6.7
Design Your Own Experiment: Factors
That Affect the Rate of Dissolving
PRESCRIBED LEARNING OUTCOMES
Time
• measure substances and solutions according to pH, solubility, and
concentration
• conduct investigations into the properties of matter
45–60 min
Key Ideas
Solutions can be measured
by concentration, solubility,
and acidity.
KNOWLEDGE
• mixtures can be classified as solutions, suspensions, or mechanical
mixtures
• solutions are mixtures that appear as a single substance
Skills and Processes
SKILLS AND ATTITUDES
• demonstrate curiosity, skepticism, creativity, open-mindedness, accuracy,
precision, honesty, and persistence as important scientific attributes
• ask questions and formulate hypotheses that are tentative and testable,
and draw conclusions from results
• recognize that an experiment must be repeated and yield consistent
results to be considered scientifically valid
• use appropriate tools and techniques to gather, analyze, interpret, and
share information
• handle chemicals and equipment safely and responsibly
ICT OUTCOMES
• access information using a variety of on-line information tools
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Observing
Communicating (sharing)
Communicating (recording)
Interpreting Observations
Measuring and Reporting
Interpreting Data
Predicting
Designing Experiments
Fair Testing
Controlling Variables
Hypothesizing
Lesson Materials
per student
• sugar cubes
• water
• beakers
• any other materials that
students may need
Program Resources
SCIENCE BACKGROUND
• The particle theory is based on the
assumption that all matter is made
up of many tiny particles (molecules)
that are always in motion. In a hot
object, the particles have a higher
energy and thus move faster than
the particles in a cooler body.
• Many factors affect the rate at which
one substance dissolves in another.
The surface area of the solute
particles, the size of the solute
particles, temperature, type of
solvent, amount of shaking/stirring,
and amount of solvent all affect how
quickly substances will mix.
• The particle theory explains the
factors that affect the rate of
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dissolving. Particles in a solution
have an attraction for each other.
The greater the amount of solvent
relative to the solute, the greater the
opportunity for interactions and
attraction between the solute and
solvent particles, and the more
uniform the distribution of the
particles. As temperature increases,
the particles move faster and spread
out, with greater chances for mixing
of the solute and solvent particles.
• Breaking up the solute crystals into
smaller pieces increases the overall
surface area of crystals exposed to
the solvent, thereby accelerating the
dissolving process.
BLM 6.7-1 Design Your Own
Experiment: Factors That
Affect the Rate of
Dissolving
Investigation Rubric 7: Design
Your Own Experiment
Investigation Rubric 8: Design
Your Own Experiment—
Self-Assessment
Science Skills and Processes
Rubric 3: Hypothesizing
Science Skills and Processes
Rubric 4: Hypothesizing—
Self-Assessment
Nelson Science Probe 7
Web site
www.science.nelson.com
Chapter 6 Matter can be classified.
273
INVESTIGATION NOTES
Related Resources
Bath, John B. Kitchen
Chemistry. Greensboro,
NC: Carson-Dellosa
Publishing, 1994.
Student Safety
Students will likely require the use of a hot plate for this activity.
Review proper procedures for using a hot plate. Remind students
not to heat to dryness, to disconnect the hot plate by pulling on the
plug not the cord, and to handle all glassware with care. Consider
setting up the hot plates in one area of the classroom for more
effective supervision.
• Check for Misconceptions
– Identify: Students may think that individual particles expand or
contract when heated or cooled.
– Clarify: Tell students that it is the space between the particles
that increases or decreases. The transfer of heat causes increased
movement of the particles, which causes the volume of the substance
to increase. As heat is removed, activity decreases and the volume
decreases.
– Ask What They Think Now: Ask students to think of particles
requiring more space when they have more energy. Students should
be able to visualize particles moving faster and further, and,
therefore, requiring more space as they collide with one another.
• To assess students, you may want to use or adapt Investigation
Rubric 7: Design Your Own Experiment and/or Investigation Rubric 8:
Design Your Own Experiment—Self-Assessment.
Question
• Before allowing students to begin their experiments, discuss what
factors might increase the rate at which a solute dissolves. Students
may already know from Section 6.6 that temperature is one factor. Ask
students to brainstorm other factors. They should think about
crushing the sugar cube (surface area), increasing the rate of stirring,
and increasing the amount of solvent.
