The figure below shows the titration curve for an acid titrated with aqueous sodium hydroxide. When titrated in solution, which of the following salts would be most likely to produce a similar titration curve?

Question

The figure below shows the titration curve for an acid titrated with aqueous sodium hydroxide.  When titrated in solution, which of the following salts would be most likely to produce a similar titration curve?

Quizplus · Accepted Answer

11ecba2d_123f_100f_a3bf_a10a31ed09dc_MD0008_00 In the titration of an acid, a measured amount of a base solution (titrant) with a known concentration is slowly added to another solution that contains an unknown concentration of an acid. As the titration proceeds, acidic protons (weakly bound hydrogen atoms that easily ionize into H⁺ ions) react with the base in an acid-base neutralization reaction, which slowly changes the pH of the acid solution being titrated. During neutralization, if an acid structure has more than one acidic proton, the acidic protons dissociate one at a time in a stepwise progression from the most acidic to the least acidic proton. Each step in the progression generates a new conjugate base, which functions together with the remaining acid as a buffer that resists changes in pH (seen in a titration curve as relatively flat regions). An equivalence point is reached when the H⁺ ions from a given intermediate acidic species are fully neutralized. On a titration curve, this is signaled by a rapid change in pH, and the equivalence point is located at the middle of this nearly vertical segment. Accordingly, the titration curve of an acid shows one buffer region and one equivalence point for each acidic proton in its structure. In this question, the given titration curve exhibits two buffer regions and two equivalence points. As such, the titrated acid must have two acidic protons. Of the four compounds listed, only KH₂PO₄ is diprotic: 11ecba2d_123f_1010_a3bf_cf03415c74cf_MD0008_00 Therefore, KH₂PO₄ would produce a titration curve similar to that given in the question. (Choice A) H₃PO₄ would exhibit three equivalence points in a titration because it has three acidic protons: 11ecba2d_123f_1011_a3bf_75785a496832_MD0008_00 11ecba2d_123f_1012_a3bf_2d210cf09405_MD0008_00 11ecba2d_123f_1013_a3bf_07d1012c4509_MD0008_00 (Choice C) Na₂HPO₄ would exhibit just one equivalence point in a titration because it has only one acidic proton: 11ecba2d_123f_3724_a3bf_49befee2c855_MD0008_00 (Choice D) K₃PO₄ is not acidic (has no acidic protons) and would show no equivalence points in a titration with a base. Educational objective: During the titration of an acid with a sufficiently strong base, the titration curve exhibits one buffer region and one equivalence point for each acidic proton in the acidic compound structure.

The Figure Below Shows the Titration Curve for an Acid