Example: The Reaction of Solid Aluminum with Aqueous Sulfuric Acid to Form Aqueous Aluminum Sulfate and Hydrogen Gas

• Since both aluminum and hydrogen occur as pure elements, balance those last.

• Sulfur and oxygen occur in only one compound on each side of the equation, so balance these first.

• Sulfur and oxygen are part of a polyatomic ion that stays intact on both sides of the equation.

• Balance polyatomic ions such as these as a unit.

• There are 3 SO42– ions on the right side of the equation, so put a 3 in front of H2SO4.