In addition to the acid-dissociation constant, K_a, another measure of the stren

Question

In addition to the acid-dissociation constant, K_a, another measure of the strength of an acid is percent dissociation, determined by the following formula: Percent dissociation = [HA] dissoclated/[HA] initial times 100% Percent dissociation increases with increasing K_a. Strong acids, for which K_a is very large, dissociate completely (100%). For weak acids, the percent dissociation changes with concentration. the more diluted the acid is, the greater percent dissociation. A certain weak acid, HA, has a K_a value of 9.8times10^-7. Calculate the percent dissociation of HA in a 0.10 M solution. Express your answer as a percent using two significant figures. Calculate the percent dissociation of HA in a 0.010 M solution. Express your answer as a percent using two significant figures.

Explanation / Answer

part A

ka = c*x^2

x = degree of dissociation = (ka/c)^(1/2)

= ((9.87*10^(-7))/0.1)^(1/2)

   = 0.00314

percent dissociation   = x*100

   = 0.00314*100 = 0.314%

part B

ka = c*x^2

x = degree of dissociation = (ka/c)^(1/2)

= ((9.87*10^(-7))/0.01)^(1/2)

   = 0.00993

percent dissociation   = x*100

= 0.00993*100 = 0.993%

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