Effects of Chloride Ions

38 Anodic polarization of chromium-nickel binary alloys in 1 N H2S04 + 1 N NaCl. Redrawn from Ref 13 

The extents of the passive potential regions have been reduced for all materials except pure chromium, and the curves for 90 and 100 wt% nickel indicate that an active-to-passive state transition no longer occurs. The magnitude of the influence of the chloride ions is emphasized by comparing the current densities for each alloy at 200 mV (SHE) with and without chloride ions present. 

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Hodge, F. G. and Wilde, B. E., Effect of Chloride Ion on the Anodic Dissolution Kinetics of Cr-Ni Binary Alloys in Dilute H2SO4 , Corrosion, 26, 146 (1970)... 

Zamin, M. and Ives, M. B., Effect of Chloride Ion Concentration on the Anodic Dissolution Behaviour of Nickel , Corrosion, 29, 319 (1973)... 

It is in this area that most work has been carried out, particularly in relation to corrosion resistance in sulphuric acid solutionsBourelier etal. and Raicheff etal. investigated the inhibitive effect of chloride ions on corrosion in sulphuric acid. The inhibition efficiency was found to depend on the alloy composition, alloy surface and chloride concentration. The more aggressive the environment, the greater the inhibition efficiency. Yagupol skaya etal studied the effect of iodine additions to sulphuric acid on the corrosion resistance of Ni and Ni-Fe alloys. Again there was an inhibitive effect caused by the halide ion. 

The beneficial effect of chloride ions on inhibitor action is brought out in... 

Figure 19. Effects of chloride ion and proton on anodic dissolution current of passive metal.20 pCl - og[CT], pH -log[H+]. p.s. pit and a.s. pit indicate polishing-state pit and active-state pit, respectively.

The effect of chloride ion on the exchange was found by these workers to be very small, whereas Plane and Taube had estimated a rate coefficient about five times larger in the presence of 10 M chloride ion than in perchlorate solution. Van der Straaten and Aten have studied the exchange in media 1 M with respect to HCl and have estimated a rate coefficient 3.0 x 10 l.mole". sec . The isotopic method ( Cr) and a separation procedure based on the precipitation of Cr(II) as the acetate complex was used. 

The effect of chloride ions was investigated first by Silverman and Dodson. These authors observed an increase in as the concentration of chloride ion was increased from 0 to 0.55 M in perchlorate media of constant acidity. The rate expression found to fit the experimental data was... 

Wada and Reynolds have investigated the effect of chloride ion, over the range 1 x 10 to 6x 10 M, on this exchange system. A rate law at constant HCIO4... 

Interest has been shown by several groups on the effect of solvent and of added anions upon the oxidation of alcohols. The oxidation of isopropanol proceeds 2500 times faster in 86.5 % acetic acid than in water at the same hydrogen ion concentration . The kinetics and primary kinetic isotope effect are essentially the same as in water. Addition of chloride ion strongly inhibits the oxidation and the spectrum of chromic acid is modified. The effect of chloride ion was rationalised in terms of the equilibrium,... 

Po and Sutin " have disputed both the extent of the catalytic effect of chloride ion reported by Wells and Salam" and the formation constant of 5.54 (25 °C, [Cl ] = 0.300 M, n = 1.00) for FeCl estimated thereby. Wells " has replied that the value of k2 of Po and Sutin at zero chloride concentration is artifically increased because of the presence of stabiliser in their peroxide, consequently masking the catalysis. 

In a follow-up study, Jameson and Blackburn studied the effect of chloride ion in more detail and reported the following concentration dependence of the pseudo-half-order rate constant for the dioxygen decay (15) ... 

The effect of chloride ion was interpreted in terms of the formation of various ternary complexes between Cu(II)-ascorbate and Cl-. It was demonstrated that the involvement of copper(I) is feasible and a corresponding mechanism was presented as an alternative to the Cu(II)/ Cu(III) model. 

To further complicate matters, when 30 ppm chloride ion is present and titanium cathode blanks are used for the copper deposition, an incomplete or lacy structure is obtained. If 30 ppm glue is, in turn, added to this solution, the effect of chloride ion is counteracted and complete coverage is again obtained. 

