Problem 10 - Chemistry: The Central Science in SI Units, Global Edition

Question

The electrodes in a silver oxide battery are silver oxide \(\left(\mathrm{Ag}_{2} \mathrm{O}\right)\) and zinc. (a) Which electrode acts as the anode? (b) Which battery do you think has an energy density most similar to the silver oxide battery: a Li-ion battery, a nickelcadmium battery, or a lead-acid battery?

Step-by-Step Solution

Answer

(a) In a silver oxide battery, the Zinc electrode acts as the anode. (b) Among Li-ion, nickel-cadmium, and lead-acid batteries, the Li-ion battery has an energy density most similar to the silver oxide battery.

Step 1: Understanding the Redox Reaction in a Silver Oxide Battery

In a silver oxide battery, the redox (reduction-oxidation) reaction occurs between silver oxide (Ag2O) and zinc. During the chemical reaction in the battery, electrons will flow from one electrode to the other, creating a potential difference that can be used to power devices.

Step 2: Identify the Anode

The anode is the electrode that undergoes oxidation, meaning it loses electrons. In the case of a silver oxide battery, the Zinc (Zn) electrode will lose electrons and will be oxidized to Zinc ion (Zn²⁺), thus acting as the anode.

Step 3: Identify the Cathode

The cathode is the electrode that undergoes reduction, receiving the electrons lost by the anode. In this case, the silver oxide (Ag₂O) electrode will receive electrons and will be reduced to silver (Ag), thus acting as the cathode. Summarizing, (a) Zinc electrode acts as the anode.

Step 4: Comparing Energy Densities

To answer part (b) of the question, we need to compare the energy densities of Li-ion, nickel-cadmium, and lead-acid batteries to the energy density of a silver oxide battery. The energy density is a measure of how much energy the battery can store per unit of mass or volume. Based on the general properties of these batteries, we can deduce the following energy densities: - Li-ion battery: High energy density; - Nickel-cadmium battery: Medium energy density; - Lead-acid battery: Low energy density. The energy density of a silver oxide battery is relatively high due to the high capacity of silver to store chemical energy. Considering that information, we can deduce that the Li-ion battery has an energy density most similar to the silver oxide battery.

Key Concepts

Silver Oxide Battery

A silver oxide battery is a type of primary battery that uses silver oxide (\(\mathrm{Ag}_2\mathrm{O}\)) and zinc as electrodes. These batteries are renowned for their compact size and reliable performance. They are commonly used in small devices such as watches, calculators, and hearing aids.
The primary advantage of silver oxide batteries is their stable output voltage. This stability makes them ideal for precision instruments. Despite being more costly compared to other battery types, the quality and the long shelf life of silver oxide batteries make them a preferred choice in specific applications. Another essential feature is their environmentally friendly design, as they do not contain harmful heavy metals like cadmium or lead.

Redox Reaction

A redox (reduction-oxidation) reaction is a chemical process in which electrons are transferred between two substances. This process is fundamental in batteries, where it generates electric current.

Oxidation and Reduction

In the context of the silver oxide battery:

• The \(\mathrm{Zn}\) electrode undergoes oxidation, meaning it loses electrons and gets converted to \(\mathrm{Zn}^{2+}\) ions.
• Conversely, \(\mathrm{Ag}_2\mathrm{O}\) undergoes reduction by gaining electrons to form \(\mathrm{Ag}\) metal.

Thus, the battery relies on a redox reaction to produce a usable flow of electricity by facilitating electron transfer from zinc to silver oxide.

Energy Density

Energy density is a term that describes how much energy a battery can store relative to its weight or volume. It is crucial in determining the battery's efficiency and suitability for various applications. Higher energy densities are preferred as they allow for longer operational times without increasing the battery size.

Comparison

When comparing energy densities:

• Li-ion batteries exhibit high energy density, making them suitable for portable electronics and electric vehicles.
• Nickel-cadmium batteries have medium energy density, often used in power tools and emergency lighting.
• Lead-acid batteries typically have low energy density, but they are cost-efficient and widely used in automotive applications.

Silver oxide batteries boast a high energy density, similar to Li-ion batteries, which is why they are used in compact, high-performance devices.

Anode and Cathode Identification

In any battery, the identification of the anode and cathode is critical for understanding and designing battery performance.

Anode and Cathode Roles

- The **anode** is the electrode where oxidation occurs. In a silver oxide battery, the zinc (\(\mathrm{Zn}\)) acts as the anode because it loses electrons during the electrochemical reaction.
- Conversely, the **cathode** is where reduction takes place. For silver oxide batteries, \(\mathrm{Ag}_2\mathrm{O}\) serves as the cathode, accepting electrons to form metallic silver.
Proper identification ensures the correct functioning of the battery, as it facilitates electron flow from anode to cathode, powering any connected device.