waterproperties.ppt civil and water engineering

Water Civil Engineering Notes for Diploma students

1. The Extraordinary The Extraordinary
Properties of WaterProperties of Water

2. WaterWater
•A water molecule (H
2O), is
made up of threethree atoms ---
one oxygen and two hydrogen.
H
H
O

3. Water is PolarWater is Polar
•In each water molecule, the oxygen oxygen
atom attracts moreatom attracts more than its "fair
share" of electronselectrons
•The oxygenoxygen end “acts” negativenegative
•The hydrogenhydrogen end “acts” positivepositive
•Causes the water to be POLARPOLAR
•However, Water is neutralneutral (equal
number of e- and p+) --- Zero Net Zero Net
ChargeCharge

4. Hydrogen Bonds Exist Hydrogen Bonds Exist
Between Water MoleculesBetween Water Molecules
•Formed between a highly Formed between a highly
Electronegative atom Electronegative atom of of
a polar molecule and a a polar molecule and a
HydrogenHydrogen
•OneOne hydrogen bond is hydrogen bond is
weakweak , but , but manymany
hydrogen bonds are hydrogen bonds are
strongstrong

5. Interaction Between Water Interaction Between Water
MoleculesMolecules
Negative Oxygen Negative Oxygen end of one water molecule is end of one water molecule is
attracted to the attracted to the Positive Hydrogen Positive Hydrogen end of another end of another
water molecule to form a water molecule to form a HYDROGEN BONDHYDROGEN BOND

6. What are What are
the the
Properties Properties
of Water?of Water?

7. Properties of WaterProperties of Water
•At sea level, pure water At sea level, pure water boils at 100 boils at 100
°C°C and and freezes at 0 °Cfreezes at 0 °C. .
•The The boiling temperature of water boiling temperature of water
decreases at higher elevations decreases at higher elevations (lower (lower
atmospheric pressure). atmospheric pressure).
•For this reason, an For this reason, an eggegg will take will take longer longer
to boil to boil at higher altitudesat higher altitudes

8. Properties of WaterProperties of Water
•CohesionCohesion

9. Properties of WaterProperties of Water
•CohesionCohesion
•AdhesionAdhesion

10. Properties of WaterProperties of Water
•CohesionCohesion
•AdhesionAdhesion
•High Specific HeatHigh Specific Heat

11. Properties of WaterProperties of Water
•CohesionCohesion
•AdhesionAdhesion
•High Specific HeatHigh Specific Heat
•High Heat of VaporizationHigh Heat of Vaporization

12. Properties of WaterProperties of Water
•CohesionCohesion
•AdhesionAdhesion
•High Specific HeatHigh Specific Heat
•High Heat of VaporizationHigh Heat of Vaporization
•Less Dense as a SolidLess Dense as a Solid

13. CohesionCohesion
•Attraction between particles of the Attraction between particles of the
same substance same substance (( why water is why water is
attracted to itself)attracted to itself)
•Results in Results in Surface tensionSurface tension (a measure (a measure
of the strength of water’s surface)of the strength of water’s surface)
•Produces a Produces a surface film surface film on water that on water that
allows insects to walk on the surfaceallows insects to walk on the surface
of water of water

14. Cohesion …Cohesion …
Helps insects walk across
water

15. AdhesionAdhesion
•Attraction between two different Attraction between two different
substancessubstances..
•Water will make Water will make hydrogen bonds with other hydrogen bonds with other
surfacessurfaces such as glass, soil, plant tissues, such as glass, soil, plant tissues,
and cotton. and cotton.
•CapillaryCapillary actionaction-water molecules will “tow” -water molecules will “tow”
each other along when in a thin glass tube.each other along when in a thin glass tube.
•Example: Example: transpirationtranspiration process which plants process which plants
and trees remove water from the soil, and and trees remove water from the soil, and
paper towels soak up water.paper towels soak up water.

16. Adhesion Causes Capillary Adhesion Causes Capillary
ActionAction
Which gives water the
ability to “climb”
structures

17. Adhesion Also Causes Adhesion Also Causes
Water to …Water to …
Form spheres &
hold onto plant
leaves
Attach to a
silken spider
web

18. High Specific HeatHigh Specific Heat
•Amount of heatAmount of heat needed to raise or needed to raise or
lower lower 1g1g of a substance of a substance 1° C1° C..
•Water Water resistsresists temperature changetemperature change, ,
both for heating and cooling.both for heating and cooling.
•Water can absorb or release large Water can absorb or release large
amounts of heat energy with little amounts of heat energy with little
change in actual temperature.change in actual temperature.

