1. Water, Mixtures, Acids, Bases , Ph and Indicators
Importance in Science and Impact on Living Things

2. Water That “polar” little molecule
Essential for Life
(65-70% of our Mass)
Universal Solvent
(Most substances are Dissolved in or Transported by Water
Ability to Dissolve Substances is due to its Polar Nature
(Opposite charges along the molecule)

3. Why are we studying water?
More about Water
Why are we studying water?
All life occurs in water
inside & outside the cell

4. WATER a non-living molecule ESSENTIAL FOR LIFE
Water is Polar
(has a positive region and a negative
Region)
The Negative End (oxygen) of one water
molecule
Attracts the Positive End (Hydrogen)
Of another water molecule
Slightly Negative
Oxygen
Hydrogen
Hydrogen
Slightly
positive
Slightly
positive

5. 1. Chemistry of water H2O molecules form H-bonds with each other
+H attracted to –O
creates a sticky molecule
APBio/TOPICS/Biochemistry/Movies AP/hydrogenbonds-Thinkwell.swf

6. Water is Cohesive
A force of attraction between molecules of the same substance is “Cohesion”
Cohesion, or the ability of molecules to “stick together" is because opposite charges attract each other
Water molecules attract other water molecules, forming HYDROGEN BONDS

7. Water is also Adhesive
Adhesion happens when there is attraction between two different substances
Because Water is POLAR, it adheres to many other substances
Water is one of the Best Solvents because other molecules are Attracted to Water
Intermolecular Hydrogen Bonding accounts for water’s properties of Cohesion and Adhesion

8. Cohesive and Adhesive Properties in Action
Water moving up roots, forming droplets, creating surface tension

9. How does H2O get to top of trees?
Transpiration is built on cohesion & adhesion
APBio/TOPICS/04Biochemistry/MoviesAP/03_03WaterTransport_A.swf
Remember the videotape!

10. In Summary….. Special properties of water 1. cohesion & adhesion
surface tension, capillary action
2. good solvent
many molecules dissolve in H2O
hydrophilic vs. hydrophobic
3. lower density as a solid
ice floats!
4. high specific heat
water stores heat
5. high heat of vaporization
heats & cools slowly
Ice! I could use more ice!

11. 2. Water is the solvent of life
Polarity makes H2O a good solvent
polar H2O molecules surround + & – ions
solvents dissolve solutes creating solutions
What dissolves in water easily?
polar or non-polar molecules?
How about Oxygen? Does that dissolve in H2O?

12. What dissolves in water?
Hydrophilic
substances have attraction to H2O
polar or non-polar?
What dissolves in water easily?
polar or non-polar molecules?
How about Oxygen? Does that dissolve in H2O?

13. What doesn’t dissolve in water?
Hydrophobic
substances that don’t have an attraction to H2O
polar or non-polar?
Oh, look hydrocarbons!
What dissolves in water easily?
polar or non-polar molecules?
How about Oxygen? Does that dissolve in H2O?
fat (triglycerol)

14. And this has made all the difference!
3. The special case of ice
Most (all?) substances are more dense when they are solid, but
not water…
Ice floats!
H bonds form a crystal
And this has made all the difference!

15. Ice floats

16. Why is “ice floats” important?
Oceans & lakes don’t freeze solid
surface ice insulates water below
allowing life to survive the winter
if ice sank…
ponds, lakes & even oceans would freeze solid
in summer, only upper few inches would thaw
seasonal turnover of lakes
sinking cold H2O cycles nutrients in autumn

17. 4. Specific heat H2O resists changes in temperature
high specific heat
takes a lot to heat it up
takes a lot to cool it down
H2O moderates temperatures on Earth

18. Specific heat & climate

19. 5. Heat of vaporization Evaporative cooling
Organisms rely on heat of vaporization to remove body heat

20. Compounds verses Mixtures
Compounds are atoms or ions joined by Chemical Bonds
Combine in Fixed proportions and a definite structural arrangement
Are changed physically and chemically
Mixtures consist of two or more substances NOT chemically combined
No definite proportions
Each substance retains its original chemical and physical properties

21. Homogeneous Mixtures (the same through out)
Solutions are generally Clear homogeneous mixtures
Consist of ….
Solvent (like Water) substance doing the dissolving
Solute (like Salt, Sugar) is the substance being dissolved

22. Dissolving
When a molecular substance Dissolves in a Liquid, the substance separates into its individual molecules
Sugar molecules spread throughout the water (going into solution)

