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Chapter 10: Problem 122

A street vendor sells you a ring he claims is pure gold. However, when you place the ring in a solution of \(\mathrm{Cu}^{2+}\) ions, copper plates out on the ring. How do you know the ring is a fake? Could it be made of silver?

Short Answer

Expert verified
When the ring is placed in the \(\mathrm{Cu}^{2+}\) solution, copper plates out on the ring, indicating that the metal in the ring is more reactive than copper. As both gold and silver are less reactive than copper, they cannot be displaced by copper ions. Thus, the ring must be a fake and cannot be made of gold or silver.

Step by step solution

01

Understanding the reactivity of metals

To determine if the ring is genuine, we need to understand the reactivity series of metals. The reactivity series is a list of metals ranked by their reactivity, with the most reactive metals at the top and the least reactive at the bottom. The reactivity series can help predict if a metal will displace another metal in a solution. The general rule is that a more reactive metal will displace a less reactive metal in a solution.
02

Reactivity of gold, silver, and copper

In the reactivity series, gold (Au) is among the least reactive metals, while silver (Ag) is slightly more reactive compared to gold. Copper (Cu) is more reactive than both gold and silver. This means that copper should not be able to displace gold or silver from a solution. If the ring were pure gold or silver, the copper ions in the \(\mathrm{Cu}^{2+}\) solution would not be able to replace the gold or silver in the ring.
03

Observing the reaction

When the ring is placed in the \(\mathrm{Cu}^{2+}\) solution, copper plates out on the ring. This implies that the metal making up the ring is more reactive than copper, and hence the metal is displaced by the copper ions in the solution. Since both gold and silver are less reactive than copper and cannot be displaced by the copper ions, the ring must be a fake and cannot be made of gold or silver.
04

Conclusion

Since the reaction between the ring and the \(\mathrm{Cu}^{2+}\) solution caused copper to plate out on the ring, it indicates that the ring is not made of gold or silver, as these metals would not be displaced by copper ions. Therefore, the ring must be a fake and cannot be made of gold or silver.

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Most popular questions from this chapter

Which of the following are electron-transfer reactions? For those that are, indicate which reactant is the reducing agent and which reactant is the oxidizing agent. (a) \(\mathrm{PF}_{3}+3 \mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{H}_{3} \mathrm{PO}_{3}+3 \mathrm{HF}\) (b) \(\mathrm{H}_{2}+\mathrm{Cl}_{2} \rightarrow 2 \mathrm{HCl}\) (c) \(2 \mathrm{Cr}_{2} \mathrm{O}_{3}+3 \mathrm{Si} \rightarrow 4 \mathrm{Cr}+3 \mathrm{SiO}_{2}\) (d) \(\mathrm{HCl}+\mathrm{NaOH} \rightarrow \mathrm{NaCl}+\mathrm{H}_{2} \mathrm{O}\)

Indicate whether each reaction is a redox reaction. If it is, which atom gets oxidized and which atom gets reduced? Consult the shortcut rules. \(\mathrm{Ca}+2 \mathrm{H}^{+} \rightarrow \mathrm{Ca}^{2+}+\mathrm{H}_{2}\)

You are trying to determine the identity of an unknown metal. You place a strip of it in a solution of \(\mathrm{Mg}^{2+}\), and no reaction occurs. You then place a strip of it in a solution of \(\mathrm{Zn}^{2+}\), and zinc metal plates out on the strip. Name one possibility for the identity of the unknown metal.

What happens to an atom's oxidation state when the atom is oxidized?

WorkPatch \(10.2\) had you assign oxidation states to the oxygen atoms in ozone. The answer was \(-1\) and 0 for the terminal (end) oxygen atoms and \(+1\) for the central oxygen atom. But now, a student claims the oxidation states are \(+1\) for the central oxygen atom and \(-1 / 2\) for the terminal oxygen atoms. He is also right. Explain why.
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