The Chemistry of Water

The Water Molecule Made of 3 atoms 2 Hydrogen atoms 1 Oxygen atom These atoms are held together by covalent bonds Covalent bond = sharing of electrons between the atoms

Water is Polar Polarity = an uneven distribution of electrons between the oxygen and hydrogen atoms. Oxygen acts as a negative charge Hydrogen acts as a positive charge HOWEVER!!! The entire water molecule has a neutral charge. This is the most important property of water

Hydrogen Bonds Polar water molecules act like magnets and attract each other Hydrogen Bonds The attraction of the Hydrogen end (+) of one molecule to the Oxygen end (-) of another water molecule. One hydrogen bond is weak, BUT many hydrogen bonds are strong

Cohesion The attraction between molecules of the same substance (e.g. water). Results in surface tension - a measure of the strength of water’s surface Allows some insects and spiders to walk on water. Or allows paper clips to float!

Adhesion Attraction between molecules of different substances Water will make hydrogen bonds with other surfaces such as glass, soil, plant tissues, and cotton. Responsible for capillary action - water molecules will “tow” each other along when in a thin tube Plants use to draw water out of soil

Homeostasis Ability to maintain a constant internal environment. Water is important to this process because: a. Makes a good insulator b. Resists temperature change c. Universal solvent d. Coolant

Solutions & Suspensions Water is usually part of a mixture. A combination of two or more substances where both maintain their individual characteristics There are two types of mixtures: Homogenous Heterogenous

Homogenous Mixtures A solution is a homogenous mixture A homogenous mixture formed when a substance is dissolved in another (ions are separated) Evenly distributed Uniform throughout A solution is a homogenous mixture Has two parts SOLUTE = Substance that is being dissolved Exp. = salt or sugar SOLVENT = Substance into which the solute dissolves Exp. = water

Solution

Heterogeneous Mixtures Components remain distinct, so you can tell them individually Sand & water form a heterogenous mixture called a suspension Over time the particles settle out

Heterogeneous Mixtures A colloid is a heterogeneous mixture in substances don’t dissolve but separate into tiny pieces. Water keeps the pieces suspended so they don’t settle out. Examples: milk & mayonnaise

Acids, Bases & pH H2O  H+ + OH- 1 water molecule in 550 million naturally break down into a Hydrogen Ion (H+) and a Hydroxide Ion (OH-) Hydrogen Ion Hydroxide Ion Acid Base H2O  H+ + OH-

Acids are substances that release hydrogen (H+) ions when dissolved in water The more H ions released, the stronger the acid Bases release hydroxide (OH-)ions when dissolved in water

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

Acids Strong Acid = pH 1-3

Bases Strong Base = pH 11 – 14

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

HOMEWORK Notes Assignment # 8