1. Packet #7 Various Chapters
Water
Packet #7
Various Chapters
Tuesday, November 20, 2018

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
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3. Forms of Water Molecules
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4. Forms of Water Molecules
H2O
Naturally occurring water consists of 99.76% H2O
The remainder consists of various isotopes
HDO & D2O
Formed with an isotope of hydrogen called deuterium 2H
Deuterium is most often found with a normal hydrogen atom but occasionally, D2O is formed
Both are called heavy water and have deleterious effect on living organisms.
18O
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5. Water as a Polar Molecule
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6. The Water Molecule
H2O is a polar molecule and results in the ability for the molecule to form hydrogen bonds
In most cases, with other water molecules to form liquid, solid or gaseous water.
Due to the opposite charges
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7. Solubility
Water, versatile solvent due to its polarity, is used to form an aqueous solution.
A solution is considered as 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.
Examples of Aqueous Solutions
Water (Solvent) and salt (Solute)
Water (Solvent) and sugar (Solute)
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8. Solubility II “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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9. Water & Ionic Compounds
The different regions of the polar water molecule can interact with ionic compounds called solutes and dissolve them
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10. Water & Proteins
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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11. Water & Biochemical Reactions
Most biochemical reactions, that occur within cells of the body, occur in water
Since most biochemical reactions occur in water, it is important to calculate the concentration of solutes in an aqueous solution
Molarity
The number of moles of a solute per liter of solution
Molality
The number of moles of a solute per 1000 g of solvent
Mole
The number of molecules of a substance in a given mass
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12. Hydrophilic vs. Hydrophobic
Hydrophilic substance
Water loving
Has an affinity for water
Hydrophobic substance
Water hating
Does not have an affinity for water
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13. Water Molecules & Hydrogen Bonds
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14. The Water Molecule & Hydrogen Bonds
Liquid, solid and gaseous water is formed as hydrogen bonds are formed, and broken, between the oxygen, and hydrogen, atoms of individual water molecules.
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15. Phases of Matter {Water}
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16. Importance of Hydrogen Bonds in Liquid Water
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17. Cohesion
Cohesion
Tendency of molecules, if in substance, to hold together by mutual attraction
The hydrogen bonding of individual water molecules result in strong cohesion forces.
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18. Cohesion & Surface Tension
What does this (strong cohesion forces) mean?
One drop of liquid 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 when the individual water molecules draw together at the surface of the drop is called surface tension.
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19. Surface Tension
Is a measure of how hard it is, the amount of force necessary, to break the surface of a liquid
Insects walking 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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20. 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 3 page background research section on cohesion forces and surface tension
PAPER MUST BE SUBMITTED to Mr. Barrow
Due 2:45pm EDT September 2009
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21. Adhesion & Capillarity Forces
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22. Adhesion
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 capillary action.
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23. Capillary Action in Plants
Xylem vessels, found in plants, are responsible for the movement of water in plants.
Xylem vessels, of a diameter 0.02mm can, in theory, support a column of water of height 1.5m by capillary forces.
Capillary action, resulting from cohesion, has one of its main biological effects being the upward movement of water from soil.
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24. Thermal Capacity
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25. Thermal Capacity Thermal capacity and specific heat go hand in hand.
Hydrogen bonding results in the necessity of heat to cause increased molecular movement
Formation of steam from liquid water for example.
When heat energy is applied to liquid, solid or gaseous water, it is first used to break hydrogen bonds
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26. Thermal Capacity II
The presence of hydrogen bonds makes liquid water resistant to temperature change
This is why the temperature of liquid water rises only very slowly for a given amount of added heat
Since water is resistant to temperature change, it is said to have a very high specific heat
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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27. Thermal Capacity & Enzymatic Reactions
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
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28. The Cooling Effect
As temperatures outside rise, the body begins to sweat.
The sweat allows water to aid in cooling as air passes over it.
With hydrogen bonds in place, at high temperatures, when humans sweat, it allows water to aid in cooling as the wind blows in areas of low humidity.
Water, with a high heat of vaporization, is most effective in cooling the body.
Heat of Vaporization
The amount of heat required to convert a unit mass of a liquid at its boiling point into vapor without an increase in temperature.
Water stays around long enough for the body to cool.
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29. Density
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30. 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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31. Dissociation & pH
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32. Dissociation
Water has a slight tendency to dissociate into ions according to the equation
2H2O  H2O+ + OH-
H2O  H+ + OH-
Hydronium ions and hydroxide ions
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33. Dissociation II
Apart from dissociating itself, water readily causes the dissociation of other substances placed in it.
Making it an excellent solvent.
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34. Neutral pH
In 1 liter of water, this dissociation produces 1/10,000,000 (10-7) mole of hydrogen ions.
Equivalent to a pH of 7
Neutral
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35. Acidic pH
If the concentration of hydrogen ions is higher than what is seen at neutral pH, then the solution would be acidic
An acid, therefore, is a substance that donates hydrogen ions
Increases hydrogen ion concentration
Example
If the concentration of hydrogen ions is 1/1000 (10-3), then the pH would be 3
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36. Basic pH
If the concentration of hydrogen ions is lower than what is seen at neutral pH, the solution would be basic
A base is a substance that is hydrogen ion acceptor
Decreases hydrogen ion concentration
Example
If the concentration of hydrogen ions is 1/1,000,000,000 (10-9) the pH would be 9.
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37. 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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38. Effect of Sudden Changes in pH
Changes in concentration of ions can have a great affect on living organisms
Particularly enzymes
Why?
Answer to come in protein & enzyme packets.
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39. pH Scale
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