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Chapter 18: Problem 63

Suppose you did a group 1 qualitative cation analysis and treated the chloride precipitate with \(\mathrm{NH}_{3}(\mathrm{aq})\) without first treating it with hot water. What might you observe, and what valid conclusions could you reach about cations present, cations absent, and cations in doubt?

Short Answer

Expert verified
Upon adding ammonia to the chloride precipitate, an ammonia smell may be detected due to the formation of ammonium chloride. Silver (\(\mathrm{Ag}^{+}\)), mercury (\(\mathrm{Hg}_{2}^{2+}\)), and lead (\(\mathrm{Pb}^{2+}\)) ions may be present, while all other ions, including barium (\(\mathrm{Ba}^{2+}\)), calcium (\(\mathrm{Ca}^{2+}\)), and sodium (\(\mathrm{Na}^{+}\)) ions, are likely absent. However, since hot water was not used first, the presence or absence of all ions is in doubt.

Step by step solution

01

Observations

Due to the acidity of the chloride, upon adding ammonia (\(\mathrm{NH}_{3}(\mathrm{aq})\)) a distinct ammonia smell would be detected. This can be due to the formation of ammonium chloride (\(\mathrm{NH}_{4}\)Cl) which gives off ammonia.
02

Determining Cations Present

From this reaction, it can be concluded that cations that form insoluble chlorides are present. These are likely to include silver (\(\mathrm{Ag}^{+}\)), mercury (\(\mathrm{Hg}_{2}^{2+}\)), and lead (\(\mathrm{Pb}^{2+}\)) ions.
03

Determining Cations Absent

Those cations that form soluble chlorides are likely absent. These are all the ions that are not present in Group 1, including barium (\(\mathrm{Ba}^{2+}\)), calcium (\(\mathrm{Ca}^{2+}\)), and sodium (\(\mathrm{Na}^{+}\)) ions.
04

Determining Cations in Doubt

As hot water was not used first, we cannot be 100% sure about the presence or absence of any cation. Therefore, all cations would be in doubt.

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Most popular questions from this chapter

A \(0.150 \mathrm{M} \mathrm{Na}_{2} \mathrm{SO}_{4}\) solution that is saturated with \(\mathrm{Ag}_{2} \mathrm{SO}_{4}\) has \(\left[\mathrm{Ag}^{+}\right]=9.7 \times 10^{-3} \mathrm{M} .\) What is the value of \(K_{\mathrm{sp}}\) for \(\mathrm{Ag}_{2} \mathrm{SO}_{4}\) obtained with these data?

Write net ionic equations for the following qualitative cation analysis procedures. (a) precipitation of \(\mathrm{PbCl}_{2}(\mathrm{s})\) from a solution containing \(\mathrm{Pb}^{2+}\) (b) dissolution of \(\mathrm{Zn}(\mathrm{OH})_{2}(\mathrm{s})\) in a solution of \(\mathrm{NaOH}(\mathrm{aq})\) (c) dissolution of \(\mathrm{Fe}(\mathrm{OH})_{3}(\mathrm{s})\) in \(\mathrm{HCl}(\mathrm{aq})\) (d) precipitation of \(\mathrm{CuS}(\mathrm{s})\) from an acidic solution of \(\mathrm{Cu}^{2+}\) and \(\mathrm{H}_{2} \mathrm{S}\)

Write net ionic equations for each of the following observations. (a) When concentrated \(\mathrm{CaCl}_{2}(\mathrm{aq})\) is added to \(\mathrm{Na}_{2} \mathrm{HPO}_{4}(\mathrm{aq}),\) a white precipitate forms that is \(38.7 \%\) Ca by mass. (b) When a piece of dry ice, \(\mathrm{CO}_{2}(\mathrm{s}),\) is placed in a clear dilute solution of limewater \(\left[\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{aq})\right]\), bubbles of gas evolve. At first, a white precipitate forms, but then it redissolves.

Which of the following would be most effective, and which would be least effective, in reducing the concentration of the complex ion \(\left[\mathrm{Zn}\left(\mathrm{NH}_{3}\right)_{4}\right]^{2+}\) in a solution: \(\mathrm{HCl}, \mathrm{NH}_{3},\) or \(\mathrm{NH}_{4} \mathrm{Cl} ?\) Explain your choices.

Describe the effects of the salts \(\mathrm{KI}\) and \(\mathrm{AgNO}_{3}\) on the solubility of AgI in water.
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