Chemistry of the Environment - Water

Chemical tests for water: Anhydrous copper(II) sulfate turns from white to blue ($CuSO_{4} + 5H_{2}O \rightarrow CuSO_{4} \cdot 5H_{2}O$) and anhydrous cobalt(II) chloride turns from blue to pink ($CoCl_{2} + 6H_{2}O \rightarrow CoCl_{2} \cdot 6H_{2}O$).

Purity of water: A chemical test only confirms the presence of water. To confirm purity, the substance must have a fixed boiling point of $100^\circ C$ and a melting point of $0^\circ C$ at standard atmospheric pressure.

Water Treatment: The process includes sedimentation (to remove large particles), filtration (through layers of sand and gravel to remove smaller insoluble solids), use of carbon (to remove tastes and odors), and chlorination (to kill bacteria and microbes using $Cl_{2}$).

Dissolved substances: Water in nature contains dissolved oxygen ($O_{2}$) for aquatic life, metal ions (such as $Ca^{2+}$, $Mg^{2+}$, and $Na^{+}$), and pollutants like nitrates ($NO_{3}^{-}$) and phosphates ($PO_{4}^{3-}$) from fertilizers.

Eutrophication: The process where excess nutrients ($NO_{3}^{-}$ and $PO_{4}^{3-}$) lead to rapid algae growth, blocking light and leading to oxygen depletion in water bodies as bacteria decompose dead algae.

Desalination: The removal of excess salts from seawater to produce potable water, typically through distillation or reverse osmosis.