Properties of water

water Covers ¾ of earth’s surface Most abundant compound in living things Liquid at the temps found over much of the earth’s surface Expands as it freezes Ice floats

The water molecule Oxygen atom has a stronger attraction for electrons Greater probability of finding the shared electrons near the oxygen than the hydrogen Creates a polar molecule: Oxygen end has a slight negative charge Hydrogen end has a slight positive charge

Hydrogen bonds Polar molecules can attract each other Hydrogen bonds form between the hydrogen atom on one water molecule and the oxygen atom on another Not as strong as covalent or ionic bonds Responsible for many of water’s special properties

cohesion Attraction between molecules of the same substance Water’s cohesion causes molecules on the surface of water to be drawn inward Forming beads This “surface tension” allows some insects and spiders to walk on a pond’s surface

adhesion Attraction between molecules of different substances Water molecules attracted to glass, so surface of water in a graduated cylinder dips in the center Also causes water to rise in a narrow tube against gravity (capillary action) In plants, Draws water out of roots up into stems & leaves

mixture solutions suspensions Composed of two or more elements or compounds that are physically mixed together but not chemically combined Salt & pepper Sugar & sand Earth’s atmosphere Two types of mixtures with water solutions suspensions

solutions Mixture of 2 or more substances in which the molecules are evenly distributed Solute: substance that is dissolved Solvent: substance in which the solute dissolved Water: greatest solvent on earth Due to its polarity

suspensions Mixtures of water and nondissolved material Blood: a solution and a suspension Mostly water with many dissolved compounds Contains cells & other undissolved particles that remain in suspension

Acids, bases, and pH A water molecule can react to form ions

The pH scale Indicates the concentration of h+ ions in solution Ranges from 0-14 At a ph of 7, the concentration of h+ ions and oh- ions is equal Pure water Each step on the ph scale represents a factor of 10

acids Any compound that forms h+ ions in solution Higher concentration of h+ ions than pure water pH values below 7 The farther away from 7, the stronger the acid is

bases Compound that produces hydroxide (OH-) ions in solution Also called alkaline Contain lower concentrations of h+ ions than pure water pH values above 7 The farther away from 7, the stronger the base is

buffers Weak acids or bases that can react with strong acids or bases to prevent sharp, sudden changes in PH Maintain homeostasis in the body