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Chapter 17: Problem 11

Indicate which of the following aqueous solutions are buffer solutions, and explain your reasoning. (a) \(0.100 \mathrm{M} \mathrm{NaCl}\) (b) \(0.100 \mathrm{M} \mathrm{NaCl}-0.100 \mathrm{M} \mathrm{NH}_{4} \mathrm{Cl}\) (c) \(0.100 \mathrm{M} \mathrm{CH}_{3} \mathrm{NH}_{2}-0.150 \mathrm{M} \mathrm{CH}_{3} \mathrm{NH}_{3}^{+} \mathrm{Cl}^{-}\) (d) \(0.100 \mathrm{M} \mathrm{HCl}-0.050 \mathrm{M} \mathrm{NaNO}_{2}\) (e) \(0.100 \mathrm{M} \mathrm{HCl}-0.200 \mathrm{M} \mathrm{NaCH}_{3} \mathrm{COO}\) (f) \(0.100 \mathrm{M} \mathrm{CH}_{3} \mathrm{COOH}-0.125 \mathrm{M} \mathrm{NaCH}_{3} \mathrm{CH}_{2} \mathrm{COO}\)

Short Answer

Expert verified
The buffer solutions are b, c, and f.

Step by step solution

01

Identifying buffer solution a

Solution a only contains \(0.100 \mathrm{M} \mathrm{NaCl}\), a salt. Since there is no weak acid or base present in the solution, it cannot act as a buffer. Hence, it is not a buffer solution.
02

Identifying buffer solution b

A buffer solution consists of a weak base or acid and its conjugate. Looking at solution b, it contains \(0.100 \mathrm{M} \mathrm{NaCl}\) and \(0.100 \mathrm{M} \mathrm{NH}_{4}\mathrm{Cl}\). Here, \(\mathrm{NH}_{4}\) is a weak acid and \(\mathrm{Cl}^{-}\) is its conjugate base. Hence, it is a buffer solution.
03

Identifying buffer solution c

Solution c consist of \(0.100 \mathrm{M} \mathrm{CH}_{3} \mathrm{NH}_{2}\) and \(0.150 \mathrm{M} \mathrm{CH}_{3} \mathrm{NH}_{3}^{+} \mathrm{Cl}^{-}\). The \(\mathrm{CH}_{3} \mathrm{NH}_{2}\) is a weak base and \(\mathrm{CH}_{3} \mathrm{NH}_{3}^{+}\) is its conjugate acid. Hence, it is a buffer solution.
04

Identifying buffer solution d

Solution d contains \(0.100 \mathrm{M} \mathrm{HCl}\) and \(0.050 \mathrm{M} \mathrm{NaNO}_{2}\). Here, \(\mathrm{HCl}\) is a strong acid and not a weak one, so it cannot form a buffer with its salt, hence it is not a buffer solution.
05

Identifying buffer solution e

Solution e contains \(0.100 \mathrm{M} \mathrm{HCl}\) and \(0.200 \mathrm{M} \mathrm{NaCH}_{3} \mathrm{COO}\). The \(\mathrm{HCl}\) is still a strong acid and hence, like in the previous solution, even though \(\mathrm{CH}_{3} \mathrm{COO}^{-}\) is a conjugate base, this solution cannot act as a buffer. Hence, it is not a buffer solution.
06

Identifying buffer solution f

Lastly, solution f consists of \(0.100 \mathrm{M} \mathrm{CH}_{3} \mathrm{COOH}\) and \(0.125 \mathrm{M} \mathrm{NaCH}_{3} \mathrm{CH}_{2} \mathrm{COO}\). Here, \(\mathrm{CH}_{3} \mathrm{COOH}\) is a weak acid and \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COO}^{-}\) is its conjugate base. Hence, it is a buffer solution.

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Most popular questions from this chapter

A 25.00 -mL sample of \(0.0100 \mathrm{M} \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}\left(\mathrm{K}_{\mathrm{a}}=\right.\) \(\left.6.3 \times 10^{-5}\right)\) is titrated with \(0.0100 \mathrm{M} \mathrm{Ba}(\mathrm{OH})_{2}\) Calculate the \(\mathrm{pH}\) (a) of the initial acid solution; (b) after the addition of 6.25 mL of \(0.0100 \mathrm{M} \mathrm{Ba}(\mathrm{OH})_{2}\) (c) at the equivalence point; (d) after the addition of a total of \(15.00 \mathrm{mL}\) of \(0.0100 \mathrm{M} \mathrm{Ba}(\mathrm{OH})_{2}\)

A solution is prepared that is \(0.150 \mathrm{M} \mathrm{CH}_{3} \mathrm{COOH}\) and \(0.250 \mathrm{M} \mathrm{NaHCOO}\) (a) Show that this is a buffer solution. (b) Calculate the pH of this buffer solution. (c) What is the final pH if 1.00 L of 0.100 M HCl is added to \(1.00 \mathrm{L}\) of this buffer solution?

What is the pH of a solution prepared by dissolving \(8.50 \mathrm{g}\) of aniline hydrochloride \(\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{3}^{+} \mathrm{Cl}^{-}\right)\) in \(750 \mathrm{mL}\) of \(0.215 \mathrm{M}\) aniline, \(\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\right) ?\) Would this solution be an effective buffer? Explain.

A \(25.00 \mathrm{mL}\) sample of \(\mathrm{H}_{3} \mathrm{PO}_{4}(\text { aq) requires } 31.15 \mathrm{mL}\) of \(0.2420 \mathrm{M}\) KOH for titration to the second equivalence point. What is the molarity of the \(\mathrm{H}_{3} \mathrm{PO}_{4}(\mathrm{aq}) ?\)

The indicator methyl red has a \(\mathrm{pK}_{\mathrm{HIn}}=4.95 . \mathrm{It}\) changes from red to yellow over the pH range from 4.4 to 6.2 (a) If the indicator is placed in a buffer solution of \(\mathrm{pH}=4.55,\) what percent of the indicator will be pre- sent in the acid form, HIn, and what percent will be present in the base or anion form, In \(^{-2}\) (b) Which form of the indicator has the "stronger" (that is, more visible) color- -the acid (red) form or base (yellow) form? Explain.
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