Name_______________
Class: _______, Period______
Date:________________
GROUP #: ___________
Lab: Identifying Unknown Liquids
INTRODUCTION
A chemist must be able to identify substances so that one substance can be distinguished from another.
Sometimes this is simple. If substance A is a green solid, substance B is a red liquid, and substance C is a colorless,
odorless gas, one can tell them apart just by looking at them. Color, odor, and state are examples of physical properties.
Chemical properties are revealed when a substance undergoes a chemical change and some new substance is
formed. For example, if two clear liquids are combined and a white solid (called a precipitate) is formed or bubbles are
produced, a chemical change has taken place and chemical properties have been revealed. Every substance has both
physical and chemical properties.
In this lab, you determine the chemical properties of six clear, colorless liquids. You will then use this information
to determine the identities of four unknown clear, colorless liquids.
MATERIALS
*Hazardous materials are marked with an asterisk*
Equipment:
(2) 24-well microplates, Thin stem pipets, toothpicks, Apron & Goggles
Knowns:
Water, Hydrochloric Acid*, Sodium Hydroxide*, Ethanol*, Hydrogen Peroxide*, Potassium Iodide*
Reagents:
Phenolphthalein, Sucrose, Bromothylmol Blue, Manganese Dioxide*, Lead Nitrate*,
Sodium Hydrogen Carbonate
PROCEDURE
Part A. Chemical Properties of the Known Liquids
1. Put on your laboratory apron and safety goggles and leave them on for the entire lab until clean-up is finished.
2. CAUTION: Always treat an unknown substance as a potential hazard. Do not let it touch your eyes, skin, or clothing.
If it is splashed on you, wash it off immediately and tell your teacher (as you are flushing) who will clean up any spills.
3. You will use a 6x6 matrix for recording your observations of the reactions of the 6 "knowns" to each of the 6 reagents.
4. Use the wells in the 24-well microplate as little test tubes for combining the known liquids with the reagents. Be sure
that the wells are clean and dry before performing tests in them.
5. Add 5 drops of the known liquids 1 - 6 to each of the 6 wells in the corresponding columns in the 24-well microplates.
6. Then add 3 drops of the reagants A - F to each of the 6 wells in the corresponding 24-well microplates.
7. Record your observations in your matrix. Some reactions will happen quickly and others will be slower. If no reaction
occurs, write "no reaction".
Clean up: Check with your teacher. After all work is complete pour all liquids into designated container. Then dunk the
well plate in the designated tub of water. Then rinse well plates at sink using the sponge on a stick. WASH HANDS.
Don't remove aprons and goggles until all materials are cleaned up and put away.
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Part A Data/Observation Matrix
A. Chemical Properties of the Known Liquids
1. Water
2. Hydrochloric
Acid
3. Sodium
Hydroxide
4. Ethanol
5. Hydrogen
Peroxide
6. Potassium
Iodide
A.
Phenolphthalein
B. Sucrose
C. Bromothymol
Blue
D. Manganese
Dioxide
E. Lead Nitrate
F. Sodium
Hydrogen
Carbonate
Part A Questions
Answer the following questions using complete sentences on a separate sheet of paper.
A. Chemical Properties of the Known Liquids
1. List three physical properties that are shared by all the “known” substances.
2. List three chemical properties of Hydrogen Peroxide: (Refer to your data table)
3. What chemical properties are the same for Hydrochloric Acid and Ethanol?
4. What chemical properties are different for Hydrochloric Acid and Ethanol?
5. If you have two unknown substances, how many of their chemical properties must be the same for you to be able to
consider them the same substance?
6. If you have two unknown substances, how many of their chemical properties must be different for you to be able to
consider them different substances?
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B. Identifying the Unknowns
1. You will be given three small samples of 4 of the unknown liquids (“W, X, Y, and Z”). That is, you will have liquids in
the spot plates before you begin. DO NOT DUMP OUT!!! Your task is to determine the which of the possible 6
unknowns you have.
Before attempting to perform tests on the unknowns you should plan out a strategy! Decide on a sequence of tests
that will give you the most information in the fewest number of steps. You will not be given any extra samples, so
make sure you have an approved plan first! Collaborate with your group so everyone has a say.
2. Use the Reagents to perform a series of tests upon the 4 unknown liquids that will allow you to identify each one in the
fewest number of steps.
3. Record what tests are performed upon each unknown and what the results of those tests are.
Clean up: After all work is complete pour all liquids into designated container. Then dunk the well plate in the designated
tub of water. Then rinse well plates at sink using the sponge on a stick. WASH HANDS.
Don't remove aprons and goggles until all materials are cleaned up and put away.
Part B. Data Table
Unknown
W
Unknown
X
Unknown
Y
Unknown
Z
A. Phenolphthalein
B. Sucrose
C. Bromothymol
Blue
D. Manganese
Dioxide
E. Lead Nitrate
F. Sodium
Hydrogen
Carbonate
POSSIBLE IDENTITY of
UNKNOWNS
Part B. Identifying the Unknowns
Write a formal lab conclusion in which you:
-Describe the purpose of the experiment. (The purpose of this experiment was to determine......)
-Provide background information. What is the question to be answered? Why would someone want to know the answer
to this question? Define terms, etc.
-Briefly summarize what was done in the experiment. Briefly.... this is not a step by step procedure.
-Summarize your qualitative and/or quantitative observations.
-Interpret the results:
-Identify your four unknowns. BE SURE to INCLUDE YOUR GROUP #
-Use your observations to back up your identifications
-Explain how your findings relate to what you have learned in class about physical and chemical properties of matter?
-Relate the process used in this lab to identify unknown substances to some “real world” situations in which someone has
unknown substances that they need to identify.
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CONCLUSION *The focus of the conclusion is on Part B of the laboratory activity.
Purpose included
Purpose reflective of class content
Background information included
Background information thorough
Question included
Question appropriate for experiment (relevant to class content)
Definitions included (Physical versus Chemical properties, Homogeneous mixtures)
- Physical Properties
- Chemical Properties
- Homogeneous mixtures (solutions)
Procedure summarized (briefly)
Observations summarized *Describe in words what Part B Data Table shows about…
Unknown W
Unknown X
Unknown Y
Unknown Z
Interpret resultsGroup number identified!! ______
Identification of W
Identification of X
Identification of Y
Identification of Z
Observations to back up Identifications
Observations for W
Observations for X
Observations for Y
Observations for Z
Relate to Class (Physical versus Chemical Properties)
Relate to “Real World”
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