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Ch 3: The Polarity of Water and Its Properties. 2016. Chapter 3: Water. International-mindedness: • There are challenges for the increasing human population in sharing water resources equitably for drinking and irrigation, electricity generation and a

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chapter 3 water
Chapter 3: Water

International-mindedness:

• There are challenges for the increasing human population in sharing water resources equitably for drinking and irrigation, electricity generation and a

range of industrial and domestic processes.

Theory of knowledge:

• Claims about the “memory of water” have been categorized as pseudoscientific. What are the criteria that can be used to distinguish scientific claims from pseudoscientific claims?

Aim 6: Probes can be used to determine the effect of different factors likely influence cooling with water.

From Topic 9.1

Understandings:

• The cohesive property of water and the structure of the xylem vessels allow transport under tension.

• The adhesive property of water and evaporation generate tension forces in leaf cell walls.

Applications and skills:

Application: Models of water transport in xylem using simple apparatus including blotting or filter paper, porous pots and capillary tubing.

From Topic 2.2

Essential idea: Water is the medium of life.

Nature of science: Use theories to explain natural phenomena—the theory that hydrogen bonds form between water molecules explains the properties of water. (2.2)

Understandings:

• Water molecules are polar and hydrogen bonds form between them.

• Hydrogen bonding and dipolarity explain the cohesive, adhesive, thermal and solvent properties of water.

• Substances can be hydrophilic or hydrophobic.

Applications and skills:

• Application: Comparison of the thermal properties of water with those of methane.

• Application: Use of water as a coolant in sweat.

• Application: Modes of transport of glucose, amino acids, cholesterol, fats, oxygen and sodium chloride in blood in relation to their solubility in water.

Guidance:

• Students should know at least one example of a benefit to living organisms of each property of water.

• Transparency of water and maximum density at 4°C do not need to be included.

• Comparison of the thermal properties of water and methane assists in the understanding of the significance of hydrogen bonding in water.

slide3

Why is water polar?

  • CrashCourse: Water http://www.youtube.com/watch?v=HVT3Y3_gHGg*
  • In a water molecule, two hydrogen atoms form single polar covalent bonds with an oxygen atom.
  • What do you notice about the charges?
slide4

Hydrogen Bonding of Water Molecules

  • Nature of science: Use theories to explain natural phenomena—the theory that hydrogen bonds form between water molecules explains the properties of water (2.2).
  • Understandings:
  • • Water molecules are polar and hydrogen bonds form between them.*
  • H2O has a variety of unusual properties because of the attractions between these polar molecules.
  • Notice how individual H2O molecules orient themselves to form an H-Bond.
slide5

4 Emergent Properties of Water

Understandings:

Hydrogen bonding and dipolarity explain the cohesive, adhesive, thermal and solvent properties of water.

Guidance:

• Students should know at least one example of a benefit to living organisms of each property of water.

Cohesion/Adhesion

Thermal Properties

Water’s Expansion Upon Freezing

Solvent Properties

slide6

1) Cohesion/Adhesion

  • Understandings:
  • • The cohesive property of water and the structure of the xylem vessels allow transport under tension.
  • • The adhesive property of water and evaporation generate tension forces in leaf cell walls.
  • Cohesion: Co---“like with like”, water molecules attracted to each other via hydrogen bonds
  • Adhesion: Ad---“like with opposite,” water molecules attracted to different molecules/surface
slide7

Application of Cohesion/Adhesion

  • Cohesion among water molecules plays a key role in the transport of water against gravity in plants, called transpiration.
  • Transpiration: http://www.youtube.com/watch?v=mc9gUm1mMzc&feature=player_embedded*
slide8

Application of Cohesion/Adhesion

  • Surface tension, a measure of the force necessary to stretch or break the surface of a liquid, is related to cohesion.*
  • Video links: **
  • Water Striders: http://www.youtube.com/watch?v=V-cXzZt2iVk&feature=player_embedded
  • Surface Tension Droplets: http://www.youtube.com/watch?v=ynk4vJa-VaQ&feature=player_embedded
  • Jesus Christ Lizard: http://www.youtube.com/watch?feature=player_embedded&v=45yabrnryXk
slide9

2) Thermal Properties

  • • Application: Comparison of the thermal properties of water with those of methane.
  • • Application: Use of water as a coolant in sweat.
  • Guidance: Comparison of the thermal properties of water and methane assists in the understanding of the significance of hydrogen bonding in water.
  • Aim 6: Probes can be used to determine the effect of different factors likely to influence cooling with water.
  • Water stabilizes air temperatures by absorbing heat from warmer air and releasing heat to cooler air.
  • Simulation Lab:
  • http://oceanservice.noaa.gov/education/pd/oceans_weather_climate/media/specific_heat.swf
slide10

