The Pure, The Mixture, The Unknown – Grade Nine
Ohio Standards
Connection:
Physical Sciences
Benchmark C
Describe the identifiable
physical properties of
substances (e.g., color,
hardness, conductivity,
density, concentration and
ductility). Explain how
changes in these properties
can occur without changing
the chemical nature of the
substance.
Indicator 9
Investigate the properties
of pure substances and
mixtures (e.g. density,
conductivity, hardness,
properties of alloys,
superconductors and
semiconductors).
Lesson Summary:
This lesson involves classroom discussions, demonstrations
and hands-on laboratory activities about pure substances
and mixtures with a focus on common household materials.
The students will investigate: What is a pure substance?
What is a mixture? How difficult is it to obtain pure
substances? How can one test for purity? What are some
methods for purifying substances? The demonstrations and
labs will introduce students to methods for determining
freezing points, melting points, boiling points, density and,
where equipment is available, conductivity. Students also
will learn to use these data for assessing the purity of
substances.
Estimated Duration: Four hours
Commentary:
This lesson is designed to help students understand the
differences between pure substances and mixtures. To begin
the lesson, students will examine household materials and
attempt to classify them by using their labels. They will
then use the context of purity to examine the properties of
materials and the methods for separating components of
impure materials (mixtures).
The lesson was field tested and reviewed by educators
across the state. Some of their comments were:
 “The hands-on nature of the lesson is great. All students
get involved.”
 Good connections (real world) by using household
substances.”
 “This lesson was well received by students and
improved their understanding of matter and its
properties.”
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The Pure, The Mixture, The Unknown – Grade Nine
Pre-Assessment:
 On the day before the lesson is taught, ask students to consider and write their answers to
the following questions as homework. See Attachment A, Pre-Assessment for a student
handout.
1. What is a pure substance?
2. What is a mixture?
3. What types of mixtures are there?
4. How do you know if something is pure?
5. How are substances purified?
6. When is it important to have pure substances?
7. What are some examples of pure substances and mixtures that can be found at home,
in grocery stores or hardware stores?
 Ask students to bring in labels from discarded containers of the pure substances and
mixtures on their lists of examples, when possible. Caution them not to remove labels
from household products which may be misidentified by family members.
 At the beginning of the lesson, have the students share and discuss their answers.
 Finally, ask students these questions:
1. What would scientists consider pure substances?
2. How do they determine when a substance is pure?
Scoring Guidelines:
The pre-assessment is not a graded activity. Its purpose is to bring out the varying views
students have of “purity” and to stimulate their interest in the topic. From the early part of the
discussion, assess how much students know and what their misconceptions are about pure
substances and mixtures. For example, some students consider a substance to be “pure” if it
is colorless, clear, safe, clean or free of bacteria. From student answers, note their differing
views of purity, some of which may be fine for everyday usage, but not for all situations and
not for use in science. From this information, decide when to provide scientific information
about substances. See instructional procedures for key information and additional questions
to use during the pre-assessment discussion. For additional answers, see Attachment B, PreAssessment Sample Answers.
Post-Assessment:
Part One
 Have students describe and/or draw diagrams of procedures for investigating the purity of
two or more of the following substances and state the scientific bases of their procedures.
 Clearly communicate to students the level of detail that is expected in their write-ups
and/or diagrams. Responses may include, details of the procedures, rational for using
the procedures, properties of the materials that make the procedures possible, optional
procedures, discussion of key points, and or listing of any problems.
1. Commercial bottle of vinegar
2. Aluminum screws that have no iron in them
3. Water from a tap
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The Pure, The Mixture, The Unknown – Grade Nine
4.
5.
6.
7.
Water from a pop machine (bottled water)
Pond water
Distilled water
Table salt (iodized and non iodized)
Part Two
Have students describe and/or draw diagrams of procedures to separate the items in one of
the following mixtures and state briefly the scientific basis for their procedures.
1. White sand, sugar and sawdust
2. Iron filings, aluminum filings and sugar
3. Powdered sulfur and table salt
4. Iron filings and coffee grounds
5. Vegetable oil and water
6. Crushed pumice, salt and sand
Scoring Guidelines:
See Attachment C, Post-Assessment Answers and Scoring Rubric.
