CHM 1046 Lecture Notes - Lecture 14: Sodium Formate, Conjugate Acid, Acid Dissociation Constant

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5 May 2016

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Calculate the ph of a solution that is . 250 m in sodium formate (nahcoo) and . 100 m in formic acid (hcooh) Strong/weak acid or base (nahcoo ionic salt hcooh weak acid) Nahcooo really exists as ions ( go to back of problems from 18. 1-. 3 for work out) Has a ph between base only and acid only versions. Contains a weak acid- base conjugate pair. The type of solution is a buffered solution (aka buffer) Ph is based on the acid conjugate base ratio. The amount of acid or base the buffer can neutralize without a significant ph change. Buffer no longer effective when outside the range (0. 1

Related Questions

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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CHM 1046 Lecture Notes - Lecture 14: Sodium Formate, Conjugate Acid, Acid Dissociation Constant

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