AUTHOR’S NAME: Maria Reyes
TITLE OF THE LESSON: Universal Solvent
DATE OF LESSON:
LENGTH OF
LESSON: 45-50 minutes
GRADE: 9-12
SOURCE OF THE
LESSON: University of Houston
TEKS ADDRESSED:
(1) Scientific processes. The student,
for at least 40% of instructional time, conducts field and laboratory investigations using safe,
environmentally appropriate, and ethical practices
(A)
demonstrate safe practices during field and laboratory investigations; and
(B)
make wise choices in the use and conservation of resources and the
disposal
or recycling of materials.
Objectives:
Students will be able to
observe which substances dissolved in water.
Students will be able to
explain why those substances dissolved in water.
Students will be able to explain
why water dissolves polar substances.
RESOURCES:
Per Group:
8 test tubes
1 test tube rack
Alcohol
Soap flakes
Cornstarch
Sugar
Salt
Vegetable Oil
Flour
Sand
Per each student
Goggles
Apron
Gloves
SAFETY
CONSIDERATIONS:
Students
should follow laboratory rules and wear, goggles, aprons, and gloves at all
times.
SUPPLEMENTARY MATERIALS:
Lab
Worksheet
Teacher Does
|
Probing Questions
|
Student responses
|
Engage:
Have
two beakers filled with water in front of the class. Show the class salt and flour. Have them predict what will dissolve and
what wont.
Add
salt to one beaker and flour to the other. The salt will dissolve and the flour will not.
Hold
up a model structure of water and review the polar nature of water.
Today
we are going to add different particles to water and see if they dissolve.
|
Will
salt dissolve in water? Why?
Will
flour dissolve in water? Why?
Is
water polar or non-polar?
What
makes it polar?
Is
the oxygen partially negative or positive?
Why?
What
about the hydrogen atoms?
Why?
|
Yes,
because it is an ionic compound.
No,
it is non-polar.
|
Explore:
Pass
out the lab worksheet and have the students do the lab. Walk around and assist when necessary. Make sure the students are practicing safe
laboratory rules. That they are
wearing their goggles and gloves throughout the lab.
|
Possible
questions to ask:
Is
the solute polar?
Is
the solute non polar?
Is
salt a solute or a solvent?
Would
water be the solvent?
|
|
Explain:
Go
over the questions in the lab worksheet.
|
What
is a polar molecule?
What
is a non-polar molecule?
Will
polar molecules or non polar molecules dissolve in water? Why?
Which
substances dissolved in water?
Which
ones did not dissolve in water?
Why
did they not dissolve in water?
Is
salt polar? Why did it dissolve?
What
is a solute?
Based
on that definition, which substances in this lab would be considered solutes?
|
Molecules
that have ends that are partially charged. The electron density isn’t equally distributed.
They
don’t have ends that are partially charged. The electron density is equally charged.
Polar
molecules, because like dissolves like. Water attracts the particles of other substances.
Salt,
sugar, soap flakes, alcohol
Sand,
oil, and flour
The
ones that didn’t dissolve were non-polar.
No. It dissolved because it is ionic and the
water broke its bond.
Particles
that dissolve in the solvent?
Salt,
sugar, alcohol, and soap flakes
|
Extend:
Talk
about how some contaminants dissolve in water.
Briefly
discuss water quality and water quality standards.
|
Can
water dissolve more than the five that were dissolved today? Why?
Will
all of the substances be safe for consumption?
Just
by looking at a glass of water, can you tell if it is pure?
How
can you determine if water has contaminants in it?
|
Yes,
because it dissolves polar and ionic molecules.
No
Yes,
No
If
it is saturated you can, or if there is a color change. But sometimes you cannot tell.
Run
tests
|
Evaluate:
For
homework each group will research and provide three examples of contaminants
that dissolve in water. You will have
to provide the chemical formula and a reason why it dissolves in water.
|
|
|
Universal
Solvent Lab
Directions:
1.
Copy table into your journal.
2. Predict if each
substance in the table will dissolve. Put a yes or no in the appropriate column.
3. Place test tubes in rack. Pour 10 ml of water in all eight test tubes. Label test tubes 1-8.
4. Pour 5 ml of alcohol in
test tube 1. Gently shake the test
tube. Record whether or not it dissolves
in water.
5. Place 1 ml of soap
flakes in test tube 2. Gently shake the
test tube. Record whether or not it
dissolves in water.
4. Place 1 ml of flour in test tube 3. Gently shake the test
tube. Record whether or not it dissolves
in water.
5. Place 1 ml of sugar in
test tube 4. Gently shake the test
tube. Record whether or not it dissolves
in water.
6. Place 1 ml of cornstarch in test tube 5. Gently shake the test
tube. Record whether or not it dissolves
in water.
7. Place 1 ml of salt in test tube 6. Gently shake the test tube. Record whether or not it dissolves in water.
8. Place 1 ml of oil in
test tube 7. Gently shake the test
tube. Record whether or not it dissolves
in water.
9. Place 1 ml of sand in test tube 8. Gently shake the test tube. Record whether or not it dissolves in water.
Record and fill out in Journal.
Contents
in Test Tubes
|
Prediction
if substances dissolved in water (yes or no)
|
Dissolves
in Water (Yes or No)
|
Alcohol
|
|
|
Soap
Flakes
|
|
|
Flour
|
|
|
Sugar
|
|
|
Cornstarch
|
|
|
Salt
|
|
|
Oil
|
|
|
Sand
|
|
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Questions:
1. Which substances dissolved in water?
2. Which ones did not dissolve in water?
3. What is the difference between polar and
non-polar molecules?
4.
Which ones (polar or non-polar) dissolved in the water? Why?
5. If hard water contains ions, how will it
affect water’s ability to dissolve polar molecules?
Lesson 1: Credibiity of Sources