Kassandra Coan Why put lime in a pond? Honors Activity 5.4
Lime is a commercial name for calcium oxide (CaO). When carbon dioxide (Co2) is removed from limestone, coral, seashells, or chalk they become lime. This product is easily accessible, because an abundance of limestone in found in the crust of the earth, and the Co2 is removed simply by heating the limestone. See formula below: 500-600 °C CaCO3(s) N CaO(s) + CO2(g)
Ponds naturally become more and more acidic throughout the day. This is because rain, pine needles, decaying plants, and clay pond bottoms all contribute to acidity. If the pH level of the pond water falls below 4, the water has become too acidic to sustain fish life. Lime can neutralize this acidity, raise the pH, with the following process: Lime is calcium oxide. Calcium oxide reacts with carbon dioxide, forming calcium carbonate. Calcium carbonate neutralizes the acids that form naturally in ponds. This happens because when the lime is in contact with the water, it chemically changes into calcium hydroxide. The important part of this step is to know that the O ions come together with the H ions, as seen below: CaO(s) + H2O(l) → Ca(OH)2(s) The OH ions are the bases. In acidic water, many H3O+ ions will be present. These are the acids. When an acid in base come together, they neutralize, or cancel each other out. They turn into water as seen below: H3O+ + OH- → 2H2O Fish can live in a wide range of pH, but if the pH changes rapidly the fish will die. Therefore, lime is put into ponds as an indirect source of OH- ions to neutralize with the H3O+ ions that form naturally from acid sources such as rain and pine needles.
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