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Chapter 14: Problem 102

Consider the following acids and bases: Choose substances from the following list that would be the best choice to prepare a \(\mathrm{pH}=9.0\) buffer solution. a. \(\mathrm{HCO}_{2} \mathrm{H}\) b. HOBr c. \(\mathrm{KHCO}_{2}\) d. \(\mathrm{HONH}_{3} \mathrm{NO}_{3}\) \(\mathbf{e} .\left(\mathbf{C}_{2} \mathbf{H}_{5}\right)_{2} \mathrm{NH}\) f. \(\left(C_{2} H_{5}\right)_{2} N H_{2} C l\) g. \(\mathrm{HONH}_{2}\) h. NaOBr

Short Answer

Expert verified
The best combination to prepare a buffer solution at pH 9.0 would be HOBr (Hypobromous Acid) and NaOBr (Sodium Hypobromite).

Step by step solution

01

Identify Acids and Bases

We must first identify which compounds are acids and which are bases from the list: a. \(\mathrm{HCO}_{2}\mathrm{H}\) - Acid (Formic Acid) b. HOBr - Acid (Hypobromous Acid) c. \(\mathrm{KHCO}_{2}\) - Base (Potassium Formate) d. \(\mathrm{HONH}_{3}\mathrm{NO}_{3}\) - Acid (Hydroxylammonium Nitrate) e. \((\mathrm{C}_{2}\mathrm{H}_{5})_{2}\mathrm{NH}\) - Base (Diethylamine) f. \((\mathrm{C}_{2}\mathrm{H}_{5})_{2}\mathrm{NH}_{2}\mathrm{Cl}\) - Acid/Base (Diethylammonium chloride, a salt of the acid and conjugate base) g. \(\mathrm{HONH}_{2}\) - Acid (Hydroxylamine) h. NaOBr - Base (Sodium Hypobromite)
02

Calculate pKa Values

Next, we need to find the pKa values of the acids. The pKa values have been tabulated and can be found in any reference material (such as a textbook or online resource): a. \(\mathrm{HCO}_{2}\mathrm{H}\) - pKa = 3.75 b. HOBr - pKa = 8.6 d. \(\mathrm{HONH}_{3}\mathrm{NO}_{3}\) - pKa = 6.1 g. \(\mathrm{HONH}_{2}\) - pKa = 6.0
03

Select Suitable Buffer Pair

To create a buffer at pH 9.0, we need to find the acid and its conjugate base combination that works best. The appropriate pKa value should be close to the target pH level: HOBr (pKa = 8.6) is closest to pH 9.0 and is the best option among the weak acids. The conjugate base for HOBr is OBr⁻, which corresponds to NaOBr in the list.
04

Conclusion

Therefore, the best combination to prepare a buffer solution at pH 9.0 would be HOBr (Hypobromous Acid) and NaOBr (Sodium Hypobromite).

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Most popular questions from this chapter

The active ingredient in aspirin is acetylsalicylic acid. A \(2.51-\mathrm{g}\) sample of acetylsalicylic acid required \(27.36 \mathrm{mL}\) of \(0.5106 M\) NaOH for complete reaction. Addition of \(13.68 \mathrm{mL}\) of \(0.5106 \mathrm{M}\) HCl to the flask containing the aspirin and the sodium hydroxide produced a mixture with \(\mathrm{pH}=3.48 .\) Determine the molar mass of acetylsalicylic acid and its \(K_{\mathrm{a}}\) value. State any assumptions you must make to reach your answer.

In the titration of \(50.0 \mathrm{mL}\) of \(1.0 \mathrm{M}\) methylamine, \(\mathrm{CH}_{3} \mathrm{NH}_{2}\) \(\left(K_{\mathrm{b}}=4.4 \times 10^{-4}\right),\) with \(0.50 M\) HCl, calculate the pH under the following conditions. a. after \(50.0 \mathrm{mL}\) of \(0.50 \mathrm{M}\) HCl has been added b. at the stoichiometric point

Calculate the volume of \(1.50 \times 10^{-2} \mathrm{M}\) NaOH that must be added to \(500.0 \mathrm{mL}\) of \(0.200 \mathrm{M}\) HCl to give a solution that has \(\mathrm{pH}=2.15\).

What quantity (moles) of HCl(g) must be added to \(1.0 \mathrm{L}\) of \(2.0 \mathrm{M}\) NaOH to achieve a pH of 0.00? (Neglect any volume changes.)

A friend asks the following: "Consider a buffered solution made up of the weak acid HA and its salt NaA. If a strong base like NaOH is added, the HA reacts with the OH - to form A Thus the amount of acid (HA) is decreased, and the amount of base \(\left(\mathrm{A}^{-}\right)\) is increased. Analogously, adding HCl to the buffered solution forms more of the acid (HA) by reacting with the base \(\left(\mathrm{A}^{-}\right)\). Thus how can we claim that a buffered solution resists changes in the pH of the solution?" How would you explain buffering to this friend?
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