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Chapter 18: Problem 65

The addition of \(\mathrm{HCl}(\mathrm{aq})\) to a solution containing several different cations produces a white precipitate. The filtrate is removed and treated with \(\mathrm{H}_{2} \mathrm{S}(\mathrm{aq})\) in 0.3 M HCl. No precipitate forms. Which of the following conclusions is (are) valid? Explain. (a) \(\mathrm{Ag}^{+}\) or \(\mathrm{Hg}_{2}^{2+}\) (or both) is probably present. (b) \(\mathrm{Mg}^{2+}\) is probably not present. (c) \(\mathrm{Pb}^{2+}\) is probably not present. (d) \(\mathrm{Fe}^{2+}\) is probably not present.

Short Answer

Expert verified
Option (a), (c), and (d) are potentially correct. \(\mathrm{Ag}^{+}\) or \(\mathrm{Hg}_{2}^{2+}\) (or both) might be present because they form a white precipitate with HCl. \(\mathrm{Pb}^{2+}\) and \(\mathrm{Fe}^{2+}\) are likely not present, as they wouldn't form precipitate with H2S under the conditions. \(\mathrm{Mg}^{2+}\) could be present without affecting the results.

Step by step solution

01

Analyze reaction with HCl

The addition of HCl to the solution results in a white precipitate, indicating the presence of ions that react with chloride ions to form a white insoluble substance. The most probable ions are the silver ion (\(Ag^{+}\)) and the mercury(I) ion (\(Hg_{2}^{2+}\)), as silver chloride (\(AgCl\)) and mercury(I) chloride (\(Hg_{2}Cl_{2}\)) are both white precipitates. So, option (a) is potentially correct.
02

Analyze reaction with H2S in HCl

The addition of H2S to the filtrate doesn't result in any precipitate. This indicates that the ions that react with H2S to form a precipitate in acidic medium are not present. These ions could include \(\mathrm{Pb}^{2+}\), which produces black lead(II) sulfide (\(PbS\)), and \(\mathrm{Fe}^{2+}\), which produces green ferrous sulfide (\(FeS\)). So, options (c) and (d) are potentially correct.
03

Non-reactivity with either reagent

\(\mathrm{Mg}^{2+}\) does not react with either HCl or H2S to form a precipitate, so does not influence the results reported from the tests. So, whether or not \(\mathrm{Mg}^{2+}\) is present in the solution, it can't be determined from the facts provided. Thus, option (b) makes an unsupported assumption and is probably not correct.

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Most popular questions from this chapter

Will AgI(s) precipitate from a solution with \(\left[\left[\mathrm{Ag}(\mathrm{CN})_{2}\right]^{-}\right]=0.012 \mathrm{M}, \left[\mathrm{CN}^{-}\right]=1.05 \mathrm{M}, \) and \(\left[\mathrm{I}^{-}\right]=2.0 \mathrm{M} ?\) For \( \mathrm{AgI}, K_{\mathrm{sp}}=8.5 \times 10^{-17} ; =\) for \(\left[\mathrm{Ag}(\mathrm{CN})_{2}\right]^{-}, K_{\mathrm{f}}=5.6 \times 10^{18}\).

Which of the following solids is (are) more soluble in an acidic solution than in pure water: \(\mathrm{KCl}\), \(\mathrm{MgCO}_{3}\), \(\mathrm{FeS}, \mathrm{Ca}(\mathrm{OH})_{2,}\) or \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH} ?\) Explain.

The best way to ensure complete precipitation from saturated \(\mathrm{H}_{2} \mathrm{S}(\mathrm{aq})\) of a metal ion, \(\mathrm{M}^{2+}\), as its sulfide, \(\mathrm{MS}(\mathrm{s}),\) is to \((\mathrm{a})\) add an acid; \((\mathrm{b})\) increase \(\left[\mathrm{H}_{2} \mathrm{S}\right]\) in the solution; (c) raise the \(\mathrm{pH} ;\) (d) heat the solution.

In the qualitative cation analysis procedure, \(\mathrm{Bi}^{3+}\) is detected by the appearance of a white precipitate of bismuthyl hydroxide, \(\mathrm{BiOOH}(\mathrm{s})\): \(\mathrm{BiOOH}(\mathrm{s}) \rightleftharpoons \mathrm{BiO}^{+}(\mathrm{aq})+\mathrm{OH}^{-}(\mathrm{aq})\) \(K_{\mathrm{sp}}=4 \times 10^{-10}\) Calculate the \(\mathrm{pH}\) of a saturated aqueous solution of \(\mathrm{BiOOH}\).

A solution is \(0.010 \mathrm{M}\) in both \(\mathrm{CrO}_{4}^{2-}\) and \(\mathrm{SO}_{4}^{2-}\). To this solution, \(0.50 \mathrm{M} \mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(\text { aq })\) is slowly added. (a) Which anion will precipitate first from solution? (b) What is \(\left[\mathrm{Pb}^{2+}\right]\) at the point at which the second anion begins to precipitate? (c) Are the two anions effectively separated by this fractional precipitation?
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