(a) Why are lead-antimony grids used as electrodes in the lead-acid battery rather than smooth plates? (b) What is the reducing agent in the lead-acid battery? (c) The lead-acid cell potential is about \(2 \mathrm{~V}\). How, then, does a car battery produce \(12 \mathrm{~V}\) for its electrical system?

When it comes to lead-acid batteries, the choice of electrode materials is crucial for their performance and longevity. In a typical lead-acid battery, lead-antimony grids are employed rather than smooth plates. This is not by chance, but a result of deliberate design to increase the efficiency of the battery. The grid structure increases the surface area available for chemical reactions. More surface area equates to higher current densities, which is essential for producing the necessary electrical power.

Additionally, these antimony alloyed grids present a stronger mechanical structure. Lead by itself is quite soft and malleable, but when alloyed with antimony, the grids become more durable and able to maintain their shape. This robustness is beneficial as it helps prevent the 'shedding' of the active material. Shedding is when the active material, such as lead dioxide on the positive electrode or sponge lead on the negative electrode, detaches from the grid, which can diminish battery capacity and cause premature failure. Hence, electrode material selection is a blend of chemistry and engineering—aiming for both electrical efficiency and mechanical stability.

In electrochemistry, the term 'reducing agent' refers to a substance that donates electrons to another compound in a chemical reaction, and in turn, becomes oxidized. Within the lead-acid battery, the reducing agent is the sponge lead (Pb) found at the negative electrode, or anode. During discharge, which is when the battery is providing electrical energy, the sponge lead undergoes an oxidation process. This means it loses electrons and transforms into lead(II) ions (Pb2+).

These lost electrons are not just disappearing; they travel through the external circuit to the positive electrode, the cathode, where they participate in reducing lead(IV) oxide (PbO2) to lead(II) ions as well. This flow of electrons is what generates the electrical current we harness to power devices. The role of the reducing agent in a battery is not just fundamental—it is the heart of the electrochemical process that enables batteries to store and deliver energy.

Voltage production in batteries is a question of both chemistry and the arrangement of cells. Each cell within a lead-acid battery has a potential of approximately 2 volts (V). However, most automotive applications, such as a car's electrical system, require a higher voltage, specifically 12V. To achieve this, individual cells are connected in series.

By connecting cells in series, their voltages are additive; this means if one cell produces 2V, then two cells produce 4V, three cells produce 6V, and so on. Therefore, a standard car battery contains six of these 2V cells connected in series to provide a cumulative voltage of 12V (6 cells x 2V per cell). This series connection not only allows multiple cells to work together to produce a larger voltage but also ensures that the current capacity of the battery remains the same as that of a single cell. Understanding this concept is fundamental when considering how batteries are designed to meet the specific voltage requirements of the devices they power.