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ACTIVITY OVERVIEW
LA
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5 0-
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Identifying Solids
BO RA
T
Students conduct tests on the solids separated from the mixture to gain information
about the physical and chemical properties of each. This information is then used to
identify each of the separated solids.
KEY CONCEPTS AND PROCESS SKILLS
(with correlation to NSE 5–8 Content Standards)
1.
Substances have characteristic properties, such as density, that are independent
of the amount of the sample. (PhysSci: 1)
2.
Scientists use appropriate tools and techniques to gather, analyze, and interpret
data. (Inquiry: 1)
3.
Scientific explanations emphasize evidence. (Inquiry: 2)
KEY VOCABULARY
conductivity
density
evidence
reactivity
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Activity 7 • Identifying Solids
MATERIALS AND ADVANCE PREPARATION
For the teacher
*
1
container for liquid waste
*
1
cork
*
1
rock
*
1
cup of water
1
Scoring Guide: ANALYZING DATA (AD) and/or
1
Scoring Guide: UNDERSTANDING CONCEPTS (UC)
For each group of four students
*
1
plastic cup containing unidentified solids
1
battery harness with alligator clips and small lightbulb
1
9-volt battery
1
30-mL dropper bottle of 100,000 ppm copper chloride
1
60-mL dropper bottle of ethanol
1
30-mL dropper bottle of water
1
piece of steel wool
2
plastic vials with caps
For each pair of students
1
50-mL graduated cylinder
1
pair of plastic forceps
1
SEPUP tray
1
cup of water
*
paper towels
For each student
*
1
pair of safety goggles
Student Sheet 5.1, “Chemical Safety Data Sheet”
1
Student Sheet 7.1, “Properties of Separated Solids” (optional)
1
Scoring Guide: ANALYZING DATA (AD) (optional) and/or
1
Scoring Guide: UNDERSTANDING CONCEPTS (UC) (optional)
*Not supplied in kit
Masters for scoring guides are in Teacher Resources III: Assessment.
Provide students with the solid samples that they separated from the mixture in Activity 5, “Separating the Mixture.” You will need one class set that will be used for multiple classes. Each set should include the three black plastic squares, three red plastic
tubes, and one aluminum cylinder, and one zinc cylinder. Do not disclose the identity
of each of the materials as this is the goal of the activity.
If conducting this activity with more than one class, reuse the vials of ethanol. Use
tape to label each vial.
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Identifying Solids • Activity 7
SAFETY
The chemicals used in this activity may cause skin irritation. Use caution when handling solutions. Always wear safety goggles, and thoroughly rinse any area that
comes into direct contact with laboratory chemicals. Use ethanol in a well-ventilated
area, and keep vials containing ethanol capped when not in use.
Disposal
Direct students to dispose of waste from the tests in appropriate waste disposal containers. At the end of all testing all liquids used for tests can be flushed down the sink
with running water. It is recommended that you do this when students are not present, since they are not certain of the identity of each liquid yet. Given that uncertainty,
they should not dump any unknown substances down the drain.
TEACHING SUMMARY
Getting Started
1.
Demonstrate the tests students will use to identify the solids.
Doing the Activity
2.
Students conduct tests to identify the properties of each solid.
Follow-Up
3.
(AD ASSESSMENT, UC ASSESSMENT) Students identify each solid based on evidence
from testing.
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Activity 7 • Identifying Solids
TEACHING SUGGESTIONS
GETTING STARTED
1.
Demonstrate the tests students will use to
identify the solids.
Up until this point in the unit, students have separated the mixture, determined if the liquids are hazardous, and identified the liquids. Now they
conduct tests to determine the physical and chemical properties of each solid to aid as evidence in its
identification.
As a class, read the introduction and Challenge for
Activity 7, “Identifying Solids.” Show students how
to perform and interpret the tests they will conduct.
As a class read Table 1, “Tests to Identify Solids,” in
the Student Book.
Based on the prior knowledge of your students,
explain each of these three properties that follow as
necessary. Conductivity is the ability of a substance
to transmit a flow of electricity. Density is the massper-unit volume of a substance. Reactivity is the
ability of a substance to react chemically with
another substance. Explain that these characteristics are inherent for specific materials. For example,
wood from a pine tree is not conductive, but tin, a
metal, is. The density of a kilogram of tin is greater
than a kilogram of pine. Tin reacts chemically with
copper chloride solution, but pine does not.
