Benzoate ions solution concentration

Notice that [H+] is less than 10% of [C6H5COOH], verifying our assumption that very little of the acid reacted.) Now we know two of the concentrations in expression (43) and, to complete the calculation, we must know the concentration of benzoate ion, [CsHsCOO-]. Since the benzoic acid was dissolved in pure water, the only source of GHsCOO- is reaction (42). This is also the source of hydrogen ion, H+(aq). Since these two ions are both produced only by reaction (42), their concentrations must be equal in this solution. That is,... 

LDHs are also promising materials as sorbents for anionic organic contaminants via both ion-exchange and reconstruction reactions. There have been a large number of reports of the use of LDHs for removal of species such as aromatic carboxylic acids, phenols, pesticides, and humic or fulvic acids. Recently, Cardoso et al. [152] found that the sorption process of terephthalate anions from aqueous solutions by calcined Mg/Al - CO3 LDHs takes place by reconstruction of the LDHs and involves the intercalation and adsorption of terephthalate anions. Calcined Mg/Al - CO3 LDHs were found to be capable of removing 40 to 85 % of the benzoate from solutions in the concentration... 

Figure 10. Surface concentration (9) and peak intensities (O) vs. solution concentration using the liquid doping technique for benzoate ions on aluminum (---)...

The next step is critical. When you determine the starting concentration of benzoate ion, you must do so by dividing the number of moles of benzoate by the volume of the new solution, which will consist of the 50.00 mL of the original solution +62.8 mL of added solution. The neutralization created 0.0125 mol C7H502, so the molarity is ... 

In a galvanic cell, the cathode consists of a Ag (1.00 M) Ag half-cell. The anode is a platinum wire, with hydrogen bubbling over it at 1.00-atm pressure, that is immersed in a buffer solution containing benzoic acid and sodium benzoate. The concentration of benzoic acid (C5H5COOH) is 0.10 M, and that of benzoate ion (CSH5COO ) is 0.050 M. The overall cell reaction is then... 

The degree of dissociation decreases with increasing electrolyte concentration. With the dissociation constant for benzoic acid, Ka = 6.25 10-5, the degree of dissociation of a benzoic acid solution is calculated to be a = 0.2 for the concentration of c = 1.25 10 3 mol/L used as an example. Therefore, such a solution contains 2.5 10-4 mol/L of oxonium ions and benzoate ions, respectively. Comparing such a benzoic acid solution with a sodium benzoate solution of the concentration c = 2.5 10-4 mol/L, an almost identical elution behavior is observed. 

If this equilibrium is disturbed by a sample injection, a new equilibrium is established via relaxation i.e., the kind of relaxation process depends on the pH value of the sample injected. If the sample pH is lower than the pH value of the mobile phase, benzoate ions in the mobile phase are protonated due to the sample injection. Thus, the concentration of molecular benzoic acid in the mobile phase increases as does the concentration of the amount adsorbed to the stationary phase. The amount not adsorbed travels through the column and appears as a chromatographic signal the system peak. A qualitatively similar chromatogram is obtained when a sample containing the solute ions and the corresponding eluent component is injected into the system. However, only the position of the system peak is comparable, not its area and direction. 

Fig. 5-12. Ion-pair chromatographic separation of nitrite, nitrate, and benzoate. - Separator column IonPac NS1 (10 pm) eluent 0.002 mol/L TBAOH + 0.001 mol/L Na2C03 / acetonitrile (82 18 v/v) flow rate 1 mL/min detection suppressed conductivity injection volume 50 pL solute concentrations 10 ppm nitrite, 10 ppm nitrate, and 20 ppm benzoate.

What must be the concentration of benzoate ion, CgH5COO, in a 0.045 M benzoic acid, CgH5COOH, solution so that the pH is 5.00 ... 

X 10 M solution of benzoic acid is 20% ionized. Thus this eluent has a hydrogen ion and a benzoate ion concentration each of 2.50 x 10 M. Comparison of this benzoic acid solution with an eluent containing 2.50 x 10 potassium benzoate shows that the two eluents give very similar retention times for inorganic anions (see Table 6.7). 

