1.Phenolphthalein is, HPhen, is a common acid-base indicator. In solutions it dissociates according to the equation:
Le Châtelier’s Principle 8
HPhen(aq) ---> H+(aq) + Ph-(aq)
clear (HPhen = weak acid) pink (Ph- = conjugate base)
If phenolphthalein is added to distilled water, the solution is clear. If a drop or two of 6 M NaOH is added to the clear solution, it turns bright pink. If to that solution one adds a few drops of 6 M HCl, the color reverts to clear.
a. Give the net ionic equation for the reaction that happens when NaOH is added to phenolphthalein. Why does adding 6 M NaOH to the clear solution of phenolphthalein tend to cause the color to change to pink? (Note that in solution NaOH exists as Na+ and OH- ions.)
b. Give the net ionic equation for the reaction that happens when HCL is added to phenolphthalein. Why does adding 6 M HCl to the red solution tend to make it turn back to clear? (Note that in solution HCl exists as H+ and Cl- ions.)
2. Iron(III) hydroxide is only very slightly soluble in water. The reaction by which it goes into solution is:
Fe(OH)3(s) Fe 3+(aq) + 3 OH-(aq)
a. Formulate the expression for the equilibrium constant, Ksp, for the above reaction.
b. Explain why Fe(OH)3 might have very appreciable solubility in 1 M HCl. (Consider the effect of Reaction 2 on the Fe(OH)3 solution reaction.)
1.Phenolphthalein is, HPhen, is a common acid-base indicator. In solutions it dissociates according to the equation:
Le Châtelier’s Principle 8
HPhen(aq) ---> H+(aq) + Ph-(aq)
clear (HPhen = weak acid) pink (Ph- = conjugate base)
If phenolphthalein is added to distilled water, the solution is clear. If a drop or two of 6 M NaOH is added to the clear solution, it turns bright pink. If to that solution one adds a few drops of 6 M HCl, the color reverts to clear.
a. Give the net ionic equation for the reaction that happens when NaOH is added to phenolphthalein. Why does adding 6 M NaOH to the clear solution of phenolphthalein tend to cause the color to change to pink? (Note that in solution NaOH exists as Na+ and OH- ions.)
b. Give the net ionic equation for the reaction that happens when HCL is added to phenolphthalein. Why does adding 6 M HCl to the red solution tend to make it turn back to clear? (Note that in solution HCl exists as H+ and Cl- ions.)
2. Iron(III) hydroxide is only very slightly soluble in water. The reaction by which it goes into solution is:
Fe(OH)3(s) Fe 3+(aq) + 3 OH-(aq)
a. Formulate the expression for the equilibrium constant, Ksp, for the above reaction.
b. Explain why Fe(OH)3 might have very appreciable solubility in 1 M HCl. (Consider the effect of Reaction 2 on the Fe(OH)3 solution reaction.)
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