Why Water is Special Why do we study water properties in biology class About 23 of the mass of a cell is water Most lifesustaining reactions occur in water solutions Polarity Polarity describes the distribution of electrons in a molecule ID: 524587
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Slide1
Properties of Water!
Why Water is SpecialSlide2
Why do we study water properties in biology class?
About 2/3 of the mass of a cell is water!Most life-sustaining reactions occur in water solutionsSlide3
Polarity
Polarity describes the distribution of electrons in a molecule
Polar molecules have an uneven distribution of electrons.
Example: Water
-
+Slide4
Water forms
Hydrogen BondsHydrogen Bonds: Form due to attraction between water molecules.Not as strong as ionic/covalent bonds
Water can form up to 4 hydrogen bonds at onceSlide5
5
Properties of waterEmergent
Properties of water contribute to Earth’s fitness for lifeCohesion/AdhesionSurface tensionSpecific Heat
Solution
pH
http://www.sumanasinc.com/webcontent/animations/content/propertiesofwater/water.htmlSlide6
Water is Cohesive
Cohesion: Water molecules are drawn tightly together (on the surface of a lake or a pond, this forms a film, which is called surface tension
)Explains why:Water beads on a surface (like the lab table)Insects can walk on waterSlide7
A Cool Example of Cohesion / Surface Tension: Water Strider Insect
Water Strider - Video
http://news.nationalgeographic.com/news/2003/08/0806_030806_skeeters.html
YouTube:
Surface Tension
YouTube:
Jesus LizardSlide8
Water is
Adhesive = Adhesion = Water adheres (sticks) to different surfacesEx: Measuring water in a graduated cylinder
Water adheres (sticks) to the glass more than it adheres to itself.Why is this property of water important to organisms? Allows water to move through bloodstream.Slide9
Cohesion Adhesion
Ex: Water Bubble
Ex: Water
on a Leaf
Surface Tension and AdhesionSlide10
Water can undergo
Capillary ActionCapillary Action=
Water can flow up a tube, against gravityEx: Plants absorbing water through their roots (Transpiration)Slide11
11
Specific HeatIs the amount of heat that must be absorbed or lost for 1 gram of that substance to change its temperature by 1ºC
Water has a high specific heat which allows it to minimize temperature fluctuations to within limits that permit lifeHeat is absorbed when hydrogen bonds breakHeat is released when hydrogen bonds formSlide12
Moderation of temperature
Water’s high specific heat
Change temp less when absorbs/loses heatLarge bodies of water absorb and store more heat warmer coastal areasCreate stable marine/land environment
Humans ~65% H
2
O
stable temp, resist temp. changeSlide13
High Heat of Vaporization
Amount of energy to convert 1g or a substance from a liquid to a gas
In order for water to evaporate, hydrogen bonds must be broken.
As water evaporates, it removes a lot of heat with it.
Sweating cools the body as heat energy from the body changes sweat into a gasSlide14
Moderation of temperature
Evaporative CoolingWater has high heat of vaporization
Molecules with greatest KE leave as gasStable temp in lakes & pondsCool plantsHuman sweatSlide15
Water has a
High Heat CapacityWater absorbs a lot of heat from the air without having a large temperature changeSo…lakes and oceans often stabilize air temperatures
Water absorbs heat when it evaporates; this is why sweating helps us cool down!Slide16
Water is Less Dense as a Solid
Which is ice and which is water?Slide17
Water is Less Dense as a Solid
Water
IceSlide18
Solid
Liquid
Gas
States of MatterSlide19Slide20
Water is
less dense in its solid formWater is less dense in its solid form than it is in its liquid form (Ice floats!)
Why might it be a bad thing for ice to sink in a pond?Slide21
Moderation of temperature
Insulation by ice – less dense, floating ice insulates liquid H2O below
Life exists under frozen surface (ponds, lakes, oceans)Ice = solid habitat (polar bears)Slide22
So why does it take so much heat to increase the temperature of water?!
You have to break the hydrogen bonds between water molecules first! Slide23
Solutions and Mixtures
A
mixture is a substance that is made of two or more elements physically mixed togetherExample: Mixing Skittles and M&Ms together
A
solution
is a type of mixture where one substance is dissolved in another.
Solut
e- the substance that is dissolved
Solvent
- the substance that does the dissolvingSlide24
Water as a solvent
Water is often referred to as the “Versatile Solvent” because of it’s ability to dissolve such a wide variety of substances.
GO WATER!!!Slide25
Solution
The different regions of the polar water molecule can interact with ionic compounds called solutes and dissolve themSlide26
Solvent of life
“like dissolves like”
HydrophilicHydrophobicAffinity for H2O
Repel H
2
O
Polar, ions
Nonpolar
Cellulose, sugar, salt
Oils,
lipidsBloodCell membraneSlide27
Water Has a
Neutral pHpH: measure of how acidic or basic a solution isscale is 0 to 14
If pH = 7, then substance is neutral (not acid or base)