Question

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

(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

(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.

(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.

(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.

(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.

Key concepts

Copper Compounds

Copper compounds are fascinating and exhibit varying characteristics due to the copper's ability to have multiple oxidation states. For example, in cuprous oxide (${\mathrm{Cu}}_2\mathrm{O}$), copper exists in the +1 oxidation state. This is because there are two copper atoms, each contributing a +1 charge, which combines to balance the -2 charge from the single oxygen atom, typically having an oxidation state of -2 in most compounds.
Cupric oxide ($\mathrm{CuO}$), on the other hand, has copper in the +2 oxidation state. In this compound, one copper atom's +2 charge balances out the -2 charge of the oxygen.
These varying oxidation states of copper allow it to form a wide range of compounds, each exhibiting distinct properties that can be exploited in different chemical applications.

Chemical Formulas

Chemical formulas are essential for understanding the composition of compounds. They provide insight into the types and numbers of atoms involved. For example, the formula for copper peroxide is ${\mathrm{Cu}}_2{\mathrm{O}}_2$. This indicates that the compound contains two copper atoms and two oxygen atoms, which is characteristic of peroxides due to their unique oxygen-oxygen bond.
When naming compounds like copper peroxide, the name gives a clue about the structure of the compound. Using systematic naming helps set expectations for the composition and chemical behavior of substances, aiding chemists in predicting possible reactions.
Writing formulas often involves considering the oxidation states of the elements, thus ensuring that the charges within the compound are balanced. This balance is crucial as it determines the stability and reactivity of the compound.

Peroxides

Peroxides are a special type of compound containing a unique oxygen-oxygen single bond. This structure gives them particular chemical properties. An example in copper compounds would be copper peroxide, which has the chemical formula ${\mathrm{Cu}}_2{\mathrm{O}}_2$.
Peroxides generally exhibit strong oxidizing behavior due to the relatively weak O-O bond, which can be easily broken to produce oxygen radicals or to participate in redox reactions.

• Peroxides are used to initiate polymerization reactions.
• They act as bleaching agents and disinfectants.

These features make them valuable in various industrial processes. Understanding their chemical behavior is key for using them safely and effectively in chemical applications.