Instructional Procedures:
1. On the first day of the lesson, ask students to share and discuss their answers to the preassessment questions. Ask them to refer to the information on the labels they brought or
that you provide.
2. As students share their examples of pure substances and mixtures, record their answers
on the board in a table like the one students used for homework. Instruct students to add
the information to their tables.
3. As the students respond, ask questions and provide information about the characteristics
of pure substances, mixtures, types of mixtures, etc.
4. The following are suggested questions to ask and key information to provide during the
discussion:
 Why do you think the substance is a pure substance or a mixture? What information
do you have about the substance? What is the source of the information? What can
you observe? What does the label tell you about the material?
 Why do companies add substances to purified bottled water?
 Scientists classify matter as pure substances and mixtures.
a. A pure substance contains only one element or one compound. A combination of
pure water and pure ice is a pure substance in two physical states.
b. A mixture contains two or more elements or compounds that are physically mixed
but are not chemically combined.
 Mixtures are classified as homogeneous or heterogeneous.
a. A homogeneous mixture is uniformly distributed at the microscopic level. A
heterogeneous mixture is not uniformly mixed at the atomic or molecular level.
Close examination by eye or microscope will show the different parts.
b. An alloy is a mixture of two or more solids.
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The Pure, The Mixture, The Unknown – Grade Nine
c. A solution is a homogeneous mixture because its parts are equally distributed at
the atomic and molecular level. The solute is the material being dissolved. The
solvent is the dissolving material. In a salt solution, salt is the solute and water is
the solvent.
 What are the properties of the substance? Which properties could be used to separate
the substance from another material? (Solubility, boiling points, magnetic properties,
chemical activity, density, etc.) Examples of separating components of a mixture are:
a. Iron filings can be removed from a mixture with a magnet.
b. Salt (sodium chloride) dissolves easily in water and can be recovered from the
solution by slow evaporation of the water and re-crystallization of the sodium
chloride.
c. Saw dust and pumice float on water and can be skimmed off of the surface of a
mixture.
d. Oil and water will separate into layers and the heavier (denser) layer can be
drained out using a separatory funnel.
 The key point is that it is extremely difficult to obtain and maintain an absolutely pure
substance. Use bottles of reagent-grade common chemicals, such as sodium chloride,
sucrose and potassium chloride to demonstrate that even the “reagent-grade
substances” that are used in labs are not 100 percent pure. Some are 99.4 percent pure
or higher, but none is 100 percent pure.
 Pure substances have unique characteristics, such as melting points, boiling points,
density and conductivity as well as characteristics, such as infrared light absorption
patterns that can be obtained with modern instrumentation. These characteristics help
judge the purity of the substances and, in some cases, help separate them from
mixtures.
5. After the class discussion of the key points about mixtures and pure substances, describe
the labs that students will do in rotations.
6. Demonstrate what is to be done at each station and describe the data that are to be
recorded. Provide students with data sheets to record data and observations. See sample
student handout in Attachment D, Data Table for Lab Rotations and Demonstrations.
Ensure that students are wearing goggles and are taking other safety precautions.
7. Have students work in groups of two to three and proceed through the lab stations listed
below.
a. Separation of liquids: Use a separatory funnel to separate two immiscible liquids
(e.g., cooking oil and water, or motor oil and vinegar).
b. Filtration: Use filter paper to separate a mixture (e.g., sand and kosher salt or sugar
and sawdust).
c. Evaporation and re-crystallization: Use a watch glass to evaporate the water from a
drop or two of a solution (e.g., salt and water or sugar and water). Use a hot plate or
other safe source of heat.
d. Liquid density determination: Use hydrometers to measure the densities of five
solutions (e.g., distilled water, two different salt solutions, rubbing alcohol and
cooking oil).
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The Pure, The Mixture, The Unknown – Grade Nine
e. Solid density determination: Measure the mass and volume of pennies from different
time periods (pre- and post-1982) and calculate the densities.
f. Conductivity: If equipment is available, test water for purity using conductivity kits
or swimming pool testers.
g. Conductivity of semiconductors: If kits are available, test the conductivity of silicon
lumps and silicon used in computer chips.
