Question

For each of the following reactions, indicate which elements are oxidized and which are reduced: a. \(4 \mathrm{Fe}+3 \mathrm{O}_{2} \longrightarrow 2 \mathrm{Fe}_{2} \mathrm{O}_{3}\) b. \(\mathrm{NiO}+\mathrm{C} \longrightarrow \mathrm{Ni}+\mathrm{CO}\) c. \(2 \mathrm{H}_{2}+\mathrm{O}_{2} \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}\)

Short answer

a. Fe is oxidized; O is reduced. b. Ni is reduced; C is oxidized. c. H is oxidized; O is reduced.

Step-by-step solution

Identify the Oxidation States of Reactants and Products in Reaction a

For reaction a, assign oxidation states: Fe starts at 0 (elemental form) and goes to +3 in Fe2O3. O2 starts at 0 (elemental form) and goes to -2 in Fe2O3.

Determine the Change in Oxidation State for Reaction a

Fe is oxidized as its oxidation state increases from 0 to +3. O is reduced as its oxidation state decreases from 0 to -2.

Identify the Oxidation States of Reactants and Products in Reaction b

For reaction b, assign oxidation states: Ni in NiO is at +2, and goes to 0 in Ni. Carbon in C starts at 0 and goes to +2 in CO.

Determine the Change in Oxidation State for Reaction b

Ni is reduced as its oxidation state decreases from +2 to 0. C is oxidized as its oxidation state increases from 0 to +2.

Identify the Oxidation States of Reactants and Products in Reaction c

For reaction c, assign oxidation states: H2 starts at 0 (elemental form) and O2 also starts at 0 (elemental form). In H2O, H is at +1 and O is at -2.

Determine the Change in Oxidation State for Reaction c

H is oxidized as its oxidation state increases from 0 to +1. O is reduced as its oxidation state decreases from 0 to -2.

Key concepts

Oxidation and Reduction

Understanding the process of oxidation and reduction is essential in chemistry, particularly in redox reactions. These changes are primarily associated with the transfer of electrons between chemicals. Oxidation refers to the loss of electrons, while reduction means the gain of electrons. In a redox process, one substance undergoes oxidation and another undergoes reduction simultaneously. For instance, in the reaction \(4 \mathrm{Fe}+3 \mathrm{O}_{2} \longrightarrow 2 \mathrm{Fe}_{2} \mathrm{O}_{3}\), the iron (Fe) loses electrons and is oxidized, while the oxygen (O) gains electrons and is reduced.It's important to remember the phrase 'LEO says GER', which stands for 'Loss of Electrons is Oxidation; Gain of Electrons is Reduction'. This mnemonic helps students easily recall the fundamental concepts of redox reactions.

Oxidation States

The oxidation state, also known as oxidation number, is a concept that provides insight into the hypothetical charge that an atom would have if all its bonds to atoms of different elements were completely ionic. Oxidation states are used to track how many electrons are lost or gained. For example:

• In \( \mathrm{Fe}_{2}\mathrm{O}_{3} \), Fe has an oxidation state of +3.
• In \( \mathrm{CO} \), C has an oxidation state of +2.

Determining the oxidation states of atoms in a chemical formula is crucial for analyzing a redox reaction and indentifying which atoms are oxidized or reduced. In the exercise, the changes in oxidation states from reactants to products provide clear evidence of the redox processes occurring.

Balancing Chemical Equations

Balancing chemical equations is about ensuring that the same number of each type of atom appears on both sides of the equation, respecting the law of conservation of mass. This process can be challenging, especially in redox reactions where the transfer of electrons must be accounted for. To balance a redox reaction, one must first separate the reaction into half-reactions — one for oxidation and one for reduction. After balancing the atoms and charges in each half-reaction, they can be combined to give a balanced overall equation. A balanced equation is essential for accurately predicting the results of a chemical reaction and for calculations in stoichiometry.

Chemical Reactions

Chemical reactions involve the transformation of substances through breaking and forming chemical bonds, resulting in new substances. Redox reactions are a type of chemical reaction where oxidation and reduction occur. They are fundamental to many processes, such as combustion, corrosion, and energy production in batteries.In the example reactions given in the exercise:

• The combustion of hydrogen gas to form water (\(2 \mathrm{H}_{2} + \mathrm{O}_{2} \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}\)) is a redox reaction where hydrogen is oxidized and oxygen is reduced.
• The reduction of nickel oxide by carbon to produce nickel and carbon monoxide (\(\mathrm{NiO} + \mathrm{C} \longrightarrow \mathrm{Ni} + \mathrm{CO}\)) is another redox reaction.

Understanding the context and the outcome of these reactions makes it clearer why mastering the concepts of oxidation, reduction, and balancing equations is so significant in chemistry.