Transcript pogil
Properties of Water
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.
Part I: Structure of Water
Answer all questions on your worksheet.
Structure of Water
(–)
This is the structural
formula of water.
A. Draw a picture of
water.
B. What is the chemical
formula of water?
(–)
O
H
(+)
H
(+)
Structure of Water
(–)
(–)
• The Hydrogen and Oxygen
in water are bonded
covalently.
O
H
(+)
• HINT: definition of
covalent!
H
(+)
D. Why does oxygen form 2
bonds and hydrogen forms one
bond?
Structure of Water
(–)
(–)
However, as the atoms share their
electrons they do not do so evenly.
O
H
(+)
E. Which atom is larger? O or H?
The oxygen in water hogs the
electrons and is therefore slightly
negative.
H
(+)
This results in the two hydrogen
atoms becoming slightly positive.
F. Add the + and – charges to your
picture in A.
Structure of Water
(–)
(–)
Water is POLAR.
Hint: what is polarity?
Polarity contributes to emergent
properties of water
O
H
H
Batteries have a
+ and – pole!
(+)
(+)
G. What is polarity?
H. Why is water considered polar?
Earth has a north
and south pole!
Hydrogen Bonds
One water molecule tends to bond
to another water molecule by
hydrogen bonding.
(–)
Hydrogen bond
The H+ on one molecule is attracted
to the O- of another.
(+)
H
O
(+)
(–)
H
(–)
(+)
(–)
(+)
Each water molecule can form a
max. of 4 hydrogen bonds 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
I. Why do hydrogen bonds form between water molecules?
J. Draw 4 water molecules connected by hydrogen bonds.
STOP!
Review as a class
Polarity video
Review as a class
Part III: Specific Heat
Write this heading on your paper and then answer all of
the questions for this section under that heading!
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)
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)
ACTIVITY
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.
B. Why does the graph level off during freezing/melting and
then again during condenses/boils?
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?)
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
Water
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.
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?
STOP!
Review as a class
Part II: Cohesion and Adhesion
Answer all of the questions for this section
under that heading!
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
See the ‘skin’ of the
water AKA surface
tension!
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 overflowing.
Follow the directions stated on your handout!
ACTIVITY: Can you float a needle on the water drops on your penny?!
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.
Wax paper: Does the water roll or slide down a surface?
Complete the instructions on your handout.
ADHESION Water molecules stick to other substances
Makes water cling to the sides of a cylinder.
F. Define adhesion.
ACTIVITY: How many pennies can two microscope slide
stuck together by water hold?
Follow the instructions on your handout.
Stack pennies
Hold here
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.’
STOP!
Review as a class
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!
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
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.
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?
ACTIVITY
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.
ACTIVITY
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 bonding.
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=Jh2qpsZe6
GA#t=32
http://www.youtube.com/watch?v=DVCYlST6mYQ
Can you define the Vocabulary?!
Polar bond
Hydrogen bond
Cohesion
Surface tension
Adhesion
Specific heat
Density
Solution
Solvent
Solute
pH
Acid
Base