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ACTIVITY OVERVIEW
LA
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Identifying Liquids
BO RA
T
Students perform tests to identify physical and chemical properties of the isolated liquids. Testing results provide evidence to assist in the identification of the two liquids
isolated from the unlabeled mixture.
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
chemical properties
miscible, miscibility
mixture
physical properties
toxic
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Activity 6 • Identifying Liquids
MATERIALS AND ADVANCE PREPARATION
For the teacher
*
*
masking tape to label liquid cups
1
copper wire with loop at one end
1
cup of water
1
cup of Liquid A
1
cup of Liquid B
1
candle
*
matches
*
marker
*
matches
*
beaker of water
*
1
overhead projector (optional)
1
Scoring Guide: ANALYZING DATA (AD)
For the class
*
1
container for liquid waste
For each group of four students
1
100 mL (3 1/4 oz.) cup of liquid A (40 mL of mineral oil)
1
100 mL (3 1/4 oz.) cup of liquid B (40 mL of iron nitrate)
1
60 mL dropper bottle of ethanol
1
30 mL dropper bottle of potassium thiocyanate
2
plastic vials with lids
1
pH color scale
For each pair of students
1
pair of plastic forceps
1
dropper
1
SEPUP tray
2
cobalt chloride paper strips
2
pieces of pH paper
*
paper towels
*
access to hot soapy water
For each student
*
1
pair of safety goggles
1
Student Sheet 5.1, “Chemical Safety Data Sheet”
1
Student Sheet 6.1, “Properties of Separated Liquids” (optional)
1
copy of Scoring Guide: ANALYZING DATA (AD) (optional)
*Not supplied in kit
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Identifying Liquids • Activity 6
Masters for scoring guides are in Teacher Resources III: Assessment.
In this activity students work with the 5,000 ppm iron nitrate solution from Activity 5.
To prepare fresh solution, dilute the 40,000 ppm iron nitrate solution as follows. For
320 mL of iron nitrate (enough to fill eight 100 mL cups), dilute 40 mL of 40,000 ppm
iron nitrate with 280 mL of water. This will provide the required dilution of 5,000 ppm
iron nitrate.
Prepare eight cups of liquid A (40 mL of mineral oil) and eight 100 mL cups of Liquid
B (40 mL of iron nitrate). Label all cups with their corresponding letter. Do not
disclose the identity of the solutions.
Any item that comes into direct contact with the mineral oil will retain an oil residue.
Lab equipment, such as SEPUP trays and droppers, must be thoroughly washed and
cleaned with hot soapy water to remove this residue. Be sure to have plenty of hot
soapy water for students to use for clean up. For more information on handling and
disposing of substances used in the mixture, see the MSDS sheets included in the kit.
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. Be sure students rinse their
hands when they are done working with the components of the mixture.
Disposal
During cleanup direct students to place all waste produced from testing in a waste-disposal containers. Any remaining liquids in cups A and B should be returned to the
teacher for use during the next class. When all testing is complete, the liquids in the
waste containers 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 liquids.
Doing the Activity
2.
Students conduct tests to identify the properties of each liquid.
3.
Demonstrate the flammability of the liquids.
Follow-Up
4.
(AD ASSESSMENT) Students identify the liquids based on evidence from testing.this
works)
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Activity 6 • Identifying Liquids
TEACHING SUGGESTIONS
GETTING STARTED
1.
Demonstrate the tests students will use to
identify the liquids.
Start by reading the introduction and Challenge for
Activity 6 with the class. Explain to students that
they will perform a series of tests to help identify the
liquids separated in Activity 5, “Separating the Mixture.” The tests will determine the chemical and
physical properties of the liquids.
Point out that for reference sake the clear oily liquid
is labeled “Liquid A” and the orange liquid is
labeled “Liquid B.” Direct students to add these
labels under, “Name” on their Chemical Data
Sheets for each of the two liquids. Stress the importance of labeling.
Review the tests students will perform in Table 1,
“Tests to Identify Liquids,” in the Student Book.
