Battery acid is the common term for the liquid found within traditional lead-acid batteries, used in automobiles, boats, and backup power systems. This fluid, known as the electrolyte, allows the battery to store and release electrical energy. Because the electrolyte is highly reactive, understanding its chemical composition is important for safe handling. This liquid causes severe chemical burns and corrosion upon contact, requiring caution near any flooded-cell battery.
The Chemical Identity of Battery Acid
The compound that makes up battery acid is sulfuric acid (H2SO4). In batteries, this acid is not used in its concentrated form but as a solution diluted with purified water. For a fully charged automotive battery, the concentration typically ranges between 29% and 37% by mass.
This mixture is classified as a strong mineral acid, meaning it fully dissociates into ions when dissolved. The high concentration of hydrogen ions (H+) released by the dissociation gives the electrolyte an extremely low pH, often around 0.8 to 1.5. This low pH is responsible for the aggressive, corrosive nature of the battery fluid, as it readily strips electrons from other materials upon contact.
How Sulfuric Acid Powers a Battery
The primary function of the sulfuric acid solution is to act as the electrolyte, a conductive pathway allowing charged particles to move between the battery’s internal plates. The battery contains two types of plates immersed in this electrolyte: one made of pure lead and the other of lead dioxide. The acid facilitates a reversible chemical reaction that forms the basis of the charging and discharging cycle.
When the battery is discharging, such as when starting a car, the sulfuric acid actively reacts with the lead and lead dioxide plates. This reaction produces lead sulfate and water, which releases the electrons that form the electrical current. As the battery discharges, the acid is consumed and the water content increases, causing the overall concentration of the acid to decrease.
When the battery is recharged, an external electrical current forces the chemical process to reverse. The lead sulfate and water are converted back into lead, lead dioxide, and sulfuric acid. This regeneration process restores the acid concentration, or specific gravity, of the electrolyte to its fully charged state. If the battery is repeatedly left discharged, the lead sulfate can crystallize, a condition called sulfation, which hinders the battery’s ability to accept a charge.
Immediate Safety Measures and Neutralization
Due to its strong corrosive properties, immediate action is necessary if battery acid contacts the skin or eyes. For skin contact, remove any contaminated clothing immediately and flush the affected area with clean water for at least 15 minutes. Eye contact requires the use of an eyewash station or clean running water for a full 15 minutes, and medical attention should be sought immediately.
For spills, the acid must be neutralized using a mild base to stop its corrosive activity. The most common neutralizing agent is baking soda (sodium bicarbonate). Applying baking soda directly to the spill causes a fizzing reaction, indicating the acid is being converted into a harmless salt and carbon dioxide gas.
Ensure the spill area is well-ventilated during this process, as hydrogen gas may also be released. The reaction is complete once the fizzing stops, at which point the residue can be safely cleaned up and the area rinsed with water. Always wear appropriate protective gear, such as gloves and eye protection, before handling any spilled battery acid.