2-3: WATER + SOLUTIONS  The chemical reactions of all living things take place in an aqueous environment (i.e. WATER)  Let’s look at some of the unique properties of water….

POLARITY  RECALL - - H + O combine by covalent bond to make 1 water molecule = H 2 O These atoms do not share electrons evenly more  Oxygen has more positive charges (8 p + ) than Hydrogen (1 p + ), thus pulling the electrons more towards its nucleus

POLARITY (cont.)  This results in a slight, uneven electrical charge in the molecule  Shape of water = bent (angle created)  Even though water is neutral, regions have slight charges Oxygen – slightly negative Hydrogen – slightly positive

Still more Polarity…  Because of these slight charged regions, water is POLAR  Is known as the “Universal Solvent” because of this property  Ionic compounds dissolve into dissociated ions, that are essential to normal body operations  Example: SALT

HYDROGEN BONDING  Hydrogen bonds hold water molecules together Positive region attracted to negative region of molecules Very weak bond – easily broken

Keep adding water molecules together…

And eventually, you get this…

Cohesion + Adhesion  Cohesion – an attractive force between like particles of the same kind  Example?  Surface tension  Adhesion – an attractive force between unlike substances  Example? If cohesion + adhesion work together, water molecules can move upwards against gravity  known as CAPILLARITY

Examples of Capillarity

TEMPERATURE MODERATION  In order to change its temperature, water must gain or lose large amounts of energy Must break/reinforce H-bonds to increase/decrease temp.  Cells can maintain temp. even if outside temp. changes

Let’s watch a video…  Properties of Water Properties of Water

SOLUTIONS  Solution – mixture in which one or more substances are uniformly distributed in another substance  Parts of a solution: Solute – substance dissolved in solution Solvent – substance that does the dissolving  Ex. Sugar in Water

SOLUTIONS (cont.)  Concentration – measurement of the amount of solute dissolved in a fixed amount of solution Ex. 2g/100mL = 2% solution  The more solute dissolved, the higher the concentration Saturated – no more solute can be dissolved

SOLUTIONS (cont.)  Aqueous – water is the solvent Universal Solvent  Marine microorganisms live in it  Plants get nutrients from it  Our cells are filled with it

ACIDS + BASES  Dissociation of water – breaking apart of water molecules into two opposite charges H 2 OH + + OH -  OH - = Hydroxide ion Free H + ion can react w/ other water molecules  H + + H 2 O H 3 O +  H 3 O + = Hydronium ion

ACIDS + BASES (cont.)  Acid Hydronium ions > Hydroxide ions Characteristics of Acids:  Low pH number (0-6)  Sour taste  Can be highly corrosive to metal

ACIDS + BASES (cont.)  Base (Alkaline) Hydroxide ions > Hydronium ions Characteristics of a base:  High pH number (8-14)  Bitter taste  Tend to feel slippery

pH  pH  pH – stands for power of Hydrogen pH scale – measures concentration of solutions – can use litmus or pH paper  Ranges from 0-14  a logarithmic scale Change in 1 pH unit = tenfold change in acidity or alkalinity  Ex. pH=3 vs. pH=4  pH of 3 has 10 times more H 3 O + ions than pH of 4  10 x (x = pH # difference)

pH = 7  Neutral Hydronium ions = Hydroxide ions  Example: Pure Water

BUFFERS  Buffer – chemical substances that neutralize small amounts of acids or bases To neutralize an acid, add a base To neutralize a base, add an acid  Buffers used to maintain homeostasis in your body  Example – an upset stomach