8. At the conclusion of the labs and demonstrations, have students write their results as
laboratory reports with procedures, data, conclusions and discussions. Additional
suggestions for materials and equipment can be found in the Materials and Resources
section of this lesson.
9. If possible, demonstrate the determination of melting and boiling points. Have the
students record observations on their data sheets. Emphasize that melting and boiling
points are unique characteristics of pure substances that can be used to identify them and,
in some cases, separate them. If the equipment is not available, video can be found on
the Internet by searching for “How to take a melting point.”
10. If possible, demonstrate distillation as a technique used for purification. Have the
students record observations on their data sheets. Again, if a live demonstration is not
possible, use video.
11. After the labs and demonstrations are complete, guide the class through sharing and
discussing the results.
12. Ask students to critique in positive ways other students’ lab reports, especially the
conclusions, by asking questions or making suggestions.
13. Use the lab report to determine what should be stressed in the conclusion of the lesson.
14. Conclude the lesson by reviewing topics. The key points students should understand are:
a. A pure substance can be purified by separating it from unwanted components of a
mixture by various lab procedures, such as separation of immiscible liquids, filtration,
evaporation and re-crystallization and distillation.
b. A substance has unique characteristics that can be used to identify it, to judge its
purity and to help isolate it (e.g., distillation uses the differences in boiling points to
separate the components of a mixture).
c. More than one technique may be needed to separate and purify a substance.
d. Some testing for purity may require “destructive” techniques on small samples, (i.e.,
chemical analyses that change the substance chemically).
Differentiated Instructional Support:
Instruction is differentiated according to learner needs, to help all learners either meet the
intent of the specified indicator(s) or, if the indicator is already met, to advance beyond the
specified indicator(s).
 In addition to or instead of written formats, have students use diagrams, pictures, flow
charts, concept maps, other graphics or visual presentations.
 Place students in mixed groups to respond to the students’ differing skills, knowledge,
experience, physical challenges, etc.
 Have students working beyond the standard use inquiry as well as further research in
areas of student interest. See suggestions in the Extensions section of this lesson.
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The Pure, The Mixture, The Unknown – Grade Nine
Extensions:
 Have students explore which properties of gold allow a practical test for the grade of gold
in jewelry and the purity of gold bars.
 Encourage students to visit the Web sites of chemical, oil, manufacturing and
pharmaceutical associations and companies.
 Have students research and prepare posters on how substances are separated and purified
on large scales (e.g., water for scientific use; crude oil to yield gasoline and other
products; sugar from sugar beets or sugar cane).
 Have students make a hydrometer from a Beral pipette and metal filings and design a
method for using it to determine the purity of some liquids such as antifreeze.
 Prepare an investigation for using chemical tests on small samples.
 Prepare an investigation that uses quantitative techniques.
Homework Options and Homework Connections:
Have students collect labels from various household materials to determine if they contain
pure substances or mixtures.
Materials and Resources:
The inclusion of a specific resource in any lesson formulated by the Ohio Department of
Education should not be interpreted as an endorsement of that particular resource, or any of
its contents, by the Ohio Department of Education. The Ohio Department of Education does
not endorse any particular resource. The Web addresses listed are for a given site’s main
page, therefore, it may be necessary to search within that site to find the specific information
required for a given lesson. Please note that information published on the Internet changes
over time, therefore the links provided may no longer contain the specific information related
to a given lesson. Teachers are advised to preview all sites before using them with students.
For the teacher:
Labels from common substances, particularly table salt, iodized table salt,
kosher salt, milk (whole, skim and1% fat), bottled water (especially one
whose label indicates that substances have been added after purification),
carbonated cola, orange juice from concentrate, aspirin, white vinegar,
household ammonia and powdered drink mix; distillation apparatus and
melting point apparatus.
For the students: Apparatus and materials for separation of liquids lab: glass separatory
funnels, rings to hold them, ring stands, beakers, flasks for holding and
transferring liquids, two immiscible liquids: cooking oil or motor oil and
water or vinegar. If separatory funnels are not available, separations can
be done with large plastic syringes without the needles, turkey basters or,
for small amounts, eyedroppers.
