1. NOTES – UNIT 5 – WATER!

2. OBJECTIVE 1:
● Understand the molecular structure of water & how its structure determines its physical properties.

3. Water Overview…
● Water is one of the rarest and most unusual substances in the universe…

4. But here on Earth, it is everywhere!
• water-filled clouds surround Earth
• more than 70% of Earth’s surface is covered by oceans (average depth = 3 km or approx. 2 miles!)

6. Water Overview… Living cells are 70%-95% water
Water covers approx. ¾ of earth.
In nature, water naturally exists in all 3 states of matter: solid, liquid and gas

7. MOLECULAR STRUCTURE OF WATER, H2O:

8. WATER IS A POLAR MOLECULE…
• the bonds that hold the hydrogen and oxygen atoms together are POLAR COVALENT BONDS…
 this means that the electrons that make up the covalent bonds are shared UNEQUALLY …they spend more time near the oxygen atom than they do near the
hydrogen atom
so, a water molecule has
a positive end and a
negative end

9. Water is POLAR…
• POLAR WATER MOLECULES attract one another, as well as ions and other polar molecules

10. Water Molecules… • The polarity of water molecules
results in HYDROGEN BONDING
• a HYDROGEN BOND is the
attraction of opposite charges
between hydrogen and oxygen
• Each water molecule can form a maximum of 4 hydrogen bonds with neighboring water molecules

13. RECALL…
*PHYSICAL PROPERTIES = properties we can observe or measure WITHOUT changing the chemical makeup of the substance

14. Examples of PHYSICAL PROPERTIES:
• APPEARANCE, COLOR, ODOR, TASTE
• FREEZING POINT: the temperature at which a substance freezes from liquid to solid

15. PHYSICAL PROPERTIES OF WATER:
• CLEAR, COLORLESS, ODORLESS, TASTELESS
• FREEZING POINT of water is 0°C.

16. PHYSICAL PROPERTIES OF WATER:
• REFRACTION:
• Water can bend light
• Objects are not always
where they appear
• DENSITY of water is:
1.00 g / mL OR g / cm3
**this means that 1 mL of water has a mass of 1.0 g

17. PHYSICAL PROPERTIES OF WATER (as a result of polarity & hydrogen bonding):
• SURFACE TENSION:
• Water molecules are “sticky”
• Water forms bubbles and droplets easily
• Water’s surface can act HARD! (belly flops hurt)

18. PHYSICAL PROPERTIES OF WATER (as a result of polarity & hydrogen bonding):
• SURFACE TENSION:
• causes water to “bead”
• creates a “skin” on the surface

20. PROPERTIES OF WATER (as a result of polarity and H-bonding):
► COHESION: molecules are held together by H-bonds
• contributes to upward
movement of water in
plants from roots to leaves

22. Properties of Water
► ADHESION: water sticks to other surfaces (by polarity or H-bonds); can counteract gravity in plant vessels

23. ► HIGH SPECIFIC HEAT (resists changes in temp)
• Water’s high specific heat means that it resists temp. changes when it absorbs or releases heat
*Heat is absorbed to break H-bonds; and given off when they form

25. ► HIGH HEAT OF VAPORIZATION
• Heat of vaporization = amt. of heat a liquid must absorb to be converted to gas state
• for water molecules to evaporate, H- bonds must be broken, which requires heat energy

26. ► EVAPORATIVE COOLING: after high temp
► EVAPORATIVE COOLING: after high temp. molecules have evaporated, the remaining liquid is cooler (ex: sweating)
-protects organisms from overheating
*(as 1 g of water evaporates
from our skin, 539 g
of body cools by 1°C)

27. The air in the shower stall is at the same temperature as the air outside, but there's less water vapor outside to condense on the skin.

28. HEAT OF VAPORIZATION (WHILE CHANGING STATE)
EVAPORATIVE COOLING
HEAT OF VAPORIZATION (WHILE CHANGING STATE)
SPECIFIC HEAT
(WHILE WATER IS HEATING)

29. ► WATER EXPANDS WHEN IT FREEZES
• because of H-bonding, water is less dense as a solid than it is as a liquid...ice floats!
• since ice is less dense, it forms on the surface at first
• as water freezes, it releases heat to the water below and insulates it!
• Oceans and lakes don’t freeze solid!!

31. ► WATER IS THE SOLVENT OF LIFE
• due to its polarity, water is a versatile SOLVENT

32. NOTES – OBJECTIVES 2 - 4: Mixtures and Solutions

33. OBJECTIVES 2-4:
2) Understand how water acts as a solvent for many different solutes. Use polarity of water to explain its ability to dissolve ionic solids. Distinguish between soluble, insoluble, unsaturated, saturated, and supersaturated solutions. 3) Describe the solubility of a substance in water. Use solubility curves to describe the effect of temperature on solubility. 4) Understand units of concentration & how to calculate the concentration of a solution.

34. NOTES - Mixtures and Solutions:

35. Mixtures and Solutions:
MIXTURE: a combination of 2 or more pure substances in which the individual components retain their own properties
Examples: sand & sugar
water & salt

36. SOLUTIONS:
SOLUTION: a mixture in which the solute(s) are evenly distributed in the solvent
Example: salt in water
**Solutions are important to living things!!

