Question

the zinc hydroxide reacts with the excess ammonia in the solution to form a colorless zinc ammonia complex, \\(\text{zn}(\text{nh}_3)_4^{2+}\\), as shown below:

\\\text{zn}(\text{oh})_2(\text{s}) + 4\text{nh}_3(\text{aq}) \longrightarrow \text{zn}(\text{nh}_3)_4^{2+}(\text{aq}) + 2\text{oh}^-(\text{aq})\\

altogether, the colorless test solution contains \\(\text{zn}(\text{nh}_3)_4^{2+}\\) and \\(\text{nh}_3\\) and \\(\text{so}_4^{2-}\\). this test solution reacts with the excess \\(\text{cuso}_4\\) or the excess \\(\text{na}_2\text{s}\\) in two different ways which yield two very different colors

• \\(\text{cu}^{2+}(\text{aq}) + 4\text{nh}_3(\text{aq}) \longrightarrow \text{cu}(\text{nh}_3)_4^{2+}\\) gives a dark blue color solution.
• \\(\text{s}^{2-}(\text{aq}) + \text{zn}^{2+}(\text{aq}) \longrightarrow \text{zns}(\text{s})\\) yields a precipitate with a dingy white/yellow color.

about this lab

in this lab, you will combine solutions of copper(ii) sulfate (\\(\text{cuso}_4\\)) and sodium sulfide (\\(\text{na}_2\text{s}\\)) to produce copper(ii) sulfide (\\(\text{cus}\\)), as found in the following chemical reaction:

write the balanced chemical equation, including the physical states, for the reaction that occurs when the test solution reacts with excess copper(ii) sulfate, \\(\text{cuso}_4\\).

balanced equation:

Explanation:

Identify the reactants in the solution

The problem states that the colorless test solution contains \([\text{Zn}(\text{NH}_3)_4]^{2+}(\text{aq})\), \(\text{NH}_3(\text{aq})\), and \(\text{SO}_4^{2-}(\text{aq})\). This solution is reacted with excess copper(II) sulfate, \(\text{CuSO}_4(\text{aq})\), which dissociates into \(\text{Cu}^{2+}(\text{aq})\) and \(\text{SO}_4^{2-}(\text{aq})\).

Determine the chemical reaction

Using the Chemical Equation Balancing knowledge point, we analyze the species present. The text provides a key reaction:

$$\text{Cu}^{2+}(\text{aq}) + 4\text{NH}_3(\text{aq}) ightarrow [\text{Cu}(\text{NH}_3)_4]^{2+}(\text{aq})$$

The source of \(\text{NH}_3\) is the complex ion \([\text{Zn}(\text{NH}_3)_4]^{2+}\). When \(\text{Cu}^{2+}\) is added, it has a higher affinity for ammonia, displacing \(\text{Zn}^{2+}\) in a ligand exchange:

$$[\text{Zn}(\text{NH}_3)_4]^{2+}(\text{aq}) + \text{Cu}^{2+}(\text{aq}) ightarrow [\text{Cu}(\text{NH}_3)_4]^{2+}(\text{aq}) + \text{Zn}^{2+}(\text{aq})$$

Include spectator ions for the full equation

The copper(II) reactant is added as \(\text{CuSO}_4(\text{aq})\). The sulfate ions \(\text{SO}_4^{2-}(\text{aq})\) act as spectator ions balancing the charges of the metal cations:

$$[\text{Zn}(\text{NH}_3)_4]\text{SO}_4(\text{aq}) + \text{CuSO}_4(\text{aq}) ightarrow [\text{Cu}(\text{NH}_3)_4]\text{SO}_4(\text{aq}) + \text{ZnSO}_4(\text{aq})$$

Verify the balanced equation and states

We check that all atoms and charges balance:

• Left side: \(1\text{ Zn}\), \(1\text{ Cu}\), \(4\text{ N}\), \(12\text{ H}\), \(2\text{ SO}_4^{2-}\)
• Right side: \(1\text{ Zn}\), \(1\text{ Cu}\), \(4\text{ N}\), \(12\text{ H}\), \(2\text{ SO}_4^{2-}\)

All reactants and products are soluble in aqueous solution, so their physical states are all \(\text{(aq)}\).

Answer:

Write the balanced chemical equation, including the physical states, for the reaction that occurs when the test solution reacts with excess copper(II) sulfate, \(\text{CuSO}_4\).

balanced equation: <blank>\([\text{Zn}(\text{NH}_3)_4]\text{SO}_4(\text{aq}) + \text{CuSO}_4(\text{aq})
ightarrow [\text{Cu}(\text{NH}_3)_4]\text{SO}_4(\text{aq}) + \text{ZnSO}_4(\text{aq})\)</blank>