formula, NaCl—for every sodium atom there is one chlorine atom. Chemists have... 

Sugar dissolves in water, but the resulting solution conducts electric current no better than does pure water. We conclude that when sugar dissolves, no charged particles result no ions are formed. Sugar must be quite different from sodium chloride. 

Calcium chloride, CaCl2, is another crystalline solid that dissolves readily in water. The resulting solution conducts electric current, as does the sodium chloride solution. Calcium chloride is, in this regard, like sodium chloride and unlike sugar. The equation for the reaction is... 

The ease with which an aqueous salt solution conducts electric current is determined by how much salt is dissolved in the water, as well as by the fact that ions are formed. A solution containing 0.1 moles per liter conducts much more readily than a solution containing 0.01 moles per liter. Thus the conductivity is determined by the concentration of ions, as well as by their presence. 

Not all substances that form conducting solutions break up, or dissociate, so completely. For example, vinegar is just an aqueous solution of acetic acid. Such a solution conducts electric current, showing that ions are present ... 

Fig. 11-1. A strong electrolyte solution conducts better than a weak electrolyte solution.

A typical example is as follows. Benzoic acid, C6H5COOH, is a solid substance with only moderate solubility in water. The aqueous solutions conduct electric current and have the other properties of an acid listed in Section 11-2.1. We can describe this behavior with reaction (42) leading to the equilibrium relation (43) ... 

A solute may be present as ions or as molecules. We can find out if the solute is present as ions 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 " mol-L ) that pure water itself does not conduct electricity significantly. 

One might also draw attention to an analogous behavior apparently observed with silver. In two patents (176, 177) finely divided silver metal is observed to dissolve in liquid alkyl and aryl isocyanides to homogeneous solutions containing up to about 10% metal (by weight). These solutions conduct an electric current. On evaporation metallic silver is deposited. 

The existence of ions in aqueous solutions was first proposed by Svante Arrhenius, a young Swedish chemist, during the 1880s, well before the electronic structure of atoms had been discovered. This insight came while Arrhenius was pursuing his PhD in chemistry, exploring why aqueous solutions conduct electricity. 

Salts are non-volatile and in the fused state or in solution conduct an electric current. Many salts are hydrated in the solid state with water of crystallization. 

We can also calculate the individual values of (with the equations reported in Section 5.2) and of by determining the concentration distribution in the diffusion layer, and from this, the distribution of solution conductivity. The resulting combined value of q> coincides with the value determined from Eq. (6.32). 

An analysis of Eq. (7.49) shows that the electrophoretic effect accounts for about 60 to 70% of the decrease in solution conductivity, and the relaxation effect for the remaining 40 to 30%. 

Auxiliary electrodes are placed into the solution to set up the electric field that is needed to produce electrophoresis or electroosmosis. Under these conditions an electric current passes through the solution and the external circuit its value depends on the applied voltage and on solution conductivity. The lower this conductivity, the higher will be the electric field strength E (or ohmic voltage drop) in the solution that can be realized at a given value of current. 

A number of special features follow from the equations reported. The linear velocity of electroosmotic transport of the liquid is independent of the geometric parameters of the porous diaphragm (the size and number of pores, the thickness, etc.), and the space velocity depends only on S. At given values of the current, the transport rate increases with decreasing solution conductivity (increasing field strength). 

Attention is thirdly focused on Figure 6.5 (C) which is obtained for the titration of a strong acid against a weak base. In this particular case, the solution conductance decreases rapidly, this result being due to the uptake of the fast-moving H+ ions and their substitution by slow-moving NH4 ions ... 

Phase Inversion The phase inversion of brine/oil/surfactant systems was established routinely by measuring solution conductivity employing a Jenway FWA 1 meter and cell. The process identifies the range over which a large decrease in conductivity occurs as the sytem under test is converted from an oil in water emulsion to a water in oil emulsion. Phase... 

