1. KEY CONCEPT Water’s unique properties allow life to exist on Earth.

2. Image: AHAJOKES.COM
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3. SC.912.L Discuss the special properties of water that contribute to Earth’s suitability as an environment for life; cohesive behavior, ability to moderate temperature, expansion upon freezing, and versatility as a solvent. ( Moderate)

4. THE PROPERTIES OF WATER :
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THE PROPERTIES OF WATER :
Water has some very unique properties that make this molecule unlike ANY other. And we are made up of about 70% water!

5. Your body is made up of mostly of water
Your body is made up of mostly of water. Approximately 85% of your brain, 80% of your blood and 70% of your muscle is water. Every cell in your body needs water to live.
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6. Covalent Bonds As you learned during centers, when water (H20) forms, 2 Hydrogen Atoms both share THEIR one electron with 1 Oxygen Atom. Oxygen has 8 electrons. 2 fill the first shell and 6 fill the second shell. In that second shell, there is room for 2 more. That is where the 2 Hydrogen atoms share their 1 electron. Oxygen then shares an electron with each of the hydrogen atoms! All shells are full!

7. Life depends on hydrogen bonds in water.
Water is a polar molecule.
Polar molecules have slightly
charged regions. See the negative top, where most of the electrons are? O H _ +
Polar molecules—molecules that have regions with slight electrical charges due to uneven
pull on electrons
Nonpolar molecules—molecules without charged regions due to equal pull on electrons
1. hydrogen bonds
2. formed by attraction between slightly positive hydrogen atom and slightly negative
(oxygen) atom
Atom 1—oxygen; slightly negative
Atom 2—hydrogen; slightly positive
Nonpolar molecules do not have charged regions.
Hydrogen bonds are weak bonds that form between
slightly positive hydrogen atoms and slightly negative
atoms. OPPOSITES ATTRACT!

8. Cohesion - water molecules Adhesion - water molecules
Hydrogen bonds are responsible for three important properties of water.
large amount of energy needed to produce an increase in temperature
High specific heat-
Cohesion - water molecules
“stick” to each other
Adhesion - water molecules
“stick” to other substances
The water’s surface (left, dyed red) is curved down because the water has a greater adhesion than cohesion. The surface of the mercury (right) is curved up because mercury has greater cohesion than adhesion.
1. High specific heat— large amount of energy needed to produce an increase in temperature
2. Cohesion— water molecules “stick” to each other
3. Adhesion— water molecules “stick” to other substances 4

9. Water’s tendency to cling together Droplets!
Cohesion
Water’s tendency to cling together
Droplets!
-Creates surface tension (how
insects walk on water).
Image:
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When the negative end of a water molecule attracts the positive end of another water molecule, and the molecules stick together, this is called cohesion.

10. This figure shows water adhesion
Adhesion, or capillary action, is when water molecules are attracted to other substances with a negative or positive charges. This is why water "climbs" up a piece of paper or a straw above the surface level of the water.        
This figure shows water adhesion
image:
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Demo straw

11. Because of the cohesive properties of water, trees such as the giant sequoia are able to transport water molecules from the soil to their leaves 300 ft. above.
WATER: STRONG COHESIVENESS
300 ft.
Water molecule released into the atmosphere
As each water molecule evaporates, it pulls additional water up through the tree because of the “sticky-ness” of the hydrogen bonds that link the water molecules.
Water molecules pulled upward
6-ft.-tall man
What is Life? A Guide to Biology
2010 W.H. Freeman and Co
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Water molecule pulled into root system

12. WATER: HIGH SURFACE TENSION
Pressure applied to water surface
Hydrogen
bond
What is Life? A Guide to Biology
2010 W.H. Freeman and Co
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“V”-shaped water molecules are held together by hydrogen bonds. The bonds are just strong enough, through cohesion, to give water a surface tension with net-like properties.

13. Surface Tension
The cohesive forces between liquid molecules
are responsible for the phenomenon known as
surface tension.
The molecules at the surface do not have other like molecules on all sides of them and consequently they cohere more strongly to those directly
associated with them on the surface.
This forms a surface "film" which makes
it more difficult to move an object
through the surface than to move it
when it is completely submersed.

14. Other unique properties of water
Only substance to that exists free in nature in all three states (solid, liquid, and gas)
High boiling point
Low freezing point
Viscosity increases as its temperature is lowered
A strong surface tension
A relatively high density to support animals with no or delicate skeletal systems
A high heat capacity which maintains relativity stable and slow changing internal temperature
Ability to dissolve most substances

15. Many compounds dissolve in water.
A solution is formed when one substance dissolves in another.
A solution is a homogeneous
mixture.
Solvents dissolve other
substances.
Solutes dissolve in a solvent.
solution
Solutions—a mixture that is the same throughout (homogeneous)
Solvents—substance present in greatest concentration; dissolves other substances
Solutes—substance present in lower concentration; dissolves in solvent
The solvent is the substance that is present in the greatest amount, and is the substance that dissolves solutes.
The solute is the substance being dissolved. 5

16. Universal Solvent
Like a magnet that pulls on things that are magnetic, water pulls on things that are electrically charged. Magnets have north & south poles, water has positive and negative poles and thus called a polar solvent. Since unlike charges attract, the negative end of water will be attracted to the positive sodium ion. The positive end of water will be attracted to the negative chloride ion. Since water is always in motion, it will pull on the ionic compound and move the ions away from each other. This dissolves the ionic compound.
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Since unlike charges attract, the negative end of water will be attracted to the positive sodium ion. The positive end of water will be attracted to the negative chloride ion. Since water is always in motion, it will pull on the ionic compound and move the ions away from each other. This dissolves the ionic compound.

17. “Like dissolves like.”
Polar solvents dissolve polar solutes.
Nonpolar solvents dissolve nonpolar solutes.
Polar substances and
nonpolar substances generally remain separate. 6

18. Common Misconceptions
Students often thinks that all solutes are solids and all solvent as are liquids.
Correcting the misconception
Solutions can involve different states of matter
Gas in Gas- AIR: If the solvent is a gas, only gases are dissolved under a given set of conditions. An example of a gaseous solution is air (oxygen and other gases dissolved in nitrogen). Nitrogen makes up 78% of air so it’s the solvent.
Gas in Liquid Stream: Oxygen in water.
Liquid in Liquid Vinegar is an acetic acid solution in water (5-9 %).  Solid in solid – alloys like Steel Steel is a metal alloy whose major component is iron, with carbon content between 0.02% and 2.14% by mass.
Liquid in solid: mercury in gold, forming an amalgam
Air image:
Stream:
Vinegar Image:
Steel image:
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19. Some compounds form acids or bases.
An acid releases a hydrogen ion when it dissolves in water.
high H+ concentration
pH less than 7
more acidic
stomach acid pH between 1 and 3
Acids—release H+ ions in solution; high H+ concentration; low pH (<7)
Neutral—neither acidic nor basic; pH of 7
Bases—remove H+ ions from solution; low H+ concentration; high pH (>7)
A pH scale is a negative logarithm. A pH of 1 is equal to the log of a H+ ion concentration of , whereas a pH of 10 is equal to the log of a H+ ion concentration of There is a tenfold difference in H+ ion concentration from one pH value to the next. Ask, What is the difference in H+ ion concentration between lemon juice (pH 2) and tomato juice (pH 4)?
Lemon juice has a H+ ion concentration 100 times greater than tomato juice. 7

20. A base removes hydrogen ions from a solution.
low H+ concentration
pH greater than 7
bile pH between 8 and 9
more basic 8

21. A neutral solution has a pH of 7.
pure water pH 7 9

22. pH Scale