Acids and pH Value

Acids and bases are substances that behave differently in water Acids give up hydrogen ions, H+. Hydrochloric acid dissociates in water to form H+ and Cl ions. Substances that release hydroxide ions, OH are called bases. For example sodium hydroxide, NaOH dissociates into OH and Na+. Acids in the stomach dissolve food, acids in soil help make nutrients available to growing plants. 

The strength of an acid and base is given by the pH value. This value denotes the negative logarithm of the H+ concentration. Pure water has a pH of 7. The H3O+ is called a hydroxonium ion and is responsible for the acidic properties of the solution. For example  

On the other hand, the hydroxide ion OH is responsible for the alkaline properties of the solution. 

The sulfuric acid is the major component of the clouds of the atmosphere of Venus. 

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E. Bosch, S. Espinosa, and M. Roses, Retention of ionizable compounds on high-performance liquid chromatography III. Variation of pK values of acids and pH values of buffers in acetonitrile-water mobile phases,/. Chromatogr. A 824 (1998), 137-146. 

Is pH 2 sensible (Always ask yourself that question at the end of a calculation.) Yes—because pH values below 7 are acidic and pH values above 7 are basic. 

Kind and concentration if liquid is acid, and pH value if known. 

Mahc acid is a relatively strong acid. Its dissociation constants are given in Table 1. The pH of a 0.001% aqueous solution is 3.80, that of 0.1% solution is 2.80, and that of a 1.0% solution is 2.34. Many of its physical properties are similar to those of citric acid (qv). Solubihty characteristics are shown in Figure 1 and Table 1, densities of aqueous solutions are hsted in Table 2, and pH values vs concentration are shown in Figure 2. 

These compounds show good solubility in acid aqueous solutions developing a sufficient depression of surface tension, but there is a strong dependence from temperature and pH value [151] (see Table 5). 

Reaction selectivity of the parent ortho-QM has also been explored with a variety of amino acid and related species.30 In these examples, the rates of alkylation and adduct yields were quantified over a range of temperatures and pH values. The initial QM3 was generated by exposing a quaternary benzyl amine (QMP3) to heat or ultraviolet radiation (Scheme 9.10). Reversible generation of QM3 was implied by subsequent exchange of nucleophiles at the benzylic position under alternative photochemical or thermal activation.30 Report of this work also included the first suggestion that the reversible nature of QM alkylation could be used for controlled delivery of a potent electrophile. 

Chlorinating the aqueous waste sludge suspension (to oxidize the chromium) at temperatures of 20 to 80°C and pH values between 4 and 13. The chlorinated sludge is then acidified with sulfuric acid to a pH of 1.0 to 3.0. The insoluble components are then separated, followed by the separation of the chromium(VI) from the solution using a fixed-bed anion exchanger (at pH values of <3). 

The thioester hypothesis can be summed up as follows the formation of thiols was possible, for example, in volcanic environments (either above ground or submarine). Carboxylic acids and their derivatives were either formed in abiotic syntheses or arrived on Earth from outer space. The carboxylic acids reacted under favourable conditions with thiols (i.e., Fe redox processes due to the sun s influence, at optimal temperatures and pH values) to give energy-rich thioesters, from which polymers were formed these in turn (in part) formed membranes. Some of the thioesters then reacted with inorganic phosphate (Pi) to give diphosphate (PPi). Transphosphorylations led to various phosphate esters. AMP and other nucleoside monophosphates reacted with diphosphate to give the nucleoside triphosphates, and thus the RNA world (de Duve, 1998). In contrast to Gilbert s RNA world, the de Duve model represents an RNA world which was either supported by the thioester world, or even only made possible by it. 

Based on the similarity of formalin-induced chemical modification between nucleic acids and proteins, the efficiency of heating protocols for DNA/RNA extraction has been demonstrated (see Chapter 3 for detail). Basic AR principle including heating condition and pH value of AR solution as well as certain chemicals may play roles to establish optimal protocols. 

Physico-chemical characteristics of the soils were summarized in Table 1. The values were comparable to that described in the previous reports about the SERS (Doi and Sakurai 2003 Doi et al. 2004 Sakurai et al. 1998). The one-way ANOVA indicated that most of the soil variables significantly reflected the land degradation with high values of bulk density, sand content and exchangeable acidity, and low values of moisture content, pH, OM, base (K, Ca, Mg) contents, EC, CEC, base saturation rate, TN and TC contents, available phosphorus and MPN on the glucose medium with no antibiotics. These results also told that the human activities induced several soil environmental gradients. 

