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Chapter 16: Problem 10

Which of the following solutions can act as a buffer: (a) \(\mathrm{KCN} / \mathrm{HCN}\) (b) \(\mathrm{Na}_{2} \mathrm{SO}_{4} / \mathrm{NaHSO}_{4}\) (c) \(\mathrm{NH}_{3} /\) \(\mathrm{NH}_{4} \mathrm{NO}_{3}\), (d) \(\mathrm{Nal} / \mathrm{HI}^{2}\)

Short Answer

Expert verified
(a), (b) and (c) can act as buffer solutions while (d) cannot.

Step by step solution

01

Identify Buffer Solution Candidate (a)

Look at solution (a) \(\mathrm{KCN} / \mathrm{HCN}\). Potassium cyanide, \(\mathrm{KCN}\), dissociates to form \(\mathrm{K}^{+}\) and \(\mathrm{CN}^{-}\) ions when in solution. Its counterpart \(\mathrm{HCN}\) is a weak acid which donates a proton to form \(\mathrm{CN}^{-}\). Therefore, the solution contains a weak acid and its conjugate base. Thus, solution (a) can act as a buffer.
02

Identify Buffer Solution Candidate (b)

Look at solution (b) \(\mathrm{Na}_{2} \mathrm{SO}_{4} / \mathrm{NaHSO}_{4}\). Here, \(\mathrm{Na}_{2} \mathrm{SO}_{4}\) dissociates to give \(\mathrm{SO}_{4}^{2-}\) ions, and \(\mathrm{NaHSO}_{4}\) is a weak acid which when donates a proton, forms \(\mathrm{SO}_{4}^{2-}\) ions. Therefore, in this solution, a weak acid and its conjugate base are present, hence it can also act as a buffer.
03

Identify Buffer Solution Candidate (c)

Now consider solution (c) \(\mathrm{NH}_{3}\) / \(\mathrm{NH}_{4}\mathrm{NO}_{3}\). In this case, \(\mathrm{NH}_{3}\) is a weak base that accepts a proton to form \(\mathrm{NH}_{4}^{+}\). \(\mathrm{NH}_{4}\mathrm{NO}_{3}\) dissociates into \(\mathrm{NH}_{4}^{+}\) and \(\mathrm{NO}_{3}^{-}\). So this solution contains a weak base and its conjugate acid, hence it can act as a buffer.
04

Identify Buffer Solution Candidate (d)

Lastly, observe solution (d) \(\mathrm{Nal}/\mathrm{HI}^{2}\). Here, \(\mathrm{Nal}\) plays a major role by completely dissociating into its constituents. However, \(\mathrm{HI}^{2}\) is not a recognized species in aqueous solution, which eliminates this option. Therefore, solution (d) cannot be considered as a buffer solution as it does not contain a weak acid/base and its conjugate.

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Most popular questions from this chapter

Explain, with balanced ionic equations, why (a) \(\mathrm{CuI}_{2}\) dissolves in ammonia solution, (b) AgBr dissolves in \(\mathrm{NaCN}\) solution, (c) \(\mathrm{HgCl}_{2}\) dissolves in KCl solution.

If \(\mathrm{NaOH}\) is added to \(0.010 \mathrm{M} \mathrm{Al}^{3+}\), which will be the predominant species at equilibrium: \(\mathrm{Al}(\mathrm{OH})_{3}\) or \(\mathrm{Al}(\mathrm{OH})_{4}^{-} ?\) The \(\mathrm{pH}\) of the solution is \(14.00 .\left[K_{\mathrm{f}}\right.\) for \(\left.\mathrm{Al}(\mathrm{OH})_{4}^{-}=2.0 \times 10^{33} .\right]\)

Both \(\mathrm{KCl}\) and \(\mathrm{NH}_{4} \mathrm{Cl}\) are white solids. Suggest one reagent that would enable you to distinguish between these two compounds.

Explain how an acid-base indicator works in a titration. What are the criteria for choosing an indicator for a particular acid-base titration?

A 0.2688 -g sample of a monoprotic acid neutralizes \(16.4 \mathrm{~mL}\) of \(0.08133 \mathrm{M}\) KOH solution. Calculate the molar mass of the acid.
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