Water and pH Ms. Bush/Ms. Cohen Biology 11/24/11

http://videos. howstuffworks http://videos.howstuffworks.com/discovery/31882-howstuffworks-show-episode-4-sticky-water-video.htm

Properties of Water Water is the most important molecule on earth. Water’s unique shape and chemical behavior make it easily bond with other molecules and itself.

Water is electrically neutral! Like all molecules, a water molecule is electrically neutral (charge of zero). Hydrogen (H+) = Charge of +1 Oxygen (O-2) = Charge of -2 2 H+ (+2) + 1 O-2 (-2) = H20 (0) (neutral charge)

Slightly negative (-) end Slightly positive (+) end Polarity Water is a POLAR molecule, which means it has an unequal sharing of electrons between its hydrogen and oxygen atoms, causing it to have a bent shape Slightly negative (-) end Slightly positive (+) end

Non-Polar Molecules Carbon dioxide is nonpolar because of its straight-line shape and equal sharing/pulling of electrons.

Hydrogen Bonds Because of their partial positive and negative charges, polar molecules can attract each other The slightly negative oxygen end of one water molecule easily attracts the positive end of another, creating a weak hydrogen bond.

Cohesion of water molecules form droplets Cohesion is an attraction between molecules of the same substance. Because of hydrogen bonding, water is extremely cohesive. Cohesion explains why some insects and spiders can walk on a pond's surface. Cohesion of water molecules form droplets

Adhesion Adhesion is an attraction between molecules of different substances. The surface of water in a graduated cylinder dips in the center because adhesion between water and glass molecules is stronger than cohesion between water molecules. Adhesion of water to glass

pH scale – used to measure how acidic or basic a substance is