Problem 32 - Chemistry: An Atoms-Focused Approach

Question

What are the formulas of the following copper minerals? a. cuprite, copper(I) oxide b. chalcocite, copper( \(I\) ) sulfide c. covellite, copper(II) sulfide

Step-by-Step Solution

Answer

Answer: The chemical formulas for these copper minerals are as follows: - Cuprite (copper(I) oxide): Cu\(_2\)O - Chalcocite (copper(I) sulfide): Cu\(_2\)S - Covellite (copper(II) sulfide): CuS

Step 1: Cuprite, copper(I) oxide formula

To find the formula of cuprite which is copper(I) oxide, we first notice that copper(I) means that copper has a +1 oxidation state. The oxide ion has a charge of −2. To balance the charges and form a neutral compound, you need two copper(I) ions for each oxide ion. The formula for cuprite is Cu\(_2\)O.

Step 2: Chalcocite, copper(I) sulfide formula

For chalcocite, which is copper(I) sulfide, the oxidation state of copper is also +1 because it is copper(I) in this compound. The sulfide ion has a charge of −2. Similar to the case of cuprite, you need two copper(I) ions for each sulfide ion to balance the charges and form a neutral compound. The formula for chalcocite is Cu\(_2\)S.

Step 3: Covellite, copper(II) sulfide formula

As for covellite which is copper(II) sulfide, copper has a +2 oxidation state because it is copper(II) in this compound. The sulfide ion has a charge of −2. In this case, you need one copper(II) ion for each sulfide ion to balance the charges and form a neutral compound. The formula for covellite is CuS.

Key Concepts

Chemical Formulas

Chemical formulas represent the elements contained in compounds and the number of atoms of each element. In the case of copper minerals, the formulas reflect the combination of copper with other elements. For example, in cuprite, the chemical formula is \( \text{Cu}_2\text{O} \), indicating the presence of two copper atoms for every oxygen atom. Similarly, chalcocite has the chemical formula \( \text{Cu}_2\text{S} \), signifying two copper atoms for each sulfur atom. Covellite differs slightly with the formula \( \text{CuS} \), showing a one-to-one ratio between copper and sulfur. These formulas help identify the basic structure of the mineral and the arrangement of its components.

Oxidation States

The oxidation state of an element in a compound indicates the number of electrons lost or gained by an atom of that element. Copper can exhibit different oxidation states, commonly +1 and +2. In copper(I) compounds like cuprite (Cu\(_2\)O) and chalcocite (Cu\(_2\)S), copper is in the +1 oxidation state. This means each copper atom has lost one electron. For copper(II) compounds such as covellite (CuS), copper takes on a +2 oxidation state, indicating the loss of two electrons per copper atom. These oxidation states dictate how copper interacts with other elements, impacting the overall structure and properties of the compounds.

Charge Balance

Charge balance is crucial in determining the formula of a compound. It ensures that the total positive charge equals the total negative charge, resulting in a neutral compound.

• In cuprite (Cu\(_2\)O), each copper(I) ion has a +1 charge, and the oxide ion has a -2 charge. Two copper(I) ions are needed to balance the -2 charge of one oxide ion.
• For chalcocite (Cu\(_2\)S), the +1 charge on each copper(I) ion requires two copper ions to balance the -2 charge from the sulfide ion.
• Meanwhile, in covellite (CuS), the copper(II) ion, with its +2 charge, perfectly offsets the -2 charge of the single sulfide ion.

Understanding how charges balance allows chemists to predict compound formulas and their structures.

Copper Compounds

Copper compounds are varied, with copper's ability to form different oxidation states and bond with various nonmetals. Known for their vibrant colors and significant utilities, copper compounds are integral in both industrial applications and natural mineral deposits.

• Cuprite (Cu\(_2\)O) appears predominantly red due to the copper(I) ion and is used in jewelry and as a minor ore of copper.
• Chalcocite (Cu\(_2\)S) is a dark gray mineral often found in copper-rich deposits and is highly valued as a copper ore.
• Covellite (CuS) has a striking indigo-blue color and serves as a notable secondary copper ore.

Each of these compounds illustrates copper's versatility and its role in various environmental and economic contexts.