Textbook Question
Using standard reduction potentials (Appendix E), calculate the standard emf for each of the following reactions: (d) 2 NO3-1aq2 + 8 H+1aq2 + 3 Cu1s2 ¡ 2 NO1g2 + 4 H2O1l2 + 3 Cu2+1aq2
Ch.20 - Electrochemistry
Chapter 20, Problem 45
A 1 M solution of Cu(NO3)2 is placed in a beaker with a strip of Cu metal. A 1 M solution of SnSO4 is placed in a second beaker with a strip of Sn metal. A salt bridge connects the two beakers, and wires to a voltmeter link the two metal electrodes. (a) Which electrode serves as the anode, and which as the cathode? (b) Which electrode gains mass, and which loses mass as the cell reaction proceeds?
Verified step by step guidance1
Identify the half-reactions for each metal in the electrochemical cell. Copper (Cu) and tin (Sn) are involved in redox reactions. Write the reduction half-reaction for Cu: \( \text{Cu}^{2+} + 2e^- \rightarrow \text{Cu} \) and for Sn: \( \text{Sn}^{2+} + 2e^- \rightarrow \text{Sn} \).
Determine the standard reduction potentials for each half-reaction. The standard reduction potential for Cu is +0.34 V, and for Sn, it is -0.14 V. Compare these values to determine which metal is more likely to be reduced.
Identify the anode and cathode based on the reduction potentials. The electrode with the higher reduction potential will be the cathode (where reduction occurs), and the electrode with the lower reduction potential will be the anode (where oxidation occurs).
Determine which electrode gains mass and which loses mass. At the cathode, reduction occurs, leading to the deposition of metal ions onto the electrode, increasing its mass. At the anode, oxidation occurs, causing the metal to dissolve into ions, decreasing its mass.
Summarize the findings: The electrode with the higher reduction potential (Cu) serves as the cathode and gains mass, while the electrode with the lower reduction potential (Sn) serves as the anode and loses mass.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Electrochemical Cells
Electrochemical cells consist of two electrodes, an anode and a cathode, where oxidation and reduction reactions occur. The anode is where oxidation takes place, leading to the loss of electrons, while the cathode is where reduction occurs, resulting in the gain of electrons. In this setup, the flow of electrons from the anode to the cathode generates an electric current, which can be measured with a voltmeter.
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Electrochemical Cells
Oxidation and Reduction
Oxidation is defined as the loss of electrons, while reduction is the gain of electrons. In the context of the given question, copper (Cu) and tin (Sn) are involved in redox reactions. The metal that is oxidized will lose mass as it dissolves into the solution, while the metal that is reduced will gain mass as it deposits from the solution onto the electrode.
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Salt Bridge Function
A salt bridge is a crucial component of electrochemical cells that maintains electrical neutrality by allowing the flow of ions between the two half-cells. It prevents the solutions from mixing while enabling the movement of ions to balance the charge as oxidation and reduction reactions occur. This balance is essential for the continuous operation of the cell and affects the overall cell potential.
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Related Practice
Textbook Question
The standard reduction potentials of the following halfreactions are given in Appendix E:
Ag+(aq) + e- → Ag(s)
Cu2+(aq) + 2 e- → Cu(s)
Ni2+(aq) + 2 e- → Ni(s)
Cr3+(aq) + 3 e- → Cr(s)
(a) Determine which combination of these half-cell reactions leads to the cell reaction with the largest positive cell potential and calculate the value.
(b) Determine which combination of these half-cell reactions leads to the cell reaction with the smallest positive cell potential and calculate the value.
Textbook Question
A voltaic cell consists of a strip of cadmium metal in a solution of Cd(NO3)2 in one beaker, and in the other beaker a platinum electrode is immersed in a NaCl solution, with Cl2 gas bubbled around the electrode. A salt bridge connects the two beakers. (a) Which electrode serves as the anode, and which as the cathode? (b) Does the Cd electrode gain or lose mass as the cell reaction proceeds? (c) Write the equation for the overall cell reaction.
Textbook Question
From each of the following pairs of substances, use data in Appendix E to choose the one that is the stronger reducing agent: (a) Fe(s) or Mg(s) (b) Ca(s) or Al(s) (c) H2(g, acidic solution) or H2S(g)