Objectives - 5 Describe the structure of a water molecule. Explain how water’s polar nature...
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Transcript of Objectives - 5 Describe the structure of a water molecule. Explain how water’s polar nature...
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Objectives - 5Describe the structure of a water molecule.Explain how water’s polar nature affects its
ability to dissolve substances.Outline the relationship between hydrogen
bonding and the different properties of water.
Identify the roles of solutes and solvents in solutions.
Differentiate between acids and bases.
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PolarityFor the most part, water’s biological
functions stem from its chemical structure.
Remember that in a molecule of water, the two hydrogen atoms covalently bond to one oxygen atom by sharing electrons.
The e- however are not shared equally.
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PolarityThe oxygen atom has a greater ability to
attract electrons to it because it pulls hydrogen’s e-’s toward its nucleus.
The region of the molecule where the oxygen atom is located has a partial negative charge.
The regions where the hydrogen atoms are located have partial positive charges.
So, even though the total charge on a water molecule is neutral, the charge is unevenly distributed across the water molecule.
Polar Compound = compound with an uneven distribution of charge.
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Solubility of WaterThe polar nature of water allows it to
dissolve polar substances.i.e., sugars, ionic compounds, some
proteinsWater does not dissolve nonpolar
substances.i.e., oil
NaCl – soluble in water…Dissolved or dissociated ions are
present in all of the aqueous solutions found in living things.They are necessary in maintaining
normal body functions.
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Hydrogen Bonding
The polar nature of water causes water molecules to be attracted to each other.
This attraction is called a hydrogen bond.
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Hydrogen Bonding, cont’d…The number of hydrogen bonds that exist
depends upon the state of matter that water is in.Solid = ice: all molecules are hydrogen bonded
and do not break.Liquid = waterGas = water vapor
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Hydrogen Bonding, cont’d…Hydrogen bonding accounts for the unique
properties of water. CohesionAdhesionAbsorb large amounts of energy as heatCool surfaces through evaporationThe density of iceDissolve many substances
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Cohesion Water molecules stick to each other as a result
of hydrogen bonding. Cohesion = is the attractive force that holds
molecules of a single substance together.
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AdhesionAdhesion = the attractive force between two
particles of different substances. i.e., water molecules and glass molecules
Capillarity = property where the attraction between molecules results in the rise of the surface of the liquid when in contact with a solid.
The forces of cohesion, adhesion, and capillarity help water rise through narrow tubes against the force of gravity.Water-conducting tubes in the stem of a flower.Capillary tubes
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Temperature ModerationWater has a high heat capacity.Water can absorb or release relatively large
amounts of energy in the form of heat with only a slight change in temperature.
This property of water is related to hydrogen bonding.
To break hydrogen bonds, energy must be absorbed.
Water’s high heat capacity also allows organisms to keep cells at an even temperature despite environment temperature changes.
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Density of IceMost solids are denser than their
liquids.This is not the case for ice / water.
Water expands when it freezes.Ice (solid water) is less dense than liquid
water.
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SOLUTIONSSolution = mixture where one or more substances
are uniformly distributed (mixed) in another substance.Plasma (liquid portion of blood) is a complex solution.
Ions, large molecules, gases – all dissolved in waterKool-aid
Solute = a substance dissolved in the solvent.Solvent = the substance in which the solute is
dissolved.Kool-aid > powder = solute; water = solventNeither the sugar or water are altered chemically.If you boil away the water, the sugar will remain.
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Solutions, cont’d…Concentration (of a solution) = the amount of
solute dissolved in a fixed amount of the solution.
Saturated solution = a solution in which no more solute can be dissolved.
Aqueous solution = water is the solvent.Important to living things.Plants – moist soil (aqueous solution)Body cells exist in aqueous solution (intercellular
fluid) and are also filled with fluid.Most chemical rxns. that happen in the body
occur in aqueous solutions.
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ACIDS AND BASESThe degree of acidity or alkalinity (baseness)
is essential in living systems.IONIZATION of WATER (separation of
water)Water molecules bump into each other as they
move about.Sometimes this results in a chemical change.One water molecule loses a p+ (a hydrogen
nucleus), and the other gains this p+.This reaction happens in two steps.
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Ionization of Water, cont’d…First: one molecule of water pulls apart
another water molecule, (dissociates) into two ions of opposite charge.H2O H+ + OH- The OH- ion is called the hydroxide ion.The free H+ ion can react with another water
molecule shown in this equation: H+ + H2O H3 O+
…the H3O+ is called the hydronium ion.
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ACIDSIn a solution, if the number of hydronium ions
is greater than the number of hydroxide ions…The solution is acidic, it is an acid.Sour tasteIn high concentrations, they are highly
corrosive to some materials.
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BASESA solution is alkaline or basic, when it
contains more hydroxide ions than hydronium ions.Bases have a bitter taste.They feel slippery, because the OH- ions react
with the oils on our skin to form a soap.Commercial soap is the product of a reaction
between a base and a fat.
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pHpH scale = scale for comparing
the relative concentrations of hydronium ions to hydroxide ions within a solution.
The scale ranges from 0 – 14.0 is the most acidic.14 is the most basic (alkaline).7 is neutral (water).
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BUFFERSThe control of pH is important to living things.Enzymes (remember: proteins, RNA molecules)
can function only within a very narrow range of pH.Buffers are chemical substances that regulate pH.Buffers neutralize small amounts of either an acid
or a base added to a solution.Figure 2.14, page 44Stomach acid = 2Urine = 6Intestinal fluid = ~8.1Blood = ~7.4
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WATER AND DIFFUSION
All objects in motion have energy of motion called kinetic energy.
A moving particle of matter will continue to move in a straight line until it collides with another particle.
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BROWNIAN MOTION
Robert Brown – Scottish scientistUsed microscope to observe pollen grains
suspended in waterGrains moved constantly in little jerks
Seemed to be struck by invisible objects He thought this was the result of a life force hidden
within the pollen grains.He repeated experiment with dye particles and
got the same results. Dye particles are not living. Brown had no explanation for the motion, now
called Brownian motion.
We know it’s the random movement of atoms and molecules.
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DIFFUSION
Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration.Diffusion of water = osmosis
Diffusion results because of the random motion of atoms and molecules (Brownian motion).Diffusion is a slow process
Relies on the random motion of atoms and molecules
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DIFFUSION, CONT’D…
Concentration:Primary controlling factorThe more concentrated the
substances, the more quickly diffusion occurs.More collisions between the particles of the substances
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DIFFUSION, CONT’D…
Temperature and Pressure:External factors that can also change the
rate of diffusionIncreased temperature causes increased
energy and will cause more rapid particle movement.This will cause an increase in the rate of
diffusion.Increasing pressure also accelerates
increased particle motion… increased rate of diffusion.
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Results of Diffusion…
Diffusion continues until equilibrium is reached.Movement continues; however, there is no overall concentration change.
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Diffusion in Living Systems…
Concentration gradientThe difference in concentration of a substance
across spaceIons and molecules move from an area of
higher concentration to lower concentration.They move with the gradient.
If no other processes interfere, diffusion will continue until there is no longer a concentration gradient.Dynamic Equilibrium
Diffusion is one of the ways that cells move substances in / out of cells.
i.e., oxygen into capillaries from air sacs of the lungs