Dissociation, percent

Thioglycolic acid, HSCH2CO2H, a substance used in depilatory agents (hair removers) has pKa = 3.42. What is the percent dissociation of thioglycolic acid in a buffer solution at pH = 3.0 ... 

From Table III we see that the difference between the free radical resonance energies of tribiphenylmethyl and triphenylmethyl is 0.07a. Hence X]/X2 = 37 = 2.2 X103. Ziegler and Ewald8 found that at 20°C the value of the dissociation constant for hexaphenylethane in benzene solution is 4.1 X10-4 and consequently we calculate for hexabiphenylethane a value of X = 2.2X103 X4.1 X 10 4 = 0.90. This value is probably too low as the compound is reported to be completely dissociated the error may not be large, however, since a dissociation constant of 0.90 would lead to 91 percent dissociation in 0.05M solution. 

Words that can be used as topics in essays 5% rale buffer common ion effect equilibrium expression equivalence point Henderson-Hasselbalch equation heterogeneous equilibria homogeneous equilibria indicator ion product, P Ka Kb Kc Keq KP Ksp Kw law of mass action Le Chatelier s principle limiting reactant method of successive approximation net ionic equation percent dissociation pH P Ka P Kb pOH reaction quotient, Q reciprocal rule rule of multiple equilibria solubility spectator ions strong acid strong base van t Hoff equation weak acid weak base... 

IQ, the acid dissociation constant, for an acid is 9 x 10-4 at room temperature. At this temperature, what is the approximate percent dissociation of the acid in a 1.0 M solution ... 

The percent dissociation of a weak acid is the fraction of acid molecules that dissociate compared with the initial concentration of the acid, expressed as a percent. (Some chemists refer to percent dissociation as percent of dissociation.] The percent dissociation depends on the value of Ka for the acid, as well as the initial concentration of the weak acid. The following Sample Problems show how to solve problems that involve percent dissociation. 

You need to find iQ and the percent dissociation for propanoic acid. 

Step 5 Calculate the percent dissociation by expressing the fraction of molecules that dissociate out of 100. 

The value of and the percent dissociation are reasonable for a weak acid. 

Calculate the pH of a sample of vinegar that contains 0.83 mol/L acetic acid. What is the percent dissociation of the vinegar ... 

Ka = 6.3 X 10 ). Its structure is shown below. Calculate the pH and the percent dissociation of each of the following solutions of benzoic acid. Then use Le Chatelier s principle to explain the trend in percent dissociation of the acid as the solution becomes more dilute. 

When the pH of the solution and the pKa are equal, 50% of the acid will have dissociated into ions. The percent dissociation of an acid or base can be calculated if the pH of the solution and the pKa of the compound are known (Guswa et al., 1984) ... 

A quantitative measure of the degree of dissociation is given by the equilibrium constant for the acid or base. The higher the equilibrium constant is, the greater the percent dissociation of the acid or base. Therefore, a higher equilibrium constant means a stronger acid or base. Equilibrium constants, K and K, are listed for several com-mon weak acids and bases in Table 13.4. 

Percent dissociation The ratio of the amount of a substance that is dissociated at equilibrium to the initial concentration of the substance in a solution, multiplied by 100. 

In addition to Ka, another useful measure of the strength of a weak acid is the percent dissociation, defined as the concentration of the acid that dissociates divided by the initial concentration of the acid times 100% ... 

Take, for example, the 1.00 M acetic acid solution in Problem 15.14a. If you solved that problem correctly, you found that 1.00 M CH3CO2H has an H30 + concentration of 4.2 X 10 3 M. Because [H30+] equals the concentration of CH3C02H that dissociates, the percent dissociation in 1.00 M CH3C02H is 0.42% ... 

In general, the percent dissociation depends on the acid and increases with increasing value of Ka. For a given weak acid, the percent dissociation increases with increasing dilution, as shown in Figure 15.8. The 0.0100 M CH3C02H solution in Problem 15.14b, for example, has [H30+] = 4.2 X 10 4 M, and the percent dissociation is 4.2% ... 

FIGURE 15.8 The percent dissociation of acetic acid increases as the concentration of the acid decreases. A 100-fold decrease in [CH3C02H] results in a 10-fold increase in the percent dissociation. 

Phenol (C5H5OH) is a weak acid used as a general disinfectant and in the manufacture of plastics. Calculate the pH and the concentrations of all species present (H30+,C6H50, C6H50H, and OH-) in a 0.10 M solution of phenol (Ka = 1.3 X 10-10). Also calculate the percent dissociation. 

A typical aspirin tablet contains 324 mg of aspirin (acetylsalicylic acid, C9H8O4), a monoprotic acid having Ka = 3.0 X 10-4. If you dissolve two aspirin tablets in a 300 mL glass of water, what is the pH of the solution and the percent dissociation ... 

Calculate the percent dissociation in each of the following solutions. What is the quantitative relationship between the percent dissociation and the concentration of the acid What is the quantitative relationship between the percent dissociation and the value of Ka ... 

Beginning with the equilibrium equation for the dissociation of a weak acid HA, show that the percent dissociation varies directly as the square root of Ka and inversely as the square root of the initial concentration of HA when the concentration of HA that dissociates is negligible compared with its initial concentration. 

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