water and its properties cp biology: chapter 2. the water molecule needed by all living things –...
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Water and its PropertiesCP Biology: Chapter 2
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The Water Molecule
needed by all living things– parts of cells, fluid around cells (humans 65% water)
– used in many chemical reactions– keeps temperatures stable– transports dissolved substances in blood or fluid
(nutrients, gases, chemical messages)
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• covalent bonds molecules • electrons are NOT shared equally
in POLAR bonds • molecule has (+) and (-) poles
POLAR molecule has regions of partial charges
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The Water Molecule
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Polar Water Molecule
Oxygen end has slight negative charge (-) poleHydrogen ends have slight positive charge (+) poles• Molecule has bent shape
(+) (-) poles give water molecule many important properties
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Water molecule is “bent”
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NONPOLAR: A molecule with covalent bonds in which electrons
ARE shared equally
Polar and Nonpolar molecules
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HYDROGEN BONDING
• + and – areas on polar molecules attract each other
• Hydrogen on one molecule oxygen on a nearby molecule (or sometimes nitrogen)
• Forms a weak bond, but usually many• Important in living things
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Hydrogen Bonds in Water
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Cohesion• Attraction between molecules of the same
substance• Hydrogen bonds make molecules stick
together• In water, bonds are fluid - constantly form,
break, form. . .
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Cohesion in Water
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Adhesion
• Attraction between molecules of different substances
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Properties of Water Caused by Cohesion
1) High surface tension• Surface molecules bond• Acts like a membrane
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Important Because…
• Help control movement into cells• Insects can “walk” on water
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High Heat Capacity
• Water absorbs a lot of heat before its temperature rises
• Absorbed energy must first break hydrogen bonds before molecules can move faster, which makes temperature rise
• Also loses a lot of heat before its temperature drops
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Important because…
• Slows temperature changes in the environment (living things can adjust to seasons)
• Keeps stable temperature in living things • Ocean temperatures stay stable all year• Evaporating water cools skin, plant leaves
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Ice Floats
• When water freezes, hydrogen bonds stay formed
• Molecules are farther apart than in liquid water
• Ice is less dense than liquid water floats
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Hydrogen bonds in ice create a stable, three-dimensional structure
Ice is less dense than liquid water
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3 States of Water
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Important because …• Surface of water freezes on ponds and lakes
– keeps liquid water below from freezing• Organisms in water can survive during cold
weather
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Water Properties caused by AdhesionWater is the “Universal solvent”• More things dissolve in water than in any
other liquid
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Important because…
• fluids carry important things into cells and throughout organisms – water dissolves most things cells need
• Water is main component in: cytoplasm, fluid between cells, blood, body fluids
• Plant sap, aquatic environments – substances that cells need are dissolved in the water
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“Like Dissolves Like”
water dissolves other polar and ionic substances, but NOT nonpolar substances
NONPOLAR POLAR
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Capillary Action
Water molecules climb up a narrow tube or spacea) Uses adhesion
- water sticks to walls of tube- hydrogen bonds: water-to-walls
b) uses cohesion, too- water molecules stick together- pulled up against gravity
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Capillary Action
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Important because…
water squeezes into small spaces–between cells–rises inside plant stems (vein = bundles
of tubes)–moves fluids like blood inside animals
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Transpiration
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Solutions and Suspensions
MIXTURE• two or more substances physically mixed• do NOT react chemically• most substances in living things are dissolved
in water
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Solution
• liquid mixture, all parts are evenly dispersed
• because water is polar, it can dissolve both ionic and other polar substances
• water easily dissolves salts, sugar, minerals, gases
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Solvent and Solute
• SOLVENT – the larger part of a mixture Substance that dissolves a solute SOLUTE – the smaller component, Substance that is dissolved ionic solute – dissociates into ions
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Covalent – dissolves into molecules
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Suspensions
• solute does not dissolve completely– larger particles
• blood is mostly water, with dissolved substances and suspended cells
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Acids, bases, and pHThe pH scaleIn liquid, some water molecules break apart into ions H2O H+ + OH-
Water hydrogen ion + hydroxide ion (actually H3O+ )
Ions can also join to form a water molecule H+ + OH- H2O
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pH in water
• In pure water, not many (1 X 10-7 moles H+/Liter) = pH 7• pH scale shows concentration of H+ ions
[H+]–below 7 is acid – have more H+ ions than
water–above 7 is basic - have fewer H+ ions than
water
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The pH Scale
Each step on pH scale is a power of 10– ex. pH 4 has 10 times more H+ than pH 5, and 100 times more H+ than pH 6
[ H+ ]
pH #
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Acids
ACID - any compound that forms H+ ions in water• Many foods are at least slightly acidic• Have a sour or tart taste Ex. lemon, vinegar,
apples• Strong acids have pH 1-3• Ex. HCl H+ + Cl- H2SO4 H+ + HSO4
-
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Bases
Base (alkali) any compound that forms OH- ions in water• have bitter taste and slippery feel (ex. soap) Ex. KOH, NaOH
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Buffers
• most cells have pH 7.0 – 7.4. • Outside this range, pH interferes with
chemical reactions in life processes• “buffers” are weak acids or bases that can
accept excess H+ or OH- ions • keep pH steady in cells
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Buffers keep pH stable in fluids
• “neutralize” strong acids and bases homeostasis
• Blood has several buffers, such as bicarbonate ions and phosphate ions
keep blood pH stable
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pH in the Human Body
• Most tissues and fluids in the body are at or near pH 7
• Stomach juices include acid (HCl) at pH 2• Juices from pancreas and liver are basic
- pH 8.5 - Neutralizes stomach acid
Neutralization reaction acid + base water + salt
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pH in Digestive System
pH of food traveling through intestines gradually returns to pH 7.