Water of crystallization degree of hydration can be critical to the resulting chemical properties. For example, anhydrous RhCl is not soluble in water and is relatively useless in organometallic chemistry whereas RhCl•3HO is versatile. Similarly, hydrated AlCl is a poor Lewis acid and thus inactive as a catalyst for Friedel-Crafts reactions. Samples of AlCl must therefore be protected from atmospheric moisture to preclude the formation of hydrates. Crystals of hydrated copper(II) sulfate consist of [Cu(HO)] centers linked to SO ions. Copper is surrounded by six oxygen atoms, provided by two different sulfate groups and four molecules of water. A fifth water resides elsewhere
Regulation of pesticides in the European Union be used as a pesticide in the EU. The concentrations of pesticides alongside other chemical substances that pose a significant risk to the environment or to human health in surface waters in the European Union are limited to Environmental Quality Standards. These are defined in the Directive on Environmental Quality Standards in the Field of Water Policy. This Directive covers a total of 45 priority substances as defined by the Water Framework Directive and 8 additional pollutants. Environmental Quality Standards set limits to the average annual concentration as well as the maximum allowable concentrations for short-term exposure and differentiates inland