Problem 15 - Chemistry and Chemical Reactivity

Question

Cobalt forms \(\mathrm{Co}^{2+}\) and \(\mathrm{Co}^{3+}\) ions. Write the formulas for the two cobalt oxides formed by these transition metal ions.

Step-by-Step Solution

Answer

The formulas are \( \mathrm{CoO} \) and \( \mathrm{Co_2O_3} \).

Step 1: Understanding Ion Charges

The exercise involves Cobalt which can form two different ions: \( \mathrm{Co}^{2+} \) and \( \mathrm{Co}^{3+} \). Oxide ions have the formula \( \mathrm{O}^{2-} \). To form a neutral compound, the total positive charge must equal the total negative charge.

Step 2: Cobalt(II) Oxide

For \( \mathrm{Co}^{2+} \), it can combine with one \( \mathrm{O}^{2-} \) ion to form a neutral compound: \( \mathrm{CoO} \). This is because one 2+ charge from cobalt cancels with one 2- charge from oxygen.

Step 3: Cobalt(III) Oxide

For \( \mathrm{Co}^{3+} \), it requires a different ratio. Two \( \mathrm{Co}^{3+} \) ions (total charge = 6+) will pair with three \( \mathrm{O}^{2-} \) ions (total charge = 6-) to form \( \mathrm{Co_2O_3} \). The compound is balanced in charge because 2 x 3 = 3 x 2.

Key Concepts

Cobalt Ions

Cobalt is a transition metal that can form different ions, specifically the cobalt ions \( \mathrm{Co}^{2+} \) and \( \mathrm{Co}^{3+} \). These ions are essential in understanding the formation of cobalt compounds. Transition metals like cobalt often have multiple oxidation states, because they have electrons in their d-orbitals that can be lost or shared in chemical bonds.

• \( \mathrm{Co}^{2+} \): This ion indicates that cobalt has lost 2 electrons.
• \( \mathrm{Co}^{3+} \): This ion signifies that cobalt has lost 3 electrons.

In chemical reactions, these ions will combine with other ions to form stable, neutral compounds. Understanding these ions' charges allows us to predict how cobalt will interact with other elements, such as forming oxides by bonding with oxygen ions.

Oxide Ions

The oxide ion is represented by \( \mathrm{O}^{2-} \) and it's one of the simplest anions, formed when oxygen gains two electrons. This gain results in a charge of \(-2\). An oxide ion is significant when forming compounds, especially with metals, as it helps in balancing the charges in ionic compounds.

Since oxide ions play a key role in combining with metal ions to form oxides, understanding their charge is critical. For instance, in the case of cobalt oxide formation:

• An oxide ion with a charge of \(+2\) balances with a \( \mathrm{Co}^{2+} \) ion to form \( \mathrm{CoO} \).
• Multiple oxide ions can pair with cobalt ions, like \( \mathrm{Co}^{3+} \), to ensure that the overall charge in the compound is neutral. This leads to the formation of different ratios in compounds like \( \mathrm{Co_2O_3} \).

Understanding the role of oxide ions helps in predicting the possible chemical formulas of compounds they form with transition metals.

Ion Charges

Ion charges are vital in chemical reactions, especially for achieving charge neutrality in ionic compounds. When creating compounds from ions, it's crucial to ensure the total positive charges equal the total negative charges, resulting in an electrically neutral compound.

In our exercise, knowing the charges of cobalt and oxide ions helps us derive the formulas for cobalt oxides:

• \( \mathrm{Co}^{2+} \) combines with \( \mathrm{O}^{2-} \) ion in a 1:1 ratio to form \( \mathrm{CoO} \).
• \( \mathrm{Co}^{3+} \) requires a 2:3 ratio with \( \mathrm{O}^{2-} \) to create \( \mathrm{Co_2O_3} \), achieving balanced charges as shown by \( \mathrm{2(3+)} + \mathrm{3(2-)} = 0 \).

These principles show how different ion combinations can result in diverse chemical compounds, each with specific properties and structures, depending on the charge and number of ions involved.