Problem 80 - Chemistry: The Central Science

Question

(a) Based on standard reduction potentials, would you expect copper metal to oxidize under standard conditions in the presence of oxygen and hydrogen ions? (b) When the Statue of Liberty was refurbished, Teflon spacers were placed between the iron skeleton and the copper metal on the surface of the statue. What role do these spacers play?

Step-by-Step Solution

Answer

(a) Yes, copper metal is expected to oxidize under standard conditions in the presence of oxygen and hydrogen ions. The standard cell potential (\(E°_cell\)) for the redox reaction involving the oxidation of copper and reduction of oxygen is +0.89V, which indicates a spontaneous reaction. (b) Teflon spacers placed between the iron skeleton and the copper metal on the surface of the Statue of Liberty prevent direct contact between the two metals, avoiding redox reactions between iron and copper. This significantly reduces the rate of oxidation and corrosion and helps maintain the structural integrity of the statue.

Step 1: Write the half-reactions

First, we need to know the half-reactions for the oxidation of copper metal and reduction of oxygen gas in the presence of hydrogen ions. Oxidation half-reaction: \[Cu (s) \rightarrow Cu^{2+} (aq) + 2e^-\] Reduction half-reaction: \[O_2 (g) + 4H^{+} (aq) + 4e^- \rightarrow 2H_2O (l)\] Now, we have both copper and oxygen half-reactions.

Step 2: Determine the standard cell potential (E°)

We need to find the values of standard reduction potentials for each half-reaction. We can search these values in a table of standard reduction potentials: Copper half-reaction: \[E°_{Cu^{2+}/Cu} = +0.34V\] Oxygen half-reaction: \[E°_{O_2/H_2O} = +1.23V\] Calculate the standard cell potential (\(E°_cell\)) for the overall redox reaction by subtracting the standard reduction potential of the oxidation half-reaction from the reduction half-reaction: \[E°_cell = E°_{O_2/H_2O} - E°_{Cu^{2+}/Cu}\]

Step 3: Calculate the standard cell potential (E°) and determine spontaneity

Now we can calculate the standard cell potential using the values and formula above: \[E°_cell = (+1.23V) - (+0.34V) = +0.89V\] Since the standard cell potential (\(E°_cell\)) is positive, the redox reaction involving oxidation of copper and reduction of oxygen in the presence of hydrogen ions is spontaneous under standard conditions. Thus, copper metal is expected to oxidize under standard conditions. #b) Role of Teflon spacers in the Statue of Liberty#

Step 1: Understand the problem with the iron-copper contact in the statue

When copper comes in contact with iron, it can act as a catalyst for redox reactions and accelerate corrosion. The copper metal can also oxidize, together with iron. This corrosion creates a reduction in structural integrity and leads to potential structural failure of the statue.

Step 2: Understand the importance of Teflon spacers in this context

Teflon spacers are added between the iron skeleton and the copper on the surface of the Statue of Liberty to prevent direct contact between the two metals. These spacers act as a barrier, preventing the exchange of ions and thus avoiding the redox reactions between iron and copper. By eliminating direct contact between the two metals, the rate of oxidation and corrosion is significantly reduced, helping maintain the structural integrity of the statue and minimizing damage.