Rosene and Manes studied the effect of pH on the total adsorption from aqueous solutions of sodium benzoate + benzoic acid by activated charcoal. They interpreted their data in terms of the Polanyi potential theory applied to bisolute adsorption (see later p. 117), in which the concentrations of neutral benzoic acid and benzoate anions depend on the pH of the solution (activity coefficient corrections were ignored). They confirmed that, at constant total equilibrium concentration, the adsorption dropped from a relatively high plateau for pH <2 down to a small adsorption at pH >10. The analysis of results is somewhat more complex than with essentially non-electrolyte adsorption, and in this case there were additional effects involving chemisorption of benzoate ion by residual ash in the carbon which had, therefore, to be eliminated. Even with ash-extracted carbon there was evidence of some residual chemisorption. The theoretical analysis correlated satisfactorily with the experimental data on the basis that at pH >10 sodium benzoate is not physically adsorbed and that the effect of pH is completely accounted for by its effect on the concentration of free acid. In addition the theory explains successfully the increase in pH (called by the authors hydrolytic adsorption ) when solutions of sodium benzoate are treated with neutral carbon. However, no account is taken in this paper of the effect of pH on the surface charge of the carbon. 

Indicators, (a) Select an indicator suitable for determining the pH of solutions with pH around 5. (b) Calculate at 25°C the pH at the equivalence point for the titration of (i) benzoic acid, HC7HSO2, with NaOH (ii) NHj with HCl. In each case assume that the concentration of the reaction product at the equivalence point is 0.100 mole/liter. For the benzoate ion Kb = 1.55 X 10 and, for the ammonium ion, Ka = 5.65 X 10 at25"C. In each case, select from Table 15.1 (page 301) an indicator suitable for the titration. 

Consider a 0.10 Ab solution of benzoic add, for which the ionization constant (/fa) is 6.5 X 10 . Using the procedure described in Sample Problem 16.12, we can determine the equilibrium concentrations of benzoic acid, H, and the benzoate ion. 

Because the Kb of C6H5COO is larger than that of N02, the benzoate ion will hydrolyze to a greater extent than the nitrite ion and will give a solution with a higher [OH ]. A sodium benzoate solution is more basic and has a higher pH than a sodium nitrite solution of the same concentration. 

Dissimilar metals in the same system Because of the specific action of many inhibitors towards particular metals, problems arise in systems containing more than one metal. In the majority of cases these problems can be overcome by the choice of a formulation incorporating inhibitors for the protection of each of the metals involved. With this procedure it is necessary not only to maintain an adequate concentration of each of the inhibitors but also to ensure that they are present in the correct proportion. This is because of two effects firstly, failure to inhibit the corrosion of one metal may intensify the attack on the other metal the best example of this is with aluminium and copper in the same system, and failure to inhibit copper corrosion — usually achieved with sodium mercaptobenzothiazole or benzotriazole—can lead to increased corrosion of the aluminium as a result of deposition of copper from copper ions in solution on to the aluminium surface. Secondly, an inhibitor of the corrosion of one metal may actually intensify the corrosion of another metal. Thus, benzoate is usually used to prevent the corrosion of soldered joints by nitrite inhibitor added to protect cast iron in the same system. A benzoate nitrite ratio of greater than 7 1 is necessary in these cases. 

As an example, suppose a chemist needs to know the hydrogen ion concentration in a solution containing both 0.010 M benzoic acid, QHsCOOH, and 0.030 M sodium benzoate, QHtCOONa. Of course, he could go to the laboratory and proceed to investigate the colors of indicator dyes placed in the solution. However, it is easier to calculate the value of [H+], using the accurate value of Ka listed in Appendix 2. 

What is the equilibrium concentration of hydroxide ions in a 0.135 M solution of sodium benzoate ... 

Direct evidence that hydrolysis reactions going by the Aac1 mechanism are kinetically first-order can be obtained, at least in principle, for reactions in strongly acidic solution, because the activity of water varies significantly with the acid concentration. Graham and Hughes 7 showed that the hydrolysis of methyl benzoate in sulphuric acid at 20°C is first-order with respect to ester concentration, but zeroth-order with respect to water in concentrations up to 1 M. Leisten6 showed further that the first-order rate coefficient for this reaction is almost independent of the initial concentration of the ester, and thus ruled out the possibility that a bimolecular attack by bisulphate ion is involved, since the ester is completely protonated in 100% sulphuric acid and tfe concentration of bisulphate ion depends on the concentration of the ester, viz. 

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