Demonstrate how to conduct each test and interpret the results. As you demonstrate the tests, the
following may assist you:
Electrical conductivity: Conductivity is the
ability of a substance to transmit an electric
current. Metals such as aluminum and steel are
better electrical conductors than such materials
as plastics and wood. To determine conductivity, make sure the battery is snapped into the
battery harness properly. Demonstrate how to
hold the alligator clips at either end of a substance and observe the lightbulb. If the bulb
lights, the material is conducts electricity. If it
does not, the substance does not conduct electricity.
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Density relative to water and ethanol: It is
important to first gauge your students’ grasp of
density. will help them understand and interpret the results of this test. To do this, select an
object that floats in water, such as a cork, and
an object that sinks in water, such as a rock.
Ask, If I place these in a cup of water, will they
sink or float? Responses are likely to indicate
that the cork will float in water and the rock
will sink. Explore this concept until you are confident that students can interpret the relativedensity test for the solids in the mixture. If a
solid, liquid, or gas floats in something else, it is
relatively less dense. If is sinks, it is more dense.
Pure water has a density of 1.0 g/cm3 at standard temperature and pressure. (Standard
temperature and pressure are universally
agreed-on temperature and pressure settings
established to allow data comparison.) Ethanol
has a density of 0.79 g/cm3. Relative to this, substances that are less dense, will float. Substances that are more dense will sink. A piece of
titanium metal with a density of 4.5g/cm3 will
sink in water and in ethanol. High-density polyethylene, with a density of 0.95 g/cm3 will float
in water since its density is less than 1.0 g/cm3,
but it will sink in ethanol. Explain to students
that conducting this test provides information
about the relative density of the solid. In other
words, the test shows if the object is more or less
dense than the ethanol or water. This concept
will be further developed in later activities.
Direct students to use forcepts to remove the
solids from the vials. The labeled vials can be
reused from one class to the next.
Reacts with copper chloride: In this test, students are asked to compare the reactivity of
each solid with copper chloride solution. Reactivity is the tendency of a substance to interact
chemically with another substance. Students
should look for signs of a chemical reaction
including color change, bubbling, cloudiness,
temperature change, or the formation of a precipitate. Assure that students understand that a
precipitate is a solid that forms in the presence
Identifying Solids • Activity 7
of some chemical reactions. If any of these signs
are observed, they can conclude that the solid is
reactive. Instruct students to use forceps to dip
the solid in water if a reaction begins. This will
stop the reaction.
Procedure step 2 directs students to make data
table 2, “Properties of Separated Solids” in their
notebook. Based on the abilities of your students and your pacing of the activity you may
choose to hand out optional Student Sheet 7.1,
“Properties of Separated Solids.”
DOING THE ACTIVIT Y
2.
Students conduct tests to identify the
properties of each solid
Stress the safety precautions students should take,
such as wearing goggles and not handling any of
the solids directly with their bare hands. Before testing the solids, students will need to clean any corrosion or residue that may have formed while the
solids were in the mixture. If they have not already
done so in Activity 5, “Separating the Mixture,”
show students how to clean the surface of the metal
pieces with steel wool while holding the piece with
the plastic forceps. Mineral oil on the pieces interferes with the test. Provide hot soapy water so that
students can rinse off the mineral oil residue.
Cleaning the solids with steel wool, hot soapy water,
and drying them will assure more accurate results.
Students will conduct each tests a total of four types
of solids, resulting in 16 tests. If you are concerned
about time, consider having each group of students
divide the tests so each pair tests only two of the
four solids. Each group of four can then share test
results. Sample results of testing the solids are
shown in the table below.
FOLLOW-UP
3.
(AD ASSESSMENT, UC ASSESSMENT) Students
identify each solid based on evidence from
testing.
Before students begin the Analysis Questions,
review the information in Table 3, “Information on
Selected Solids,” as a class. Answer questions students may have about the information in the table.
Students will use the information in Table 3 with
their data collected from this activity to identify the
solids from the mixture.
Provide students with feedback and assess students’
answers to Analysis Question 1 using the ANALYZING
DATA (AD) Scoring Guide. A sample Level 3
response is provided below. For more information
on the use of the scoring guide see Teacher
Resources III: Assessment. A correct and complete
answer will demonstrate that the student has used
the data from the activity to make a decision and
refers to the data in their response.
Analysis Question 4 directs students to add information gained in this activity to Student Sheet 5.1
“Chemical Safety Data Sheet” for all four unidentified solids. Once they have answered Analysis
Question 1, students will have identified both of the
plastic pieces as high-density polyethylene (HDPE),
even though they have very different appearances.
