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Chapter 20: Problem 88

Copper corrodes to cuprous oxide, \(\mathrm{Cu}_{2} \mathrm{O},\) or cupric oxide, \(\mathrm{CuO},\) depending on environmental conditions. (a) What is the oxidation state of copper in cuprous oxide? (b) What is the oxidation state of copper in cupric oxide? (c) Copper peroxide is another oxidation product of elemental copper. Suggest a formula for copper peroxide based on its name. (d) Copper(III) oxide is another unusual oxidation product of elemental copper. Suggest a chemical formula for copper(III) oxide.

Short Answer

Expert verified
(a) The oxidation state of copper in cuprous oxide (Cu₂O) is +1. (b) The oxidation state of copper in cupric oxide (CuO) is +2. (c) The formula for copper peroxide is Cu₂O₂. (d) The chemical formula for copper(III) oxide is Cu₂O₃.

Step by step solution

01

(a) Find the oxidation state of copper in cuprous oxide (Cu₂O)

Oxidation state of oxygen in most compounds is -2. In Cu₂O, there are two copper atoms, and they have a combined oxidation state of +2 to balance the -2 charge from the oxygen atom. Therefore, the oxidation state of each copper atom in Cu₂O is +1.
02

(b) Find the oxidation state of copper in cupric oxide (CuO)

Just like in (a), the oxidation state of the oxygen atom is -2. In CuO, there is only one copper atom, which has an oxidation state of +2 to balance the -2 charge from the oxygen atom.
03

(c) Suggest a formula for copper peroxide based on its name

Peroxides are compounds that contain an oxygen-oxygen bond, and the general formula for a metal peroxide is M₂O₂, where M is the metal. Since the name is copper peroxide, we can replace the metal M with Cu (copper), thus the formula for copper peroxide is Cu₂O₂.
04

(d) Suggest a chemical formula for copper(III) oxide

The Roman numeral (III) in the name copper(III) oxide indicates that the copper atom has an oxidation state of +3. We can write the oxidation states as Cu(+3) and O(-2) for copper and oxygen, respectively. To balance the charges in the compound, we need two copper atoms for every three oxygen atoms, resulting in the chemical formula Cu₂O₃ for copper(III) oxide.

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Most popular questions from this chapter

A voltaic cell is constructed with two \(\mathrm{Cu}^{2+}-\mathrm{Cu}\) electrodes. The two half-cells have $\left[\mathrm{Cu}^{2+}\right]=0.100 \mathrm{M}\( and \)\left[\mathrm{Cu}^{2+}\right]=1.00 \times 10^{-4} \mathrm{M}$, respectively. (a) Which electrode is the cathode of the cell? (b) What is the standard emf of the cell? (c) What is the cell emf for the concentrations given? (d) For each electrode, predict whether \(\left[\mathrm{Cu}^{2+}\right]\) will increase, decrease, or stay the same as the cell operates.

Some years ago a unique proposal was made to raise the Titanic. The plan involved placing pontoons within the ship using a surface-controlled submarine-type vessel. The pontoons would contain cathodes and would be filled with hydrogen gas formed by the electrolysis of water. It has been estimated that it would require about \(7 \times 10^{8} \mathrm{~mol}\) of \(\mathrm{H}_{2}\) to provide the buoyancy to lift the ship (J. Chem. Educ., 1973, Vol. 50, 61). (a) How many coulombs of electrical charge would be required? (b) What is the minimum voltage required to generate \(\mathrm{H}_{2}\) and \(\mathrm{O}_{2}\) if the pressure on the gases at the depth of the wreckage \((3 \mathrm{~km})\) is \(30 \mathrm{MPa} ?(\mathbf{c})\) What is the minimum electrical energy required to raise the Titanic by electrolysis? (d) What is the minimum cost of the electrical energy required to generate the necessary \(\mathrm{H}_{2}\) if the electricity costs 85 cents per kilowatt-hour to generate at the site?

At \(298 \mathrm{~K}\) a cell reaction has a standard cell potential of $+0.63 \mathrm{~V}\(. The equilibrium constant for the reaction is \)3.8 \times 10^{10}\(. What is the value of \)n$ for the reaction?

(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?

Disulfides are compounds that have \(S-S\) bonds, like peroxides have \(\mathrm{O}-\mathrm{O}\) bonds. Thiols are organic compounds that have the general formula \(\mathrm{R}-\mathrm{SH}\), where \(\mathrm{R}\) is a generic hydrocarbon. The \(\mathrm{SH}^{-}\) ion is the sulfur counterpart of hydroxide, \(\mathrm{OH}^{-}\). Two thiols can react to make a disulfide, \(\mathrm{R}-\mathrm{S}-\mathrm{S}-\mathrm{R} .\) (a) What is the oxidation state of sulfur in a thiol? (b) What is the oxidation state of sulfur in a disulfide? (c) If you react two thiols to make a disulfide, are you oxidizing or reducing the thiols? (d) If you wanted to convert a disulfide to two thiols, should you add a reducing agent or oxidizing agent to the solution? (e) Suggest what happens to the H's in the thiols when they form disulfides.
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