II. Properties of Water *Water is the single most abundant compound in most living things. A. The Water Molecule 1. Polarity Polar molecule – a molecule in which the charges are unequally distributed. -Water is a neutral, bent molecule. Its bent shape makes the oxygen end (pole) slightly negative & its hydrogen end slightly positive. -Water molecules are polar because there is an uneven distribution of electrons between the oxygen & hydrogen atoms.

Hydrogen Bonding 2. Hydrogen Bonds Hydrogen bonding – weak attraction between polar molecules, ex : water. **Is the weakest type ** of bonding. of bonding. -Being polar, water molecules are attracted to each other (hydrogens to oxygens).

Cohesion vs. Adhesion -Water is very cohesive. Cohesion – an attraction between molecules of the same substance, ex : spiders on water. Adhesion – an attraction between molecules of different substances, ex : the meniscus of water in a graduated cylinder. -Adhesion is responsible for capillary action (water rising in a narrow tube against gravity) in plants.

B. Solutions & Suspensions -Water is sometimes part of a mixture – a material composed of 2 or more elements or compounds that are physically mixed but not chemically combined, ex : salt & pepper.

2 Types of mixtures made with water : 1. Solutions – mixture of 2 or more substances in which the molecules of the substances more substances in which the molecules of the substances are evenly distributed. are evenly distributed. -Solutions involve solutes – a substance that is dissolved (salt) & solvents – substances in which the solute dissolves (water). -Water is the universal solvent. 2. Suspensions – mixtures of water and non-dissolved materials, ex : blood.

C. Acids, Bases, and pH pH scale – measurement system used to indicate the concentration of hydrogen ions (H+) in solution; it ranges from 0 to 14. -A pH of 7 has an equal amount of H+ & OH- ions, making it neutral. Pure water is neutral. -pH below 7 is acidic & pH above 7 is basic or alkaline. Higher pH = more basic solution.

Acids, Bases, and Buffers Acid – any compound that forms H+ (hydronium) ions in solution, ex: stomach acid, lemon juice, tomato juice, acid rain, etc. -Anything below 7 on the pH scale. Base – a compound that produces OH (hydroxide) ions in solution, ex : bleach, soap, ammonia, sea water, lye, etc. -Anything above 7 on the pH scale. Buffers – weak acids or bases that can react with strong acids or bases to prevent sharp, sudden changes in pH. - Are used by body to maintain homeostasis by keeping chemical reactions pH balanced.