Properties of Water

Learning Goals

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1. You will be able to describe the structure of water.

2. You will be able to identify the 6 properties of water.

3. You will be able to describe how these properties are essential to sustaining life

Water

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Types of Bonds: Hydrogen Bonds

Water (H2O or H–O–H) is a polar molecule Electrons spend more time with O than H’s

H’s become slightly +, O slightly –

Hydrogen Bonding

Hold water molecules together The hydrogen bonds joining water molecules are

weak, about 1/20th as strong as covalent bonds. They form, break, and reform with great frequency Extraordinary Properties that are a result of hydrogen

bonds. Cohesive behavior Resists changes in temperature High heat of vaporization Expands when it freezes Versatile solvent

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Think-pair-share

Think about the following… What are the atoms that make up a water

molecule? Which type of bonds hold the atoms together? What does polarity mean?

Turn to your shoulder partner and share your answers

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Properties of Water

1. Polar Molecule

2. Cohesion

3. High Specific Heat

4. Density- greatest at 4C

5. Universal Solvent of Life

6. Neutral pH

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1. Polarity

Water has a variety of unusual properties because of attractions between these polar molecules.The slightly negative regions of one molecule

are attracted to the slightly positive regions of nearby molecules, forming a hydrogen bond.

Each water molecule can form hydrogen

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This leads to Hydrogen Bonding!!!

2. Cohesion

When water molecules stick to other water molecules holding them together

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Why is this important?

Organisms Depend on CohesionCohesion among water molecules plays a key role in the transport of water against gravity in plants

Adhesion, clinging of one substance to another, contributes too, as water adheres to the wall of the vessels.

Surface Tension

Surface tension, a measure of the force necessary to stretch or break the surface of a liquid, is related to cohesion.

Water has a greater surface tension than most other liquids because hydrogen bonds among surface water molecules resist stretching or breaking the surface.

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Surface Tension

Some animals can stand, walk, or run on water without breaking the surface.

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Water as a Transport Medium

Water evaporates, pulling the watercolumn from the roots to the leaves.

Water molecules cling together andadhere to sides of vessels in stems.

Water enters a plant at root cells.

H2O

H2O

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3. High Specific Heat

Moderate Temperatures on Earth• Temperature is the measurement of the

movement of molecules• In order for molecules to move faster (get

warmer) the hydrogen bonds holding the molecules together have to break.

• In order for the molecules to move slower (get cooler) the hydrogen bonds holding the molecules together have to form.

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Specific Heat

Specific Heat is the amount of heat that must be absorbed or lost for one gram of a substance to change its temperature by 1oC.

Water has a High Specific Heat which means it takes a lot of energy to break or form the hydrogen bonds between water molecules

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Specific Heat

Why is this important?

1. Prevention of temperature changes that are outside the range suitable for life.

2. Coastal areas having a mild climate

3. A stable marine environment

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Evaporative Cooling

The cooling of a surface occurs when the liquid evaporates

This is responsible for:Moderating earth’s climateStabilizes temperature in aquatic

ecosystemsPreventing organisms from overheating

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Ms. Laslow’s Random Fact of the Day!!

Most animals cannot sweat like humans can. They have developed many ways to cope with the heat.

Many of which involve evaporative cooling

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Evaporative Cooling of Animals

freezing occurs evaporation occurs

a. Calories lost when 1 g of liquid water freezes and calories required when 1 g of liquid water evaporates.

b. Bodies of organisms cool when their heat is used to evaporate water.

Gas

Liquid

Solid

0 20 40 8060 100 120

600

800

80calories

Temperature (°C)

Cal

orie

s of

Hea

t Ene

rgy

/ g

540calories

400

200

0

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© Grant Taylor/Getty Images

4. Density

Why is this important?

1. Prevents water from freezing from the bottom up.

2. Ice forms on the surface first—the freezing of the water releases heat to the water below creating insulation.

3. Makes transition between season less abrupt.

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More dense at 4CContracts until 4CExpands from 4C to 0C

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Density-Ice

Frozen water less dense than liquid water

Otherwise, oceans and deep lakes would fill with ice from the bottom up

Ice acts as an insulator on top of a frozen body of water

Melting ice draws heat from the environment

Density

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A Pond in WinterCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

ice layer

Protists providefood for fish.

River otters visitice-covered ponds.

Aquatic insects survivein air pockets.

Freshwaterfish takeoxygenfrom water.

Common frogs and pond turtles hibernate.

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5. Universal Solvent

Solutions consist of: A solvent (the most abundant part) and A solute (less abundant part) that is dissolved in the solvent

Polar compounds readily dissolve; hydrophilic Nonpolar compounds dissolve only slightly;

hydrophobic Ionic compounds dissociate in water

Na+

Attracted to negative (O) end of H2O Each Na+ completely surrounded by H2O

Cl- Attracted to positive (H2) end of H2O Each Cl- completely surrounded by H2O

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Universal Solvent

H

H

H H HH H

H H H

H

An ionic saltdissolves in water.

H H

Cl–Na+

O

O

O OO O

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d-

d- d-

d+ d+

d+ d+

d-

Science 360

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Universal Solvent

N

O

O

O O

H H

H

H

H

A polar moleculedissolves in water.

H

HH

H H

H

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d+

d+

d+

d+

d+

d-

d-

d- d-

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6. Neutral pH

pH scale used to indicate acidity and alkalinity of a solution.Values range from 0-14

0 to <7 = Acidic7 = Neutral>7 to 14 = Basic (or alkaline)

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The pH Scale

pH value

10–1

10–2

10–3

10–4

10–5

10–6

10–7

10–8

10–9

10–10

10–11

10–12

10–13

10–14

10 0

Examples

hydrochloric acid

aci

dic

ba

sic

stomach acid, lemon juicevinegar, cola, beertomatoesblack coffeeurinepure waterseawaterbaking sodaGreat Salt Lakehousehold ammonia

household bleach

sodium hydroxide

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234567891011121314

H+ IonConcentration

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Buffers in Biology

Health of organisms requires maintaining pH of body fluids within narrow limits Human blood normally 7.4 (slightly alkaline)

Many foods and metabolic processes add or subtract H+ or OH- ions

Reducing blood pH to 7.0 results in acidosis

Increasing blood pH to 7.8 results in alkalosis

Both life threatening situations

Bicarbonate ion (-HCO3) in blood buffers pH to 7.4