PROPERTIES OF WATER waterwiseeducation.org/.../power points/MRCWaterWalk_waterpro pertiesqu...

I. Structure of the Water Molecule Polarity and Hydrogen Bonds

Structure of the Water Molecule H + H + O  H 2 O (chemical formula) HH O Structural formula

Water Molecules are Polar Polar – has a positive end and a negative end. As a result, polar molecules have a slightly negative charge. H+ O-O-

How is a Water Molecule Polar?  The oxygen atom attracts the shared electrons more strongly than the hydrogen atoms do.  As a result, the electrons spend more time near the oxygen atom than they do near the hydrogen atoms. H+ O-O-

How Do Water Molecules Bond With Each Other?  Hydrogen bonds form between neighboring water molecules   The positve H of one molecule “sticks” to the negative O of another molecule.

Hydrogen Bonding  They do not share electrons, so they are weaker than covalent bonds.  They easily break and form again

Cold Call Questions:  What does polar mean?  What makes a water molecule polar?  What kind of bonds exist between water molecules?  How does a hydrogen bond form?  What kind of bonds does a water molecule have within the molecule itself?  What kind of bond is stronger?  Why is that important?

II. Physical Properties and States of Matter

Physical Properties  Water in its pure state is… Colorless Colorless Odorless Odorless Transparent Transparent  Distilled water is considered “pure”  Rain water is not   Precipitation of any kind (snow, rain, hail) contains dissolved minerals, gasses, acids, dust, pollen grains, viruses and microorganisms!

Water pH   Pure water (distilled) has a pH of 7   Seawater is slightly basic, with a pH of about 8   Most natural water has a pH of between 6-8   Acid rain can have a pH as low as 4

States of Matter

Three States of Water  Water is the only naturally occurring substance that can exist in all three physical states on the planet Gas Water Vapor Widely spread, un- bonded molecules. Liquid Liquid water Density = 1 Small clumps of bonded molecules. Solid Ice Density <1 Hexagonal crystal lattice

States of Matter  Which is ice and which is water?

Water Phase Changes  Freezing   Water expands when it freezes and becomes less dense  Melting

Water Phase Changes  Condensation   When water vapor cools it takes up less space and contracts, allowing water molecules to stick to one another forming clouds and precipitation.  Evaporation

Water Phase Changes  Frost Formation  Sublimation

Cold Call Questions:  What is sublimation?  Where on the planet would sublimation occur?  Why would the evaporation of surface water be important?  Why would condensation of water molecules into clouds be important?

III. The Density of Water

Density  The density of water: increases as temperature decreases, until 4 o C increases as temperature decreases, until 4 o C Decreases from 4 o C until 0 o C (the freezing point) Decreases from 4 o C until 0 o C (the freezing point) At 0 o C, Hydrogen bonds relax to form crystal lattice At 0 o C, Hydrogen bonds relax to form crystal lattice

Density of water  If density of object is = to or < than water it will float. Density of pure water is 1.0 Density of pure water is 1.0 Density of pure ice is Density of pure ice is Density of sea water is 1.03 Density of sea water is 1.03   Most solids are more dense than their liquids. This makes solids sink   Ice is less dense than liquid water due to H- Bonds

Importance of Water’s Density  Ponds don’t freeze from the bottom up (and don’t freeze solid)  Ice floats, and forms an insulating layer for life below polar sea ice polar sea ice  Stabilizes ocean temperatures and climate (causes turnovers…we’ll learn about this later)

IV. Surface Tension

Description  Cohesion water molecules stick together and draw inward water molecules stick together and draw inward This forms a tight layer on the surface. This forms a tight layer on the surface. This layer is resistant to being broken apart, and is called surface tension. This layer is resistant to being broken apart, and is called surface tension.  Surface tension measures the strength of water molecules attracting to one another.  Due to hydrogen bonding.

Importance  Some insects can walk on water  Formation of funnels, water drops, and waves

What Affects Surface Tension?  Gravity Changes the shape of droplets as they fall Changes the shape of droplets as they fall  Warmer temperature Hot water is a better cleaning agent because the lower surface tension makes it a better "wetting agent" to get into pores and fissures rather than bridging them with surface tension. Hot water is a better cleaning agent because the lower surface tension makes it a better "wetting agent" to get into pores and fissures rather than bridging them with surface tension.  Soaps and detergents Breaks the surface tension Breaks the surface tension

Capillary Action and Adhesion  Adhesion is the attraction of water molecules to stick to other substances, and is also a result of its hydrogen bonds.  This property allows water to creep up or flow in tubes, such as a plant’s xylem and phloem, or a human’s blood vessels). This is called capillary action and is important for many life processes.

Cohesion-Adhesion Theory -As water evaporates from leaves, it tugs on the water molecules below -Cohesion and adhesion pull water up and replace missing water molecules -Water enters the roots by osmosis Did you ever wonder: How does water move from roots to leaves when a tree doesn’t have a heart to pump the water?

V. High Specific Heat Capacity

Description  Due to Hydrogen bonds  Water has the highest specific heat of all natural liquids  Most of the sun’s heat energy is used to break the hydrogen bonds only a little bit left to increase the vibrations of the molecules (which increases the temp.) only a little bit left to increase the vibrations of the molecules (which increases the temp.)

Importance  Large bodies of water can absorb and release a lot of heat with little temperature change  Plays a major role in ocean currents and controlling climate through thermal conductivity

VI. High Heat of Vaporization

Description  Takes a lot of energy to make water evaporate.  Most of the initial energy is used to break the hydrogen bonds.  This causes water to be resistant to temperature changes

Importance  Slows evaporation of water bodies  Helps our bodies and our planet maintain a certain stable temperature range

True or False?  Water boils and evaporates at higher altitudes faster than at sea level.

True At sea level water boils at 100o C. At 2,400 m, water boils at 92o C. This is because as the altitude gets higher, the lower air pressure makes it easier for the water molecules to break their bonds and attraction to each other and, thus, it boils more easily.

True or False  It takes more energy to heat cold water to boiling (212 o F or 100 o C) than it does to change boiling water to steam.

False   It takes 5x as much energy to turn boiling water into steam then it takes raise cool water to boiling 212o F.

VI. Water is the Universal Solvent

What Does This Mean?  Water has the ability to dissolve both bases and acids, so it is called a universal solvent.  Everything else dissolves in water as well…except lipids  The movement of water and its hydrogen bonds cause this

Water As An Inert Solvent  Water is not altered by any substance it dissolves, and in turn, those substances being dissolved are not altered by the water.  This makes water an inert solvent.

Hydrophilic vs. Hydrophobic Substances  Hydrophilic “Water loving” “Water loving” Substances that are easily dissolved in water Substances that are easily dissolved in water Ex. Nutrients, minerals, etc. Ex. Nutrients, minerals, etc.  Hydrophobic “Water hating” Water won’t form solutions with these substances Ex. Lipids (fats, oils waxes)

True or False  More things can be dissolved in a strong acid than in water.

False   The movement of liquid water along with its ability to form hydrogen bonds, allows water to pull substances apart and dissolve them better but not always faster then an acids!

A Recap on the Importance of Water

Remember Homeostasis?  Helps maintain a constant physiological condition of cells, and organisms’ global ecosystems because… a. Makes a good insulator a. Makes a good insulator b. Resists temperature change b. Resists temperature change c. Universal solvent c. Universal solvent d. Acts as a coolant d. Acts as a coolant e. Controls climate e. Controls climate