1. Water and Its Properties Honors Biology Ms. Kim

2. Water: Molecule That Supports All of Life
Water is the biological medium here on Earth
Provides an environment where metabolic rxns can happen
H20 is often a product or reactant in biological rxns
All living organisms require water more than any other substance (cells ~80%H20 )

3. ¾ of the Earth’s surface is submerged in water
The abundance of water is the main reason the Earth is habitable
Figure 3.1

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

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

6. Polar and Nonpolar Molecules
Polar Molecule – Unequal distribution of charges
One side is more positive
One side is more negative
Dissolve in water
Ex: Water
Nonpolar Molecule – no separation of charge, so no positive or negative poles are formed.
Do not dissolve in water
Ex: CO2, O2, lipids
Think of the interaction of two magnets and how they either are attracted to each other or repel.

7. How do water molecules interact with each other?
Polar water molecules can be attracted to each other
The hydrogen atom with its’ partial positive charge (+) is attracted to the oxygen atom (partial negative charge) of a different water molecule!
This is known as a hydrogen bond

8. Hydrogen Bonds Bonding between molecules
Very weak, but very important for the various
characteristics of of water…

9. Polar covalent bonds

10. Polar Structure

11. 5 Characteristics of Water
1. Cohesion 2. Adhesion 3. High Specific Heat 4. Less Dense as a Solid 5. Water is a terrific solvent

12. Water Properties **H-bonding is responsible for these properties
1. Cohesion (“co-” means “together”)
Tendency of molecules of the SAME “kind” to stick together
Partial - & partial + ends attract each other
Examples: water “sticking” to itself, transpirational-pull, surface tension
2. Surface Tension:
Measure of how difficult it is to stretch or break the surface of a liquid/ resist an external force.
H2O has high surface tension
Due to H-bonds

13. Water “sticks” to itself

14. Transpirational Pull a result of cohesion
Helps pull water up through the microscopic vessels of plants w/out expending energy

15. Surface tension another type of cohesion
a measure of how hard it is to break the surface of a liquid
Water molecules form a “barrier” by H-bonding together
Water does NOT pull apart very easily  acts like elastic

16. Surface Tension

17. The type of attraction that happens between two different molecules
2. Adhesion
The type of attraction that happens between two different molecules
Partial - & partial + ends of water attract to ends of other molecules
Water will make hydrogen bonds with other surfaces such as glass, soil, plant tissues, and cotton
Adhesion forms stronger bonds than cohesion
Examples: water “sticking” to stuff (i.e.-towels, clothes, paper, glass)
More Examples:
Meniscus forming on graduated
cylinder!
Transpiration - plants and
trees remove water from the soil
Paper towels soaking up water

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

19. Another Example of Cohesion and Adhesion…

20. 3. 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
Water has a high specific heat, meaning it resists temperature change!
Because of the hydrogen bonds between water molecules
Water has to absorb more heat energy to increase overall temperature compared to other compounds
Ex: Lake Michigan is really cold until ~ August…it takes a long time to warm up!!
Helps to regulate cell temperatures in organisms

21. Water has a high specific heat so its temperature does NOT fluctuate very much  allows life to live in water
moderate Earth's climate by buffering large fluctuations in temperature.

22. How come icebergs float?

23. 4. Low Density in Solid Form
Allows for insulation of bodies of water by floating ice
Solid water (i.e.-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

24. Ice floats because ice is less dense than liquid water!
This is because the H bonds hold the water molecules farther apart than in liquid water

25. Hydrogen bonds constantly break and re-form Hydrogen bonds are stable
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 stable

26. 5. The Solvent of Life
Water is a great solvent (Water is the universal solvent)
Solute – gets dissolved (Hot Cocoa mix)
Solvent – does the dissolving (Water)
Solution – uniform mixture of two or more substances

27. 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

28. Why is water a good solvent?
Water is called the universal solvent because more substances dissolve in water than in any other chemical.
This has to do with the polarity of each water molecule. The hydrogen side of each water (H2O) molecule carries a slight positive electric charge, while the oxygen side carries a slight negative electric charge.
This helps water dissociate ionic compounds into their positive and negative ions. The positive part of an ionic compound is attracted to the oxygen side of water while the negative portion of the compound is attracted to the hydrogen side of water.
Despite its name as the "universal solvent" there are many compounds water won't dissolve or won't dissolve well. Such as nonpolar and hydrophobic substances.

29. Hydrophilic and Hydrophobic Substances
A hydrophilic substance
Has an affinity for water
Water “loving”
Dissolves in water
Example: salt and sugar
A hydrophobic substance
Does not have an affinity for water
Water “fearing”
Does NOT dissolve in water
Example: Oil

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

31. Dissociation of water molecules leads to acidic and basic conditions that affect living organisms
Dissociation = the separation of ions when an ionic compound dissolves
H2O  H+ (hydrogen ion) + OH- (hydroxide ion)
H+ + H2O  H3O (hydronium ion)

33. Acids
Number of hydronium ions in solutions is greater than the number of hydroxide ions
HCl  H+ + Cl-

34. Bases
Number of hydroxide ions in solution is greater than the number of hydronium ions
NaOH  Na+ + OH-

35. Acids and Bases
An acid
compound that releases/donates a proton (H+) when dissolved in water
Increases H+ concentration in solution
Ex: HCl
A base
compound that accepts H+ and removes them from a solution
Is any substance that reduces the hydrogen ion concentration of a solution
The more basic the solution, the higher the OH- concentration
Ex: NaOH pH
Measure of acidity or alkalinity of an aqueous solution

36. pH Scale Measures how acidic or basic a substance is: Scale:
Determined by the concentration of H+ ions within a solution
Uses a numerical scale of 1 to 14 scale
Scale:
1 – 7: ACIDIC
7 – 8: NEUTRAL
8 – 14: BASIC
Buffers – resist pH changes
Can accept OR donate H+
Important in humans…why?

37. the lower the pH the stronger the acid
the higher the pH the stronger the base
pH 7.0 is neutral

38. Buffers Buffers keep a neutral pH (pH 7) Buffers
substances that minimize changes in [ ] of H+ and OH- ions in a solution
Buffers keep a neutral pH (pH 7)
The internal pH of most living cells must remain close to pH 7

39. The pH scale and pH values of various aqueous solutions
Increasingly Acidic
[H+] > [OH–]
Increasingly Basic
[H+] < [OH–]
Neutral
[H+] = [OH–]
Oven cleaner 1 2 3 4 5 6 7 8 9 10 11 12 13 14
pH Scale
Battery acid
Digestive (stomach)
juice, lemon juice
Vinegar, beer, wine,
cola
Tomato juice
Black coffee Rainwater
Urine
Pure water
Human blood
Seawater
Milk of magnesia
Household ammonia
Household bleach
Each increase or decrease is 10x

41. 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)

42. Real Life Example…. The Threat of Acid Precipitation
Refers to rain, snow, or fog with a pH lower than pH 5.6
Is caused primarily by the mixing of different pollutants with water in the air

43. Acid precipitation Can damage life in Earth’s ecosystems More acidic1 2 3 4 5 6 7 8 9 10 11 12 13 14
More acidic
Acid rain
Normal rain
More basic