The Unknown Substance Lab

Purpose/Problem: The student will use chemical and physical properties to identify unknown substances.

1) Introduction: Physical properties were documented for each substance including visual description, solubility in water and density. A physical property is an observable property of a system and can be either intrinsic or extrinsic if the amount of the substance changes its properties. In addition to physical properties, the substances were evaluated using their chemical properties of reactivity with iodine and acetic acid (vinegar) and whether a precipitate formed using silver nitrate. A chemical property is a property that is observed during a chemical reaction and is a change in the substance’s internal structure. By testing and observing a substance’s physical and chemical properties and comparing it to known substances, a substance can be identified. The unknown samples in this laboratory contain only a single substance. In real life applications, an unknown sample may contain more than one major component and will likely contain minor impurities. The identification of unknown samples is a vital and important application of modern chemistry.

Materials: Solubility Station
1) Goggles
2) 5 labeled cups each containing one of the following
a. Sugar (granulated)
b. NaCl (table salt)
c. Epson salt
d. Talc
e. Corn starch
3) 5 clean test tubes
4) Water in a squirt bottle
5) Test tube stoppers to fit test tubes
6) 5 scoops

Precipitate Station
1) Goggles
2) NaCl
3) Sugar
4) Baking soda
5) Epson salt
6) Silver nitrate
7) 4 clean test tubes
8) Water
9) Test tube stoppers to fit test tubes
Materials (cont.):
Visual Properties of Matter Station
1) Goggles
2) 5 labeled cups each containing one of the following:
a. Sugar (granulated)
b. NaCl (table salt)
c. Epson salt
d. Talc
e. Corn starch
3) Hand lens
4) Black construction paper
5) 5 scoops

Reactivity Station
1) Goggles
2) 5 labeled cups each containing one of the following:
a. NaCl (table salt)
b. Epson salt
c. Talc
d. Corn starch
3) 4 scoops
4) Vinegar
5) Tincture of iodine
6) Pipettes
7) 2 reaction plates

Density Station
1) Goggles
2) Unknown metals that fit into a graduated cylinder
3) Water
4) Ruler
5) Graduated cylinder
6) Triple beam balance
7) Calculator
8) Cups to hold metal samples

Procedures: Solubility Station
1) Draw the data table to document data
2) Put on goggles
3) Add a small amount of water to a test tube
4) Add a small amount of one substance to the test tube
5) Fill the test tube ½ full of water

Procedures (cont.): Solubility Station (cont.):
6) Put stopper into the top of the test tube
7) Vigorously shake the test tube
8) Visually check to see if the substance dissolved in the water as was soluble
9) Mark data table as soluble or insoluble
10) Repeat steps for the other substance with clean test tubes
11) Clean station and wash out test tubes Precipitate Station
1) Decide how to organize your data
2) Put on goggles
3) Add a small amount of water to a test tube
4) Add a small amount of NaCl to a test tube
5) Fill the test tube ½ full of water
6) Put stopper into the top of the test tube
7) Vigorously shake the test tube
8) Take the stopper out of the test tube and add a couple of drops of silver nitrate solution
9) Observe and see if a precipitate forms
10) Repeat steps 2 to 9 with a clean test tube using sugar, baking soda and Epson salt
11) Clean up station

Visual Properties of Matter Station
1) Decide how to organize your data
2) Put on goggles
3) Put a small amount of one of the substance son a piece of black construction paper
4) Carefully look at the substance using a hand lens
5) Write a description of each substance
6) Repeat steps 3-5 with all of the substance
7) Clean up station

Reactivity Station
1) Decide how to organize your data
2) Put on goggles
3) Put a small amount of each substance in a different well of the reaction plate
4) Put a few drops of vinegar (acetic acid) on each of the substances in the