Salt solutions anion reaction with water

The corrosivity of a salt solution depends upon the nature of the ions present in the solution. Those salts which give an alkaline reaction will retard the corrosion of the iron as compared with the action of pure water, and those which give a neutral reaction will not normally accelerate the corrosion rate appreciably except in so far as the increased conductivity of the solution in comparison with water permits galvanic effects to assume greater importance. Chlorides are dangerous because of the ability of the anions to penetrate otherwise impervious barriers of corrosion products. 

STRATEGY The solution contains N02 , a base, so we expect the pH to be i higher than that of nitrous acid alone. The K+ ion has no protons to donate j and cannot accept a proton, so it has no measurable effect on the pH of the ] solution. Identify the proton transfer equilibrium and use it to find the pH by means of an equilibrium table. Consider the initial molarity of HN02 (before reaction with water) to be 0.500 mol-L1. Because nitrite ions have also been added to the solution, set their initial molarity equal to the molar-5 ity of added salt (each KN02 formula unit supplies one N02 anion). Then proceed as described in Toolbox 10.1. Because the concentrations of the 1 added ions are much higher than 10-7 mol-L 1, we assume that we can S ignore the contribution to the pH from the autoprotolysis of water. 

The acidic ammonium chloride solution is an example of the second category of salts, where the NH4 cation is the conjugate acid of the weak base NH3, and the Cl anion is the conjugate base of the strong acid HCl. The hydrolysis reaction is given in Equation 9.47, where H30 is used to emphasize the reaction with water ... 

The variation in pH values can be accounted for by examining the ions formed when each of these salts dissociates. If the ions formed are from weak acids or bases, they react chemically with the water molecules, and the pH of the solution will have a value other than 7. A reaction between water molecules and ions of a dissolved salt is hydrolysis. If the anions react with water, the process is anion hydrolysis and results in a more basic solution. If the cations react with water molecules, the process is cation hydrolysis and results in a more acidic solution. 

J.I3 Na As04 is a salt of a weak base that can accept more than one proton, (a) Write the chemical equations for the sequential proton transfer reactions of the anion with water. Identify the acid and the base in each reaction, (b) If 35.0 g of Na3As04 is dissolved in water to make 250.0 ml. of solution, how many moles of sodium cations are in the solution ... 

To determine whether the solution of a salt will be acidic, basic, or neutral, we must consider both the cation and the anion. First we examine the anion to see whether it is the conjugate base of a weak acid. If the anion is neither acidic nor basic, we examine the cation to see whether it is an acidic metal ion or the conjugate acid of a weak base. If one ion is an acid and the other a base, as in NH4F, then the pH is affected by the reactions of both ions with water and both equilibria must be considered, as in Section 10.19. 

The pH of the aqueous solution of an amphiprotic salt is equal to the average of the pKlts of the salt and its conjugate acid. The pH of a solution of a salt of the final conjugate base of a polyprotic acid is found from the reaction of the anion with water. 

If a salt contains the cation of a strong base and the anion of a strong acid, neither ion reacts with water. Therefore, the solution has a pH of 7. Sodium chloride is an example of such a salt. It is formed by the reaction of sodium hydroxide (a strong base) and hydrochloric acid (a strong acid). Salts of strong bases and strong acids dissolve in water and form neutral solutions. 

Hydrolysis is the general term of the chemical reaction of anions with water. Salts of weak acids and bases hydrolyze in aqueous solutions. 

With the knowledge that 14 can activate aldehydes in 1, the role of 1 in the reaction was explored further. Specifically, the relative rates of C—H bond activation and guest ejection, and the possibility of ion association with 1, were investigated. The hydrophobic nature of 14 could allow for ion association on the exterior of 1, which would be both cn t h al pi cal I y favorable due to the cation-it interaction, and entropically favorable due to the partial desolvation of 14. To explore these questions, 14 was irreversibly trapped in solution by a large phosphine, which coordinates to the iridium complex and thereby inhibits encapsulation. Two different trapping phosphines were used. The first, triphenylphosphine tris-sulfonate sodium salt (TPPTS), is a trianionic water-soluble phosphine and should not be able to approach the highly anionic 1, thereby only trapping the iridium complex that has diffused away from 1. The second phosphine, l,3,5-triaza-7-phosphaadamantane (PTA), is a water-soluble neutral phosphine that should be able to intercept an ion-associated iridium complex. 

The pH of a solution of a salt of the final conjugate base of a polyprotic acid is found from the reaction of the anion with water. 

