Question 6A257

The electrolyte in a lead-acid storage cell is a solution of **dilute sulfuric acid** (H2SO4) and water, not concentrated acid. This dilute solution allows for the necessary electrochemical reactions to occur safely and efficiently, storing and releasing electrical energy. When the cell is fully charged, the concentration of sulfuric acid in the electrolyte is at its highest, typically around 35-38% acid by mass. This concentration results in a **specific gravity** (the ratio of the density of the electrolyte to the density of water) of approximately **1.280 to 1.300**. As the battery discharges, sulfate ions leave the electrolyte to form lead sulfate on the plates, and water is produced, which dilutes the acid and lowers its specific gravity. Therefore, both descriptions in B and C are correct regarding a fully charged lead-acid cell.