The Chemistry of Life Properties of Water

The Water Molecule Polarity –Polar molecules have a region with a slight positive charge and a slight negative charge. –A water molecule is polar because there is an uneven distribution of electrons between the oxygen and hydrogen atoms. Oxygen has 8 protons and a larger pull on the electrons than Hydrogen with just 1 proton.

Hydrogen Bonds Polar water molecules act like magnets and attract each other Hydrogen Bonds –The attraction of the Hydrogen end (+) of one molecule for the Oxygen end (-) of another water molecule.

Hydrogen Bonds

Cohesion The attraction between molecules of the same substance (e.g. water). Allows some insects and spiders to walk on water.

Adhesion Attraction between molecules of different substances Responsible for Capillary forces in plants

Solutions & Suspensions Water is usually part of a mixture. There are two types of mixtures: –Solutions –Suspensions

Solution Made of a solute and solvent. Ionic compounds disperse as ions in water (NaCl becomes Na+ Cl-) Evenly distributed SOLUTE –Substance that is being dissolved SOLVENT –Substance into which the solute dissolves

Solution

Suspensions Substances that don’t dissolve but separate into tiny pieces. Water keeps the pieces suspended so they don’t settle out.

Acids, Bases & pH 1 water molecule in 550 million naturally dissociates into a Hydrogen Ion and a Hydroxide Ion Hydrondium Ion Hydroxide Ion Acid Base H 2 O  H + + OH -

The pH Scale Indicates the concentration of H + ions Ranges from 0 – 14 pH of 7 is neutral pH 0 – 6.99 is acid … H + pH 7.01 – 14 is basic… OH - Each pH unit represents a factor of 10 change in concentration

Acids Strong Acid = pH 1-3 H + ions

Bases Strong Base = pH 11 – 14 OH - ions

Buffers Weak acids or bases that react with strong acids or bases to prevent sharp, sudden changes in pH. Weak Acid Weak Base