Salt solutions combined cation-anion effect

Salts of diazonium ions with certain arenesulfonate ions also have a relatively high stability in the solid state. They are also used for inhibiting the decomposition of diazonium ions in solution. The most recent experimental data (Roller and Zollinger, 1970 Kampar et al., 1977) point to the formation of molecular complexes of the diazonium ions with the arenesulfonates rather than to diazosulfonates (ArN2 —0S02Ar ) as previously thought. For a diazonium ion in acetic acid/water (4 1) solutions of naphthalene derivatives, the complex equilibrium constants are found to increase in the order naphthalene < 1-methylnaphthalene < naphthalene-1-sulfonic acid < 1-naphthylmethanesulfonic acid. The sequence reflects the combined effects of the electron donor properties of these compounds and the Coulomb attraction between the diazonium cation and the sulfonate anions (where present). Arenediazonium salt solutions are also stabilized by crown ethers (see Sec. 11.2). 

Recall that the conjugate base of a strong acid has virtually no affinity for protons as compared with that of the water molecule. For this reason strong acids completely dissociate in aqueous solution. Thus, when anions such as Cl and NOa are placed in water, they do not combine with and therefore have no effect on the pH. Cations such as and Na" from strong bases have no affinity for and no ability to produce H, so they too have no effect on the pH of an aqueous solution. Salts that consist of the cations of strong bases and the anions of strong acids have no effect on [H ] when dissolved in water. This means that aqueous solutions of salts such as KCl, NaCl, NaNOs, and KNO3 are neutral (have a pH of 7). 

The mutual effects of cations and anions on the water reorientation rates have also been studied. A comparison between solutions of 4 m aqueous LiCl, Csl, and CsF shows that there is a considerably larger amount of slow water in the CsF solutions, but hardly any effects in the former two salt solutions. The combination of a strongly hydrated ion (F ) with a weakly hydrated one (Cs ) is responsible for this effect according to Tiehooij et al. [124]. In aqueous alkali metal formate solutions, the time constant for the slow water was estimated as T j 20ps, and its fraction increased in the order Cs" < < NH < Li < Na (note the out-of-order position of Na" ). This,... 

Strategy First, decide what ions are present in the solution. Then classify each cation and anion as acidic, basic, or neutral, using Table 13.5. Finally, consider the combined effects of the two ions in each salt. 

Another important factor for coordination chemists is the general principle stated simply by Basolo solid salts separate from aqueous solution easiest for combinations of either small cation-small anion or large cation-large anion, preferably with systems having the same but opposite charges on the counter ions. Other factors governing solubility of salts are pH, interionic attraction, and the diverse ion effect, which will not be covered in detail here. 

A different effect occurs with the use of polycarboxy-lates in combination with zeolites. Small amounts of polycarboxylates or phosphonates can retard the precipitation of sparingly soluble calcium salts such as CaCOs (the threshold effect ). As they behave as anionic polyelectrolytes, they bind cations (counterion condensation), and multivalent cations are strongly preferred. Whereas the pure calcium salt of the polymer is almost insoluble in water, mixed Ca/Na salts are soluble, i.e. only overstoichiometric amounts of calcium ions can cause precipitation. Polycarboxylates are also able to disperse many solids in aqueous solutions. Both dispersion and the threshold effect result from the adsorption of the polymer on to the surfaces of soil and CaCOs particles, respectively. 

Ion exchange resins are cross-linked polymers that form salts with ions from aqueous solutions. The ion exchange resins that are used to effect such exchanges are of two types cation exchange and anion exchange resins. By using the two types either singly or in combination, it is relatively simple to alter, remove, or recover the ionic content of dilute solutions at will. 

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