37. SOLUTIONS: SOLUTE: the substance that is dissolved
SOLVENT: the substance in which the solute dissolves (usually water)

38. We do not often encounter PURE WATER…many substances dissolve readily in water, so many liquids are actually water solutions, or…
AQUEOUS SOLUTIONS: water-based solutions

39. Example: in a salt-water solution, the solute is and the solvent is .

40. Example: in a salt-water solution, the solute is SALT and the solvent is WATER.

42. MIXTURES
• HETEROGENOUS MIXTURE = composition is NOT the same throughout
 SUSPENSION: particles are large enough to settle out; separates easily
 COLLOID: particles are small and float in liquid; make liquid appear cloudy

44. OBJECTIVE 3: Dissolving Ionic Compounds

45. How do solutes dissolve in water
How do solutes dissolve in water? What types of substances dissolve in water?

46. RECALL: Water molecules are electrically POLAR….what does this mean?
The electrons in a POLAR MOLECULE are not distributed equally…the result is an uneven distribution of electrical charge.

47. POLAR MOLECULES… SO, a polar molecule has:
a POSITIVE region on one end, and
a NEGATIVE region on the other end.

48. Water molecules are “V-shaped”, with oxygen in the middle of 2 hydrogens:
the oxygen “end” is the electrically NEGATIVE end;
the 2 hydrogen
“ends” are electrically
POSITIVE.

50. • POLAR water molecules are attracted to:
other polar substances
ionic compounds
(composed of charged
particles)

51. • So, when an ionic compound dissolves in water, the water molecules are attracted to ions on the surface of the ionic solid…
the negative (oxygen) end is attracted to the crystal’s positive ions;
 the positive (hydrogen) ends are attracted to the crystal’s negative ions

54. The general rule for what will dissolve: “LIKE DISSOLVES LIKE”
POLAR will dissolve POLAR (or IONIC!)
 NONPOLAR will dissolve NONPOLAR

55. Substances that can dissolve or be suspended in water and harm living things:
-HEAVY METALS
-ACIDS & BASES
-MOLECULAR SUBSTANCES
-DISSOLVED OXYGEN GAS

57. OBJECTIVE 3: Solubility of Solids

58. Suppose you wanted to make a water solution of potassium nitrate, KNO3.
 First, you add a scoopful of the white solid to water;
 As you stir the water,
the crystals dissolve and
disappear.

59. In this solution,
-the SOLUTE is KNO3 and
-the SOLVENT is water.

60.  What if you added more KNO3?...
 If you continue to add more crystals, eventually some will remain undissolved…

61. This is the concept of SOLUBILITY.
SOLUBILITY = the maximum amount of a substance that will dissolve in a certain quantity of water at a specified temperature.

62. Solubility… For example, we might describe the solubility of KNO3 as:
“grams KNO3 per 100 g water
at 50°C”
**this is NOT the same as how QUICKLY something dissolves!

63. Factors Affecting the Rate (Speed) of Dissolving:
1) size of crystals / particles: (e.g. if you crush larger crystals into smaller crystals, they will dissolve faster);

64. Factors Affecting the Rate of Dissolving:
2) stirring / agitation: if you stir or shake a solution, dissolving will be faster;

65. Factors Affecting the Rate of Dissolving:
3) temperature: solids dissolve into solution more quickly at higher temperatures.

66. Factors Affecting the Rate of Dissolving:
 the first 2 factors (particle size and stirring) may speed up the dissolving process, but they do NOT increase the AMOUNT of substance that will dissolve, or the SOLUBILITY of a substance.

67. **so, what does affect SOLUBILITY?
TEMPERATURE: in general, the solubility of a solid substance increases with increasing temperature

68. We can see this visually on a graph called a SOLUBILITY CURVE.

69. Types of Solutions:
SATURATED: contains the maximum possible amount of dissolved solute at that temperature
UNSATURATED: contains less dissolved solute than the solvent can normally hold at that temp.
SUPERSATURATED: contains more solute than could usually dissolved at that temp.

70. SATURATED SOLUTION:

71. **How do we produce a SUPERSATURATED SOLUTION?
1) Make a saturated solution at a higher temperature;
2) Allow it to cool without agitating it – at this cooler temperature, the solution now would contain more solute than could usually be dissolved at that temperature.
**if you agitate this solution or provide a “seed” crystal, the extra solute will come out of solution and form crystals.

74. NOTES –OBJECTIVE 4: Solution Concentration
Describing a solution as “saturated” or “unsaturated” is not always precise enough – sometimes we need an exact, numerical measure of CONCENTRATION.

