Q. How to balance Ca(OH)2 H2SO4 → CaSO4 H2O

The balanced equation for this acid-base neutralization reaction is Ca(OH)2 + H2SO4 → CaSO4 + 2H2O. The key to balancing this equation lies in recognizing that calcium hydroxide provides two hydroxide ions (OH-) that must react with the two hydrogen ions (H+) from sulfuric acid to form two molecules of water. Start by writing the skeleton equation, then count atoms on each side: calcium and sulfur are already balanced with one atom each, but you have two hydrogen atoms and two oxygen atoms in the water product area that need accounting for.

To properly balance this equation, place a coefficient of 2 in front of H2O on the product side. This ensures that all four hydrogen atoms from the reactants (two from Ca(OH)2 and two from H2SO4) appear as products, and all oxygen atoms are accounted for. The balanced equation represents a classic double displacement reaction where calcium hydroxide (a base) neutralizes sulfuric acid to produce calcium sulfate (a salt) and water. This reaction occurs readily at room temperature and is commonly used in industrial neutralization processes, water treatment, and soil pH adjustment applications where excess sulfuric acid must be safely neutralized.