Apparatus and materials for filtration lab: ring stands, rings, funnels with
matching filter paper, sand and kosher salt or sugar and sawdust.
Apparatus and materials for evaporation and re-crystallization lab: watch
glasses, pipettes, test tubes, distilled or de-ionized water, salt and/or sugar.
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The Pure, The Mixture, The Unknown – Grade Nine
Apparatus and materials for liquid density lab: hydrometers (from
chemistry labs, aquarium shops or made from Beral pipettes (see
extensions)), cylinders, flasks and the following liquids in flasks labeled
with a letter but without their names: Liquid A (distilled water), Liquid B
(salt solution with about four parts water and one part salt), Liquid C (salt
solution with about eight parts of water and one part salt), Liquid D
(rubbing alcohol, preferably 70 percent), Liquid E (clear cooking oil or
mineral oil).
Apparatus and materials for solid density lab: pennies (50 or more)
minted before 1982 and pennies (50 or more) minted after 1982, 100 mL
graduated cylinders, water, balance and flask.
Conductivity: conductivity kits, if available.
Safety Equipment: goggles, aprons, gloves, shields, and other protective
equipment.
Instructional Tip:
Confer with the chemistry chairperson and obtain from the chemical storage room a
collection of chemicals with their assays or purities noted on the labels. Get bottles of
technical-reagent-and analytic-grade chemicals, like sodium chloride, sucrose and potassium
chloride, and use them to point out the different levels of purity in these lab materials.
Vocabulary:
 assay
 crystallization
 evaporation
 distillation
 filtration
 precipitation
 conductivity
 density
 solution
 solvent
 solute
 homogeneous mixture
 heterogeneous mixture
 microscopic level
 atomic level
 molecular level
 colloid
 alloys
 pure substance
 mixture
 compound
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The Pure, The Mixture, The Unknown – Grade Nine
Technology Connections:
 Use graphing calculators to record and plot data on melting points, heating curves and/or
boiling points.
 Use spectrophotometers to demonstrate or analyze the purity of substances by their color
characteristics.
 Use conductivity equipment or kits to demonstrate or to analyze the purity of substances.
 Use the Internet to learn about and look up properties of substances.
 Learn of other technological equipment that is used in science, industry and health
services to determine the purity of substances.
 Use a spreadsheet for data tabulation and analyses.
Research Connections:
Marzano, R. et al. Classroom Instruction that Works: Research-Based Strategies for
Increasing Student Achievement. Alexandria, VA: Association for Supervision and
Curriculum Development, 2001.
Cooperative learning has a powerful effect on student learning. This type of grouping
includes the following elements:
 Positive interdependence;
 Face-to-face promotive interaction;
 Individual and group accountability;
 Interpersonal and small-group skills;
 Group processing.
General Tips:
Prior to the lesson, it may be helpful to talk with the chemistry chairperson for equipment
setups, available chemicals and videotapes.
Have on hand for this lesson appropriate references, including:
1. Handbook of Chemistry
2. Chemical supply company catalogs
3. Online resources about properties of substances
4. Merck Index
5. Material Safety Data Sheets (MSDS)
Attachments:
Attachment A, Pre-Assessment
Attachment B, Pre-Assessment Sample Answers
Attachment C, Post-Assessment Answers and Scoring Rubric
Attachment D, Data Table for Lab Rotations and Demonstrations
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The Pure, The Mixture, The Unknown – Grade Nine
Attachment A
Pre-Assessment
Pure Substances and Mixtures
1. What is a pure substance?
2. What is a mixture?
3. What types of mixtures are there?
4. How do you know if something is pure?
5. How are substances purified?
6. When is it important to have pure substances?
7. What are some examples of pure substances and mixtures that can be found at home, in
grocery stores or hardware stores? Record them in the table below and complete as much
of the information about them as possible.
Pure
Components;
Name
Properties
Substance or
Homogeneous or
Mixture?
