Percent ionization, calculation

A 0.040 M solution of a monoprotic acid is 14 percent ionized. Calculate the ionization constant of the acid. 

Show by calculation that when the concentration of a weak acid decreases by a factor of 10, its percent ionization increases by a factor of 10l/2. 

When we know the pH and initial concentration of a weak acid solution, we can calculate the percent ionization quickly. Eor the solution of HE in Example, we have pH = 1.92, from which [H3 O ]gq= 1.2x 10 M and we have [HFUal - 0-25 M. Substituting, we find... 

To determine percent ionization, we need to know the equilibrium concentration of hydronium ions. This requires an equilibrium calculation, for which we follow the seven-step method. We need to set up the appropriate equilibrium expression and solve for [H3 O, after which we can use Equation to... 

Acids and bases are a big part of organic chemistry, but the emphasis is much different from what you may be familiar with from your general chemistry course. Most of the attention in general chemistry is given to numerical calculations pH, percent ionization, buffer problems, and so on. Some of this returns in organic chemistry, but mostly we are concerned with the roles that acids and bases play as reactants, products, and catalysts in chemical reactions. We ll start by reviewing some general ideas about acids and bases. 

Consider a solution of a monoprotic weak acid with acidity constant Ka. Calculate the minimum concentration, C, for which the percent ionization is less than 10%. 

Notice the diversity in structure of lhe.se proton dunurs. They include the classical hydrochloric acid (reaction a). Ihc weakly acidic dihydrogen phosphate anion (reaction b). the ammonium cation as is found in ammonium chloride (reaction c), the carboxylic acetic acid (reaction d). Ihc cnolic form of phenobarbital (reaction e), Ihe carboxylic acid moiety of indomelhacin (reaction j), Ihc imidc of saccharin (reaction g). and the prolonaied amine of ephedrine (reaction h). Because all are proton donors, they mu.st be treated as acids when calculating the pH uf a solution or percent ionization of the drug. At the same lime, as nuted below, there are important differences in the pharmaceutical properties of ephedrine hydrochloride (an acid salt of an amine) and lho.se of indomelhacin. phenobarbital. or saccharin. 

Lactic acid, C2H4(OF[)COOH, is found in sour milk. It is also formed in muscles during intense physical activity and is responsible for the pain felt during strenuous exercise. It is a weak monoprotic acid and therefore a weak electrolyte. The freezing point of a 0.0100 m aqueous solution of lactic acid is —0.0206°C. Calculate (a) the / value and (b) the percent ionization in the solution. 

X = 0.0011 m = molality of the acid that ionizes We can now calculate the percent ionization. 

A 0.0100 m formic acid solution freezes at —0.0209°C. Calculate the percent ionization of HCOOH in this solution. 

Calculate the percent ionization of a 0.10 M solution of acetic acid. 

The pKa values are also temperature-dependent, often in a nonlinear and unpredictable way. Samples measured by potentiometry are therefore held at a constant temperature bath and therefore, pK value should be quoted at a specific temperature. Often a temperature of 25°C is chosen to reflect room temperature whereas this may be quite different from the body temperature. Percent ionization at different temperatures can be calculated as ... 

Let us calculate the dipole moment of a hypothetical, 100 percent ionized Li H ion pair with a separation of 159.6 pm, i.e., assuming a point charge at each nucleus. 

Calculate the molar concentration at which an acetic acid solution is 2.0 percent ionized. Ka for... 

The acetic acid, which is only a few percent ionized, depending on the concentration, is neutralized to water and an equivalent amount of the salt, sodium acetate. Before the titration is started, we have 0.1 MHOAc, and the pH is calculated as described for weak acids in Chapter 7. Table 8.2 summarizes the equations... 

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