Emphasize that students will take a sample of the
liquid being tested using a dropper, place it in the
SEPUP tray and test in the tray.
Review each of the tests students will perform and
how to interpret the results. Explain that these are
just some of the many tests that can be used to identify an unknown. Stress that they will need to transfer a sample of each liquid into a cup in the SEPUP
tray in order to conduct each test. Please note the
following when demonstrating the liquid identification tests:
Appearance: Encourage students to be as
descriptive when observing each liquids’ color,
state (solid, liquid, or gas), transparency, and
thickness. This is a good time to reinforce the
difference between observations and inferences.
For example, if a student observes, “The liquid is
colorless and transparent,” this is a quality
observation. In contrast, “It is water” is an inference since the identity of the liquid has not yet
been established.
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Miscible in water and ethanol: Review the pronunciation of the word miscible (MIS-a-bull).
Make sure that the caps are tight on the vials
after adding liquids. Explain that if the liquid
being mixes when you drop a dropper full of the
liquid into water or ethanol, it is miscible. If it is
not miscible, it will remain in a separate layer
and bead-up or separate into two separate layers similar to oil and vinegar. When cleaning
up, direct the students to pour the solutions in
the waste bucket.
Contains water: Cobalt chloride strips indicate
the presence of water. When dipped in a solution, if the strip turns pink if water is present.
Students commonly think that all liquids contain water. You may explore this misconception
by testing several liquids (vegetable oil, tea,
etc.) with the cobalt chloride strips. Prompt
them to predict what will happen before dipping a strip of cobalt chloride paper in each.
Note: If before testing the strips appear pink,
remove the strips from the container and place
them in a microwave for 40 seconds. In the
presence of water vapor, they may turn pink.
Microwaving them will evaporate the water and
the strips will return to blue.
Corrosive: The corrosive nature of each liquids
is determined in this activity by measuring its
pH. For the purposes of this investigation, a liquid is classified “corrosive” if the pH is relatively
more acidic or basic (a pH of less than 3 or more
than 11) relative to a liquid with a more neutral
pH of 3-11. Show students how to dip the pH
paper in solution, and compare the resulting
color with the pH color scale.
Toxic: Explain that a toxic substance is one that
is harmful to the health of organisms.This test
involves the addition of one drop of potassium
thiocyanate to the liquid to be tested. If the solution turns red, the liquid is considered toxic. The
presence of a red precipitate indicates the presence of iron. While not a direct test of toxicity,
the presence of iron in high enough concentrations is toxic.
Identifying Liquids • Activity 6
Flammable: This test is a teacher demonstration. The procedure for this test follows the procedure used to demonstrate “Flammability” in
Activity 2, “Types of Hazards.” For instructions,
see Teaching Step 2 below. If you demonstrate
this test, instruct students to add a “flammable”
row to their data table.
Stress the safety precautions students should take,
such as not handling the liquids directly with their
bare hands. Remind them that the components in
the mixture are to be treated as hazardous until
their identities have been established and their
hazards can be referenced.
Based on the needs of your students you may hand
out optional Student Sheet 6.1, “Properties of Separated Liquids,” or have students construct Table 2,
“Properties of Separated Liquids” in their science
notebooks. For more information on meeting the
diverse needs of students, see Teacher Resource II:
Diverse Learners.
DOING THE ACTIVIT Y
2.
Students conduct tests to identify the
properties of each liquid
Distribute the materials and allow students to conduct the tests on each liquid.
The following table contains sample results.
3. Demonstrate the flammability of the liquids.
Ask students, Which of the liquids do you think will
be flammable? What makes you think this? After
sharing the class’ predictions, put on goggles and
conduct the test for liquids A and B. With a cup of
water nearby, dip the loop of the wire into the liquid
to be tested. Move the loop over the flame of a lit
candle. If the liquid is flammable, it will ignite or
spark. Dip the wire loop in a cup of water, dry the
loop, and then repeat the test with the second liquid. Note: Use caution when performing this
demonstration because mineral oil is slightly flammable and will spark and “pop” when held over a
flame.
