Ozone oxidation-reduction potential

Ozone can be analyzed by titrimetry, direct and colorimetric spectrometry, amperometry, oxidation—reduction potential (ORP), chemiluminescence, calorimetry, thermal conductivity, and isothermal pressure change on decomposition. The last three methods ate not frequently employed. Proper measurement of ozone in water requites an awareness of its reactivity, instabiUty, volatility, and the potential effect of interfering substances. To eliminate interferences, ozone sometimes is sparged out of solution by using an inert gas for analysis in the gas phase or on reabsorption in a clean solution. Historically, the most common analytical procedure has been the iodometric method in which gaseous ozone is absorbed by aqueous KI. 

The need for oxidants can be determined by measuring the oxidation reduction potential (ORP) of the water to be treated. If the ORP measures above negative 170 millivolts, Filox can be used without the use of additional oxidants. Lower than negative 170 millivolts will require additional oxidants. Air, hypochlorite, hydrogen peroxide, ozone, and potassium permanganate are all suitable oxidants to use with Filox. Note that weaker oxidants, such as air and hypochlorite will be sufficient for most applications. 

Oxidation-reduction potential measurements were made with a platinum-calomel electrode system connected to a Beckman Model H-2 pH meter. The buffered bacterial suspensions were similar to those in the dose-contact time experiments. To these suspensions, successive equal aliquots of an ozone solution were added at 1°, and the oxidation-reduction potential was measured in millivolts. 

To obtain additional information about ozone activity at the concentrations of greatest biological interest, oxidation-reduction potentials of buffered bacterial suspensions were determined after addition of various amounts of ozone. It was reasoned that the oxidation-reduction potential at or close to the lethal concentration would exhibit a demonstrable change indicative of the corresponding activity. Figure 2 presents the results of the experiment there is a sharp break in the redox potential at an ozone concentration comparable to the level found to represent the lethal dose in the dosage-contact time experiments. A differential plot of the same data emphasizes this information (Figure 3). 

Figure 2. Effect of added ozone on oxidation-reduction potential...

The last general category—namely, the reaction of ozone with aromatic hydrocarbons, has received an enormous amount of attention by ozone chemists. Most of this attention has concerned rate and reactivity studies in an attempt to correlate these experimental quantities with some known parameters of the hydrocarbons. Several reactivity correlations have been proposed, including those with bond localization energy, atom localization energies, and oxidation-reduction potentials. This category is also represented by a paper in this section, in which a possible correlation between ozone reactivity and carcinogenicity of some polycyclic aromatic compounds is explored. 

Chemical oxidizers used to disinfect RO systems include hydrogen peroxide (peroxide), halogens, and ozone. Although halogens (and specifically chlorine) are the most popular oxidizers using in conjunction with RO pretreatment, they do not have the highest oxidization-reduction potential (ORP). Table 8.8 lists the ORP for several oxidizers. As the table shows, ozone and peroxide have nearly twice the ORP or oxidative power as chlorine. Despite the relatively low ORP, chlorine is the most commonly used disinfectant in brackish water RO pretreatment due to its ease of use and its ability to provide residual disinfection (for seawater desalination using RO, bromine (as HOBr)... 

To obtain additional information about ozone activity at the concentrations of greatest biological interest, oxidation-reduction (OR) potentials of buffered bacterial suspensions were determined after addition of various amounts of ozone. 

Ozone (O3) is still stronger because its high free energy relative to oxygen provides an additional driving force for oxidation reactions, as shown by its high halfcell reduction potential in acidic aqueous solution ... 

Effectiveness questioned Possible future regulations High oxidation capacity Does not form dangerous chloramine compounds More effective than chlorine due to high reduction potential Higher effectiveness than ozone in reducing viable aerobes on whole lettuce... 

The reaction illustrates the two most characteristic chemical properties of ozone its strongly oxidizing nature and its tendency to transfer an O atom with coproduction of O2. Standard reduction potentials in acid and in alkaline solution are ... 

The occurrence of ozone in the lower atmosphere has brought land-bound organisms into contact with an oxygen compound whose oxidative potential exceeds that of dioxygen by far. The standard reduction potential of the reaction... 

The ozone molecule is paramagnetic as it lacks unpaired electrons. Its oxidative potential is almost as high as that of atomic oxygen and is only exceeded by few other compounds such as F2, S2Og , H4Xe06, and KrF2 [331]. This is reflected in the standard reduction potential, E° +1.65 V for the reduction of ozone [330] ... 

Ozone (O3) is a powerful oxidizing agent. The reduction potential is high in both acidic and basic media, as was shown in Table 3.1 (2.07 and 1.24 V, respectively) for the following reactions. 

Ozone is a stronger oxidizing agent tlian dioxygen. One measure of fhis oxidizing power is Ihe high sfandard reduction potential of O3, compared to fhat of O2 -... 

The standard reduction potential of O ig) to 02(g) is +2.07 V. Write a half-equation for this reduction in acid solution. How does ozone compare with chlorine gas, Cl2( ), as an oxidizing agent Of what practical, beneficial, environmental importance is the oxidiang abiUty of ozone Hint Refer to Chapter 11 if need be.)... 

Use standard reduction potentials to analyze the thermodynamic possibility of using ozone to oxidize bromate to perbromate. Hint Use Table 12.2, p. 332.)... 

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