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Chapter 16: Problem 83

Both \(\mathrm{Ag}^{+}\) and \(\mathrm{Zn}^{2+}\) form complex ions with \(\mathrm{NH}_{3}\). Write balanced equations for the reactions. However, \(\mathrm{Zn}(\mathrm{OH})_{2}\) is soluble in \(6 \mathrm{M} \mathrm{NaOH},\) and \(\mathrm{AgOH}\) is not. Explain.

Short Answer

Expert verified
Ag+ and Zn2+ react with NH3 to form complex ions [Ag(NH3)2]+ and [Zn(NH3)4]2+ respectively. Zn(OH)2 is soluble in NaOH as it forms a complex ion [Zn(OH)4]2- but AgOH doesn't form a complex ion with OH- and hence remains insoluble.

Step by step solution

01

Formation of complex ions

The metal ions react with ammonia to form complex ions as follows:\n\n\(\mathrm{Ag}^{+}(aq) + 2\mathrm{NH}_{3}(aq)\) -> \(\mathrm{Ag(NH_{3})_{2}}^{+}(aq)\)\n\n\(\mathrm{Zn}^{2+}(aq) + 4\mathrm{NH}_{3}(aq)\) -> \(\mathrm{Zn(NH_{3})_{4}}^{2+}(aq)\)\n\nAmmonia acts as a ligand bonding with the metal ions to form complex ions.
02

Solubility in Sodium Hydroxide

Both \(\mathrm{AgOH}\) and \(\mathrm{Zn(OH)_{2}}\) react with \(\mathrm{NaOH}\) differently. \(\mathrm{Zn(OH)_{2}}\) forms a complex ion with \(\mathrm{OH}^{-}\) ions thus making it soluble. Meanwhile, \(\mathrm{AgOH}\) doesn't form complex ions with \(\mathrm{OH}^-.\)\n\n\(\mathrm{Zn(OH)_{2}(s) + 2OH^{-}(aq)\) -> \(\mathrm{Zn(OH)_{4}}^{2-}(aq)\)\n\n\(\mathrm{AgOH}\) doesn't react with \(\mathrm{OH}^{-}\) thus implying that it remains insoluble.
03

Explanation of the solubility difference

The difference in solubility can be explained by complex ion formation. \(\mathrm{Zn(OH)_{2}}\) can form complex ions with \(\mathrm{OH}^{-}\) due to zinc's empty d orbitals allowing it to form coordinate bonds with the oxygen in \(\mathrm{OH}^{-}\). In contrast, silver doesn't have the ability to form such a complex with hydroxide, recently it doesn't have empty d orbitals.

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Most popular questions from this chapter

Describe how you would prepare a 1-L \(0.20 \mathrm{M}\) \(\mathrm{CH}_{3} \mathrm{COONa} / 0.20 \mathrm{M} \mathrm{CH}_{3} \mathrm{COOH}\) buffer system by (a) mixing a solution of \(\mathrm{CH}_{3} \mathrm{COOH}\) with a solution of \(\mathrm{CH}_{3} \mathrm{COONa},\) (b) reacting a solution of \(\mathrm{CH}_{3} \mathrm{COOH}\) with a solution of \(\mathrm{NaOH},\) and (c) reacting a solution of \(\mathrm{CH}_{3}\) COONa with a solution of \(\mathrm{HCl}\).

Amino acids are building blocks of proteins. These compounds contain at least one amino group \(\left(-\mathrm{NH}_{2}\right)\) and one carboxyl group \((-\mathrm{COOH})\) Consider glycine \(\left(\mathrm{NH}_{2} \mathrm{CH}_{2} \mathrm{COOH}\right) .\) Depending on the pH of the solution, glycine can exist in one of three possible forms: $$ \begin{array}{l} \text { Fully protonated: } \mathrm{NH}_{3}-\mathrm{CH}_{2}-\mathrm{COOH} \\ \text { Dipolar ion: } \mathrm{NH}_{3}-\mathrm{CH}_{2}-\mathrm{COO}^{-} \\ \text {Fully ionized: } \mathrm{NH}_{2}-\mathrm{CH}_{2}-\mathrm{COO}^{-} \end{array} $$ Predict the predominant form of glycine at \(\mathrm{pH} 1.0\), 7.0, and 12.0. The \(\mathrm{p} K_{\mathrm{a}}\) of the carboxyl group is 2.3 and that of the ammonium group \(\left(-\mathrm{NH}_{3}^{+}\right)\) is 9.6

Which of the following solutions can act as a buffer. (a) \(\mathrm{KCl} / \mathrm{HCl}\), (b) \(\mathrm{KHSO}_{4} / \mathrm{H}_{2} \mathrm{SO}_{4}\) (c) \(\mathrm{Na}_{2} \mathrm{HPO}_{4} /\) \(\mathrm{NaH}_{2} \mathrm{PO}_{4}\) (d) \(\mathrm{KNO}_{2} / \mathrm{HNO}_{2} ?\)

Phenolphthalein is the common indicator for the titration of a strong acid with a strong base. (a) If the \(\mathrm{p} K_{\mathrm{a}}\) of phenolphthalein is \(9.10,\) what is the ratio of the nonionized form of the indicator (colorless) to the ionized form (reddish pink) at pH \(8.00 ?\) (b) If 2 drops of \(0.060 M\) phenolphthalein are used in a titration involving a \(50.0-\mathrm{mL}\) volume, what is the concentration of the ionized form at pH \(8.00 ?\) (Assume that 1 drop \(=0.050 \mathrm{~mL}\).)

A \(0.054 M \mathrm{HNO}_{2}\) solution is titrated with a \(\mathrm{KOH}\) solution. What is \(\left[\mathrm{H}^{+}\right]\) at half way to the equivalence point?
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