Question

Assign the oxidation state for the element listed in each of the following compounds: \(\mathrm{S}\) in \(\mathrm{MgSO}_{4}\)_______ \(\mathrm{Pb}\) in \(\mathrm{PbSO}_{4}\)______ \(\mathrm{O}\) in \(\mathrm{O}_{2}\)___________ \(\mathrm{Ag}\) in Ag _________________________ \(\mathrm{Cu}\) in \(\mathrm{CuCl}_{2}\)_______

Short answer

The oxidation states of the elements in the given compounds are: $\mathrm{S}$ in $\mathrm{MgSO}_{4}$: \(+6\) $\mathrm{Pb}$ in $\mathrm{PbSO}_{4}$: \(+2\) $\mathrm{O}$ in $\mathrm{O}_{2}$: \(0\) $\mathrm{Ag}$ in $\mathrm{Ag}$: \(0\) $\mathrm{Cu}$ in $\mathrm{CuCl}_{2}$: \(+2\)

Step-by-step solution

Rule 1: Oxidation State of a Pure Element

The oxidation state of a pure element is always zero. For example, O in O₂ will have an oxidation state of zero.

Rule 2: Oxidation State of Homoatomic Ions

The oxidation state of a monoatomic ion equals its charge. For example, Ag in Ag will have an oxidation state of zero since it's an uncharged, pure element.

Rule 3: The Sum of Oxidation States in a Compound

The sum of oxidation states of all elements in a compound is equal to the total charge of the compound. For electrically neutral compounds, the sum is zero. Now we will apply these rules to find oxidation states for the remaining elements in the given compounds.

Assigning Oxidation State of S in MgSO₄

We can use Rule 3 and the properties of the individual ions to deduce the oxidation state of S in MgSO₄. We know Mg is a group 2 element, so it forms an ion with a charge of +2. The charge on SO₄²⁻ is -2 (since it's a sulfate ion) and O has an oxidation state of -2. Let x be the oxidation state of S. Mg²⁺ + x + 4(-2) = 0 (as the compound is neutral) Solving for x: x = 2 - 4*(-2) = 2 + 8 = +6 The oxidation state of S in MgSO₄ is +6.

Assigning Oxidation State of Pb in PbSO₄

We can use Rule 3 and the properties of individual ions to deduce the oxidation state of Pb in PbSO₄. We know that SO₄²⁻ has a charge of -2 and O has an oxidation state of -2. Let x be the oxidation state of Pb; x + 4(-2) = 0 (as the compound is neutral) Solving for x: x = 4*(-2) = - 8 The oxidation state of Pb in PbSO₄ is +2.

Assigning Oxidation State of Cu in CuCl₂

We can use Rule 3 and the properties of individual ions to deduce the oxidation state of Cu in CuCl₂. We know that Cl⁻ has a charge of -1. Let x be the oxidation state of Cu; x + 2(-1) = 0 (as the compound is neutral) Solving for x: x = 2*(-1) = + 2 The oxidation state of Cu in CuCl₂ is +2. In conclusion, the oxidation states of the elements in the given compounds are: S in MgSO₄: +6 Pb in PbSO₄: +2 O in O₂: 0 Ag in Ag: 0 Cu in CuCl₂: +2

Key concepts

Chemical Compounds

Chemical compounds are substances formed by the chemical combination of two or more elements. These elements are joined together by chemical bonds, and the ratio of the elements in the compound is fixed. For example, in the compound magnesium sulfate, written as \( \text{MgSO}_4 \), magnesium (Mg), sulfur (S), and oxygen (O) are chemically bonded together through ionic and covalent bonds.
Understanding chemical compounds helps us predict how different substances will react with each other. A key property of these compounds is that they often form to reach a stable electronic configuration. This can result in the compound having a very specific and unique structure and properties.
Elements within a chemical compound might have a different oxidation state than they do in their free form due to sharing or transferring electrons. The oxidation state is crucial for studying the role each element plays in the compound's chemical reactions.

Electroneutrality Principle

The electroneutrality principle is a concept in chemistry that states that every stable compound must be electrically neutral. This means the total positive charge must equal the total negative charge, ensuring the compound remains stable. For instance, in our example of \( \text{MgSO}_4 \), the charges must balance out for the compound to be electrically neutral.
When calculating oxidation states, keeping this principle in mind is essential. For each compound, you sum the oxidation states of all atoms, and this sum should be equal to the net charge of the compound. This is particularly helpful when dealing with ionic compounds that include polyatomic ions like sulfate \((\text{SO}_4^{2-})\), where the oxidation states within the ion must also sum up to equal the ion's charge.
The electroneutrality principle ensures that when elements come together to form compounds, they do so in a way that keeps the compound's charge balanced. This principle is key to understanding various oxidation state assignments in compound chemistry.

Oxidation Rules

Oxidation rules are systematic guidelines used to assign oxidation states to elements in chemical compounds. Understanding these rules helps identify how many electrons have been gained or lost in comparison to the elemental form.

• By default, the oxidation state of an element in its pure elemental form (like \( \text{O}_2 \) or \( \text{Ag} \)) is zero.
• For monoatomic ions, the oxidation state is equal to the charge of the ion. For example, \( \text{Cl}^- \) has an oxidation state of -1.
• In a neutral compound, the sum of the oxidation states of all atoms must be zero, as explained by the electroneutrality principle, which we've covered earlier.

These rules help systematically determine unknown oxidation states within compounds. For example, understanding that oxygen typically has an oxidation state of -2 allows us to deduce the oxidation state of sulfur in magnesium sulfate by following the sequence of rules and applying simple algebra. By becoming proficient in these rules, students will better predict chemical behavior and solve complex chemical equations.