1. Water and Its Properties AP Biology Ms. Day

2. Water is a polar molecule The polarity of water molecules
Allows it form many hydrogen bonds
Contributes to many properties of water
Oxygen has a greater “pull” on e-’s than hydrogen forms partial – and partial + end of molecule
(dipole nature) + H
 –

3. Bonds in H2O Where is the Polar Covalent Bond in water?
What is the difference btw a “POLAR COVALENT BOND” and a “NONPOLAR COVALENT BOND?

4. What is “polarity”?
A molecule that has different charges on each end or “pole”
Asymmetrical ends = polar
Water polarity allows for H-bonding (attraction)

5. Polar covalent bonds

6. Water Properties **H-bonding is responsible for these properties
1. Cohesion (“co-” means “together”)
a high % of H20’s bond to neighboring H20’s
Partial - & partial + ends attract each other
Examples: water “sticking” to itself, transpirational-pull, surface tension

7. Water “sticks” to itself

8. Transpirational Pull a result of cohesion
Helps pull water up through microscopic vessels of plants w/out using energy (ATP)

9. Surface tension another type of cohension
a measure of how hard it is to break the surface of a liquid
H20’s form a “barrier” by H-bonding together
Water does NOT pull apart very easily  acts like elastic
At the surface of a liquid, the molecules are only puller downward and towards the sides.

10. The surface tension of water is GREATER than the pull of gravity on the needle or spider’s tiny feet!

11. Surface Tension
At the surface of a liquid, the molecules are only puller downward and towards the sides.

12. 2. Water demonstrates Adhesion
a high % of H20’s bond to other different molecules
Partial - & partial + ends of water attract to ends of other molecules
Examples: water “sticking” to stuff (i.e.-towels, clothes, paper, glass)

13. Cohesion & Adhesion Acting Together
Helps pull water up through the microscopic vessels of plants
Called capillary action

14. Another Example of Cohesion and Adhesion…

15. 3. Water has a HIGH heat capacity
Water changes temp slowly
Absorbs large amounts of energy before it begins to get hot  needs to break A LOT of H-bonds
Releases heat slowly too
Allows large bodies of water to remain stable even when temperature of air changes

16. Water has a High Specific Heat
specific heat = amount of heat that must be absorbed or lost for 1 gram of substance to change its temp. by 1ºC
WHY IS THIS PROPERTY IMPORTANT TO BIOLOGY?
Contents of cells unlikely to freeze  stable internal temperature despite fluctuating external temp’s
Helps moderates Earth's climate by buffering large fluctuations in temperature.

17. Water has a High heat of Vaporization
Amount of energy to convert 1g of 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 (cooling effect)

18. Water on Earth
Water is the only substance that exists under NORMAL conditions on Earth as solid, liquid and gas

19. 4. Low Density in Solid Form
Allows for insulation of bodies of water by floating ice
Solid water (ice)
Is less dense than liquid water
Floats in liquid water
Since ice floats in water 
Life can exist under frozen surfaces of lakes/polar seas

20. Polar Structure Separated by 105o when in the gaseous or liquid phase
109.5o when ice.

21. The hydrogen bonds in ice
Are more “ordered” than in liquid water, making ice less dense
Liquid water
Hydrogen bonds constantly break and re-form
Ice
Hydrogen bonds are more stable

22. 5. Water is an Excellent Solvent
Water is a versatile solvent (“dissolver”)due to its polarity
It can form aqueous (“watery”) solutions very easily!
MOST biochemical reactions occur in water!!!

23. Ex: salt water solution
Solution = a UNIFORM mixture of 2+ substances
LOOK the same (uniform) throughout
Solvent = substance that is doing the dissolving
The “dissolver”
Solute = substance(s) getting dissolved
Ex: salt water solution

24. The different ends of the polar water molecule can interact with ionic compounds (the solutes) and dissolve them +
Cl – –
Na+
Cl–

26. Hydrophilic and Hydrophobic Substances
A hydrophilic substance
Has affinity for water
Water “loving”
A hydrophobic substance
Does not have affinity for water
Water “fearing”
Dissociation = the separation of ions when an ionic compound dissolves

27. Changes in [ ] of these ions have great affect on living organisms
Water can dissociate
Into hydronium ions and hydroxide ions
H2O + H2O  H3O OH-
Changes in [ ] of these ions have great affect on living organisms
Hydronium
ion (H3O+)
Hydroxide
ion (OH–) +

28. Acids vs. Bases
Hydrogen Ion Hydroxide Ion
Acid Base
H2O  H+ + OH-

29. Acids and Bases
An acid
any substance that increases hydrogen ion (H+) concentration of a solution
A base
any substance that reduces hydrogen ion concentration of a solution pH
Measure of acidity or alkalinity of an aqueous solution

30. The pH Scale The pH of a solution high in an acid (Higher [H+] )
determined by relative [ ] of H+’s
high in an acid (Higher [H+] )
low in a base (Lower [H+] thus higher [OH-] )

32. Acids = low pH #’s
HIGH [ ] of H+
Bases = High pH #’s
HIGH [ ] of OH-
Remember….
A…..B…. In the alphabet and 1….14
A= 1st letter (H+ has 1 letter)
B= 2nd letter (OH- has 2 letters)

33. Buffers NEUTRALIZATION!!! Buffers
substances that minimize changes in [ ] of H+ and OH- ions in a solution
Consist of an acid-base pair that can REVERSE changes
NEUTRALIZATION!!!
The internal pH of most living cells must remain close to pH 7 (Ex: H2CO3)
Need biological buffers to regulate systems (absorbs excess H+ or OH-)
Most important buffer in humans = bicarbonate ion

34. Let’s Practice in Groups…
pH 2 has more _____ ions and is an acid or base? Weak or strong?
pH 12 has more _____ ions and is an acid or base? Weak or strong?
pH 9 has more _____ ions and is an acid or base? Weak or strong?
pH 7 has more _____ ions and is an acid or base? Weak or strong?

35. More Practice in Groups…
Why is water a versatile (universal) solvent?
In general, what kinds of materials will not dissolve in water? Why?

36. More Practice…Which Property?
During winter, air temp’s in northern United States can remain below 0∘C for months; however, fish and other animal living in the lakes survive.
When you pour water into a 25ml graduated cylinder, a meniscus forms at the top of the water column.
Sweating and evaporation of sweat from the body surface help reduce a human's body temperature.
Water drops fall on a surface of a leaf & form beads.
If you touch the edge of a paper towel to a drop of colored water, the water will move into the towel
helps Earth have a “global blanket”
helps maintain homeostasis in cells