Heterogeneous
9
The Pure, The Mixture, The Unknown – Grade Nine
Attachment B
Pre-Assessment Sample Answers
Milk, whole
Pure Substance
or Mixture?
Mixture
Milk, skim
Mixture
Carbonated drink
(e.g., Cola)
Mixture
Sugar
Nearly pure but
not as pure as
sucrose used in
scientific labs
Mixture
Name
Air of classroom
Properties
Orange juice
freshly squeezed
from oranges
Orange juice from
concentrate
Mixture
Salt, iodized
Mixture
Salt, kosher
Pure substance
Well water
Mixture
Tap water
Mixture
Mixture
Components; Homogeneous
or Heterogeneous
Heterogeneous mixture of
water, proteins, fat
Heterogeneous mixture of
water, proteins, slight fat
Homogeneous mixture of
sugar, coloring, flavor, carbon
dioxide, water; solution while
capped; heterogeneous
mixture shortly after opening
(CO2 released)
Homogeneous; sucrose
Homogeneous mixture of
oxygen, nitrogen, water,
carbon dioxide and other
gases; heterogeneous mixture
when dust and other particles
are taken into account.
Heterogeneous mixture of
water, protein, sugar,
vitamins, etc.
Heterogeneous mixture of
water, protein, sugar, vitamins
and, perhaps, additives
Heterogeneous mixture of
sodium chloride, sodium
iodide, silicates
Homogeneous; sodium
chloride; no silicate added; no
iodide added
Homogeneous mixture
(solution) of water and
dissolved minerals and gases
Homogeneous mixture
(solution) of water and
dissolved minerals and gases
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The Pure, The Mixture, The Unknown – Grade Nine
Attachment B (continued)
Pre-Assessment Sample Answers
Bottled water
Mixture
Distilled water
Pure substance
in most cases
White vinegar
Mixture
Ammonia,
household
Mixture
Copper penny
Mixture
Nickel
Mixture
Medicinal oxygen
Very pure
Powdered drink
crystals
Mixture
Gasoline
Mixture
Aspirin
Mixture
Coal
Mixture
Plain chocolate
candy bar
Chocolate candy
bar with nuts
Mixture
Homogeneous mixture
(solution) of water and
dissolved minerals and gases
Homogeneous; pure
compound; homogenous
mixture (solution) if dissolved
gases are considered
Homogeneous mixture
(solution) of acetic acid in
water
Homogeneous mixture
(solution) of ammonia gas
dissolved in water; may
contain detergents
Homogeneous mixture; alloy
copper and zinc (pre-1982)
Homogeneous mixture; alloy
of copper and nickel
Homogeneous; pure element;
homogeneous mixture
(solution) if small amounts of
other gases and water are
present
Heterogeneous mixture of
sugar, favoring, coloring,
other substances
Homogeneous mixture
(solution) of octane, other
petroleum products, additives
Heterogeneous mixture of
aspirin (acetyl salicylic acid),
starch, maybe cellulose,
glycol, other chemicals
Coated pills also have gelatin,
titanium dioxide, dye,
glycerin.
Heterogeneous mixture of
many chemicals, including
water and heavy metal salts
Homogenous mixture
Mixture
Heterogeneous mixture
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The Pure, The Mixture, The Unknown – Grade Nine
Attachment C
Post-Assessment Answers and Scoring Rubric
Answers: Sample answers are provided, but student answers will vary.
Part One: Investigating the purity.
1. Commercial bottle of vinegar:
Determine the boiling point(s) and compare it to established values. Pure substances
have specific boiling points.
2. Aluminum screws that have no iron in them
Determine the melting point and/or density and compare them to established values. Pure
substances have specific melting points and densities.
3. Water from a tap
Determine the boiling point and compare it to the established value; evaporate a sample
and examine the container for residue. Pure substances have specific boiling points.
Pure water should evaporate completely and leave no residue. A residue indicates the
presence of a contaminant.
4. Water from a pop machine (bottled water)
Determine the boiling point and compare it to the established value; evaporate a sample
and examine the container for residue. Pure substances have specific boiling points.
Pure water should evaporate completely and leave no residue. A residue indicates the
presence of a contaminant.
