ABSTRACT
It is also important to understand the chemistry of the changes that happen when waste is dumped in landfill sites. Anaerobic processes lead to the formation of biogas, which is hazardous unless collected and burnt as a fuel. Water percolating through rotting landfill can dissolve harmful chemicals such as the ions of toxic metals, which can be recovered from the liquids by ion exchange if waste disposal is managed correctly. w ater (H 20 ) is a familiar liquid with remarkable properties. Despite the small size of its molecules, water is a liquid at room temperature because of hydrogen bonding. The O — H bonds in water molecules are highly polar because oxygen is so electro negative. Water molecules too are polar because they are not linear, owing to the two lone pairs of electrons that help to determine the shape of the molecule. As a polar solvent, water can hydrate ions and dissolve salts. Water can also dissolve some organic compounds because it can form hydrogen bonds with hydroxyl groups in alcohols, sugars or carboxylic acids and with — NH groups in amines. Water plays an important part in many reactions:
• hydration reactions - water forms aquo complex ions with metal ions • acid-base reactions - water acts as both an acid and as a base because it is
an amphoteric compound • redox reactions - reactive metals such as group 1 elements reduce the
hydrogen in water to hydrogen gas • hydrolysis reactions - this includes the hydrolysis of nonmetal chlorides and
of organic compounds such as esters (acid catalysis or base catalysis). w ater cycle: the cycling of water in the environment between the oceans, the atmosphere and the crust of the Earth.