When some molecules containing only covalent bonds are dissolved in water, they react with the water to produce ions in solution. For example, pure hydrogen chloride, HCI, and pure ammonia. NH3, consist of molecules containing only covalent bonds. When cooled to sufficiently low temperatures (-33°C for NH -85°C for HCI) these substances condense to liquids. However, the liquids do not conduct electricity, since they are still covalent and contain no ions. In contrast, when HCI is dissolved in water, the resulting solution conducts electricity well. Aqueous solutions of ammonia also conduct, but poorly. In these cases, the following reactions occur to the indicated extent to yield ions ... 

In the choice of an analytical technique for following the course of a reaction, it is important to recognize that no aspect of the measurement should affect the kinetic processes occurring in the system. For example, a solution conductivity method that uses platinized electrodes should not be used in the study of a reaction that is catalyzed by platinum black. 

Solvated electrons were first produced in liquid ammonia when Weyl (1864) dissolved sodium and potassium in it the solution has an intense blue color. Cady (1897) found the solution conducts electricity, attributed by Kraus (1908) to an electron in a solvent atmosphere. Other workers discovered solvated electrons in such polar liquids as methylamine, alcohols, and ethers (Moissan, 1889 Scott et al, 1936). Finally, Freed and Sugarman (1943) showed that in a dilute metal—ammonia solution, the magnetic susceptibility corresponds to one unpaired spin per dissolved metal atom. 

The time constant defined by Eq. (3.8) depends on the solution conductivity and the boundary-layer thickness but is independent of the applied current density. 

Electrolytes are defined as substances whose aqueous solutions conduct electricity due to the presence of ions in solution. Acids, soluble bases and soluble salts are electrolytes. Measuring the extent to which a substance s aqueous solution conducts electricity is how chemists determine whether it is a strong or weak electrolyte. If the solution conducts electricity well, the solute is a strong electrolyte, like the strong acid, HC1 if it conducts electricity poorly, the solute is a weak electrolyte, like the weak acid, HF. 

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. 

Quantitative measurements of the strength of an acid are best based on electrometric measurements of the pH of the partly neutralized solution. Conductivity measurements are likely to give ionization constants that are too high due to the presence of conducting impurities. Estimates of acid strength from rate data are also somewhat unreliable... 

In a Daniell cell, the pieces of metallic zinc and copper act as electrical conductors. The conductors that carry electrons into and out of a cell are named electrodes. The zinc sulfate and copper(II) sulfate act as electrolytes. Electrolytes are substances that conduct electricity when dissolved in water. (The fact that a solution of an electrolyte conducts electricity does not mean that free electrons travel through the solution. An electrolyte solution conducts electricity because of ion movements, and the loss and gain of electrons at the electrodes.) The terms electrode and electrolyte were invented by the leading pioneer of electrochemistry, Michael Faraday (1791-1867). 

Fig. 10-3. Energy diagrams for an n-type semiconductor electrode (a) in the daik and (b) in a photoexdted state S = aqueous solution = conduction band edge level at an interface cy = valence band edge level at an interface = Fermi level of oxygen...

Perhaps no two classes of compounds are more important in chemistry than acids and bases. All acids have several properties in common They have a sour taste, and they all react with most metals to form hydrogen gas (Hj) and with baking soda to form carbon dioxide (CO2). All acids turn blue litmus paper red, and their solutions conduct electricity because acids form ions when dissolved in water. t 11 bases also share several common properties They have a bitter taste, their solutions feel slippery like soapy water, and they turn red litmus paper blue (the opposite of acids). Solutions of bases also conduct electricity because they too form ions in water. Acids are similar because they produce hydrogen ion, (aq), in water. Bases, on the other hand, all form hydroxide ion, 0 [ (aq), in water. These ions are responsible for the properties of acids and bases. 

As long as the measurement frequency/ RJ2nC, the capacitive effects can be neglected, and the solution conductance G= l/R is measured directly. 

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