Which chemical is added to soil to raise pH during lime stabilization?

• A. Calcium carbonate
• B. Ammonia
• C. Sodium chloride
• D. Sulfuric acid

Answer: (A)

Raising soil pH in lime stabilization relies on neutralizing acidity with a carbonate-containing material that also supplies calcium. Calcium carbonate does this effectively: when added to acidic soil, it reacts with hydrogen ions and other acidic components, reducing acidity and increasing pH. A simple way to think of it is CaCO3 reacting with H+ to form Ca2+, CO2, and H2O, which shifts the soil toward a less acidic (higher pH) condition. This makes calcium carbonate the best choice among the options for lime stabilization. Ammonia is a base but isn’t used as the lime source and can introduce unwanted nitrogen; sodium chloride is a neutral salt with little impact on pH; sulfuric acid would lower pH rather than raise it.