Question

Instructions:Drag the tiles to the correct boxes to complete the pairs. Not all tiles will be used.
Compare the exponential functions f, g, and h which are shown below.

Determine which functions match each of the given characteristics.

Answer 1

1) The equation for the equilibrium state of acetic acid in water is;-

                  CH3COOH + H2O <---> H3O+ + CH3COO-

(2) Ka = [H3O+] [CH3COO-] / [CH3COOH]

(3) The acid dissociation constant for acetic acid (Ka) = 1.8 * 10^-5

(4) pH = -log[H3O+]

The chemical equation in (1.) tells us that, at equilibrium, the concentration of the ions H3O+ and CH3COO- must be equal.  So we can say that [H3O+] = [CH3COO-]

Therefore the equation for Ka in this case becomes;-

Ka = [H3O+] [H3O+] / [CH3COOH]

or;

Ka = [H3O+]^2 / [CH3COOH]

Rearranging this equation we get;-

[H3O+]^2 = Ka *  [CH3COOH]

or;

[H3O+] = SQRT( Ka *  [CH3COOH])

Since we know that Ka for acetic acid is  1.8 * 10^-5, and the concentration of the acetic acid was given as 1.0M, we can now substitute these values into this equation;-

[H3O+]  = SQRT( 1.8 * 10^-5 * 1.0)

[H3O+]  = SQRT( 1.8 * 10^-5 )

[H3O+]  =0.004243

Substituting this value for [H3O+] into the equation  pH = -log[H3O+]  we get;-

pH = -log[0.004243]

pH = 2.37