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UW-Milwaukee BIOSCI 150 - Water

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BIO SCI 150 1st EditionLecture 7WaterMajor component of planet surface Major component of living cells 70-95%Small polar moleculeCan form multiple Hydrogen bonds (temporary and weak)At high temperatures the hydrogen bonds break and molecules are free as gas (to vaporize, a water molecule must break all H bonds, so they can rise and leave the rest)At moderate temperatures hydrogen bonds break and reform, giving a liquid (energy is absorbed as ice melts)At low temperatures multiple hydrogen bonds produce solid ice (Water freezes when all H bonds form, this expands the structure since H bonds do not allow molecules to move closer, energy is released when forming into a solid)The hydrogen bonds produce:Cohesion - molecules bound to like molecules, forms streamsAdhesion - molecules bound to different substance produces wettingSurface tension - hydrogen bonding to each other along surface and belowBecause of hydrogen bonding, water has a high specific heat.Water stabilizes air temperature by storing and releasing heatKinetic energy - movement of atomsTemperature - intensity of heat, averageAmount of heat - temperature and massAn ounce of melted lead has a higher temperature than a warm bathtub,however, the warm bath water contains far more heat than the molten leadUnits of MeasurementCelsius- 0° freeze 37° human 100 boilCalorie- amount of heat energy needed to raise temperature of lg of water 1°CA kilocalorie amount of heat energy needed to raise temp of 1kg water, or liter 1° CSpecific HeatAmount of heat needed to change temperature of lg 1°C (one calorie)Water as a solventPolar nature of water makes it a good solvent for polar or ionic solids (like salt)Solution: homogeneous mixture of 2 or more substancesSolvent: liquid in solutionSolute: dissolved substancePolar nature of water determines its behavior with other substancesHydrophilic: likes water dissolve or absorb ionic, polarHydrophobic: repels water, and will not dissolve in it (oil)SolutionsSolution: homogeneous mixture of 2 or more substancesSolvent: liquid in solutionSolute: dissolved substanceMoleMolecular weight number (M) grams, not daltonsContains 6.02(10^23) molecules -this number is also 1 molar solution of any elementDissociation of Water MoleculesIf a hydrogen atom leaves one water molecule, but leaves its electron behind, the water molecule gains a negative charge and is called a hydroxide ion. The hydrogen atom without its electron is a hydrogen ion, a single proton with a charge of +1. If another water molecule acquires this proton it becomes ahydronium ion with a charge of +1. Water exists as an equilibrium – it can lose a hydrogen or gain one.Acids and BasesSubstances that cause an unbalance in the ration of hydrogen and hydroxide ions are called acid or baseAcid: increases H+ concentrationBase: increases OH+ concentration or decreases H+ concentrationA strong acid, like (like HCl) dissociates completely, a weak acid (like H2CO3) dissociates reversiblyCarbonic acid Bicarbonate ion Hydrogen ionA buffer will maintain a balance by shifting the direction if there is a change in H+ concentrationThe pH scaleThe concentration of H+ ions in a solution can be determined using pH.pH = - log of H+ concentrationLow pH = acid = more hydrogen ionsHigh pH = base = less hydrogen ionsIncrease of 1 pH unit = 10 x increase in HIncrease of 2 pH units = 100 x increase in


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