We can prepare a buffer of almost any pH provided we know the pAa of the acid and such values are easily calculated from the Ka values in Table 6.5 and in most books of physical chemistry and Equation (6.50). We first choose a weak acid whose pKa is relatively close to the buffer pH we want. We then need to measure out accurately the volume of acid and base solutions, as dictated by Equation (6.50). 

Rate constants and the products formed in the hydrolysis of Cl Reactive Red 194 (7.76) at 50 °C and pH values in the 10-12 region were determined by high-pressure liquid chromatography. In addition to the normal hydrolysis of the two reactive systems, the imino link between the triazine and benzene nuclei was also hydrolysed [67]. The heterobifunctional copper formazan dye Cl Reactive Blue 221 and two blue anthraquinone monofunctional reactive dyes of the bromamine acid type, namely the aminochlorotriazine Blue 5 and the sulphatoethylsulphone Blue 19, were compared in terms of their sensitivity to... 

It must be noted that the partition coefficient is not the ratio of the pollutant solubilities in the two pure liquids. This change can result in significant differences, particularly with compounds of low aqueous solubility. The measurement of partition coefficients may be complicated by the involvement of other equilibrium processes such as pKa and pH values. For example, the following reaction shows the dissociation of a monoprotic organic acid ... 

They present strong acidities (the pH values of aqueous solutious of heteropolyacids indicate that they are strong acids) both in solid and in liquid solution (Figure 13.2). In addition, they can be prepared in an wide range of surface areas (partially salified heteropolyoxometalates permit the modification of the surface areas of these materials) or be supported in metal oxides. 

Acrylic acid and ammonium ions (Abdelmagid and Tabatabai, 1982 Brown and Rhead, 1979 Kollig, 1993) were reported as hydrolysis products. The hydrolysis rate constant at pH 7 and hydrolysis half-lives are reduced significantly at varying pHs and temperature. At 88.0 °C and pH values of 2.99 and 7.04, the half-lives were 2.3 and 6.0 d, respectively (Ellington et al., 1986). Decomposes between 175 and 300 °C (NIOSH, 1994). 

Irradiation of an aqueous solution at 296 nm and pH values from 8 to 13 yielded different products. Photolysis at a pH nearly equal to the dissociation constant (undissociated form) yielded pyrocatechol. At an elevated pH, 2-chlorophenol is almost completely ionized photolysis yielded cyclopentadienic acid (Boule et al., 1982). Irradiation of an aqueous solution at 296 nm containing hydrogen peroxide converted 2-chlorophenol to catechol and 2-chlorohydroquinone (Moza et al, 1988). In the dark, nitric oxide (10 vol %) reacted with 2-chlorophenol forming 4-nitro-2-chlorophenol and 6-nitro-2-chlorophenol at yields of 36 and 30%, respectively (Kanno and Nojima, 1979). 

The hydrolysis half-life in three different natural waters was approximately 48 d at 25 °C (Macalady and Wolfe, 1985). At 25 °C, the hydrolysis half-lives were 120 d at pH 6.1 and 53 d at pH 7.4. At pH 7.4 and 37.5 °C, the hydrolysis half-life was 13 d (Freed et al, 1979). At 25 °C and a pH range of 1-7, the hydrolysis half-life was about 78 d (Macalady and Wolfe, 1983). However, the alkaline hydrolysis rate of chlorpyrifos in the sediment-sorbed phase were found to be considerably slower (Macalady and Wolfe, 1985). In the pH range of 9-13, 3,5,6-trichloro-2-pyridinol and 0,0-diethyl phosphorothioic acid formed as major hydrolysis products (Macalady and Wolfe, 1983). The hydrolysis half-lives of chlorpyrifos in a sterile 1% ethanoFwater solution at 25 °C and pH values of 4.5, 5.0, 6.0, 7.0, and 8.0 were 11, 11, 7.0, 4.2, and 2.7 wk, respectively (Chapman and Cole, 1982). 

