The metal cadmium tends to form Cd²⁺ ions. The following observations are made: (i) When a strip of zinc metal is placed in CdCl₂(aq), cadmium metal is deposited on the strip. (ii) When a strip of cadmium metal is placed in Ni(NO₃)(aq), nickel metal is deposited on the strip. (b) Which elements more closely define the position of cadmium in the activity series?

Verified step by step guidance

1. Identify the reactions occurring in each observation. For (i), the reaction is: Zn(s) + Cd^{2+}(aq) \rightarrow Cd(s) + Zn^{2+}(aq). For (ii), the reaction is: Cd(s) + Ni^{2+}(aq) \rightarrow Ni(s) + Cd^{2+}(aq).
2. Determine the direction of electron flow in each reaction. In (i), zinc is oxidized to Zn^{2+} and cadmium is reduced to Cd. In (ii), cadmium is oxidized to Cd^{2+} and nickel is reduced to Ni.
3. Use the observations to infer the relative reactivity of the metals. Since zinc can displace cadmium from Cd^{2+}, zinc is more reactive than cadmium. Since nickel can displace cadmium from Cd^{2+}, nickel is more reactive than cadmium.
4. Position cadmium in the activity series based on its reactivity relative to zinc and nickel. Cadmium is less reactive than both zinc and nickel.
5. Conclude that the elements zinc and nickel more closely define the position of cadmium in the activity series, with cadmium being less reactive than both.

Key Concepts

Activity Series of Metals

The activity series is a list of metals ranked by their ability to displace other metals from solutions of their ions. More reactive metals, like zinc, can displace less reactive metals, such as cadmium, from their compounds. This series helps predict the outcomes of single displacement reactions and the relative reactivity of metals.

Redox Reactions

Redox (reduction-oxidation) reactions involve the transfer of electrons between substances, leading to changes in oxidation states. In the given observations, cadmium ions are reduced to cadmium metal, while zinc is oxidized, demonstrating the electron transfer that characterizes these reactions. Understanding redox processes is crucial for analyzing metal displacement.

Electrochemical Series

The electrochemical series is a list of standard electrode potentials for various half-reactions, indicating the tendency of a species to gain or lose electrons. Metals higher in the series are more likely to be oxidized, while those lower are more likely to be reduced. This concept is essential for determining the relative positions of cadmium, zinc, and nickel in the activity series.