FOLLOW-UP
4.
(AD ASSESSMENT) Students identify the
liquids based on evidence from testing.
Analysis Question 1 asks students to analyze the
information they collected during the activity to use
the data to draw a conclusion about the identity of
Liquid A and Liquid B from the mixture. Ask students to share with the class how they determined
the identity of a particular liquid using evidence
from the activity and Table 2 to support their con-
Sample Student Results, “Properties of Separated Liquids”
Test
Liquid A
Liquid B
Appearance
Colorless, transparent liquid that is oily
and slightly thick.
Orange-brown, transparent liquid that is
not thick.
Miscible in water
Not miscible
Miscible
Miscible in ethanol
Not miscible
Miscible
Contains water
No water present
Water present
Corrosive
Not corrosive
Corrosive
Toxic
Not toxic
Toxic
Flammable
Slightly flammable
Not flammable
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Activity 6 • Identifying Liquids
clusion. If appropriate, take this opportunity to
show students how to draw a conclusion based on
the evidence available. You may wish to make a
transparency of Table 3, and show students how to
cross out the liquids that are eliminated as information from Table 2 is considered.
To provide feedback to students and assess this
question, us the ANALYZING DATA (AD) Scoring
Guide. A sample Level-3 response is provided below.
For more information on the use of the AD Scoring
Guide, see Teacher Resources III: Assessment.
Analysis Question 2 asks students to determine the
hazard category for each of the liquids from the
mixture. According to their testing results, and the
information in Table 3, “Information on Selected
Liquids,” they will determine that the mineral oil is
slightly flammable, while the iron nitrate solution is
toxic and corrosive.
Analysis Question 3 directs students to add evidence gained in this activity to Student Sheet 5.1
“Chemical Safety Data Sheet” for both liquids. Students should be able to fill in the physical description and hazard information for both liquids.
Prompt students to write out how the liquids should
be safely handled and stored. This should be based
on the hazard(s) determined for each liquid.
SUGGESTED ANSWERS TO QUESTIONS
1.
(AD ASSESSMENT) Look at Table 3, “Information
on Selected Liquids,” on the next page (in student
book).
a. Compare the information from this activity with
the information in the table. Look for similarities.
b. Based on their properties, what are the identities
of liquid A and liquid B?
c. Support your answer with at least three pieces of
evidence for each liquid.
Level 3 Response
One of the liquids in the mixture is mineral oil.
The evidence is that this liquid is transparent,
has a mild oily odor, is not miscible in water or
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ethanol, and does not container water. Students
may also add that it is not corrosive, nor is it
toxic, and it is slightly flammable. The second
liquid is iron nitrate. The evidence that supports
this identification is that it is transparent,
orange, and miscible in both water and ethanol,
contains water, is not flammable, and is corrosive and toxic.
2.
Based on the information in Table 3,
“Information on Selected Liquids,” would you label
liquid A or liquid B from the mixture as hazardous?
Liquid A, mineral oil, should be labeled, “Flammable.” Liquid B, iron nitrate solution should be
labeled “Toxic and Corrosive.”
3.
Using evidence from this activity, add the following to Student Sheet 5.1 for Liquid A and Liquid B
a. The name of the liquid you identified.
b. Under “Hazards,” write yes or no for those categories that apply.
The following information should be added on
Student Sheet 5.1 “Chemical Safety Data Sheet”
a. Liquid A is mineral oil, Liquid B is iron
nitrate solution
b.
Liquid A
(Mineral Oil)
Liquid B
(Iron Nitrate
Solution)
Corrosive
No
Yes
Flammable
Slightly
No
No
Yes
Hazard
Toxic
Name
Date
Properties of Separated Liquids
Test
Liquid A
Liquid B
Appearance
Miscible
in water
Miscible
in ethanol
Contains
water
©2007 The Regents of the University of California
Corrosive
Toxic
Flammable
Issues and Physical Science • Student Sheet 6.1
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