Problem 84 - 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, under standard conditions, copper metal will oxidize in the presence of oxygen and hydrogen ions, as the total standard reduction potential for the reaction is positive, with a value of +0.89V. (b) The Teflon spacers placed between the iron skeleton and the copper metal on the surface of the Statue of Liberty prevent galvanic corrosion. They act as an insulator, avoiding direct contact between the two metals and thereby eliminating the possibility of galvanic corrosion, ensuring the monument's longevity and structural integrity.

Step 1: (a) Determine if Copper will Oxidize in the Presence of Oxygen and Hydrogen Ions under Standard Conditions

To determine if copper will oxidize in the presence of oxygen and hydrogen ions under standard conditions, we should compare the standard reduction potentials of the half-reactions. The relevant half-reactions are: 1. \(Cu^{2+}(aq) + 2e^{-} ⟶ Cu(s)\) - standard reduction potential (SRP) = +0.34 V 2. \(O_2(g) + 4H^{+}(aq) + 4e^{-} ⟶ 2H_2O(l)\) - standard reduction potential (SRP) = +1.23 V If the sum of the standard reduction potentials is positive, the reaction is spontaneous, meaning the oxidation of copper will occur. In order to find out if the reaction is spontaneous, the half-reactions must be added together, where the second reaction is kept as it is, and the first reaction is reversed (oxidation). The reversed reaction for the first half-reaction is as follows: 3. \(Cu(s) ⟶ Cu^{2+}(aq) + 2e^{-}\) with a standard reduction potential of -0.34V. Now, we will add the half-reactions and their corresponding standard reduction potentials: 4. \( Cu(s) + O_2(g) + 4H^{+}(aq) ⟶ Cu^{2+}(aq) + 2H_2O(l)\) with a total SRP = -0.34V + 1.23V = +0.89V Since the total standard reduction potential is positive (+0.89V), the reaction is spontaneous and copper will oxidize under standard conditions in the presence of oxygen and hydrogen ions.

Step 2: (b) Role of Teflon Spacers in the Refurbishment of the Statue of Liberty

The Statue of Liberty is made of copper, and its supporting structure is made of iron. When two metals with different standard reduction potentials (like copper and iron) come into contact in the presence of moisture, a process called galvanic corrosion can occur. In this process, the metal with a lower reduction potential (iron in this case) will corrode, while the metal with a higher reduction potential (copper) will be protected. Teflon spacers were placed between the iron skeleton and the copper metal on the surface of the Statue of Liberty during its refurbishment to prevent this galvanic corrosion. These spacers act as an insulator, preventing direct contact between the copper and iron metals, and thus eliminating the possibility of galvanic corrosion. This helps to ensure the longevity and structural integrity of both the copper surface and the iron supporting structure, preserving the monument for future generations to appreciate.