Water & Life

Chapter 3

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H2O is why we are here

H2O molecules are polar What does their polarity contribute to?

Each H2O molecule can form __ Hydrogen bonds?

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Cohesion & Adhesion

Caused by Hydrogen bonding

Cohesion – Water-to-water

Adhesion – Water-to-something other than water

When water travels upward in a straw, is that cohesion or adhesion? Why?

Diameter of straw: small or large? Why?

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Transpiration (Plants)

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Structure & Function in Water Transport

What structural feature of water enables it to be transported upward?

What structural feature of plant vessels enables water to be transported upward?

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Properties of Water

1. High Surface Tension

2. Temperature Moderation

3. Evaporative Cooling

4. Significant Solvency

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Surface Tension

Surface Tension – water can stand above the rim of a glass due to hydrogen bonds

Is surface tension a result of cohesion or adhesion? Why?

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Temperature Moderation

Temperature – measure of average kinetic energy of molecules

-- Water does this because it has a high specific heat

Water can absorb large amounts of heat but change little in temperature

Guess what type of bonding is responsible for high specific

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Sea Breeze? (cranberry juice & …)

Day, land heats up faster (low specific heat)

Air over land rises Onshore breeze

Night, lands cools faster Hot air rises over water Offshore breeze

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Evaporative Cooling

Water has high specific heat due to?

Responsible for cooling Heat is released as liquid is vaporized into gas Highest energy molecules are vaporized first Vaporization involves the breaking of which bonds?

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Hydrogen Bonding is cool

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Water

Which is more dense, liquid or solid H2O?

As temperature increases, what happens to density?

Why?

What does this mean for ocean stratification?

Which temperature (Celsius) is H2O the most dense?

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Properties of Water

1. There are two cities, Davie and Pompano Beach, which will have a higher temperature during summer? Why can we not use Weston instead of Davie?

2. What bonds are broken during evaporative cooling?

3. What force is responsible for cohesion?

4. What force is responsible for adhesion?

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Like dissolves like…

Water is polar so it dissolves polar substances Also dissolves ionic solids (salts) Polar substances = hydrophilic

Hydro = water -philic = to like (Dendrophiliac – one who likes trees)

Water does not dissolve nonpolar substances Nonpolar substances = hydrophobic

Hydro = water -phobe = to fear (Triskaidekaphobe – one who fears the number 13)

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Remember…

Hydrophilic = polar molecule Will dissolve in water

Hydrophobic = nonpolar molecule Will NOT dissolve in water

What about ionic compounds?