• Direct students to use Reading and Thinking Strategies: Make
Connections to help them plan their experiment.
Hypothesis
• The students’ hypotheses should be stated as a cause-and-effect
relationship. Students are to use “If … then the sugar will dissolve
more quickly.”
• Possible hypotheses might include the following:
– If the temperature of the water is increased, then the sugar will
dissolve more quickly.
– If the sugar cube is crushed into crystals, then the sugar will dissolve
more quickly.
– If the water is stirred more quickly, then the sugar will dissolve more
quickly.
– If more water is added, then the sugar will dissolve more quickly.
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Unit B: Chemistry
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Materials
• Ensure that students’ list of materials is complete and that it includes
quantities required to conduct the experiment. Students should have
all necessary materials before beginning their experiment, and the
materials should be checked to ensure they are safe.
• Additional materials that students may require for this experiment
include
– hot plate
– something to crush sugar cubes (mortar and pestle, spoon and a
bowl)
– stirring rod
Procedure
• Help students identify all of the variables that may affect their results.
If students are having difficulty, refer them to Conducting an
Investigation in the Skills Handbook to review independent,
dependent, and controlled variables. Ensure that students’ procedures
address each question related to planning their experiments and that
students are aware of all safety precautions.
• Ensure students have a controlled variable(s) in their experiment.
Students will have to test one factor at a time and will, therefore, have
to control all other factors. Students will probably recognize that, to
have a fair test, the amount of solute will have to be controlled in all
situations.
• This experiment is about the rate of dissolving. Therefore, time will
have to be a variable. Students may consider time to be a controlled
variable; that is, they will make their observations of both conditions
(e.g., stirring and no stirring) after the same period of time. This is to
ensure that they can be reasonably certain that it is the stirring and not
some other factor (i.e., time) that determined the dissolving.
• If time is used as a controlled variable, students will have to
subjectively determine which situation caused the most dissolving in
the same time period by visually comparing the two set-ups.
• Alternatively, students may use time as the independent variable, and
observe and record how much has dissolved in each situation
independently after regular intervals. For example, they will observe
the set-up with no stirring and record their observations after every
five minutes for 30 minutes. Then they will observe the set-up with
stirring, and record their observations at the same intervals over the
same period of time. This method will also produce subjective
observations, because students will have to judge or estimate how
much of the solute has dissolved after each time interval. Although
quite acceptable from a science inquiry perspective, this method is
obviously more time consuming and will not likely produce results
that are any more valid or reliable.
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Chapter 6
Matter can be classified.
275
• Students can use BLM 6.7-1 Design Your Own Experiment: Factors
That Affect the Rate of Dissolving as they are working through this
experiment.
• Once the experiment is complete, assign the Check Your
Understanding questions.
Data and Observations
• Have students prepare a data table.
• Remind students to set specific times to record their observations
(e.g., every five minutes). Explain that making observations at specific
and regular intervals is important when attempting to investigate the
rate at which something is happening.
Analysis—Suggested Answers
1.
Specific answers will vary depending upon variables selected. Ensure
that students rely on both qualitative and quantitative observations
when analyzing and evaluating the effect of the selected variable, and
that responses are reflected in their data tables. Students should find
that their results are similar to their classmates’ results.
2.
Stirring or increasing the temperature increases the rate of dissolution.
Increasing the temperature of the solvent causes the particles to move
faster. The particles of the solute are able to move more quickly away
from their solid form. Stirring causes greater movement of the solute
particles and assists them in moving away from their solid form.
Crushing or grinding the solute exposes more solute particles to the
solvent (increasing its surface area), thereby increasing the rate of
dissolving.
Conclusion
• Ensure that the conclusions reached are based upon, and can be
verified by, the data table. Students will likely conclude that stirring,
crushing, and increasing the temperature all increase the rate at which
a solute dissolves in a solvent.
Applications—Suggested Answers
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Unit B: Chemistry
1.
Bouillon powder will speed up the soup-making process. The
powdered bouillon dissolves faster because more bouillon particles are
exposed to the soup than would be on the surface of a bouillon cube.
