Make a sketch of a concentration cell employing two Zn/Zn²⁺ half-cells. The concentration of Zn²⁺ in one of the half-cells is 2.0 M and the concentration in the other half-cell is 1.0×10^–3 M. Label the anode and the cathode and indicate the half-reaction occuring at each electrode. Also indicate the direction of electron flow.

Verified step by step guidance

1. Draw two separate half-cells, each containing a Zn electrode immersed in a solution of Zn2+ ions. Label one half-cell with a Zn2+ concentration of 2.0 M and the other with a Zn2+ concentration of 1.0x10^-3 M.
2. Identify the anode and the cathode based on the concentration of Zn2+ ions. The anode will be the half-cell with the higher concentration of Zn2+ (2.0 M) because oxidation (loss of electrons) will occur more readily where there is a higher concentration of ions to accept electrons. The cathode will be the half-cell with the lower concentration of Zn2+ (1.0x10^-3 M) because reduction (gain of electrons) will occur more readily where there is a lower concentration of ions.
3. Write the half-reaction occurring at the anode: \( Zn(s) \rightarrow Zn^{2+}(aq) + 2e^- \). This indicates that zinc metal is being oxidized to zinc ions while releasing electrons.
4. Write the half-reaction occurring at the cathode: \( Zn^{2+}(aq) + 2e^- \rightarrow Zn(s) \). This indicates that zinc ions are being reduced to zinc metal by gaining electrons.
5. Indicate the direction of electron flow from the anode to the cathode. This is because electrons flow from a site of higher chemical potential (anode) to a site of lower chemical potential (cathode) in a spontaneous reaction.

Key Concepts

Concentration Cells

A concentration cell is a type of electrochemical cell where two half-cells have the same electrodes but different concentrations of the same ion. The cell generates an electromotive force (EMF) due to the concentration gradient, driving the spontaneous flow of electrons from the half-cell with higher concentration to the one with lower concentration. This setup illustrates the principles of electrochemistry and the Nernst equation.

Half-Reactions

Half-reactions represent the individual oxidation or reduction processes occurring at the electrodes in an electrochemical cell. In a zinc concentration cell, the oxidation half-reaction occurs at the anode, where zinc metal is oxidized to Zn2+ ions, while the reduction half-reaction occurs at the cathode, where Zn2+ ions are reduced back to zinc metal. Understanding these half-reactions is crucial for identifying the flow of electrons and the overall cell reaction.

Electron Flow

In electrochemical cells, electrons flow from the anode to the cathode through an external circuit. In the context of a concentration cell, electrons move from the half-cell with the higher concentration of Zn2+ (anode) to the half-cell with the lower concentration (cathode). This flow is driven by the potential difference created by the concentration gradient, and it is essential for the functioning of the cell and the generation of electrical energy.