Ap Chem Acid Base Worksheet Page 3

HIn

+ H

  In

+ H

(aq)

(l)

(aq)

5. The indicator HIn is a weak acid with a pKa value of 5.0. It reacts with water as represented

in the equation above. Consider the two beakers below. Each beaker has a layer of colorless oil

(a nonpolar solvent) on top of a layer of aqueous buffer solution. In beaker X the pH of the

buffer solution is 3, and in beaker Y the pH of the buffer solution is 7. A small amount of HIn is

placed in both beakers. The mixtures are stirred well, and the oil and water layers are allowed to

separate.

a. What is the predominant form of HIn in the aqueous buffer in beaker Y, the acid form or

the conjugate base form? Explain your reasoning.

b. In beaker X the oil layer is yellow, whereas in beaker Y the oil layer is colorless.

Explain these observations in terms of both acid-base equilibria and interparticle forces.

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