1. THE IMPORTANCE OF WATER TO LIFE

2. Hydrogen Bonds Give Water Unique Properties
Water molecules are polar molecules
Unequal sharing of electrons & V-like shape
They can thus form hydrogen bonds with each other and with other polar molecules
Each hydrogen bond is very weak
However, the cumulative effect of enormous numbers can make them quite strong
Hydrogen bonding is responsible for many of the physical properties of water

3. HYDROGEN BONDING: DRAW 2-3 MOLECULES OF WATER & INDICATE THE HYDROGEN BONDS
Not effective over long distances
WEAK BONDS
Formed by the attraction of opposite partial electric charges between two polar molecules

4. COHESIVE PROPERTIES

5. Heat vs Temperature
Heat= is a measure of the total amount of kinetic energy due to molecular motion in a body of matter.
Calorie= the amount of heat it takes to raise the temperature of 1g of water by 10C
Kilocalorie= 1,000 calories
Joule (J) one joule = calories and 1 calorie= 4.184J
Temperature= the intensity of heat due to the average kinetic energy of the molecules.
We will use Celsius to indicate temperature

6. THERMAL PROPERTIES High Heat of Vaporization High Specific Heat
Water absorbs a lot of heat, hydrogen bonds break, then water turns to vapor & then evaporates.
Water can absorb or release a lot of heat without changing its own temperature by very much. It’s ability to store heat
Makes water a good coolant
Have to add a lot of heat to change its temp.
Heat needed for the evaporation of water in sweat is taken from the tissues of the skin
Helps keep oceans relatively stable

7. WATER AS ICE, FLOATS
Ice
Liquid water

8. Salt dissolves when all ions have separated from the crystal
SOLVENT PROPERTIES
Most of the important molecules in and out of the cell are polar molecules. These molecules create solutions that enable for biochemical processes to occur.
Water is a versatile solvent because of its polarity
Protein synthesis & glycolysis
Gas Exchange
Salt dissolves when all ions have separated from the crystal
Water forms a hydration shell around each solute ion.
Light independent processes of photosynthesis

9. HYDROPHILLIC vs HYDROPHOBIC
Molecules that “love” water
With positive or negative charges including polar molecules
Molecules that “fear” water
Do not have positive or negative charges & are nonpolar
EX: all substances that dissolve in water like glucose
EX: all substances that do not dissolve in water like fats & oils
If substances are soluble in water can be freely transported in the blood plasma. Ex: glucose amino acids, & sodium chloride
If they are hydrophobic they are transported inside a lipoprotein complex. EX: fats and cholesterol

10. Solute Concentration in Aqueous Solutions
Molecular mass: sum of the masses of all the atoms in a molecule. = number of daltons
Measuring is done in moles=6.02 x 1023
Once the molecular mass of a molecule is determined, that number is used with a unit in grams.

11. How would you make 1 liter of a 1M solution of sucrose (C12H22O11)
Review Avogadro’s number (a mole)
There are 6.02 x 1023 daltons in 1g.
Carbon has an atomic mass of 12 & there are 12 carbons so 12 x 12 = 144
Hydrogen has an atomic mass of 1& there are 22 hydrogens so 1 x 22 = 22
Oxygen has an atomic mass of 16& there are 11 oxygens so 16x 11 = 176
For a total of ….342 daltons
So, this means you would need 342g of sucrose in a liter of 1M sucrose solution

12. Calculate the solutions of sucrose (C12H22O11)
Grams of Sucrose
Total Volume in Flask
0.2 M
0.4M
0.6M
0.8M
1.0M
342g
1,000mL
68.4g
1,000mL
136.8g
1,000mL
205.2g
1,000mL
273.6g
1,000mL

13. Water Ionizes
Covalent bonds within a water molecule sometimes break spontaneously
H2O +
OH–
hydroxide ion H+
hydrogen ion
Simplified version
This process of spontaneous ion formation is called ionization
It is not common because of the strength of covalent bonds

