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Chapter 21: Problem 31

When 6\(M\) ammonia is added gradually to aqueous copper(II) nitrate, a white precipitate forms. The precipitate dissolves as more 6\(M\) ammonia is added. Write balanced equations to explain these observations. [Hint: \(\mathrm{Cu}^{2+}\) reacts with \(\mathrm{NH}_{3}\) to form \(\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}^{2+} . ]\)

Short Answer

Expert verified
The short answer for the formation of the white precipitate and its subsequent dissolving is as follows: 1. Formation of the white precipitate: \(\mathrm{Cu^{2+}(aq) + 2OH^-(aq) \rightarrow Cu(OH)_2(s)}\) 2. Dissolving of the white precipitate: \(\mathrm{Cu(OH)_2(s) + 4NH_3(aq) \rightarrow Cu(NH_3)_4^{2+}(aq) + 2OH^-(aq)}\)

Step by step solution

01

Formation of the white precipitate

When ammonia is added gradually to the aqueous copper(II) nitrate solution, it reacts with water to form ammonium ions (\(\mathrm{NH}_4^+\)) and hydroxide ions (\(\mathrm{OH}^-\)). The hydroxide ions then react with the copper(II) ions, forming the insoluble white precipitate copper(II) hydroxide. Balanced equation for the formation of the white precipitate: \(\mathrm{Cu^{2+}(aq) + 2OH^-(aq) \rightarrow Cu(OH)_2(s)}\)
02

Dissolving the white precipitate

When more ammonia is added, it reacts with copper(II) hydroxide to form the soluble complex ion, \(\mathrm{Cu}(\mathrm{NH}_3)_4^{2+}\), which dissolves in the solution. Balanced equation for the dissolving of the white precipitate: \(\mathrm{Cu(OH)_2(s) + 4NH_3(aq) \rightarrow Cu(NH_3)_4^{2+}(aq) + 2OH^-(aq)}\) So, the two balanced equations that explain the observations are: 1. \(\mathrm{Cu^{2+}(aq) + 2OH^-(aq) \rightarrow Cu(OH)_2(s)}\) 2. \(\mathrm{Cu(OH)_2(s) + 4NH_3(aq) \rightarrow Cu(NH_3)_4^{2+}(aq) + 2OH^-(aq)}\)

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Most popular questions from this chapter

A certain first-row transition metal ion forms many different colored solutions. When four coordination compounds of this metal, each having the same coordination number, are dissolved in water, the colors of the solutions are red, yellow, green, and blue. Further experiments reveal that two of the complex ions are paramagnetic with four unpaired electrons and the other two are diamagnetic. What can be deduced from this information about the four coordination compounds?

Acetylacetone, abbreviated acacH, is a bidentate ligand. It loses a proton and coordinates as acac \(^{-},\) as shown below, where \(\mathrm{M}\) is a transition metal: Which of the following complexes are optically active: cis-$\mathrm{Cr}(\mathrm{acac})_{2}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2},\( trans-Cr(acac) \)_{2}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2},\( and \)\mathrm{Cr}(\mathrm{acac})_{3} ?$

What is the electron configuration for the transition metal ion(s) in each of the following compounds? a. $\left(\mathrm{NH}_{4}\right)_{2}\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2} \mathrm{Cl}_{4}\right]$ b. $\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{2}\left(\mathrm{NH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2}\right)_{2}\right] \mathrm{I}_{2}$ c. \(\mathrm{Na}_{2}\left[\mathrm{TaF}_{7}\right]\) d. $\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{I}_{2}\right]\left[\mathrm{PtI}_{4}\right]$ Pt forms \(+2\) and \(+4\) oxidation states in compounds.

Why are \(\mathrm{CN}^{-}\) and \(\mathrm{CO}\) toxic to humans?

Almost all metals in nature are found as ionic compounds in ores instead of being in the pure state. Why? What must be done to a sample of ore to obtain a metal substance that has desirable properties?
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