2) Thermal Properties

  • The specific heat of a substance is the amount of heat that must be absorbed or lost for 1g of that substance to change its temperature by 1⁰C.
    • - Or another way of thinking about it is… a measure of how well a substance resists changing its temperature when it absorbs or releases heat.
  • One way to measure heat is calorie (cal).*
  • H2O has a high specific heat of 1 cal/g/⁰C. Why?
    • Properties of Water: http://www.sumanasinc.com/webcontent/animations/content/propertiesofwater/water.html
  • Compare H2O’s specific heat to Methane (CH4), which is 0.55 cal/g/ ⁰C. Compare it to Iron (Fe) 0.1 cal/g/⁰C.**
slide11

Application of Thermal Properties

  • Heat of vaporization is the quantity of heat that a liquid must absorb for 1 g of it to be converted from the liquid to the gaseous state.
    • 580 cal of heat is to evaporate 1g of water at room temperature.
    • This is double the heat required to vaporize the same quantity of alcohol or ammonia.
    • Why?*
slide12

Application of Thermal Properties/Cohesion

  • Application: Use of water as a coolant in sweat.
  • Aim 6: Probes can be used to determine the effect of different factors likely to influence cooling with water.
  • As a liquid evaporates, the surface of the liquid that remains behind cools called evaporative cooling.
  • Evaporative cooling moderates temperature in lakes and ponds and prevents terrestrial organisms from overheating.
  • Evaporative cooling keeps plants and animals cool. For humans, it’s in the form of sweating.
  • Video Links:*
  • Evaporative and Cooling:
  • https://www.youtube.com/watch?v=HNyoeoHVnio&feature=player_embedded
  • NPR Science: How Much Heat Can You Take?
  • https://www.youtube.com/watch?feature=player_embedded&v=lqwPS6wJN-c
slide13

3) Water Expansion Upon Freezing

  • Guidance: Transparency of water and maximum density at 4°C do not need to be included.
  • Ice floats on liquid water. Why? http://www.sumanasinc.com/webcontent/animations/content/propertiesofwater/water.html
  • - This allows oceans and lakes not to freeze.
  • Notice the spacing between water molecules in solid and liquid form.
slide14

Application of Water Expansion Upon Freezing

  • Since ice is less dense the liquid water, ice floats on top of the cool water below.
  • This oddity has important consequences for life. Why?
slide15

4) Solvent Properties

  • Application: Modes of transport of glucose, amino acids, cholesterol, fats, oxygen and sodium chloride in blood in relation to their solubility in water.
  • The dissolving agent is the solvent and the substance that is dissolved is the solute.
    • - In our example, water is the solvent and sugar the solute.
  • In an aqueous solution, water is the solvent.
    • - Water is not a universal solvent, but it is very versatile because of the polarity of water molecules.
slide16

4) Solvent Properties

  • Water is an effective solvent because it so readily forms hydrogen bonds with charged and polar covalent molecules.
  • Repeat animation?
    • http://www.sumanasinc.com/webcontent/animations/content/propertiesofwater/water.html
slide17

Hydrophilic vs. Hydrophobic

  • Understandings: Substances can be hydrophilic or hydrophobic.
  • Hydrophilic: “water loving,” any substance that has an affinity for water is.
    • Ex: polar or ionic substances
    • Cotton is hydrophilic because it has numerous polar covalent bonds in cellulose, which is its major constituent. Water molecules form hydrogen bonds in these areas.
    • Hydrophobic: “water fearing,” any substance that is repelled by water.
      • Ex: nonpolar substances
slide18

4) Application of Solvent Properties

  • Each dissolved ion is surrounded by a sphere of water molecules, a hydration shell.
  • Even large molecules, like proteins, can dissolve in water if they have ionic and polar regions.*
slide19

Acids and Bases

  • An acid is a substance that increases the hydrogen ion concentration in a solution.
  • Any substance that reduces the hydrogen ion concentration in a solution is a base.
    • In a neutral solution [H+] = 10^-7 M, and the pH = 7.
  • Buffers resist changes to the pH of a solution when H+ or OH- is added to the solution.
  • Blood Buffering: https://www.youtube.com/watch?feature=player_embedded&v=NJyAme5GVF8
  • Ocean Acidification: https://www.youtube.com/watch?v=RnqJMInH5yM
  • Buffers: Acid Rain Slayer https://www.youtube.com/watch?v=8Fdt5WnYn1k
slide20

International-mindedness: There are challenges for the increasing human population in sharing waterresources equitably for drinking and irrigation, electricity generation and arange of industrial and domestic processes.

Video Links:

BBC America (long): http://www.youtube.com/watch?v=Gg-ac0EaYDQ

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