23. When Ionic compounds Dissolve they also Dissociate
When Ionic compounds are dissolved, the ionic bonds holding them together are broken due to the attractive forces of the water molecule
NaCl (table salt) dissociates
To form Na+ and Cl- Ions

24. Ionization of water & pH
Water ionizes
H+ splits off from H2O, leaving OH–
if [H+] = [-OH], water is neutral
if [H+] > [-OH], water is acidic
if [H+] < [-OH], water is basic
pH scale
how acid or basic solution is
1  7  14
H2O  H+ + OH–

25. tenfold change in H+ ions
pH Scale
10–1
H+ Ion
Concentration
Examples of Solutions
Stomach acid, Lemon juice 1 pH
100
Hydrochloric acid
10–2 2
10–3
Vinegar, cola, beer 3
10–4
Tomatoes 4
10–5
Black coffee, Rainwater 5
10–6
Urine, Saliva 6
10–7
Pure water, Blood 7
10–8
Seawater 8
10–9
Baking soda 9
10–10
Great Salt Lake 10
10–11
Household ammonia 11
10–12
Household bleach 12
10–13
Oven cleaner 13
10–14
Sodium hydroxide 14
tenfold change in H+ ions
pH1  pH2
10-1  10-2
10 times less H+
pH8  pH7
10-8  10-7
10 times more H+
pH10  pH8
10-10  10-8
100 times more H+
In pure water only 1 water molecule in every 554 million is dissociated

26. What is Ph and What can it tell us?
Ph is a way of representing the Hydrogen ion [H+] concentration of an acidic or basic solution
Defined as the –log of [H+]
In other words, the greater the number of H+ produced by a dissolved substance, the smaller the Ph value
Ph can tell us if something is an acid or a base AND its strength!

27. Dissociation produces Acids and Bases
Acids produce excess H+ ions
Bases produce excess OH- ions

28. Ph Scale The stronger the acid the lower the ph value
Acids have the highest concentrations of H+
Ph scale goes from
0-14
The stronger the Base the higher the ph value
Bases have the lowest concentrations of H+
High [OH-]

29. Acids Verses Bases
Produce Excess Hydrogen ions (H+ ) when they dissociate in water
Ph values less than 7
Taste Sour
Corrode metals
Produce Excess Hydroxide ions(OH-) when they dissociate in water
Ph values greater than 7
Taste Bitter
Emulsify Fats (droplets)
Slippery (soapy)

30. Common Acids and Bases Citric Acid (lemons oranges, limes)
Acetic Acid (vinegar)
Carbonic Acid (soda)
Hydrochloric Acid (HCl) stomach
Sulfuric and Nitric Acids (acid rain)
Sodium Hydroxide (NaOH) Lye, Draino
Sodium Bicarbonate (Baking Soda)
Ammonia (NH3) cleaners

31. Indicators “indicate” if something is an acid or a base
An indicator is a substance that changes color when the pH goes above or below a certain pH range.
So, indicators can tell us when any given substance is either more acidic or more basic by simply Changing color

32. Examples of Indicators
Litmus turns Red in an acid; but will change Blue in a Base
Methyl Orange changes from Yellow to Orange in acids (pH <3)
Phenolphthalein changes from colorless/clear to Pink in bases (pH >8)

33. Neutralization Results when an Acid is Mixed with a Base
Neutralization means that the pH is no longer acidic or basic; it reaches a pH of 7 (neutral)
NaOH + HCl H2O + NaCl
The H+ of the acid combines with OH- of the base to produce water and salt
Neutralization Reaction
Strong Base
Strong Acid
Water
Salt
pH =12
pH = 2
pH = 7

34. Buffers are chemicals that neutralize excess acids or bases
Buffers are compounds that act differently depending on “what they are mixed with”
When mixed with a Strong Acid; a buffer behaves like a weak base -- neutralizing the Acid
When mixed with a Strong Base; a buffer acts like a weak acid ----- neutralizing the Base
TUMS, Milk of Magnesia are examples of buffers that neutralize excess stomach acid

35. Buffers & cellular regulation
pH of cells must be kept ~7
pH affects shape of molecules
shape of molecules affect function
pH affects cellular function
Control pH by buffers
reservoir of H+
donate H+ when [H+] falls
absorb H+ when [H+] rises 1 2 3 4 5 6 7 8 9
Amount of base added
Buffering
range pH
Exercise = acidic in muscles
CO2 = carbonic acid
lactic acid
body uses buffers to counter act this

36. Any Questions? Do one brave thing today…then run like hell!
He’s gonna earn a Darwin Award!
Any Questions?
Do one brave thing today…then run like hell!