Question

In each of the following reactions, identify which element is oxidized and which is reduced by assigning oxidation states. a. \(2 \mathrm{B}_{2} \mathrm{O}_{3}(s)+6 \mathrm{Cl}_{2}(g) \rightarrow 4 \mathrm{BCl}_{3}(l)+3 \mathrm{O}_{2}(g)\) b. \(\operatorname{GeH}_{4}(g)+\mathrm{O}_{2}(g) \rightarrow \operatorname{Ge}(s)+2 \mathrm{H}_{2} \mathrm{O}(g)\) c. \(\mathrm{C_{2} H_{4}(g)+C l_{2}(g) \rightarrow C_{2} H_{4} C l_{2}(l)}\) d. \(\mathrm{O}_{2}(g)+2 \mathrm{F}_{2}(g) \rightarrow 2 \mathrm{OF}_{2}(g)\)

Short answer

In the given reactions: a. Chlorine (Cl) is oxidized, going from an oxidation state of \(0\) to \(-1\), and oxygen (O) is reduced, going from \(-2\) to \(0\). b. Germanium (Ge) is oxidized from \(-4\) to \(0\), and oxygen (O) is reduced from \(0\) to \(-2\). c. Chlorine (Cl) is oxidized from \(0\) to \(-1\), and carbon (C) is reduced from \(-2\) to \(-1\). d. Fluorine (F) is oxidized from \(0\) to \(-1\), and oxygen (O) is reduced from \(0\) to \(+2\).

Step-by-step solution

Reaction a: B2O3 + 6Cl2 -> 4BCl3 + 3O2

First, assign the oxidation states: B2O3: O is -2, so B is +3. Cl2: Both Cl atoms are elemental, so they have a 0 oxidation state. BCl3: Cl is -1, so B is +3. O2: Each O atom is elemental, so O has a 0 oxidation state. Oxidation: Cl (0) -> Cl (-1) [Reducing agent] Reduction: O (-2) -> O (0) [Oxidizing agent]

Reaction b: GeH4 + O2 -> Ge + 2H2O

Again, assign the oxidation states: GeH4: H is +1, so Ge is -4. O2: Each O atom is elemental, so O has a 0 oxidation state. Ge: Elemental Ge has a 0 oxidation state. H2O: O is -2, so H is +1. Oxidation: Ge (-4) -> Ge (0) [Reducing agent] Reduction: O (0) -> O (-2) [Oxidizing agent]

Reaction c: C2H4 + Cl2 -> C2H4Cl2

Assign the oxidation states: C2H4: H is +1, so each C is -2. Cl2: Both Cl atoms are elemental, so they have a 0 oxidation state. C2H4Cl2: H is +1, Cl is -1, so each C is -1. Oxidation: Cl (0) -> Cl (-1) [Reducing agent] Reduction: C (-2) -> C (-1) [Oxidizing agent]

Reaction d: O2 + 2F2 -> 2OF2

Assign the oxidation states: O2: Each O atom is elemental, so O has a 0 oxidation state. F2: Both F atoms are elemental, so they have a 0 oxidation state. OF2: O is +2, and F is -1. Oxidation: F (0) -> F (-1) [Reducing agent] Reduction: O (0) -> O (+2) [Oxidizing agent]

Key concepts

Oxidation States

Oxidation states are a handy tool in chemistry that helps us track electron transfer in chemical reactions. They are essentially a bookkeeping system for electrons. Every atom in a chemical reaction is assigned an oxidation state. This state is a theoretical charge an atom would have if all bonds to its atoms were purely ionic. Here’s how this system works:

• Elements in their elemental form always have an oxidation state of zero. For example, in oxygen gas (\(O_2\)) and chlorine gas (\(Cl_2\)), each atom has an oxidation state of 0.


• For ions composed of only one atom, the oxidation state is equal to the charge of the ion. For example, \(Na^+\) has an oxidation state of +1, whereas \(Cl^-\) has an oxidation state of -1.


• In compounds, common rules apply, like hydrogen usually being +1 and oxygen usually being -2, unless a more specific rule applies.

By calculating the change in oxidation states, we can identify which elements are oxidized and which are reduced.

Reducing Agent

A reducing agent, also known as a reductant, is a substance that donates electrons to another substance in a chemical reaction, thereby getting oxidized itself. In this way, it helps reduce another substance. Think of it as a superhero sacrificing itself to save another!

• Reducing agents lose electrons, which increases their oxidation states. For example, in the reaction of \(GeH_4\) and \(O_2\), germanium (\(Ge\)) in \(GeH_4\) acts as the reducing agent as it goes from an oxidation state of -4 to 0.


• They are crucial for any reduction process, which typically involves gaining at least one electron.


• Clue: Consider the atom or molecule that increases in oxidation state during the reaction; that’s your reducing agent.

Recognizing the reducing agent can be key to understanding the flow of electrons in chemical reactions.

Oxidizing Agent

The oxidizing agent is the substance in a chemical reaction that accepts electrons and thus, facilitates the oxidation of another substance. This process means the oxidizing agent is reduced by gaining electrons.

• As oxidizing agents gain electrons, they decrease in oxidation state. For example, in the reaction \( O_2 + 2F_2 -> 2OF_2 \), oxygen acts as the oxidizing agent because it goes from an oxidation state of 0 to +2, accepting electrons in the process.


• Oxidizing agents are essential in oxidation-reduction (redox) reactions as they drive the loss of electrons.


• To spot the oxidizing agent, look for the element that decreases in oxidation state, meaning it has undergone a gain of electrons.

This dual role of gaining electrons while causing oxidation makes the oxidizing agent a cornerstone in redox reactions.

Chemical Reactions

Chemical reactions involve the transformation of reactants into products and are fundamental to chemistry. The reaction process generally includes breaking and making chemical bonds while atoms are reorganized.

• Redox reactions, involving oxidation and reduction, are a particular type of chemical reaction where electron transfer occurs. These reactions are represented by simultaneous changes in oxidation states.


• Understanding the balanced equation is crucial since it tells you how reactants convert into products. For example, in the equation \(2B_2O_3 + 6Cl_2 \rightarrow 4BCl_3 + 3O_2\), each reactant and product must have molecule quantities that balance in terms of atoms and charge.


• Identifying key players, such as oxidizing and reducing agents, helps reveal the nature of the transformation.

Knowing how to analyze chemical reactions can help you predict products and understand the material universe at a molecular level.

Elemental States

Elemental states refer to how elements exist in their purest form—distinct from how they might appear in compounds. In its elemental state, an element isn't combined chemically with any other element.

• Elements that are uncombined like \(N_2\), \(O_2\), \(H_2\), and \(Cl_2\), are considered in their elemental states and have an oxidation number of 0.


• Elemental states are often starting or intermediary states in reactions. For example, in the reaction \(O_2 + 2F_2 -> 2OF_2\), both \(O_2\) and \(F_2\) start as elemental substances.


• Recognizing these states aids in determining the changes in chemistry, as reactions often involve moving from elemental to compound forms or vice versa.

Understanding elemental states is vital for recognizing how elements interact to form complex chemical structures and react.