Class Padlet

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Chapter 3: Water

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.

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:

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• _{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?}

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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}

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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.

1) Cohesion/Adhesion 2) Thermal Properties

3) Water’s Expansion Upon Freezing 4) Solvent Properties

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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

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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_e mbedded

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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:

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2) Thermal Properties: Important Terms

• 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.

Heat

is the total energy of molecular motion (kinetic

energy) in a substance while

Temperature

is a measure of the average energy of

molecular motion in a substance.

Which has a higher heat a human body

or the ocean?

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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.

• 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

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2) Thermal Properties

• _{Water stabilizes air temperatures by absorbing heat from}

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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.

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Application of Thermal Properties/Cohesion

Application: Use of water as a coolant in sweat.

• _{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=HNyoeo HVnio&feature=player_embedded

• _{NPR Science: How Much Heat Can You} Take?

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2) Thermal Properties: Evaporative Cooling

1.) Body Temperature reaches “threshold” (you get hot enough) 2.) Your body secretes water

droplets onto surface of skin

3.) Heat flows from your body into the water droplet

4.) Water droplet absorbs lots of heat

5.) Fastest water droplet

evaporates taking heat energy with it

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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}

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3) Water Expansion Upon Freezing

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

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Application of Water Expansion Upon Freezing

• _{Since ice is less dense than liquid water, ice floats on top of}

the cool water below.

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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.}

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4) Solvent Properties

• _{Water is an effective solvent}

because it so readily forms hydrogen bonds with

charged and polar covalent molecules.

• _{Repeat animation?}

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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.

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4) Application of Solvent Properties

• _{Each dissolved ion is}

surrounded by a sphere of water molecules, a

hydration shell.

• _{Even large molecules,}

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Diffusion vs. Osmosis

• Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.

• Application: Tissues or organs to be used in medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis. • Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions

• Osmosis experiments are a useful opportunity to stress the need for accurate mass and volume measurements in scientific experiments.

• Diffusion: the tendency for molecules of any substance to spread out evenly into the available space.

• Osmosis: the passive transport of water across a membrane (from high to low concentration).

• Hypertonic – A solution with a greater concentration of solute.

• Hypotonic – A solution with a lower concentration of solute

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Question: Identify the following:

1)At which sucrose molarity is the potato core increasing in mass?

2) At which sucrose molarity is the potato core decreasing in mass?

3) At which sucrose molarity is the potato core neither increasing or decreasing in mass?

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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://

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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.

Video Links: