Aqueous solutions dissociated ions

The dissociation of an acidic or basic compound in aqueous solution produces ions that interact with water. The pH of the aqueous solution is determined by the position of equilibrium in reactions between the ions that are present in solution and the water molecules. Pure water contains a few ions, produced by the dissociation of water molecules ... 

One characteristic difference between organic and aqueous solution, therefore, lies in the cation-anion relationship. In aqueous solution the ions are dissociated from each other, the cation s coordination shell is saturated with water, and the anion and cation interact primarily electrostatically. In organic solution they are covalently associated to give a neutral molecular species. 

Strong acids in aqueous solution dissociate completely into anions and protons. The concentration of hydrogen ion [H+] is therefore equal to the total concentration CHA of the acid HA that is added to the solution. Thus the pH of the solution of a strong acid is simply —log CHa-... 

Many reactions, particularly those that involve ionic compounds, take place in aqueous solution. Substances whose aqueous solutions contain ions and therefore conduct electricity are called electrolytes. Ionic compounds, such as NaCl, and molecular compounds that dissociate substantially into ions when dissolved in water are strong electrolytes. Substances that dissociate to only a small extent are weak electrolytes, and substances that do not produce ions in aqueous solution are nonelectrolytes. Acids dissociate in aqueous solutions to yield an anion and a hydronium ion, H30 +. Those acids that dissociate to a large extent are strong acids those acids that dissociate to a small extent are weak acids. 

You know that ions are present in an aqueous solution of an acid. These ions result from the dissociation of the acid. An acid that dissociates completely into ions in water is called a strong acid. For example, hydrochloric acid is a strong acid. All the molecules of hydrochloric acid in an aqueous solution dissociate into H+ and Cl ions. The H+ ions, as you know, bond with surrounding water molecules to form hydronium ions, H30+. (See Figure 10.6.) The concentration of hydronium ions in a dilute solution of a strong acid is equal to the concentration of the acid. Thus, a 1.0 mol/L solution of hydrochloric acid contains 1.0 mol/L of hydronium ions. Table 10.4 lists the strong acids. 

As you know, all aqueous solutions contain ions. Even pure water contains a few ions that are produced by the dissociation of water molecules. Remember The double arrow in the equation shows that the reaction is reversible. The ions recombine to form water molecules. 

From the time of his first paper on the coordination theory in 1893 30, 98), Werner had been aware of the role of the solvent in electrolytic dissociation and had insisted that hydration, i.e., aquation, preceded ionization. In his paper, Zur Theorie der Basen" (1907) 91), he applied this concept to his new definition of a base Any compound, which with water forms a hydrate which dissociates in aqueous solution into a complex positive ion and hydroxyl ions, is an anhydro base.. . . Aquo bases, or simply bases, are water addition compounds which in aqueous solution dissociate into hydroxyl ions." For example ... 

Like the aqueous solution of HCI you saw in Figure 10-11, sodium hydroxide (NaOH) in an aqueous solution dissociates into its ions sodium (Na+) and hydroxide (OH ). Copper chloride (CUCI2) also dissociates into its ions,... 

Hydrido complexes. With NH3 or amines, quite stable octahedral hydrido complexes can be obtained for rhodium. Thus the reduction of RhCl3 3H20 inNH40H by Zn in presence of SO leads to the white, air-stable, crystalline salt [RhH(NH3)5]S04. In aqueous solution the ion dissociates [RhH(NH3)5]2+ + HzO = [RhH(NH3)4H,012+ + NH3 2 x 10"4... 

The complexes of monodentate oxygen ligands are less stable than those of chelates and tend to dissociate in aqueous solution the ions associate in aqueous solution with both nitrate and sulfate to give species such as MNOj +, MS04, etc., and anionic carbonate complexes are known. Many crystalline compounds or salts have been obtained from the lanthanide salts in ethanolic solutions (a) with hexamethylphosphoramide,27 which appears to give 6-coordinate species, [M(HMPA)6](C104)3, (b) with triphenyl-... 

Any substance whose aqueous solution contains ions is called an electrolyte. Any substance that forms a solution containing no ions is a nonelectrolyte. Electrolytes that are present in solution entirely as ions are strong electrolytes, whereas those that are present partly as ions and partly as molecules are weak electrolytes. Ionic compounds dissociate into ions when they dissolve, and they are strong electrolytes. The solubility of ionic substances is made possible by solvation, the interaction of ions with polar solvent molecules. Most molecular compounds are nonelectrolytes, although some are weak electrolytes, and a few are strong electrolytes. When representing the ionization of a weak electrolyte in solution, half-arrows in both directions are used, indicating that the forward and reverse reactions can achieve a chemical balance called a chemical equilibrium. 

