Question

The hydronium ion concentration of an aqueous solution of 0.539 M morphine (a weak base with the formula G7Hi90N) is .. (H,01- M.

Answer 1

1) The generic reaction is:

A- + H2O = HA + OH-

From the expression of Kb we have:

Kb = [HA] * [OH-] / [A-]

we replace:

1.62x10 ^ -6 = X ^ 2 / 0.539 - X

We assume that - X is negligible and we clear:

X = [OH-] = √1.62x10 ^ -6 * 0.539 = 9.34x10 ^ -4 M

We calculate the concentration of H3O +:

[H3O +] = Kw / [OH-] = 10 ^ -14 / 9.34x10 ^ -4 = 1.07x10 ^ -11 M

2) We calculate the pOH of the solution:

pOH = 14 - pH = 14 - 10.783 = 3.217

The concentration of OH- is calculated:

[OH-] = X = 10 ^ -pOH = 10 ^ -3.217 = 6.07x10 ^ -4 M

The Kb is calculated from its expression:

Kb = X ^ 2 / 0.539 - X = (6.07x10 ^ -4) ^ 2 / 0.539 - 6.07x10 ^ -4 = 6.84x10 ^ -7

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