Hydronium ion in water

Specific acid catalysis is catalysis by the hydronium ion (in water) or the lyonium ion in general. Acid-catalyzed ester hydrolysis is an example. 

Recall that an Arrhenius acid is a compound that produces hydronium ions in water and an Arrhenius base is a compound that produces hydroxide ions in water. 

Interpreting the equation from right to left, the conjugate base of the acid, A , has no tendency to combine with hydronium ions in water. Therefore, it is a weak base. In fact, the anion that is formed by a strong acid is a much weaker base than water, so it does not react with water. Consequently, when a salt that contains the anion of a strong acid is dissolved in water, the anion has no effect on the pH of the solution. 

However, we should remember that H+ are present as hydronium ions in water, so we should add two H20 molecules to each side of this equation to obtain... 

Pure water at 25 °C has a pH of 7.00. This means that the concentration of hydronium ions in water must be 10-7 mol dm-3 (of course, it is actually the other way round the hydronium ion concentration in pure water is 10-7 mol dm-3 hence its pH is 7.00). Hydronium ions in pure water can arise only from the self-dissociation or autoprotolysis of water. 

Basicity can also be expressed with acidity constants. With amines, Ka defines the equilibrium in the direction of the ammonium salt ionizing to the free amine and hydronium ion in water. Since this is the opposite of the definition of Kb, small Ka s and large pKa s mean strong basicity. 

When the concentration of hydroxide and hydronium ions in water are muitipiied together, the product is fixed at that temperature. 

FIGURE 8.8 The hydronium ion in water is stabilized by hydrogen bonds with water... 

The H3O ion is the hydronium ion. In water, H ions always associate with H2O molecules. Chemists often use H aq) and H30 (aq) interchangeably, however, to refer to the same thing—a hydronium ion. 

Reference was made above to involvement of the solvent in a reaction as catalyst. In a protic solvent, reaction may be catalyzed by the solvonium ion only (the hydronium ion in water). This is specific hydrogen-ion catalysis. On the other hand, the reaction may be catalyzed by any acidic species present in the solution (general acid catalysis). The solvent molecule itself may be a catalyst. Base catalysis, similarly, may be... 

The H30 ion is called the hydronium ion. In water, ions always associate with H2O molecules to form hydronium ions and other associated species with the general formula H(H20) . For example, an ion can associate with two water molecules to form H(H20)2, with three to form H(H20)3, and so on. Chemists often use and... 

Since metals evolve hydrogen when reacting with either hydronium ions in water or ammonium ions in ammonia,... 

It is customary to consider that the hydrogen ion occurs as a solvated proton, for example, the hydronium ion in water or the ammonium ion in liquid ammonia ... 

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