Contributed by:
The highlights are:
1. Structure of water
2. Hydrogen bonds
3. Specific heat
4. Cohesion and adhesion
5. Water is a universal solvent
2.
Directions
Read information about the properties of
water and carry out the experiments using
the materials at your lab station.
Answer all the questions on the
worksheet provided as you go through
this PowerPoint & complete all
experiments.
3.
Part I: Structure of Water
Answer all questions on your worksheet.
4.
Structure of Water
(–)
This is the structural
(–)
formula of water.
A. Draw a picture
O of water.
H H
B. What is the
chemical formula
(+)
of water?
5.
Structure of Water
(–) (–)
• The Hydrogen and Oxygen
O
in water are bonded
covalently.
H H • HINT: definition of covalen
t!
(+) (+)
D. Why does oxygen
form 2 bonds and
hydrogen forms one
bond?
6.
Structure of Water
(–) (–)
However, as the atoms share their
electrons they do not do so evenly.
O E. Which atom is larger? O or H?
The oxygen in water hogs the
H H electrons and is therefore slightly
negative.
(+)
This results in the two hydrogen
atoms becoming slightly positive.
F. Add the + and – charges to
your picture in A.
7.
Structure of Water
(–) (–)
Water is POLAR.
Hint: what is polarity?
O Polarity contributes to
emergent properties of water
H H
Batteries have
a
(+) (+) + and – pole!
G. What is polarity?
H. Why is water
Earth has a
considered polar?
north and
south pole!
8.
Hydrogen Bonds
One water molecule tends to
(–) bond to another water
Hydrogen bond molecule by hydrogen bonding.
(+) The H+ on one molecule is
attracted to the O- of
H another.
Each water molecule can form
(–)
O a max. of 4 hydrogen bonds
(+) H with 4 other water molecules
(–) (+) A single hydrogen bond is
(–) weaker than a single covalent
(+) bond. However, groups of
hydrogen bonds are very
strong
Responsible for the “stickiness”
of water molecules
9.
I. Why do hydrogen bonds form between water
J. Draw 4 water molecules connected by
hydrogen bonds.
10.
STOP!
Review as a class
11.
Polarity video
Review as a class
12.
Part III: Specific Heat
Write this heading on your paper and then
answer all of the questions for this section
under that heading!
13.
Specific Heat
HIGH SPECIFIC HEAT - amount of heat a substance
needs for a given increase of temperature
Takes a lot of energy to raise 1 g of water by 1° C
because you must break Hydrogen bonds
So… Liquid H2O can absorb large amounts of heat
with small changes in temperature
So… It heats up more slowly and retains heat longer
than surroundings
This is important for many reason – for instance in
organisms it helps us maintain a constant
temperature (homeostasis)
14.
HIGH HEAT OF VAPORIZATION-
Takes a lot of energy to convert liquid H2O into vapor
(hydrogen bonding-restricts movement)
Vaporization (evaporation) is the change from liquid
to gas; Molecules of liquid escape and enter air
Evaporation of water produces cooling effect
Again this is important for many reasons – for
instance in some organisms sweat/pant to cool off
when hot (evaporative cooling)
15.
Click this link and complete the exercise.
Changing Matter
A. As you do describe what happens to the
water molecules as you melt the ice cube.
16.
B. Why does the graph level off during
freezing/melting and then again during
17.
C. What property of water makes it able
to absorb a great deal of energy before it
changes from solid to liquid to gas? (Hint:
what has to break to release water
molecules from each other?)
18.
Water expands when it freezes (one of few
substances that does this)
SO . . . ICE IS LESS DENSE THAN LIQUID WATER
Hydrogen bonds keep molecules “at arm’s length” when
freezing so ice floats
Again this is important for many reasons – for
instance it insulates bodies of water. Lakes freeze
from top down; allowing living things to survive in
winter when the lake freezes
19.
Alcohol This blue ice cube floats
in water because ice is
less dense than liquid
water.
The blue ice cube sinks
in alcohol because ice
has a greater density
than alcohol.
