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This 3 page Class Notes was uploaded by Shira Clements on Wednesday February 17, 2016. The Class Notes belongs to BSCI105 at University of Maryland taught by Norma Allewell in Fall 2015. Since its upload, it has received 16 views. For similar materials see Principles of Biology I in Biology at University of Maryland.
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Date Created: 02/17/16
Shira Clements BSCI105 Chapter 3- Water and Life Water is 75% of Earth- ice, vapor, water- all three physical states Water- V shape molecularly- 2 Hydrogens (slightly pos) covalently bonded to oxygen (more slightly neg) and electrons spend more time with oxygen (more electronegative)- so polar covalent - Natures best solvent - When in liquid form the bonds are super weak- so form break and reform often (bonds with neighbors sometimes) - Polar molecules are hydrophilic, while nonpolar molecules are hydrophobic- do not dissolve in water o Hydrophilic substances can create a colloid- large polar molecules that do not dissolve, suspension of particles in liquid Cohesion of Water Molecules- water molecules stay close together because of hydrogen bonding - Cohesion- hydrogen bonds hold substance together o Contributes to transport of water in plants o Surface tension- measure how hard it is to break at the surface of a liquid Clings to each other through hydrogen bonding at the surface and below surface (water can go a little higher than what cup can hold) - Adhesion- clinging of one substance to another- water clings to other things Water absorbs heat from air and release it to make it cooler, and it will change very slightly in its own temperature. Kinetic Energy- energy of motion- faster, then the greater the energy Heat- form of energy, measure of matter’s total kinetic energy due to molecules moving- so depends on volume- pool contains more heat than a hot cup of coffee because of its volume - Heat goes from hotter to colder until same temperature- when two objects are brought together - Calorie- amount of heat it takes to raise temp 1 C or amount of heat that 1 g of water release wen it cool 1 C- that amount is known as specific heat- 1 cal per gram in 1 C=1 (quite high- alcohol quite low)- resistance of substance to change temp o Heat disrupts hydrogen bonds before molecules move faster and when water temperature drops slightly, more hydrogen bonds form- releasing energy as heat o Burn yourself on stove of pot when water inside is lukewarm because 1C will raise iron’s degree much quicker than waters Temperature- measure of heat intensity which represents average kinetic energy (regardless of volume)- measured in Celsius Evaporative Cooling- as liquid evaporates, the surface of the liquid that remains cools down (hottest molecules leave as gas, so average heat is lower) - when molecules move fast enough (to overcome the attraction amongst other water molecules in liquids) will enter the air as a gas- vaporization/evaporation- higher temperature will escape more easily because the average kinetic speed is raised so molecules move faster - Heat of Vaporization- amount of heat to be absorbed to convert 1 g of liquid to gas (water has high heat of vaporization because of hydrogen bonds which must be broken) o helps moderate Earth’s climate Water - Water is less dense as a solid- ice floats in water- water expands when solid because of hydrogen bonding- temp above 4 C water is like other liquids- expanding when warms and contracts when cools, but between 4 to 0, molecules are moving too slow to break hydrogen bonds (begins to freeze), 0 C they completely freeze- hydrogen bonds keep molecules far enough to make ice less dense - Solution- liquid that is homogenous (equally spread throughout) mixture of two or more substances- aqueous solution- water is solvent - Solvent- dissolving agent - Solute- substance that is dissolved - when a polar substance enters water, water surrounds each individual ion (separates Na and Cl for ex) and creates a hydrogen shell and dissolves it, homogenous solution with 2 solutes Mole (mol)- exact number of objects = 6.02 x 10 Daltons in one g- Avagadro’s number - Molarity- number of moles of solute per liter of solution- unit concentration Sometimes, a hydrogen atom participating in a hydrogen bond between two molecules shifts from one molecule to the other, leaving the electron behind, and only the hydrogen proton is being transferred. Water molecule that lost proton is OH (hydroxide ion), water molecule that gained proton is now H O 3 + (hydronium ion). Acids- substance that increases the hydrogen ion concentration of solution, more H+ Bases- substance that reduces the hydrogen ion concentration of solution, either dissociating itself with H+ or having higher concentration of OH- pH Scale- at 25C, product of the H+ and OH- concentrations is constant as 10 = [H ][OH ]=10 -14 + -7 - -7 -3 - H =10 M, OH =10 M- if acid is added, then it will increase to 10 or an increased exponent and opposite with base - pH= -log[H ], neutral solutions= -log10 = -(-7)=7, pH declines as H+ increases o solution with pH of 10= hydrogen ion concentration of 10 -10and hydroxide ion concentration of 10 M -4 o pH less than 7 is acid, pH more than 7 is basic, 7= neutral (water) o when pH changes slightly the concentrations of H+ or OH- changes substantially because of the scientific method Buffer- substances that minimizes change of concentrations of H+ and OH- - accepts hydrogen ions when there are excess and donating when there is not enough - carbonic acid- helps blood stay with constant pH of 7.4- forms when C02 reacts with blood plasma, or HCO3- (the base) - Acid precipitation- rain, snow, fog- pH lower than 5.2- can hurt life in lakes and plants
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