5. Pond water
Determine the boiling point and compare it to the established value; evaporate a sample
and examine the container for residue. Pure substances have specific boiling points.
Pure water should evaporate completely and leave no residue. A residue indicates the
presence of a contaminant.
6. Distilled water
Determine the boiling point and compare it to the established value; evaporate a sample
and examine the container for residue. Pure substances have specific boiling points.
Pure water should evaporate completely and leave no residue. A residue indicates the
presence of a contaminant.
7. Table salt (iodized and noniodized)
Determine the melting point and compare it to established values. Pure substances have
specific melting points.
Part Two: Separating Components of a Mixture
1. White sand, sugar and sawdust
Add water and stir thoroughly. Wait a few minutes to allow the mixture to settle. Scoop
the sawdust from the surface of the water. Pour the remaining mixture through filter
paper and recover the sand in the filter paper. Evaporate the water from the remaining
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The Pure, The Mixture, The Unknown – Grade Nine
2.
3.
4.
5.
6.
mixture to recover the solid sugar. Sawdust is not soluble in water and has a density that
is less than water, so it will float on top of the water. Sand is not soluble in water and
has a density that is greater than water, so it sinks to the bottom. Sugar dissolves in
water. It can be separated from water by evaporating the water.
Iron filings, aluminum filings and sugar
Separate the iron filings from the mixture with a magnet. Add water to dissolve the sugar.
Pour the remaining mixture through filter paper and recover the aluminum filings in the
filter paper. Evaporate the water from the remaining mixture to recover the solid sugar.
Iron is attracted to a magnet, but aluminum is not. Aluminum is not soluble in water and
is denser that water, so when it is mixed with water, it sinks to the bottom. Sugar
dissolves in water.
Powdered sulfur and table salt
Add water and stir thoroughly. Wait a few minutes to allow the mixture to settle. Pour
the mixture through filter paper to recover the solid sulfur. Evaporate the water from
the remaining mixture to recover the solid salt. Sulfur is not soluble in water; table salt
is soluble.
Iron filings and coffee grounds
Separate the iron filings from the mixture with a magnet. Iron is attracted to a magnet,
but coffee grounds are not.
Vegetable oil and water
Use a separatory funnel to separate the two immiscible liquids. Oil and water do not
mix. The less dense oil rises above the water to form a separate layer.
Crushed pumice, salt and sand
Add water and stir thoroughly. Wait a few minutes to allow the mixture to settle. Scoop
the pumice from the surface of the water. Pour the remaining mixture through filter
paper and recover the sand in the filter paper. Evaporate the water from the remaining
mixture to recover the solid salt. Neither pumice nor sand dissolves in water; salt does
dissolve in water.
Rubric: Use the following rubric to score the post-assessment.
Criteria
Description
Level 4
Depth of
Understanding
Evidence of
Inquiry
Communication
Level 3
Level 2
Level 1
Scientific information and ideas
are accurate, thoughtfully
explained.
Scientific information
and ideas are accurate.
Scientific
information has
major inaccuracies or
is overly simplified.
Procedures are clearly identified
and formulated in a manner that
can be replicated.
Scientific information is
communicated clearly and
precisely.
Procedures are clearly
identified.
Scientific
information has
occasional
inaccuracies or is
simplified.
Procedures are
implied.
Scientific
information has
some clarity.
Scientific
information is
unclear.
Scientific information is
communicated clearly.
Procedures are
unclear or absent.
Adapted from Council of Chief State School Officers State Collaborative on Assessment and
Student Standards Science Project, April’1997.
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The Pure, The Mixture, The Unknown – Grade Nine
Attachment D
Data Table for Lab Rotations and Demonstrations
Separating and Identifying Characteristics of Components of a Mixture
For each lab station and demonstration:
1. Briefly describe the procedure;
2. Record all observations and data.
Station
Procedure
1. Separation of
Liquids
Data and Observations
2. Filtration
3. Evaporation and
re-crystallization
4. Liquid density
determination
14
The Pure, The Mixture, The Unknown – Grade Nine
5. Solid density
determination
6. Conductivity
7. Melting point
determination
8. Boiling point
determination
9. Distillation
15