20.
D. Describe the structure of ice vs. liquid
water and explain why ice is less dense
than water.
See this link for help: Why does ice float?
21.
STOP!
Review as a class
22.
Part II: Cohesion and
Adhesion
Answer all of the questions for this section
under that heading!
23.
COHESION
Water molecules 'stick to each other' (due to
hydrogen bonding)
Makes water act as if it has invisible “skin”
Called SURFACE TENSION (how difficult it is
to break surface)
A. Define cohesion
24.
See the ‘skin’ of the
water AKA surface
tension!
25.
ACTIVITY: How much water can one penny hold?
Fill the top of a penny with water until a clear
bubble has formed on top but it is NOT
Follow the directions stated on your
26.
ACTIVITY: Can you float a needle on the water drops on your
Slower & softly place a needle on the water on top of the penny.
Answer question 2 and 2a.
With your finger, spread one small drop of detergent on the
surface of a dry penny.
Fill the top of a penny again with water until a clear bubble has
formed on top but it is NOT overflowing. Does the needle float?
3. Could this penny hold more, less or the same amount
of water?
3a. Did the detergent make a difference? Describe the
effect of the detergent.
27.
Wax paper: Does the water roll or slide down a
surface?
Complete the instructions on your handout.
28.
Water molecules stick to other substances
Makes water cling to the sides of a cylinder.
F. Define adhesion.
29.
ACTIVITY: How many pennies can two
microscope slide stuck together by water hold?
Follow the instructions on your handout.
Stack pennies Hold here
30.
CAPILLARY ACTION
Movement of liquid through a narrow passage
or substance
Result of cohesion of water molecules to each
other and adhesion to another surface. Makes
water ‘travel.’
31.
STOP!
Review as a class
32.
Part IV: Water is the
Universal Solvent
Write this heading on your paper and then
answer all of the questions for this section
under that heading!
33.
Water is the ‘universal
solvent’
Solution = liquid consisting of uniform mixture of two or
more substances
Two parts of a solution:
Solvent = liquid (dissolving agent)
Solute = substance dissolved
(EX: Water = solvent; Koolaid powder/sugar = solutes; Kool-
aid = solution)
To make a solution you need to remember the rule -
“like dissolves like”
Since water is polar it will dissolve ions and polar
substances
Since water is polar it will NOT dissolve anything nonpolar
34.
Non polar molecules are
hydrophobic
Oil is an example of a nonpolar
molecule. It does not form
hydrogen bonds.
Like dissolves like, therefore, oil
(nonpolar) does not dissolve in
water (polar).
Nonpolar molecules are called
hydrophobic or 'water hating’
because they do not mix with
water.
35.
A. Briefly explain what a solution is and its
parts.
B. You make instant coffee in the morning
by adding a tablespoon of coffee to a hot
cup of water. Label the solution, solute
and solvent in this scenario.
C. Why doesn’t oil and water mix?
36.
Using the pipettes provided add 2ml of water
to a test tube.
Gently add 2 ml of cooking oil to the same
tube by tilting the test tube of water slightly
and letting the oil run slowly down the inside
of the test tube.
D. Describe what happened.
37.
Add a few drops of food coloring to each test tube.
Place your finger over the test tube and gently shake
to mix the oil and water.
F. How does the food coloring act in each test
tube? Does it mix into the oil? Into the water?
G. Explain why water molecules and oil molecules
separate from each other.
Your explanation should discuss polar and non-polar
molecules, and the effects of polarity on the
interactions between water molecules, and hydrogen
38.
Review
If you have time watch this quick video to
review the PPT. Make sure to use
headphones!
http://www.youtube.com/watch_popup?
v=Jh2qpsZe6GA#t=32
http://www.youtube.com/watch?
v=DVCYlST6mYQ
39.
Can you define the
Vocabulary?!
Polar bond
Hydrogen bond Density
Cohesion Solution
Surface tension Solvent
Adhesion Solute
Specific heat pH
Acid
Base
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