Problem 75 - Chemistry: An Atoms-Focused Approach

Question

How are the gains or losses of electrons related to changes in oxidation numbers?

Step-by-Step Solution

Answer

Answer: Oxidation numbers are numbers assigned to atoms in a compound or ion to represent their degree of oxidation or reduction. They help us track electron transfer during chemical reactions. An increase in oxidation number indicates a loss of electrons (oxidation), while a decrease suggests a gain of electrons (reduction). For instance, in the formation of water from hydrogen and oxygen, hydrogen's oxidation number increases from 0 to +1 indicating it loses an electron, while oxygen's decreases from 0 to -2, indicating it gains two electrons. This demonstrates the relationship between electron transfer and changes in oxidation numbers during a redox reaction.

Step 1: Define oxidation and reduction

Oxidation refers to the loss of electrons by a species in a chemical reaction, while reduction refers to the gain of electrons by a species. These processes always occur simultaneously, as electrons cannot be gained without being lost by another species in the reaction.

Step 2: Introduce oxidation numbers

Oxidation numbers are assigned to atoms in a compound or ion to indicate the degree of oxidation (loss of electrons) or reduction (gain of electrons) of the atoms. Oxidation numbers can be positive, negative, or zero, and they help us keep track of electron transfer during chemical reactions.

Step 3: Explain changes in oxidation numbers

When an atom undergoes oxidation or reduction, its oxidation number changes accordingly. An increase in oxidation number represents the loss of electrons (oxidation), while a decrease in oxidation number represents the gain of electrons (reduction).

Step 4: Provide an example

Let's consider the redox reaction between hydrogen and oxygen to form water: 2H2(g) + O2(g) -> 2H2O(l) The oxidation numbers before the reaction are: H (in H2) : 0 O (in O2) : 0 The oxidation numbers after the reaction are: H (in H2O) : +1 O (in H2O) : -2 In this reaction, hydrogen has its oxidation number increased from 0 to +1, meaning it loses one electron (oxidation). Oxygen, on the other hand, has its oxidation number decreased from 0 to -2, meaning it gains two electrons (reduction).

Step 5: Summarize the relationship

In summary, the gains or losses of electrons in a chemical reaction are related to changes in oxidation numbers. An increase in oxidation number corresponds to the loss of electrons (oxidation), while a decrease in oxidation number corresponds to the gain of electrons (reduction). By tracking changes in oxidation numbers, we can better understand the electron transfer taking place in redox reactions.