The soup particles would have more opportunity to slip past the
powdered bouillon, making the bouillon dissolve faster.
2.
Students will know from experience that warm soda is more likely to
fizz than cold soda. Warm soda contains less dissolved carbon dioxide
than cold soda. When the cap is removed, the warm soda gives a loud
whoosh as the gas escapes. Students may say that increasing the
temperature of the liquid solvent decreases the amount of gas that can
be dissolved—the inverse of the effect of temperature on the
solubility of a solid in a liquid. (Students may also mention the effect
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of shaking the pop bottle. When the pop bottle is shaken, the
pressure builds up within the bottle. When the cap is removed, the
pop will fizz much louder and, in some cases, will spray out.
Increasing pressure in this manner results in more gas remaining
dissolved in the soda, regardless of temperature. When the cap is
opened, the pressure is released, allowing the escape of any gas that
had been forced to remain dissolved.)
Student answers may vary. Some possible answers include the
following:
• Making a bouillon base: Stirring or increasing the temperature will
increase dissolving.
• Making Jell-O: increasing the temperature of the water will help
Jell-O powder dissolve.
• Making iced tea from crystals: Using a bit of boiling water will help
to dissolve the crystals faster before adding cold water.
• Timed release of some medications: A coating over medications will
slow down the dissolution of pills in the stomach and ensure that
the medication is available over longer periods of time.
• Chemical weathering of marble statues and limestone buildings:
Coatings or other protection of these structures will slow down the
dissolving process that occurs with acid precipitation.
3.
CHECK YOUR UNDERSTANDING—SUGGESTED ANSWERS
1. Answers will vary. The independent variable is the variable selected to
manipulate (temperature, amount of water, surface area of sugar cube, amount
of stirring). The dependent variable is the rate of dissolving of the sugar cubes.
2. Accept any reasonable answers. Examples could include adding a third
component to the mixture, using a larger beaker, etc.
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Chapter 6
Matter can be classified.
277
LEARNING TIP
Make a web to show what
you already know about
substances that dissolve
in water.
Reading and Thinking Strategies: Make
Connections
Solubility
You can make orange drink because the orange-drink crystals
dissolve in water. Another way to say that a substance dissolves in
water is to say that it is soluble in water. Can you think of some
other substances that are soluble in water? If the orange-drink
crystals did not dissolve in water, you would not be able to make
the drink. An insoluble substance is a substance that does not
dissolve. Can you think of some substances that are insoluble
in water? Can a substance that is insoluble in water be dissolved
in another solvent?
• Before beginning this experiment, remind students of
the information they learned in Section 6.6. They need
to recall factors that affect solubility. They should also
recall information that they may have from everyday
experiences. For example, they may recall that stirring,
or crushing something into a powder, helps it dissolve
faster.
TRY THIS: OBSERVE DIFFERENT SOLVENTS
Skills Focus: predicting, observing, classifying
Predict whether salt, sugar, butter, and wax will dissolve in water and in
ethanol. Now try to dissolve each of these solutes in the two different
solvents (Figure 2). Record your results.
Observe Different Solvents
Dissolves in water?
Dissolves in ethanol?
salt
sugar
butter
wax
Figure 2
Adding sugar to ethanol to see if the sugar dissolves
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Unit B
Chemistry
Meeting Individual Needs
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Extra Support
• Have students work in carefully selected pairs.
ESL
• Provide language support to help students better understand what to
do. Consider having ESL students work in small groups. Encourage
group members to support each other.
Extra Challenge
• Have students research how soda pop is made; specifically, how the gas
is put into the pop.
www.science.nelson.com
GO
ASSESSMENT FOR LEARNING
What To Look For in Student Work
Suggestions for Teaching Students Who Are Having Difficulty
Evidence that students can
• explain how solutions can be measured
• design a fair test to determine the effect of
the variable
• make a hypothesis to provide an answer
to a testable question
• write a conclusion that refers back to the
hypothesis
• interpret data accurately
• create products that are complete
(e.g., a lab)
Help students identify specific variables for each of the factors that could affect
the outcome of this experiment. For example: Time—length of time sugar cubes
are left in the beaker. Measurement—temperature of the liquid. Quantity—amount
provided.
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Unit B: Chemistry
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