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Chapter 15: Problem 45

Which of the following mixtures would result in buffered solutions when \(1.0 \mathrm{~L}\) of each of the two solutions are mixed? a. \(0.1 \mathrm{M} \mathrm{KOH}\) and \(0.1 \mathrm{M} \mathrm{CH}_{3} \mathrm{NH}_{3} \mathrm{Cl}\) b. \(0.1 \mathrm{M} \mathrm{KOH}\) and \(0.2 \mathrm{M} \mathrm{CH}_{3} \mathrm{NH}_{2}\) c. \(0.2 \mathrm{M} \mathrm{KOH}\) and \(0.1 \mathrm{M} \mathrm{CH}_{3} \mathrm{NH}_{3} \mathrm{Cl}\) d. \(0.1 \mathrm{M} \mathrm{KOH}\) and \(0.2 \mathrm{M} \mathrm{CH}_{3} \mathrm{NH}_{3} \mathrm{Cl}\)

Short Answer

Expert verified
The mixture (a) \(0.1 \mathrm{M} \mathrm{KOH}\) and \(0.1 \mathrm{M} \mathrm{CH}_{3}\mathrm{NH}_{3} \mathrm{Cl}\) will result in a buffered solution when mixed.

Step by step solution

01

Identify weak acids/bases and their conjugates

First, we need to identify the weak acids and bases present in the solutions and their conjugate acids/bases. The weak base present in all the given mixtures is \(\mathrm{CH}_{3}\mathrm{NH}_{2}\) (methylamine), and its conjugate acid is \(\mathrm{CH}_{3}\mathrm{NH}_{3}^{+}\) (methylammonium ion). KOH, on the other hand, is a strong base, and its conjugate acid is water, which doesn't participate in the buffering effect.
02

Analyzing each mixture

Now that we've identified the weak base and its conjugate, let's analyze each given mixture to determine if it forms a buffered solution: a. \(0.1 \mathrm{M} \mathrm{KOH}\) and \(0.1 \mathrm{M} \mathrm{CH}_{3}\mathrm{NH}_{3} \mathrm{Cl}\): In this mixture, KOH will react with the weak acid \(\mathrm{CH}_{3}\mathrm{NH}_{3}^{+}\), forming the weak base \(\mathrm{CH}_{3}\mathrm{NH}_{2}\) and water. The final solution will contain equal concentrations of the weak base and its conjugate acid, forming a buffered solution. b. \(0.1 \mathrm{M} \mathrm{KOH}\) and \(0.2 \mathrm{M} \mathrm{CH}_{3}\mathrm{NH}_{2}\): In this case, the KOH will react with a part of the weak base \(\mathrm{CH}_{3}\mathrm{NH}_{2}\) and form its conjugate acid \(\mathrm{CH}_{3}\mathrm{NH}_{3}^{+}\). After the reaction, the concentrations of the weak base and its conjugate acid will not be equal. Thus, this mixture will not result in a buffered solution. c. \(0.2 \mathrm{M} \mathrm{KOH}\) and \(0.1 \mathrm{M} \mathrm{CH}_{3}\mathrm{NH}_{3} \mathrm{Cl}\): In this mixture, the strong base KOH will overwhelm the weak acid, leading to \(0.1 \mathrm{M}\) of the weak base and its conjugate acid after the reaction. This will not result in a buffered solution. d. \(0.1 \mathrm{M} \mathrm{KOH}\) and \(0.2 \mathrm{M} \mathrm{CH}_{3}\mathrm{NH}_{3} \mathrm{Cl}\): In this case, KOH will react with some of the weak acid \(\mathrm{CH}_{3}\mathrm{NH}_{3}^{+}\) to form the weak base \(\mathrm{CH}_{3}\mathrm{NH}_{2}\), ultimately resulting in an unequal concentration of the weak base and its conjugate acid. Thus, this mixture will not result in a buffered solution.
03

Conclusion

Based on the analysis of each mixture, only the mixture (a) \(0.1 \mathrm{M} \mathrm{KOH}\) and \(0.1 \mathrm{M} \mathrm{CH}_{3}\mathrm{NH}_{3} \mathrm{Cl}\) will result in a buffered solution when mixed.

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Most popular questions from this chapter

A \(225-\mathrm{mg}\) sample of a diprotic acid is dissolved in enough water to make \(250 . \mathrm{mL}\) of solution. The \(\mathrm{pH}\) of this solution is \(2.06\). A \(6.9 \times 10^{-3} M\) solution of calcium hydroxide is prepared. Enough of the calcium hydroxide solution is added to the solution of the acid to reach the second equivalence point. The \(\mathrm{pH}\) at the second equivalence point (as determined by a pH meter) is \(7.96 .\) The first dissociation constant for the acid \(\left(K_{\Delta}\right)\) is \(5.90 \times\) \(10^{-2}\). Assume that the volumes of the solutions are additive, that all solutions are at \(25^{\circ} \mathrm{C}\), and that \(K_{a_{1}}\) is at least 1000 times greater than \(K_{a_{2}}\). a. Calculate the molar mass of the acid. b. Calculate the second dissociation constant for the acid \(\left(K_{\mathrm{a}}\right)\).

Amino acids are the building blocks for all proteins in our bodies. A structure for the amino acid alanine is All amino acids have at least two functional groups with acidic or basic properties. In alanine, the carboxylic acid group has \(K_{\mathrm{a}}=4.5 \times 10^{-3}\) and the amino group has \(K_{\mathrm{b}}=7.4 \times 10^{-5} .\) Because of the two groups with acidic or basic properties, three different charged ions of alanine are possible when alanine is dissolved in water. Which of these ions would predominate in a solution with \(\left[\mathrm{H}^{+}\right]=1.0 M ?\) In a solution with \(\left[\mathrm{OH}^{-}\right]=\) \(1.0 M ?\)

Methyl red has the following structure: CN(C)c1ccc(N=Nc2ccccc2C(=O)O)cc1 It undergoes a color change from red to yellow as a solution gets more basic. Calculate an approximate \(\mathrm{pH}\) range for which methyl red is useful. What is the color change and the \(\mathrm{pH}\) at the color change when a weak acid is titrated with a strong base using methyl red as an indicator? What is the color change and the \(\mathrm{pH}\) at the color change when a weak base is titrated with a strong acid using methyl red as an indicator? For which of these two types of titrations is methyl red a possible indicator?

Calculate the \(\mathrm{pH}\) of a solution that is \(0.60 \mathrm{M} \mathrm{HF}\) and \(1.00 \mathrm{M} \mathrm{KF}\).

Calculate the \(\mathrm{pH}\) of a solution prepared by mixing \(250 . \mathrm{mL}\) of \(0.174 \mathrm{~m}\) aqueous \(\mathrm{HF}\) (density \(=1.10 \mathrm{~g} / \mathrm{mL}\) ) with \(38.7 \mathrm{~g}\) of an aqueous solution that is \(1.50 \% \mathrm{NaOH}\) by mass (density \(=1.02\) \(\mathrm{g} / \mathrm{mL}\) ). \(\left(K_{\mathrm{a}}\right.\) for \(\mathrm{HF}=7.2 \times 10^{-4}\).)
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