Related ammonium salts derived from amines, such as [CH3NH3]C1, [(CH3)2NH2]C1, and [(CH3)3NH]C1, also give acidic solutions because they too have cations with at least one dissociable proton. The pH of a solution that contains an acidic cation can be calculated by the standard procedure outlined in Figure 15.7. For a 0.10 M NH4C1 solution, the pH is 5.12. Although the reaction of a cation or anion of a salt with water to produce H30+ or OH - ions is sometimes called a salt hydrolysis reaction, there is no fundamental difference between a salt hydrolysis reaction and any other Bronsted-Lowry acid-base reaction. 

A solution of N-(4-pyridinyl)-lH-indol-l-amine (6 g) in 25 ml of dimethylformamide was slowly added to an ice-cooled suspension of NaH (1.3 g of 60% NaH dispersion in mineral oil was washed with hexanes, the liquid was decanted and the residual solid was dispersed in 5 ml of dimethylformamide). After anion formation, a solution of 1-bromopropane (4 g) in 5 ml of dimethylformamide was added. After one hour of stirring at ambient temperature, the reaction mixture was stirred with ice-water and extracted with dichloromethane. The organic extract was washed with water and saturated sodium chloride solution, was dried over anhydrous magnesium sulfate, filtered and concentrated to 8 g of oil. This oil was purified by HPLC (silica, ethyl acetate) and thereafter by column chromatography (alumina, ether) to give 6.4 g oil. This oil was converted to the maleate salt and recrystallized from methanol/ether to give 6.8 g of crystals, m.p. 115-116°C. 

If we replace the chloride ion in the above reaction with an anion such as nitrate or sulfate that is energetically much more difficult to oxidize, the water is oxidized instead. Electrolysis of a solution of sulfuric acid or of a salt such as NaN03 results in the decomposition of water at both electrodes ... 

Besides the effect of the electrode materials discussed above, each nonaqueous solution has its own inherent electrochemical stability which relates to the possible oxidation and reduction processes of the solvent,the salts, and contaminants that may be unavoidably present in polar aprotic solutions. These may include trace water, oxygen, CO, C02 protic precursor of the solvent, peroxides, etc. All of these substances, even in trace amounts, may influence the stability of these systems and, hence, their electrochemical windows. Possible electroreactions of a variety of solvents, salts, and additives are described and discussed in detail in Chapter 3. However, these reactions may depend very strongly on the cation of the electrolyte. The type of cation present determines both the thermodynamics and kinetics of the reduction processes in polar aprotic systems [59], In addition, the solubility product of solvent/salt anion/contaminant reduction products that are anions or anion radicals, with the cation, determine the possibility of surface film formation, electrode passivation, etc. For instance, as discussed in Chapter 4, the reduction of solvents such as ethers, esters, and alkyl carbonates differs considerably in Li or in tetraalkyl ammonium salt solutions [6], In the presence of the former cation, the above solvents are reduced to insoluble Li salts that passivate the electrodes due to the formation of stable surface layers. However, when the cation is TBA, all the reduction products of the above solvents are soluble. 

In wet PC or EC solutions with TBAP, the inorganic carbonate anion C032-becomes a major reduction product. EUR spectra of the major reduction product of the wet PC/TBAP solution, precipitated as a Li salt, is characteristic of Li2C03 (two peaks around 1500 and 1480 cnE1 and a sharp peak around 880 cm-1). It should be emphasized, however, that FTIR measurements conducted during electrolysis proved that the R0C02 species are present as intermediates on the reaction path [3], Thus, in the case of wet EC or PC/TBAP solutions, the solvents are reduced to R0C02Li species, as described in Scheme 4, and these solvents reduction products further react with water, as shown in Scheme 5. 

From this you can see that the cation from the salt comes from the base and the anion comes from the acid. Salts can act as Bronsted-Lowry acids or bases to produce solutions that are acidic or basic. The salts react with water in a reaction known as hydrolysis to yield either a conjugate acid and a hydroxide ion or a conjugate base and a hydrogen (hydronium) ion. If you know the origins of the components of a salt, you can make some predictions about the pH of the solution formed from a hydrolysis of a salt ion. 

The salt is insoluble in water and in solvents such as hexane or toluene and may, therefore, be separated from dicobalt octacarbonyl which is readily soluble in hydrocarbon solvents. Thus, two analyses and the requisite simple calculations permit the estimation of both [Co(CO)4]2 and Co(CO)4-. A convenient apparatus for the determination has been described (Orchin and Wender, 41). Alternately, the concentration of dicobalt octacarbonyl may be measured by adding pyridine to the solution containing the carbonyls. All the dimer is converted to the anion with the evolution of carbon monoxide according to Equation (2). After gas evolution has ceased, a solution of iodine in pyridine may be added. This reagent is similar to aqueous iodine and liberates all the carbon monoxide in the anion originally present as well as that formed from the dimer by reaction with pyridine. 

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