Percentage ionization

Percentage ionization is the percentage expression of the degree of ionization. What is the degree of ionization of a weak acid Degree of ionization is the fractional amount of the weak acid that gets ionized. 

Find the degree of ionization of 0.1 Msolution of acetic acid (CH COOH). Also find the pH of the solution. 

We will logically dissect the events that lead to the dissociation. At first we do not have any and CHjCOO ions. Let s say we have a unit volume (a liter) of acetic acid and x Af (mol/L) of it was ionized. We can represent the equation as follows  

With the concentrations at equilibrium we can substitute the concentrations in the acid-ionization constant expression. 

Even though this has to be solved using a quadratic equation, we can skip that elaborate process by making some chemically acceptable assumptions. Since the acid-ionization constant is very small, we can assume the same with the value of X. So the expression changes as follows. For the MCAT, you won t be given problems that require extensive calculations. The problems will test mostly concepts, and when calculations are involved the numbers will usually be manageable ones. 

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A. Speransky, the vap. press, p of a sat. soln. of sodium nitrate at T° K. can be represented by Bertrand s formula log p=7 5172+50 log [(T—74 8)/T], The mol. wt. calculated from the lowering of the vap. press, corresponds with a very large percentage ionization, and the decrease which occurs with an increasing cone, shows that there is a disturbing facto —hydration. Similar remarks apply to the results with potassium nitrate soln. G. Tammann has studied the lowering of the vap. press, of water, at 100°, by soln. of the alkali nitrates. E. B. R. Prideaux studied the vap. press, of soln. of sodium and potassium nitrates, and studied the deliquescence and drying of these salts. 

Percentage concentration. Equivalents per litre. Specific resistance. Specific conductivity. Molecular conductivity. Percentage ionization. 

The temp. coeS. is negative at the higher temp, and positive at the lower temp. this also agrees with the observations of A. N. Campbell on the conductivity of phosphoric acid at 0°, and those of P. Kohlrausch at 18°. A. A. Noyes and coworkers calculated that the percentage ionization, a, of soln. of phosphoric acid when the cone, are expressed in milli-formula-weights per litre at 4°. 

Figure 2.1 Nomogram relating pK values of acids to percentage ionization at various solutions pH values. (Reprinted from Ref. 17 with permission.)...

M. F. Hopgood, Nomogram for calculating percentage ionization of acids and bases, J. Chromatogr., 47A5 (1970). 

Type of salt Percentage ionization in 0.1 equivalent solution... 

Find the percentage ionization of acetic acid in molal solution. Take the value of the ionization constant as 0.000018 and solve the quadratic equation by the method of approximation. 

What Is the percentage ionization ol ephednna HCI lpKj,9.6) In an Intestinal Iract buttered at pH 8.0 (see example D Use Equation 2-14 because this is a BH add... 

Local anesthetics are weak bases and are usually made as HCl salts which are soluble and stable in water. The pK of the compound determines when the ionized and unionized forms are equal (see Table 1 for values of pK and percentage ionization at pH 7.4). The time of onset of the block is related to diffusion of the anesthetic into the nerve fiber, which occurs only in the unionized, or non-proton-ated form. Sodium bicarbonate is often added (1 mEq(lOml) lidocaine or 0.1 mEq(lOml) ... 

Figure 7. Percentage ionization of iron additives predicted by buffers and actually found in foods. El, elemental iron FS, ferrous sulfate FOP, ferric orthophosphate SFEDTA, sodium ferric EDTA trihydrate. (Reproduced, with permission, from Ref. 43. Copyright 1981, Institute of Food Technologists.)...

Fig. 2.6. Calculation of percentage ionization of amobarbital. Calculation indicates that 80% of the molecules are in the acid (or protonated) form, leaving 20% in the conjugate base (ionized) form.

Calculate the percentage ionization of phenylpropanolamine at pH 2.0, 5.5, and 8.0. Compare these results with those obtained in Problem 1. 

Calculate the percentage ionization of sulfacetamide in the stomach, duodenum, and ileum. Draw the structure of the predominate form of the drug in each tissue. 

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