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Exercise 3:
Identifying an Unknown
Introduction
Making, recording and interpreting data is the cornerstone of all science. Chemistry is
centered on making observations about the chemical and physical properties of matter. Physical
properties are characteristics of a substance that can change without the substance changing into
a different substance. Chemical properties are characteristics of a substance that result in the
original substance changing into a different substance(s). In this experiment you will observe
physical properties (phase, density, solubility/miscibility) of two unknowns, one a solid, the
other a liquid. On the basis of your observations and your interpretation of the data, you will
identify those two unknowns.
In one part of the experiment will observe the solubility (if your unknown is a solid) or
the miscibility (if your unknown is a liquid) of your unknown is several solvents. If the
unknown solid dissolves in the solvent, the solid is said to be soluble. If the solid does not
dissolve in the solvent, the unknown solid is said to be insoluble. If the unknown liquid mixes
completely with the solvent, the unknown liquid is said to be miscible. If the unknown liquid
does not mix with the solvent, the unknown liquid is said to be immiscible. Immiscible mixtures
of liquids are distinguishable by the clear separation of the two liquid layers (like oil and water).
There are varying degrees of solubility and miscibility, but they will not be covered here. The
solvents you will use to determine the solubility/miscibility of your unknown are distilled water,
and ethyl alcohol.
In the second part of the experiment, you will calculate the density of your unknowns
using the values of several measurements you have made. The density of the substance is
determined by dividing the mass of the substance by the volume of the substance:
Density 
mass of substance
volume of substance
Determining the density of the liquid is straight forward. The procedures for measuring
the mass and volume of a liquid are listed below. Determining the mass of a solid is also equally
straightforward. Determining the volume of a solid requires caution. In order to use the
displacement method listed below, two things must be true about the solid and liquid. First, the
solid must not float. If the solid floats on the unknown liquid, the displacement procedure cannot
be used. Second, the solid must not be soluble in the liquid. Therefore, you must choose a liquid
for use in the displacement procedure that does not dissolve your solid. When your unknown
solid is placed in a graduated cylinder partially filled with the liquid that meets the two criteria
above, the apparent increase in the liquid’s volume is the volume of the object.
Procedures
Part A. Solubility of Unknown Solid
1. Clean and dry four small test tubes.
2. Using two of the clean test tubes, place 20 drops of water into one test tube and 20 drops of
ethyl alcohol into a second test tube
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3. Into test tube with filled with water, add 1-2 grains of your unknown solid. Add 1-2 grains of
your unknown solid into the test tube filled with ethyl alcohol.
4. Mix the test tubes using your stir rod. Wash and dry the stir rod between uses. Record your
observations in the Data Table 1. Write “sol” to indicate soluble and “ins” to indicate
insoluble.
Part B. Miscibility of Unknown Liquid
1. Using the two remaining clean test tubes, place 20 drops of water into one test tube, 20 drops
of ethyl alcohol into the other test tube.
2. Into test tube with filled with water, add 20 drops of your unknown liquid. Add 20 drops of
your unknown liquid into the test tube filled with ethyl alcohol.
3. Mix the test tubes using your stir rod. Wash and dry the stir rod between uses. Record your
observations in Data Table 1. Write “mis” to indicate miscible and “imm“ to indicate
immiscible.
Part C. Density of the Solid Unknown
1. Determine which of the two liquids to use for your density determination (determined in part
A) and record in Data Table 2 (1).
2. Add 5-6 mL of liquid to your 10 mL graduated cylinder. Read the volume to 0.01 mL and
record, with units, in Data Table 2 (5).
3. Weigh the graduated cylinder (with liquid) to the nearest 0.01 g and record the mass, with
units, in Data Table 2 (2).
4. To the graduate cylinder with liquid, add enough unknown solid to increase the total volume
by 3-4 mL. Be sure not to splash out any of the liquid when adding the unknown solid and
make certain the level of the liquid inside the graduated cylinder does not go above the 10
mL mark. Read the new volume to 0.1 mL and record, with units in Data Table 2 (6).
5. Find the mass graduated cylinder and its contents to the nearest 0.01 g and record, with units,
the mass in Data Table 2 (3).
6. Complete Data Table 2.
Part D. Density of Unknown Liquid
1. Clean and dry your 10-mL graduated cylinder.
2. Find the mass of your graduated cylinder to the nearest 0.01 g and record the mass, with units
in Data Table 3 (1).
3. Add between 7 to 10 mL of the unknown liquid to the cylinder. Read the volume to 0.01 mL
and record, with units, in Data Table 3 (4).
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Table of Unknown Liquids and Solids.
Substance
Phase
Density
(g/mL)
Water
Ethyl Alcohol
Acetic Acid
Liquid
1.05
Miscible
Miscible
Ammonium sulfate
Solid
1.77
Soluble
Insoluble
Benzoic Acid
Solid
1.27
Insoluble
Soluble
Calcium carbonate
Solid
2.83
Insoluble
Insoluble
Cyclohexane
Liquid
0.78
Immiscible
Miscible
Ethylene Glycol
Liquid
1.11
Miscible
Miscible
Glycerol
Liquid
1.26
Miscible
Miscible
Heptane
Liquid
0.68
Immiscible
Immiscible
Hexane
Liquid
0.66
Immiscible
Miscible
Methanol
Liquid
0.79
Miscible
Miscible
Potassium chloride
Solid
1.99
Soluble
Insoluble
Potassium nitrate
Solid
2.11
Soluble
Insoluble
Sodium sulfate
Solid
2.70
Soluble
Insoluble
Water
Liquid
0.99
Miscible
Miscible
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Data Sheet for Exercise 3:
Identifying an Unknown
Data Table 1. Solubility and Miscibility Data Table
Solid Unknown Letter
Water
Ethyl Alcohol
Water
Ethyl Alcohol
_____
Liquid Unknown Number
_____
Data Table 2. Density of Unknown Solid
1. Liquid used for density determination
________________
2. Mass of cylinder + liquid
________________
3. Mass of cylinder + liquid + unknown solid
________________
4. Mass of unknown solid
________________
5. Volume of liquid in cylinder
________________
6. Volume of liquid + unknown solid
________________
7. Volume of unknown solid
________________
8. Density of unknown solid
________________
Data Table 3. Densities of Unknown Liquid
1. Mass of the cylinder
________________
2. Mass of the cylinder + unknown liquid
________________
3. Mass of the unknown liquid
________________
4. Volume of the unknown liquid
________________
5. Density of unknown liquid
________________
Based on the phase, solubility and density, the unknown solid is ______________________
Based on the phase, miscibility and density, the unknown liquid is _____________________