Handle battery acid in splash goggles and chemical-resistant gloves, always pour acid slowly into water and never water into acid, flush any skin or eye contact with water for 15 to 30 minutes, and neutralize spills on surfaces with dry baking soda until fizzing stops. A litre of working-strength electrolyte takes roughly 0.65 to 0.8 kg of baking soda to neutralize, so keep a real quantity of it beside the battery.
Part of Battery Building and Maintenance
Protective equipment, mixing practice, spill neutralization and first aid for the sulfuric acid in battery electrolyte.
Sulfuric Acid Burns Hardest When It Is Concentrated, And Still Burns When Dilute
Concentrated sulfuric acid destroys tissue and reacts violently with water; even the 10–20% acid used in electrolyzers burns skin and eye tissue within seconds (Safety: Electrochemistry and Electroplating). Battery electrolyte is weaker than concentrated acid but still dangerous: an eye splash can blind. Chemical burns keep progressing until the chemical is diluted or removed (Chemical Burns).
What You Need
- Splash goggles — sealed, not safety glasses; a face shield over them for mixing
- Gloves — nitrile at minimum, neoprene or butyl for stronger acid; never latex
- Apron or clothes you can strip quickly, and closed footwear
- Clean water in quantity and an eyewash bottle at eye height
- Dry baking soda or ground limestone for spills (Neutralization)
- Containers — glass or glazed ceramic with a known lead-free glaze; not iron, steel, copper, aluminium or wood (Sulfuric Acid)
- Labels on every container
Method: Mix, Move And Clean Up
Step 1: Mix by adding acid to water. Put the water in the vessel first, then pour acid in a thin stream while stirring (Electrolyte Preparation).
Step 2: Move acid in a closed container with two hands, and carry it low.
Step 3: Stand cells in trays that hold their whole volume, and wipe drips at once.
Step 4: Skin contact. Remove contaminated clothing, flood with water for 15 to 20 minutes (do not use a neutralizer on skin, because the neutralization heat adds to the burn), then get medical care for anything beyond a small area (Spill Response).
Step 5: Eye contact. Hold the eyelids open and flush for 20 to 30 minutes without rubbing; do not judge severity yourself.
Step 6: Spills on surfaces. Cover with dry baking soda or ground limestone, add more until fizzing stops, then sweep up the resulting salt and rinse the area with plenty of water. Do not use water alone on a strong spill (Neutralization).
Worked Example: How Much Baking Soda For A Litre
The reaction is H₂SO₄ + 2 NaHCO₃ → Na₂SO₄ + 2 H₂O + 2 CO₂. The molar masses are general knowledge, not from the other articles: sulfuric acid 98.08 g/mol, sodium bicarbonate 84.01 g/mol.
- Electrolyte at SG 1.265 weighs 1.265 kg per litre. At the lead-acid article’s 37% acid by weight that is 0.37 × 1.265 = 0.468 kg of acid, or 468 ÷ 98.08 = 4.77 mol. Baking soda needed: 2 × 4.77 = 9.54 mol × 84.01 g/mol = 801 g.
- At the 30% figure from the rechargeable-batteries article: 0.30 × 1.265 = 0.380 kg, 380 ÷ 98.08 = 3.87 mol, 7.74 mol × 84.01 = 650 g.
So 0.65 to 0.8 kg of baking soda per litre. The reaction makes 2 mol of carbon dioxide per mole of acid, about 9.5 mol, or roughly 230 litres of gas at room temperature (using 24 L/mol, general knowledge) for the first case, which is why the powder foams. Add it gradually and expect a lot of froth. With ground limestone the amount is 1 mol per mol of acid.
Common Mistakes
- Using water alone on a strong spill — it spreads the acid and can spatter
- Neutralizing on skin — flush with water instead
- Storing acid in a metal funnel or an aluminium pot — the metal dissolves, and zinc or aluminium release hydrogen
- Unlabelled bottles — someone drinks or pours the wrong one
Safety
Water added to strong acid boils at the surface and sprays acid
Sulfuric acid is far denser than water and releases a lot of heat on dilution. Water poured onto it floats on top (general knowledge, not from the other articles), the heat is released in that thin layer, and the water flashes to steam and throws acid. Acid poured slowly into stirred water sinks and is diluted by the whole volume. Always acid into water; wear goggles and a face shield; and never mix in a closed vessel.
What’s Next
- Learn next: Hydrogen Gas Hazard — the gas that charging adds
- Combine with: Lead Exposure Prevention — the other poison in a battery shop