19. High Heat of VaporizationHigh Heat of Vaporization
•Amount of energy to convert 1g or a Amount of energy to convert 1g or a
substance from a substance from a liquid to a gasliquid to a gas
•In order for water to evaporate, In order for water to evaporate,
hydrogen bonds must be brokenhydrogen bonds must be broken..
•As water evaporatesAs water evaporates, it removes a , it removes a
lot of lot of heatheat with it. with it.

20. High Heat of VaporizationHigh Heat of Vaporization
•Water's heat of vaporization is 540 540
cal/g.cal/g.
•In order for water to In order for water to evaporateevaporate, ,
each gram must each gram must GAIN 540 GAIN 540 calories calories
(temperature doesn’t change --- (temperature doesn’t change ---
100100
oo
C).C).
•As water evaporatesAs water evaporates, it removes a , it removes a
lot of lot of heatheat with it with it (cooling effect)(cooling effect)..

21. •Water vapor Water vapor forms a kind of
global ‘‘blanket” which helps to
keep the Earth warm.
•Heat radiated from the sun Heat radiated from the sun
warmed surface of the earth is
absorbed and held absorbed and held
by the vaporby the vapor.

22. Water is Less Dense as a Water is Less Dense as a
SolidSolid
•Ice is less denseIce is less dense as a solid than as a
liquid (ice floats)
•Liquid water has hydrogen bonds hydrogen bonds that
are constantly being broken and constantly being broken and
reformed.reformed.
•Frozen waterFrozen water forms a crystal-like crystal-like
latticelattice whereby molecules are set at
fixed distances.

23. Water is Less Dense as a Water is Less Dense as a
SolidSolid
•Which is ice and which is water?Which is ice and which is water?

24. Water is Less Dense as a Water is Less Dense as a
SolidSolid
WaterWater IceIce

25. HomeostasisHomeostasis
•Ability to maintain a Ability to maintain a steady state steady state
despite changing conditionsdespite changing conditions
•Water is important to this process Water is important to this process
because:because:
a. Makes a a. Makes a good insulatorgood insulator
b. Resists temperature changeb. Resists temperature change
c. c. Universal solventUniversal solvent
d. Coolantd. Coolant
e. Ice protects against temperature e. Ice protects against temperature
extremes ( extremes (insulatesinsulates frozen lakes) frozen lakes)

26. Solutions & SuspensionsSolutions & Suspensions
•Water is usually part of a Water is usually part of a
mixture.mixture.
•There are two types of There are two types of
mixtures:mixtures:
–SolutionsSolutions
–SuspensionsSuspensions

27. SolutionSolution
•Ionic compounds disperse as Ionic compounds disperse as ionsions in in
waterwater
•Evenly distributedEvenly distributed
•SOLUTESOLUTE
–Substance that is being dissolvedSubstance that is being dissolved
•SOLVENTSOLVENT
–Substance into which the solute Substance into which the solute
dissolvesdissolves

28. SolutionSolution

29. SuspensionsSuspensions
•Substances that
don’t dissolve but don’t dissolve but
separate separate into tiny
pieces.
•Water keeps the Water keeps the
pieces suspended pieces suspended
so they don’t
settle out.

30. Acids, Bases and pHAcids, Bases and pH
One water molecule One water molecule in 550 million in 550 million
naturally naturally dissociatesdissociates into a Hydrogen into a Hydrogen
Ion Ion (H+) (H+) and a Hydroxide Ion and a Hydroxide Ion (OH-)(OH-)
Hydrogen Ion Hydroxide IonHydrogen Ion Hydroxide Ion
Acid Acid BaseBase
H
2O  H
+
+ OH
-

31. The pH ScaleThe pH Scale
•Indicates the concentration of Hconcentration of H
++
ions ions
•Ranges from 0 – 140 – 14
•pH of 7 is neutral7 is neutral
•pH 0 up to 7 is acid 0 up to 7 is acid … H
+

•pH above 7 – 14 is babove 7 – 14 is basic… OH
-

•Each pH unit represents a factor of
10X 10X change in concentration
•pH 3 is 10 x 10 x 10 (1000) stronger pH 3 is 10 x 10 x 10 (1000) stronger
than a pH of 6than a pH of 6

32. AcidsAcids
•StrongStrong
Acids Acids
have a pH have a pH
of of 1-31-3
•Produce Produce
lots of lots of
H H
+ +
ionsions

33. BasesBases
•Strong Strong
Bases Bases have
a pH of 11 11
to 14 to 14
•Contain lots lots
of OHof OH
--
ions ions
and fewer
H+ ions

34. BuffersBuffers
•Weak acids or bases that react with Weak acids or bases that react with
strong acids or bases to prevent strong acids or bases to prevent
sharp, sudden changes in pH sharp, sudden changes in pH
(neutralization).(neutralization).
•Produced naturally by the body Produced naturally by the body to to
maintain homeostasismaintain homeostasis
Weak AcidWeak Acid Weak BaseWeak Base