1. Water
Packet #7
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2. Introduction Most abundant liquid in the world
Makes up at least half of all living organisms and up to 95% of some species.
75% of earth is submerged in water
Naturally occurring water consists of 99.76% H2O
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3. Water--Isotopes The remainder consists of various isotopes 2H 18O
Deuterium
Most often found with a normal hydrogen atom
Forms HDO
Occasionally, D2O is formed
Both are called heavy water and have deleterious effect on living organisms.
18O
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4. The Water Molecule Recall that H2O is a polar molecule
This results in the ability to form hydrogen bonds and an attraction between individual water molecules
Due to the opposite charges
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5. The Water Molecule
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6. Properties of Water I Cohesion and Surface tension Cohesion
Tendency of molecules, if in substance, to hold together by mutual attraction
The hydrogen bonding of water results in strong cohesion forces.
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7. Cohesion & Surface Tension
What does this (string cohesion forces) mean?
One drop of water will assume the smallest possible area on a surface
The water molecule will form a sphere
Water molecules, at the surface of the drop, will be drawn together forming a skin-like layer off molecules on the surface.
The force formed is called surface tension.
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8. Homework Assignment
Conduct experiment determining how much water can a penny hold
Must use an old and a new penny
Difference in composition
Must complete at least 20 trials for each penny
Must complete a full lab report with a 5 page background research section on cohesion forces and surface tension
PAPER MUST BE SUBMITTED AT TURNITIN.COM
Due 2:45pm EDT Friday September 7th 2007
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9. Surface Tension
Is a measure of how hard it is to break the surface of a liquid
Insects waling on the surface of water and the movement of water up plants are two biological processes that can occur as a result of the cohesive properties of water molecules.
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10. Properties of Water I Adhesion and capillarity Adhesion
The attraction of molecules of different compounds to one another.
The ability of water to cling readily to other molecules is responsible for the upward movement of water when a small-bore tube is dipped into it.
This phenomenon is called capillarity
Xylem vessels of a diameter 0.02mm can, in theory, support a column of water of height 1.5m by capillary forces.
Capillary forces has one of its main biological effects being the upward movement of water in the soil
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12. PROPERTY #2 Thermal Capacity/Moderation of Temperature
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13. Thermal Capacity
Hydrogen bonding results in the necessity of heat to cause increased molecular movement
Formation of water in the gas form (steam)
Heat energy first used to break hydrogen bonds
Resistance to temperature change
This is why the temperature of water rises only very slowly for a given amount of added heat
Water has a very high specific heat
And vice versa
The amount of heat that must be absorbed or lost for 1 gram of that substance to change its temperature by 1˚C
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15. Thermal Capacity II
Why is the use of heat energy for breaking hydrogen bonds important?
Allows thermal stability so that enzymatic reactions(biochemical reactions) in water mediums are not subjected to large temperature fluctuations and can take place at a more constant rate.
If there were no hydrogen bonds, water would be a gas at most temperatures
Also helps in the cooling affect
Sweating
Heat of vaporization
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16. Density
PROPERTY #3
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17. Density Water has a maximum density at 4ºC
This is when water is in a liquid state
H2O (l) is more dense than H2O (s)
Water freezes from top downward allowing ice to form at the top
Ice at top can insulate the warmer water below that layer from colder temperatures above
Prevents large bodies of water from freezing solid and allowing the survival of aquatic organisms
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18. Solubility
PROPERTY #4
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19. Solubility Water is a versatile solvent due to its polarity
Can form an aqueous solution
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20. Definitions
Mixture
A portion of matter that can be separated into two or more substances by physical means alone
Substance composed of 2 or more elements or compounds that are mixed together, but are not chemically combined
A composition of two or more substances that are not chemically combined with each other and are capable of being separated.
Salt and pepper
Sugar and sand
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21. Definitions II Solution
A homogeneous (of uniform structure or composition throughout ) mixture of two or more substances, which may be solids, liquids, gases, or a combination of these.
Homogenous mixture
Sugar in water (Sugar-water)
One component (Major), of a solution, is found in a greater amount
Solvent
One component (Minor), of a solution, is found in a lesser amount
Solute
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22. The different regions of the polar water molecule can interact with ionic compounds called solutes and dissolve them
Negative oxygen regions of polar water molecules are attracted to sodium cations (Na+). +
Cl – –
Na+
Positive hydrogen regions of water molecules cling to chloride anions (Cl–).
Cl–
Figure 3.6
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23. Water can also interact with polar molecules such as proteins
This oxygen is attracted to a slight positive charge on the lysozyme molecule.
This oxygen is attracted to a slight negative charge on the lysozyme molecule.
(a) Lysozyme molecule in a nonaqueous environment
(b) Lysozyme molecule (purple) in an aqueous environment such as tears or saliva
(c) Ionic and polar regions on the protein’s Surface attract water molecules. + –
Figure 3.7
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24. Solubility “Likes dissolves likes” Oil and water are dislikes
Polar with polar
Non-polar with non-polar
Oil and water are dislikes
Water = polar
Oil = non-polar
We say that oil and water are nearly completely immiscible
The oil is suspended
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25. Other Important Points II
Hydrophilic substance
Water loving
Has an affinity for water
Hydrophobic substance
Water hating
Does not have an affinity for water
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26. Other Important Points II
Remember, most biochemical reactions occur in water
It Is important to calculate the concentration of solutes in an aqueous solution
Mole
The number of molecules of a substance in a given mass
Molarity
The number of moles of a solute per liter of solution
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27. DISSOCIATION
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28. Dissociation (Ionization), pH & Buffers
Water has a slight tendency to dissociate into ions according to the equation
2H2O  H2O+ + OH-
H2O  H+ + OH-
Hydronium ions and hydroxide ions
In 1 liter of water, this dissociation produces 1/10,000,000 mole of hydrogen ions.
Equivalent to a pH of 7
Neutral
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30. Dissociation II
If the concentration of hydrogen ions is higher, 1/1000 (10-3) the pH would be 3 and the solution would be acidic
An acid, therefore, is a substance that donates hydrogen ions
Increases hydrogen ion concentration
A base is a hydrogen ion acceptor
Decreases hydrogen ion concentration
Changes in concentration of ions can have a great affect on living organisms
Particularly enzymes
Why?
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31. Dissociation III
Apart from dissociating itself, water readily causes the dissociation of other substances placed in it.
Making it an excellent solvent.
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32. Buffers
A buffer solution is one that retains a constant pH despite the addition of small quantities of acids or bases.
Buffers contain both hydrogen ion donors and acceptors.
Hydrogen carbonate ions may act as an acceptor or a donor
Hydrogen carbonate salts and phosphate salts are responsible for the buffering of blood.
pH of 7.4
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33. Osmosis More to come later
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