Solubility and Bonding I and II

Patricia A. Riley Lincoln Park High School
6145 N. Sheridan Rd 16C 2001 N. Orchard St. Mall
Chicago IL 60660 Chicago IL 60614
(773) 534-8130 x 148

Objectives:

A high school student will be able to:
1. define solubility.
2. identify a substance's bonding (ionic or covalent) from its chemical
formula.
3. predict a substance's solubility in water and oil from its chemical
formula.
4. determine the effects of temperature and surface area on the solubility
of CuSO₄, copper(II) sulfate.
5. determine the surface area of two different objects, using a ruler and
the formula: Surface Area = Sum of the Surface Areas of All Sides.
6. use the scientific method to gather, organize, and analyze data.

Materials Needed:

Teacher demonstration: Each group of 3 or 4 students:
wave bottle Elmer's Glue, white school variety
Color Spectrum toy (American Science Center) artist oil pastels
vinegar paint thinner/odorless turpentine
salt tempera paint powder
vegetable oil copper(II) sulfate crystals
ammonia (root killer in a hardware store)
iodine crystals paint brushes
liquid furniture polish/cleaner plastic cups
colorless, transparent plastic cups plastic spoons
construction paper signs toothpicks
masking tape construction paper
water hammer
coffee percolator (hot water source) graduated cylinder
water: hot, iced, room
temperature
metric ruler
cuisinaire rod and component
blocks

Strategy:

Miniteach I:
1. Hold a wave bottle and gently tilt it. Ask class to describe what they
see. Draw out the following points: there are two different liquids, the
liquids do not mix but keep separating, the same liquid is always on top. Ask
why the two liquids do not mix. Why is the same liquid always on top?
2. Have students observe the Color Spectrum toy (any toy involving
substances that are immiscible will work) and explain how it works. Point out
that density and solubility are different concepts.
3. Ask class to define solubility and write it on the chalk board.
4. Remind students of the two different types of bonds that they have
studied, ionic (electron transfer) and covalent (electron sharing). Tape paper
labels on the board. Ask students how they can predict the bonding in a
substance from its formula: ionic, metal and nonmetal; covalent, nonmetals
only. Write these rules of thumb under the appropriate labels. Show the class
such common household substances as water (H₂O), salt (NaCl), vinegar (CH₃COOH),
sugar (C₁₂H₂₂O₁₁), iodine crystals (I₂), ammonia (NH₃) and classify them as
ionic or covalently bonded and to tape a paper label with the name and formula
for each under the correct category sign on the board. Remind the class that
covalent substances are either polar (not symmetrical, the molecule has two
different ends: water, sugar, vinegar, ammonia) or nonpolar (symmetrical, both
ends of the molecule are the same: I₂). Have the students reclassify the
covalent substances into polar covalent and nonpolar covalent categories.
4. Fill a number of colorless, transparent plastic cups with water. Show
students a variety of common household substances (vinegar, salt, vegetable
oil, ammonia, liquid furniture polish, iodine crystals). Ask students to
predict whether each will dissolve in water and then test it. Repeat with oil
instead of water. Have students keep track of the solubilities at their seats
and on the board chart. Now ask students to analyze the board chart for any
patterns or relationships they can see. Draw out that substances that are ionic
or polar covalent dissolve in water which is itself polar covalent, while
substances that are nonpolar covalent do not. Nonpolar covalent substances
dissolve in vegetable oil. State the solubility rule: Like dissolves like!
The fact that water and vegetable oil will not dissolve in each other suggests
that vegetable oil has what type of bonding???
5. Divide the class into groups of three or four. Each group must
determine the bonding type of a number of substances for which they do not know
the chemical formula by seeing what they dissolve in, water or vegetable oil.
The substances should include Elmer's Glue (white school variety), artist oil
pastels, paint thinner, Root Killer (CuSO₄, available in hardware stores),
powdered tempera paint, and food coloring. Students should try different
combinations, for example: artist pastel and water, artist pastel and paint
thinner, Root Killer crystal in water, Root Killer crystal in Elmer's Glue, etc.
What conclusions can be drawn about solubility? about bonding? Students should
enter these substances in the board chart.
6. Point out applications for solubility and bonding. Artists use
solubility in the creative process. Examples include:
Turpentine Wash: artist pastel washed (i.e., painted over with a brush)
with turpentine or paint thinner. Crayons dissolve in
turpentine.
Water Resist: water soluble tempera paints brushed over artist pastels.
Crayons do not dissolve in water solutions.
Collage: many different media are assembled and glued together. Should
the pieces dissolve in the glue?

Miniteach II:
1. Remind students of the previous lesson: Like dissolves like. Briefly
review what is meant by "like": ionic and polar covalent substances dissolve in
polar covalent solvents; nonpolar covalent substances dissolve in nonpolar
covalent solvents.
2. Raise the question: How might we make a solute, such as sugar,
dissolve better? Write the suggestions on the chalk board; they will include
stirring, heating, adding more solvent (water), and crushing. How could these
suggestions be tested? Have students suggest procedures. What variables would
need to be considered in each test? What data would have to be collected? What
safety issues need to be considered?
3. Divide the class into groups of 3 or 4. Give each group a set of
procedures that summarize the discussion in 2:
A. Construct a group data table.
B. Determine the volume of water to be used in each trial.
C. Select 5 CuSO₄ crystals of equal size.
D. Control:
1) Fill a cup with 100 mL room temperature water.
2) Add 1 of the crystals to the cup and record the time.
3) Record the time when the crystal has completely dissolved.
E. Effect of Temperature on Dissolving: Repeat Step D using
1) Hot water from the coffee pot.
2) Ice water from the labeled bottle.
F. Effect of Stirring on Dissolving: Repeat Step D but this time stir
continuously with a plastic spoon.
G. Effect of Surface Area on Dissolving:
1) Repeat Step D but crush the crystal first. (Place the crystal
between two sheets of clean paper and hit with a hammer.)
2) Measure the dimensions of a cuisinaire rod with a metric ruler
and calculate the surface area of the rod:
Surface Area of a side = length x height
Surface Area of the rod = Sum of the Surface Areas of all the
sides
3) Count out the number of cuisinaire cubes needed to equal the
rod used in 2). Calculate the Total Surface Area of all the
cubes used:
Total Surface Area of cubes = Surface Area of 1 cube x number
of cubes used
4. When the groups have finished, compare results. Consider the following
questions: What is the effect of temperature on dissolving? of stirring? of
surface area? Why was a control used? How was it used? How many variables
were measured in each test? Have the students explain what they saw in terms of
molecular motion and the Kinetic Theory as much as possible.

Assessment:

Students will be assessed on their participation in the discussions and on
their safe performance of all laboratory exercises. Each group will submit a
written lab report.

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