75. CONCENTRATION…
● SOLUTION CONCENTRATION: the QUANTITY of solute dissolved in a specific QUANTITY of solvent.

76. How do we express CONCENTRATION?
1) mass of solute dissolved in a given mass of water:
Example: 25 g of KNO3 in 100 g water

77. 2) percent solution (what percent of a solution’s mass is solute?):
Example 1):
 if we dissolve 5 g of salt in 95 g water – this produces 100 g of solution. What is the PERCENT SOLUTION?
% solution = 5 g salt / 100 g solution = X 100% =
5% salt solution

78. Percent Solution: Example 2):
 if we dissolve 30 g of salt in 200 g of water – what is the percent salt solution?
ANSWER: total mass of solution =
30 g g = 230 g
% solution = 30 g salt / 230 g
= X 100% = 13%

79. 3) PARTS PER MILLION – used for solutions containing much smaller quantities (e.g. in environmental testing of water samples)
Example: a sample of water from a river contains 15 ppm of a certain pesticide (this means that there are 15 pesticide molecules per every million molecules of the river sample).

82. Example: what is the concentration in PPM for a 5% salt solution?
ANSWER: 5% of 1,000,000 = 50,000
so, a 5% salt solution is 50,000 PPM.

83. NOTES - OBJECTIVE 5: Acids, Bases, and pH
OBJECTIVE 5: Explain what acids and bases are. Classify a substance as acidic, basic, or neutral, given the pH.

84. ACIDS & BASES
In living things, chemical reactions depend on the pH of the environment
Water molecules (H2O) can split apart into H+ and OH- ions
When H+ and OH- are present in equal amounts, the solution is NEUTRAL.

86. ACIDS & BASES
ACID: a compound that forms H+ in solution (& adds H+ ions to the solution)
BASE: a compound that forms OH- in solution (& adds OH- ions to the solution)

87. ACIDS & BASES
pH = a measure of how acidic or basic a solution is

88. The pH scale: ACID: a solution with a pH below 7
BASE: a solution with a pH above 7

89. • the pH scale helps us determine if a solution is:
ACIDIC, BASIC, or NEUTRAL

90. • the pH scale range is from 0 to 14:

91. • ACIDS: solutions with a pH less than 7
• BASES: solutions with a pH greater
than 7
• NEUTRAL: solutions with a pH of exactly 7

92. Properties of: ACIDS: BASES: • turn litmus red • turn litmus blue
• conduct electricity
• corrosion (“eats away” other materials)
• sour taste
• bitter taste; slippery feel
• typically have H+ ions in formula/solution
• many have hydroxide ions (OH-) in formula
• can leach metal ions from soil into water
• can dissolve organic materials (i.e. skin, fish scales)

93. BUFFERS
BUFFERS: dissolved compounds that prevent sharp, sudden changes in pH
example: blood contains a number of buffers that help maintain a constant blood pH of 7.4

94. NOTES – OBJECTIVE 6: Evaluate the Risks of Contaminants in a Water Supply

95. Metal Ions:
• Many metal ions found in drinking water are essential / beneficial to living things:
-iron (II) (Fe2+) -calcium (Ca2+)
-potassium (K+) -magnesium (Mg2+)

96. **Not all metal ions dissolved in water are good for us – some heavy metal ions are even harmful to living things…
Two heavy-metal ions of particular concern:
1) lead (Pb2+);
2) mercury (Hg2+)

97. • How are these heavy-metal ions toxic?
 they bind to proteins in biological systems (i.e. your body, a pond, aquatic ecosystem) and prevent the proteins from doing their job

98. • Even in a body of water where they are not very concentrated (just a few PPM), they can become concentrated in the bodies of fish and shellfish - - then when other organisms eat these fish / shellfish, they get a big dose of the heavy metals

100. How do we prevent heavy metal poisoning?
 prevent it from entering the water system in the first place;
 produce / use materials that do not contain these ions;

101. Lead (Pb): -used in: • pottery • automobile batteries • paints
• cooking vessels
• pesticides
• water pipes
• automobile fuel

102. Mercury (Hg): -used in: • thermometers & thermostats
• vapor street lamps
• fluorescent light bulbs
• some paints
**can be absorbed directly through skin

103. OBJECTIVE 7: Water Cycle!
OBJECTIVE 7: Describe the function and operation of the hydrologic cycle.

104. WATER CYCLE: ● Life depends on water
● 6 major steps to the water cycle
-Precipitation
-Evaporation
-Transpiration
-Condensation
-Infiltration
-Runoff

105. -falling products of condensation in the atmosphere
● PRECIPITATION:
-falling products of condensation in the atmosphere
-4 types
● Rain
● Hail
● Sleet
● Snow

106. ● CONDENSATION:
-process where water vapor condenses to droplets to form clouds or fog
● EVAPORATION:
-changing from a liquid
to a gas
(water vapor)
● TRANSPIRATION:
-passage of water from plant leaf to atmosphere

108. Water Cycle (cont.) ● INFILTRATION:
-seepage of water into rock or soil
-how water gets back into the ground
● RUNOFF:
-water that drains or flows into streams or other bodies of water

110. ● Where does the water cycle start?
-at any of the 6 stages
● Does the water cycle go in the same order?
-No…
● some water droplets stays frozen for years (glaciers, snow capped mountains)
● some water droplets
may evaporate then
condense repeatedly
● some water may stay
in the ground for year
(aquifers)…etc.