Let s Review Bonding Chapter 3 Water and Life Covalent Ionic Hydrogen Van der Waals Interactions Between nonmetals Between metal and non-metal All important to life H bonds to other electronegative atoms Fleeting attractions between close atoms and Form cell s Strongest bond Quick reactions/ responses Weaker bond especially in water Break polar Even weaker Depend on relative orientation of Weakest bond All bonds affect molecule s SHAPE affect molecule s FUNCTION Similar shapes become mimics morphine, heroin, opiates mimic endorphin (euphoria, relieve pain) Chemical Reactions Reactants Products ex: 6CO 2 + 6H 2 O C 6 H 12 O 6 + O 2 Some reactions are reversible: ex: 3H 2 + N 2 2NH 3 Chemical equilibrium: point at which forward and reverse reactions offset one another exactly Reactions still occurring, but no net change concentrations of reactants/products (dynamic equilibrium) WATER AND SOLUTIONS universal solvent in organisms one of few liquid compounds found naturally on earth, most solid expands in solid form covers > 75% of earth most abundant compound in living organisms (human body ~ 70%) most important compound in organisms - cells surrounded by it - filled with it - cellular events occur in it) - carries or dissolves other substances H 2 O can form up to 4 bonds Properties of Water 1. Polar molecule (polarity) Will carry or dissolve other substances in it which are vital for life. - Hydrophilic: substances that dissolve rapidly in water *Generally polar or ions (unlike charges highly attracted to each other) - Hydrophobic: substance that are insoluble in water *Generally non-polar (water are more attracted to each other than the non polar ) 1
Water is the solvent of life - Polarity makes H2O a good solvent - polar H2O surround +& ions - solvents dissolve solutes creating solutions 2. Cohesion/Adhesion Cohesion: attraction of same substances of same kind H bonding between like (water to water) Adhesion: attraction of water to other materials - oxygen end: negative charge - hydrogen end: positive charge. The hydrogens of one water molecule are attracted to the oxygen from other water. This attractive force is what gives water its cohesive and adhesive properties. Examples of cohesion and adhesion: Transpiration: movement of water up plants H 2 O clings to each other by cohesion; cling to xylem tubes by adhesion Water is a sticky molecule due to adhesion Ex: ice- floats, less dense than water H bonds form a crystal Adhesion of water to vessels walls counters downward pull of gravity. 3. Surface Tension: cohesion of water at the surface of a body of water - Each molecule in the water drop is attracted to the other water in the drop. - surface attractive forces greater - All the water on the surface of the bead are creating surface tension. (like a large group of people tightly holding hands) 4. Capillary Action adhesion of water to other substances which allow it to be drawn up the surface of the other subst. Ex: meniscus plants pull water into themselves water climbing up a straw 2
5. Moderation of Temperature Acts as a heat bank: absords or releases a relatively large amount of heat with only slight change in its own temperature. This property keeps temperature fluctuations to a minimum in order support life on land and in water. How does this work? Heat: total amount of KE in system Temperature: measure intensity of heat due to average KE of Whenever two objects of different temp. are brought together, heat passes from the warmer to the cooler object until two are same temp. Calorie: amount of heat it takes to change 1g H2O by 1*C (1 cal/g *C) Kilocalorie: 1000 calories (1 kcal/g *C) Specific Heat: amount of heat that must be absorbed or lost for 1g H2O to change its temp by 1*C H2O has a high specific heat - H2O resists changes in temperature - takes a lot to heat it up - takes a lot to cool it down - due to H bonding (heat needed to disrupt H bonds) Heat of Vaporization: quantity of heat a liquid must absorb for 1g to be converted to a gas - water has a high heat of vaporization (high amount of E needed to vaporize H2O - i.e. break H bonds) - importance: temperature moderation Evaporative Cooling Molecules with greatest KE leave as gas Surface of remaining liquid cools down Stable temperatures in lakes & ponds Cools plants Prevents terrestrial organisms from overheating H2O moderates temperatures on Earth Large bodies of water absorb and store more heat warmer coastal areas Create stable marine/land environment Humans ~65% H 2 O stable temp, resist temp. change 3
Insulation by ice less dense, floating ice insulates liquid H 2 O below 10% less dense then H2O Life exists under frozen surface (ponds, lakes, oceans) Ice - solid habitat (polar bears) Solution Homogeneous mixture Solvent: dissolving agent Solute: dissolved substance Aqueous solution: water is solvent Hydration shell: sphere of H2O around each dissolved ion Water is the solvent of life. Rule of solubility: like dissolves like Hydrophilic Hydrophobic Affinity for H 2 O Repel H 2 O Polar, ions Nonpolar IONS AND LIVING CELLS Salt is a very important polar molecule. - When mixed with water, the ionic bonds are broken and the Na and Cl ions separate (dissociation) - The charged ends of each ion are attracted to the polar ends of water Cellulose, sugar, salt Blood Oils, lipids Cell membrane - This is very important because ions such as Na, Cl, K, and Ca are involved in many reactions inside the cell Ionization Process of water (non-ionic) being converted into ions H atom shifts from one molecule to another Result: H + + H 2 O H 3 O + (hydronium ion) H 2 O H + OH - (hydroxide ion) ph: number of H ions in a solution Acid: any compound that releases H ions into water - H 3 O + (hydronium ion is formed) ex: hydrochloric acid in water HCl H+ + Cl- **** Most reactive ion due to no electrons- attacks bonds in many reversible process Base: compound that releases OH- ions into water Ex: NaOH Na+ + OH- 4
Neutralization reaction: production of H 2 O from mixture of strong acid and base The ph scale Acid: below ph 7 (more H+) Base: above ph 7 (more OH-) neutral H = OH acidic H > OH basic, alkaline H < OH IMPORTANCE OF PH: Most organisms ph ~ 7 most reactions in organisms can only occur with enzymes enzymes very ph specific ***failed kidney function is most often reason for inability to maintain normal blood ph Calculating ph [H + ][OH - ] = 10-14 If [H + ] = 10-6 M, then [OH - ] = 10-8 If [H + ] = 10-2 -log 10-2 = -(-2) = 2 Therefore, ph = 2 If [OH - ] = 10-10 [H + ] = 10-4 -log 10-4 = -(-4) = 4 Therefore, ph = 4 ph = -log [H + ] Buffer: substance which resists changes in ph when small quantities of an acid or an alkali are added to it ph controlled by buffers reservoir of H+ donate H+ when [H+] falls absorb H+ when [H+] rises blood ph 7.4 controlled by carbonic acid/bicarbonate buffer system Carbonic acid Bicarb ion Ocean acidification threatens coral reef ecosystems CO2 mixes with seawater and creates carbonic acid lowering ph. 5