They can then use the information provided in
Table 3, “Information on Selected Solids” in the
student book to look up hazard information.
Sample Student Results, “Properties of Separated Solids”
Red tube
Black square
Light metal
cylinder
Dark metal
cylinder
No
No
Yes
Yes
Density relative to water
Floats
Floats
Sinks
Sinks
Density relative to ethanol
Sinks
Sinks
Sinks
Sinks
Reacts with copper chloride
None
None
Reacts
Reacts
Test
Electrical conductivity
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Activity 7 • Identifying Solids
Analysis Question 5 provides an opportunity for you
to review and reinforce students’ understanding of
safety procedures. You may wish to assess this question using the UNDERSTANDING CONCEPTS (UC) Scoring
Guide. When reviewing student work, check that
they explain the safety guidelines they followed
while performing the activity. A sample level-3
response is provided below.
Were you able to identify what material
each solid was made of? Explain.
From the data obtained in this activity, students
should identify that both the red plastic tubes
and the black plastic squares are made of highdensity polyethylene. They do not have enough
evidence from this activity to determine what
the metallic pieces are made from.
3. In this activity you performed four tests on each
solid. Which tests identified:
SUGGESTED ANSWERS TO QUESTIONS
1.
2.
(AD ASSESSMENT) Look at Table 3, “Information
on Selected Solids,” on the next page.
a. physical properties of the solids?
b. chemical properties of the solids?
a. Compare your data with the information in the
table. Look for similarities.
The tests for physical properties were conductivity and density relative to water and to
ethanol. Reactivity with copper chloride is a
chemical property.
b. Based on their properties, what are the solids?
c. Support your answer with at least three pieces of
evidence for each solid.
Level 3 Response
4. Using evidence from this activity, add the following
to your Chemical Data Sheets each type of solid
The black squares and the red tubes are both
high-density polyethylene (HDPE) plastic. is
the evidence to support this is that they are
not conductive, they float in water and sink
in ethanol, and do not react with copper
chloride. The two silver metallic pieces are
conductive, sink in water and ethanol, and
react with copper chloride, but based on the
information in Table 3, “Information on
Selected Solids” they could be any of the
metal solids. So it is not possible to tell what
they are made from.
a. The name of the solid material you identified.
b. Under “Hazards,” write yes or no for those categories that apply.
Based on the information from this activity,
and information listed in Table 3, “Information on Selected Solids” in the Student Book,
students should add the information below
follows on Student Sheet 5.1, “Chemical
Safety Data Sheet.”
Sample Student Sheet 5.1, “Chemical Safety Data Sheet”
Red tube
Density
More dense than
ethanol, less dense
than water
Black square
More dense than
ethanol, less dense
than water
Light metal cylinder
Dark metal cylinder
More dense than
ethanol and water
More dense than
ethanol and water
Reactive
No
No
Yes
Yes
Flammable
No
No
No
No
Toxic
No
No
No
No
Use goggles and apron
Use goggles and apron
None
None
Store away from other
reactive substances
Store away from other
reactive substances
Safety
precautions
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Identifying Solids • Activity 7
5.
(UC ASSESSMENT) You have been asked to submit
a report to your state’s Hazmat Training Center
explaining the safety procedures you followed while
identifying the solids. Write a letter to the hazmat
director that explains:
a. all safety steps taken during this activity.
b. why each was necessary.
Level 3 Response
May 31, 2006
Dear Hazmat Director,
I am writing to you about a recent lab activity that I did to identify solids. I want to tell
you about the safety procedures that I followed so that you can be sure that I followed
the correct safety procedures. In this lab I
was working with four different types of
solids. When I first started out with them, I
didn’t know their identity, so I treated them
as potentially hazardous. Because of this I
wore goggles to prevent substances from getting in my eyes. I handled them with forceps,
so that they would not touch my skin or mix
with any other chemicals. When I was done
with the tests, I washed all of the equipment
that I used and washed my hands really well.
I hope you find that this procedure follows
safety regulations.
Thank you for your time.
Sincerely,
Peggy Smith
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Issues and Physical Science • Student Sheet 7.1
©2007 The Regents of the University of California
Reacts with
copper
chloride
Density
relative to
ethanol
Density
relative to
water
Electrical
conductivity
Tests
Name
Date
Properties of Separated Solids
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