How does a natural buffer like carbonate in lakes help resist pH changes from acid rain?

• A. Carbonate ions react with bases to form more soluble salts.
• B. Carbonate ions react with water to release hydrogen ions.
• C. Carbonate ions react with acids to form bicarbonate, buffering pH by absorbing H+ and stabilizing water.
• D. Carbonates convert to carbonic acid that dissolves metals.

Answer: (C)

Lakes with carbonate buffering resist pH changes by consuming added hydrogen ions from acids. When acid rain releases H+ into the water, carbonate ions (CO3^2−) readily react with those H+ to form bicarbonate (HCO3−). This reaction uses up the extra hydrogen ions, so the water’s pH doesn’t drop as much as it would without a buffer. The bicarbonate can continue to neutralize more acid by forming carbonic acid (H2CO3), which quickly decomposes to CO2 and water. This sequence provides a stabilizing effect, keeping the lake’s pH relatively steady despite acidic input. This is why carbonate-rich lakes, often underlain by limestone, can проявлят robustness against acid rain. The other ideas don’t describe buffering: reacting with bases would not neutralize added acidity; releasing hydrogen ions would worsen acidity; and forming carbonic acid that dissolves metals describes a different consequence, not the buffering reaction that absorbs H+.