Chemical/Physical. The hydrolysis half-lives of atrazine in aqueous buffered solutions at 25 °C and pH values of 1, 2, 3, 4, 11, 12 and 13 were reported to be 3.3, 14, 58, 240, 100, 12.5, and 1.5 d, respectively (Armstrong et al., 1967). Atrazine does not hydrolyze in uncatalyzed solutions, even under elevated temperatures. The estimated half-life of atrazine in neutral, uncatalyzed water at pH 6.97 and 25 °C is 1,800 yr. Under acidic conditions, hydrolysis proceeds via mono- and diprotonated forms (Plust et al., 1981). Atrazine is stable in slightly acidic or basic media, but is hydrolyzed to hydroxy derivatives by alkalies and strong mineral acids (Windholz et al., 1983). Atrazine reacts with strong mineral acids forming hydroxyatrazine (Montgomery and Freed, 1964). 

CASRN 52315-07-8 molecular formula C22H19CI2NO3 FW 416.30 Soil. The major soil metabolite was 3-phenoxybenzoic acid (Hartley and Kidd, 1987). Chemical/Physical. The hydrolysis half-lives of cypermethrin in a sterile 1% ethanol/water solution at 25 °C and pH values of 4.5, 6.0, 7.0, and 8.0, were 99, 69, 63, and 50 wk, respectively (Chapman and Cole, 1982). 

These data were measured at or extrapolated to ambient temperature and pH values. The data are discussed in the text. NA = not available. b/ Kq = soil water distribution coefficient (K ) divided by the organic carbon content of the soil, cj Whenever possible, half-life for soil dissipation is derived from the field data half-lives described in the text rather than lab data. As such, it may not represent a true first-order process. Value has been estimated from the equation in ref. 20. e/ Hydrolysis of total residues (aldicarb + sulfoxide + sulfone). pK for p -phthalic acid is 3.5. The chlorine atoms of DCPA should lower the pK to about 2. Conditions optimized for soil metabolism. 

The imidazole side-chain of histidine has a value of 6.0, making it a weaker base than the unsubstituted imidazole. This reflects the electron-withdrawing inductive effect of the amino group, or, more correctly the ammonium ion, since amino acids at pH values around neutrality exist as doubly charged zwitterionic forms (see Box 4.7). Using the Henderson-Hasselbalch equation, this translates to approximately 9% ionization of the heterocyclic side-chain of histidine at pH 7 (see Box 4.7). In proteins, plCa values for histidine side-chains are estimated to be in range 6-7, so that the level of ionization will, therefore, be somewhere between 9 and 50%, depending upon the protein. 

This technique uses both direct and back titrations of weak acids and bases. Values of are obtained directly. In purely aqueous media, over the pH range 2-10, the titration of dilute (0.005 to 0.05 M) solutions of weak monovalent acids and bases with a glass electrode can lead to reliable thermodynamic pKs. Over this pH interval, the activity coefficients of the ionic species can be calculated by means of the Debye-Hiickel equation. Also, the activity coefficients of the neutral species remain essentially constant and... 

Oxidations are catalyzed by acids, bases, pH values that are higher than the optimum, polyvalent metal ions, peroxides, hydroperoxides, and exposure to oxygen and ultraviolet (UV) illumination. These reactions may necessitate the use of antioxidant chemicals, inert atmospheres, and opaque packaging. Chelating agents... 

After hydrolyzate acidification with hydrochloric acid at pH values lower than 1, quinoxaline-2-carboxylic acid is quantitatively extracted into ethyl acetate, chloroform, or dichloromethane, since at these strongly acidic conditions the ionization of their carboxylate moiety is suppressed (pK, 2.88), and then back-extracted into aqueous buffered solutions at pH 6.0 or higher. These liquid-liquid partitioning procedures isolate quinoxaline-2-carboxylic acid from a complex mixture of tissue hydrolysates, and provide an aqueous extract suitable for further purification by solid-phase extraction. This has been accomplished either with the strong cation-exchange resin AG MP-50 (419, 420) or with a polar silica column (422). 

In order to obtain better insight into buffer effects on swelling rates, extensive studies were performed with buffers containing acetic acid (HAc), methoxyacetic acid (MeOHAc), and chloroacetic acid (ClHAc), at various buffer concentrations and pH values and at I = 0.1 M, in MMA/DMA 70/30 gels [44]. These studies had the advantage that only two possible charge states on the buffer (0 and — 1) are possible. However, the relatively low pK values of the buffers (4.62, 3.42, and 2.74 for HAc, MeOHAc, and ClHAc, respectively) meant that studies had to be performed in regions of low pH. 

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