14. BELOW IS A BEAKER OF DISTILLED WATER
WHAT IS THE CHEMICAL FORMULA FOR THIS BEAKER OF DISTILLED WATER?
H2O +H H3O OH-
H2O H OH-
Simplified version
Is the concentration of water in the beaker the same as the total concentration of H+ + OH- ? NO
What does it mean to be at equilibrium?
The reactions is flowing back & forth, but there is no longer any net gain in either the concentration of the products or the reactants.
Which is in higher concentration in this beaker; H2O or H+ + OH- ?
H2O

16. pH
A convenient way to express the hydrogen ion concentration of a solution pH =
log [H+] _
The pH scale is logarithmic
A difference of one unit represents a ten-fold change in H+ concentration
Acid
Dissociates in water to increase H+ concentration
Base
Combines with H+ when dissolved in water

18. Remember: The pH scale is logarithmic.
A change in one pH number actually represents a tenfold change in hydrogen ion concentration
EX: pH of 3 is actually ten times more acidic than a pH of 4.

19. CALCULATE THE RATIO OF DISSOCIATED TO INTACT WATER MOLECULES IN A BEAKER OF DISTILLED WATER OF pH at 250 C
If pH =7, then the concentration of hydrogen [H+ ] = 1 x 10-7 , which is the same as…
[H+ ] = 1/10,000,000 , which is the same as
Saying there is 1 dissociated molecule of H2 O for every 10 million intact H2 O molecules in the beaker of distilled water on the table.
IN OTHER WORDS….
If you could reach in & pick out a single molecule from the beaker of water, 9,999,999 times out of 10,000,000 you would pull out a molecule of H2 O & 1 out of 10,000,000 times you would pick out a hydrogen ion.

20. pH chart (from WS) 1 1 X 10-1 0.1 1/10 1 X 10-13 4 1 X 10-4 0.0001
pH level
Exponetial notation
Decimal notation
Fraction notation
OH- 1
1 X 10-1
0.1
1/10
1 X 10-13 4
1 X 10-4
0.0001
1/10,000
1 X 10-10 7
1 X 10-7
1/10,000,000 10
1/1,000,000,000 14
1 X 10-14
1/10,000,000,000,000
1 X 10-0

21. DISCUSSION QUESTIONS
Considering the equation H2O H+ + OH- at equilibrium to answer the following questions
Does the equation tend to one direction of the other? If so, which direction does it tend to go?
This reaction tends towards the left
Which is in higher concentration in the above equation: (H2O) or (H+ + OH- )
H2O

22. DISCUSSION QUESTIONS
How many times different is a change in one unit of the pH scale?
10X more or less concentrated
What’s the difference in hydrogen concentration between pH5 & pH2?
pH2 has 1,000 times the concentration of H+ than a solution of pH5
What is the difference between a strong acid/base & a weak acid/base?
A strong acid/base dissociates readily because the differences in the electronegativity of the ions are greater; a weak acid/base has atoms that are not as different in their electronegativity so they don’t tend to the dissociated side of the equation as easily.

23. DISCUSSION QUESTIONS
Which acids/bases are weaker & which are stronger --- HCl, NH3, H2CO3 & NaOH?
Cl & Na both have very high electronegativity – they are both in column VII of ther periodic table with nearly full valence shells - & so they tend to dominate the electrons of H+ or OH- since the electronegativity of these atoms are very low. This huge difference in electronegativity causes a strong tendency for NaOH and HCl to dissociate.
When the H+ or OH- dissociate from the Na & the Cl they are free to react with other molecules making them strong acids & bases.
N & CO3 don’t have as strong of an electronegative difference with H since they are in columns IV-VI. Because of their lower electronegativity they do not dissociate as readily as HCl & NaOH so they are considered weaker acids & bases.

24. Buffers Hydrogen ion reservoirs that take up or release H+ as needed
The key buffer in blood is an acid-base pair (carbonic acid-bicarbonate buffering system)
Response to a rise in pH
H2O
Water in
blood plasma
CO2
Carbon dioxide +
H2CO3
Carbonic acid + –
HCO3–
Bicarbonate
ion H+
Hydrogen
Response to a drop in pH

25. Acid Precipitation