Ho MW, O Brien JS (1971) Differential effect of chloride ions on beta-galactosidase isoenzymes a method for separate assay. Clin Chim Acta 32 443-450... 

VC13 treated with Bu NC produces mer-[VCl3(CNBu,)3]. The structure was determined by X-ray diffraction.182 The HNMR spectra in CDC13 showed that the free ligand exchanges more rapidly with the isocyanide tram to chloride than with the trans isocyanide groups. Therefore, the kinetic trans effect of chloride ion is larger than that of isocyanide. 

The pK value for this dissociation is about 9.14. Reports of lower values (15) may result from the formation of polyborate ions or from the presence of chloride ions. If a knowledge of Ka is important in a particular study, the possible effect of chloride ion should be investigated before it is introduced into the system. Dilute boric acid solutions probably contain only two boroxy species, trigonal boric acid and tetrahedral borate anion. 

Choride ion is considerably less reactive than the azide ion. Thus, although values of kc 1/ kn2o have been quite widely available from mass law effects of chloride ion on the solvolysis of aralkyl halides, normally the reaction of the chloride ion cannot be assumed to be diffusion controlled and the value of kn2o cannot be inferred, except for relatively unstable carbocations (p. 72). Mayr and coworkers251 have measured rate constants for reaction of chloride ion with benzhydryl cations in 80% aqueous acetonitrile and their values of logk are plotted together with a value for the trityl cation19 in Fig. 7. There is some scatter in the points, possibly because of some steric hindrance to reaction of the trityl cations. However, it can be seen that chloride ion is more... 

Chloride catalysis is significant, and may lead to auto-catalysis " . A marked effect of chloride ion on reaction rate between pH 1 and 7 has been demonstrated , viz. 

A solution of hypochlorite is stable in an excess of alkali, whereas in acid there is a slow conversion to chlorate. The minimum stability of hypochlorite solutions is at pH 6.7 (6.68 and 7-7.13 have also been reported - ) and the maximum stability is at pH 13. There is also a region of high stability in strong acid, where the solute is predominantly composed of chlorine and only very little hypochlorous acid. The rate of decomposition at pH 6.7-7.2 is proportional to the chloride concentration and to the square of the hypochlorite concentration. In slightly alkaline solution the rate is proportional to [0C1-][H0C1]. The catalytic effect of chloride ion is well known buffers " such as acetate, borate and carbonate also have an effect. It has been recommended that the concentration of phosphate buffers be kept below 0.25 M to prevent decomposition of hypochlorite solutions. The catalytic effect of heavy metals, especially copper and iron, has been noted. The effect of various cations is shown in the greater stability of lithium hypochlorite in comparison with the sodium and potassium salts. ... 

Figure 9.8 shows clearly the effect of chloride ion and other anions such as methane sulfonate on the apparent partition coefficient of chlorpromazine. The nature of the anion significantly affects the partitioning of the drug. Ion pairing in the gastrointestinal tract obviously could influence absorption. 

The twofold inhibiting effect of chloride ions according to their inverse square concentration in eq. (9) is explained through the replacement of a chloride ligand by the olefin according to eq. (8) followed hy replacement of another chloride ligand by a water molecule according to eq. (10) ... 

The solid curve in Figure 11 -2 illustrates the effect of chloride ion concentration on the solubility of silver chloride data for the curve were obtained by substituting various chloride concentrations into Equation 11-41. Note that at high concentrations of the common ion, the solubility becomes greater than that in pure water. The broken lines represent the equilibrium concentrations of the various silver-containing species as a function of Ckci- Note that at the solubility minimum, undissociated silver chloride, AgCl(ag), is the major silver species in the solution, representing about 80% of the total dissolved silver. Its concentration is invariant, as has been demonstrated. 

Figure 11 -2 The effect of chloride ion concentration on the solubility of AgCl. The solid curve shows the total concentration of dissolved AgCl. The broken lines show the concentrations of the various silver-containing species.

Fig. 5.36 Effect of chloride-ion concentration in near-neutral water on anodic polarization of type 304 stainless steel. Dashed lines added to show approximate locations of transpassive and anodic-peak sections of the cu rve. Based on Ref 34...

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