Like other acids, phosphoric acid in aqueous solutions dissociates into ions according to... 

Carbonic acid in aqueous solutions dissociates to form the bicarbonate ion (hCO and a hydrogen ion (H+). 

Metal ions with a charge of +2 or higher are acidic. In aqueous solution, metal ions bind several water molecules to form M(H20)"in which electrons from oxygen are shared with the metal ion. Many metal ions bind w = 6 water molecules, but large metal ions can bind more water. A proton can dissociate from M(H20)" to reduce the positive charge on the metal complex. 

Some molecular compounds can also form ions in solution. Usually such compounds are polar. Ions are formed from solute molecules by the action of the solvent In a process called ionization. The more general meaning of this term is the creation of ions where there were none. Note that ionization is different from dissociation. When an ionic compound dissolves, the ions that were already present separate from one another. When a molecular compound dissolves and ionizes in a polar solvent, ions are formed where none existed in the undissolved compound. Like all ions in aqueous solution, the ions formed hy such a molecular solute are hydrated. The energy released as heat during the hydration of the ions provides the energy needed to break the covalent bonds. 

The situation changes completely when the dissolved chains are polyelectrolytes rather than electrically neutral macromolecules. Polyelectrolytes in a, usually aqueous, - solution dissociate in polyions with fixed positive or negative charges and mobile counter-ions. The arising Coulomb forces are much stronger than the van der Waals forces and result in quite unusual solution properties. 

Problem For the cell reaction of hydrogen gas and chlorine gas to produce HCl in aqueous solution (dissociated into ions), how does temperature affect the cell voltage given that the standard state molar entropy for the products is 56.3 J moH ... 

Here, we describe the application and typical modelling results for a G model (MSA-NRTL) as well as for an EOS (ePC-SAFT). In addition to strong electrolytes which are almost fully dissociated, we also consider some weak electrolytes (acids like HE or ion-paired electrolytes) that do only partially dissociate in aqueous solution. Here, ion pairing is accounted for by an association/dissociation equilibrium between the ion pair and the respective free ions in solution. 

Precipitation Reactions. Exchange reactions involve ionic compounds. Some ionic compounds are soluble in water and others are not. When an ionic compound dissolves in water, it dissociates into ions when an ionic compound is completely converted to ions and forms an aqueous solution, it is referred to as a strong electrolyte. An electrolyte is a substance whose aqueous solution contains ions and conducts electricity. 

A special corrverrtion exists concerning the free errergies of ions in aqueous solution. Most themrodyrramic iirfomration about strong (fiilly dissociated) electrolytes in aqueous solutions comes, as has been seen, from measiiremerrts of the eirrf of reversible cells. Sirrce tire ions in very dilute solution (or in the hypothetical... 

In a weak electrolyte (e.g. an aqueous solution of acetic acid) the solute molecules AB are incompletely dissociated into ions and according to the familiar chemical equation... 

The bond dissociation energy of the hydrogen-fluorine bond in HF is so great that the above equilibrium lies to the left and hydrogen fluoride is a weak acid in dilute aqueous solution. In more concentrated solution, however, a second equilibrium reaction becomes important with the fluoride ion forming the complex ion HFJ. The relevant equilibria are ... 

Phenyldiazonium chloride and other similar diazonium compounds are very soluble in water, are completely insoluble in ether and other organic solvents, and are completely dissociated in aqueous solution to organic cations and inorganic anions (e.g., chloride ions) a convenient formulation is therefore, for example, CjHjNj+CP. 

Strong and Weak Bases Just as the acidity of an aqueous solution is a measure of the concentration of the hydronium ion, H3O+, the basicity of an aqueous solution is a measure of the concentration of the hydroxide ion, OH . The most common example of a strong base is an alkali metal hydroxide, such as sodium hydroxide, which completely dissociates to produce the hydroxide ion. 

The equihbrium constant of this reaction is 5.4 x 10 at 25°C, ie, iodine hydrolyzes to a much smaller extent than do the other halogens (49). The species concentrations are highly pH dependent at pH = 5, about 99% is present as elemental at pH = 7, the and HIO species are present in almost equal concentrations and at pH = 8, only 12% is present as and 88% as HIO. The dissociation constant for HIO is ca 2.3 x 10 and the pH has tittle effect on the lO ion formation. At higher pH values, the HIO converts to iodate ion. This latter species has been shown to possess no disinfection activity. An aqueous solution containing iodate, iodide, and a free iodine or triodide ion has a pH of about 7. A thorough discussion of the kinetics of iodine hydrolysis is available (49). 

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