Ammonia ionization constant

The volatility of ammonia at ppm levels can be calculated from the ionization constant of ammonia combined with volatility data measured at higher concentrations of ammonia. 

As a base NH2 OH resembles ammonia and other amines. Although its basic ionization constant is considerably lower than that of NH3 and N2 H4 it forms a series of ammonia-like inorg and org salts. In general, these salts are more stable than the parent base. Therefore, hydroxylamine is usually prepd and shipped in the free form of its salts... 

This ionization constatil in terms of activities is called the true or thermodynamic ionization constant. It docs not differ too much from the K in Eq. (14) for sufficiently low ionic strengths. The two differ more markedly for appreciable ionic strengths. Nuw suppose a salt with no common ion is added to the solution. The ionic strength of the solution will be increased. This increase in ionic strength causes a decrease in the activity coefficients of the ions except in very concentrated solutions. Thus for K of Eq. (18) to stay constant the concentrations of the ions must increase to offset the decrease in their activity coefficients. The ammonia must therefore increase in ionization and K as defined by Eq. (14) must increase. This is known as a salt effect. 

Comparing these two equilibria, it is seen that methanol is a much weaker acid than ammonium ion by about 107 (i.e., the pKA of methanol is larger by about seven logarithm units than the pKa of ammonium) thus its conjugate base methoxide should be a much stronger base than ammonia by 107. Either method of analyzing the situation is acceptable, and each gives the same relative basicities without die need for two sets of ionization constants, Aa and K. ... 

Hydrogen Exchange in Liquid Ammonia and Ethanol at 120° and Ionization Constants of Organic Compounds... 

For a classical molecular weak base, such as ammonia, the reaction NH3 -i-HjO NH4 -1- OH leads to equations identical to (3-27) or (3-28) with KJK replaced by K, the classical ionization constant of a weak base. 

The ammonia can be distilled into an excess of standard sulfuric acid, and the excess determined by back titration. Preferably, the distilled ammonia can be absorbed into a solution of boric acid or other weak acid. Direct titration of the boric acid distillate with standard acid, using bromophenol blue, with a blank determination gives excellent results. As a routine method for determining traces of nitrogen, Milner and Zahner distilled the ammonia into a dilute boric acid solution. Urban suggested an aqueous solution of p-hydroxybenzoic acid (ionization constant 2.9 X 10 ) as an ammonia-absorbing solution. 

Write the base ionization constant expression for ammonia. 

Now let us consider the behavior of ammonia in aqueous solutions. The reaction of ammonia with water and its ionization constant expression are... 

Soil and water temperature (Figure 8.33e) Assuming relatively high ammonia concentrations and alkaline pH conditions, an increase in temperature increases the conversion of ammonium ions to ammonia. The dissociation constants for ammonium-ammonia equilibrium and water ionization constants are influenced by the temperature (Table 8.4). Thus, the fraction of undissociated ammonia present in the water column or soil pore water is regulated by temperature. In addition, temperature also affects the solubility of ammonia in the water. Thus, at higher temperature, solubility of ammonia in water is less and diffusion is greater, which promotes increased rate of ammonia volatilization. The Ammonia volatilization rate was shown to increase approximately from 1.3 to 3.5 times for each 10°C rise in temperature. 

Effect of Temperature on Solubility and Dissociation Constants for Ammonia and Ionization Constants for Water... 

Just like the acid-ionization constant, there is also the base-ionization constant. Consider the ionization of ammonia in water. 

Derive an expression for the relaxation time of the given mechanism and determine as many of the individual rate constants as possible. The ionization constant of methyl-ammonia is 1.22 X 10" M and that of water is 0.63 x 10" " M at 19°C... 

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