In addition to the acid-dissociation constant, Ka, another measure of the streng

Question

In addition to the acid-dissociation constant, Ka, another measure of the strength of an acid is percent dissociation, determined by the following formula: Percent dissociation = [HA] dissociated/[HA] initial times 100% Percent dissociation increases with increasing Ka Strong acids, for which Ka 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 Ka value of 4.7 times 10-7. Calculate the percent dissociation of HA in a 0.10 M solution. Express your answer as a percent using two significant figures. % My Answers Give Up Review Part Calculate the percent dissociation of HA in a 0.010 M solution. Express your answer as a percent using two significant figures. % My Answers Give Up Review Part

Explanation / Answer

since the electrolyte is weak as its dissociation constant Ka is small....

so using ostwalds dilution law ...

degree of dissociation = square root of Ka/M

where Ka = 4.7 X 10^-7

A)

and M = 0.1 M

so degree of dissociation = square root of 4.7 X 10^-7/0.1

degree of dissociation = 2.16*10^-3

percentage dissociation = 2.16*10^-3 X 100 = 0.2167

B)

and M = 0.010 M

so degree of dissociation = square root of 4.7 X 10^-7/0.010

degree of dissociation = 6.85*10^-3

percentage dissociation = 6.85*10^-3 X 100 = 0.68556

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