Concept explainers
Interpretation:
The concentration of the
Concept introduction:
When an acid is dissolved in water, it donates a proton to water, producing hydronium ions and its conjugate base. In most cases, only a fraction of the dissolved acid dissociates (donates a proton to water), and an equilibrium between the products and undissociated acid is set up. The concentrations of the undissociated acid and the products depend on the strength of the acid, and are determined by the acid dissociation constant Ka. The difference between the initial concentration of the acid, and the concentration of at equilibrium divided by the initial concentration is fractional dissociation, which when multiplied by 100 gives the percent dissociation.
Answer to Problem 6.40P
The concentration of the
The acid percent dissociation is
Explanation of Solution
The initial concentration of phenol is calculated as
Phenol dissociation in aqueous solution can be represented as:
The dissociation constant of phenol is
The equilibrium concentration is calculated by setting up a chart listing the concentrations of the acid and dissociation products as below. The fraction of the initial concentration that dissociates, equal to the difference in initial and equilibrium concentrations, is assumed to be ‘x’.
Initial | ||||
Change | ||||
Equilibrium |
The acid dissociation constant expression can then be written in terms of the equilibrium concentrations from the chart. Substituting the values of initial concentration and the acid dissociation constant, the expression is solved for the value of ‘x’.
‘x’ is also the concentration of hydronium ions and the conjugate base
Therefore, the concentration of the
The formula to calculate the percent dissociation as follows:
Therefore, the percent dissociation is
The concentration of the
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Chapter 6 Solutions
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