Life 102 1st Edition Lecture 3 Outline of Last Lecture (CH. 2)I. Elemental MatterII. Atomic StructureIII. Chemical BondsIV. Chemical ReactionsOutline of Current Lecture (CH. 3)I. Water is cohesiveII. Water moderates temperaturesIII. Water expands upon freezingIV. Water is an excellent solventV. pH affects all living organisms Current LectureCHAPTER 3: PROPERTIES OF WATERWater is cohesiveI. Cohesive means that the water molecules ‘stick’ together. Why? Because of hydrogen bonds.A. Polar covalent bonds within molecules polarize regions of the molecule to be positive or negative B. To be specific, the oxygen atom becomes more negative, and the hydrogen atoms become more positiveC. The slightly positive hydrogen atoms are attracted to the slightly negative oxygen atoms and a weak, temporary connection called a hydrogen bond is formedD. Cohesiveness also means it has high surface tension: a measure of how hard it is to stretch/break the surface of a liquida. That’s why certain animals can walk on waterWater moderates temperatureThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.I. Water has an unusually high specific heat: amount of energy required to raise 1 gram of water CA. Water changes it’s temperature less than other liquids when it absorbs the same amount of energy B. Water HEATS UP….hydrogen bonds are BROKEN (and heat is absorbed) water COOLS DOWN….hydrogen bonds FORM (and heatis released)C. Water has a high heat of vaporization (it takes a lot of energy to vaporize water)a. Evaporative cooling: as a liquid evaporates, its remaining surface coolsb. This helps stabilize temperatures in organisms and bodies of waterExample: sweating Water expands upon freezingI. Unlike most liquids, water’s solid form FLOATS on its liquid formII. Water is most dense at 4C, NOT 0CA. At 4 C, hydrogen bonds are still breaking and reforming, but at their slowest speedB. At 0C, the molecules stop moving, but the hydrogen bonds keep each molecule at “arms length” and they actually freeze farther apart, thus, expandinga. If ice sank, all bodies of water would eventually freeze solid, and life would not be possible on earthWater is an excellent solventI. Water is a Polar solvent: forms hydrogen bonds easilyA. Solvent: the dissolving agent of a solutionII. Compounds dissolve in water to form a solutionA. Solute: the substance being dissolved B. Most biological reactions occur in waterIII. Hydrophilic substances: high affinity for waterA. Ions, polar moleculesIV. Hydrophobic substances: low affinity for waterA. Non-polar molecules, non-ionic elementsV. Solute concentrations:A. RATES of biological reactions depend on the CONCENTRATION of the reactantsa. High concentrations of reactants can influence other chemical reactionsB. Concentration: how much solute is present per volume of solvent in moles [Molar (M)]a. 1 M = 1 mole of solute per liter of solventb. 1 mole = 6 x 1023 molecules VI. Molecular Weight (mw) of a compound: the sum of the masses of all the atoms in a moleculeA. The weight of it’s atoms in Daltons (Da)B. The weight of 1 mole of the compounds in gramsC. Example: Glucose (C6H12O6)Carbon 12 (x6) = 72Hydrogen 1 (x12) = 12Oxygen 16 (x6) = 96 MW = 180 grams/molepH affects all living moleculesI. A hydrogen atom in a hydrogen bond between two water molecules can shift from one to the otherA. The hydrogen atom leaves its electron behind and is transferred as proton or hydrogen ion (H+) B. The molecule with an extra proton is a hydronium ion (H3O+), though it is often represented as H+ C. The molecule that lost the proton is now a hydroxide ion (OH–)II. Pure Water: H+ and OH- concentrations are equal : [H+] = [OH-] = 10-7 M A. The dissociation of water molecules produces: H2O H+ + OH- III. Acids and Bases impact biological processesA. They change the concentrations of hydrogen and hydroxide ions in a solution-Both very reactive moleculesB. Acid: Any substance that increases the [H+] of a solutionC. Base: Any substance that reduces the [H+] of a solutionD. pH: a measure of the concentration of the H+ ions in a solutiona. Pure water: [H+] = 10-7 M  pH = 7 (a neutral pH)b. The greater the [H+], the more acidic the solution pH Scale: 0 - 14acidicpH< 7 = acidic pH7 = neutralpH > 7 = basicIV. For any changes in pH by 1 unit, [H+] changes 10-foldA. Example:- Cola: pH 3 [H+] = 10-3M- Pure water: pH 7 [H+] = 10-7MCola has a 10,000 times higher [H+] than pure water…!! V. Two ways for a base to reduce the [H+] in a solutionA. Take up H+ ions NH3 + H+  NH4+ B. Some OH- can interact with H+ to form water and to reduce [H+] -KOH + H+  K+ + OH- + H+  K+ + H2O VI. Controlling pH is important for cellsA. Why? Because biological reactions have an optimal pH (6-8)B. Buffer: substance that minimizes changes in [H+] and [OH-] in a solution-most consist of an acid-base pair that reversibly combines with [H+]C. Example: H2CO3  HCO3- + H+