Mystery Powders
Purpose
To identify eight common household chemicals by using qualitative analysis, a method of determining a
substance’s identity by subjecting it to a series of tests.
Background Information
Household
chemical
Test #2
Iodine
Cornstarch
Test #1
Solubility in
water
Insoluble
Test #3
PHTH
Test #4
Acetic acid
Test #5
NaOH
+
-
+
-
-
Chalk
Insoluble
-
-
-
-
-
Powdered
sugar
Baking
powder
Epsom salt
Insoluble
-
-
+
-
-
Insoluble
+
-
+
-
-
Soluble
-
-
-
+
-
Baking soda
Soluble
-
+
-
-
-
Sugar
Soluble
-
-
-
-
Rectangle w/
pointed ends
Table salt
Soluble
-
-
-
-
Cube-shaped
Materials
Household chemicals:
Cornstarch
White Chalk
Plaster of Paris -or- Powdered Sugar
Epsom Salt
Baking Soda
Baking Powder
Sugar
Table Salt
Reagents:
Iodine
Phenolphthalein (PHTH)
5% Acetic Acid
Sodium Hydroxide (NaOH) (0.3 M)
Test #6
Crystal shape
Safety
You will be working with unknown chemicals. Handle them carefully and never, ever taste them! If
you are unsure about any procedure, ask your instructor. Avoid spillage. Use small quantities, no
more than is required for each test. Never place unused chemicals back in their original container;
doing so can contaminate the stock material. Consult your instructor for proper disposal.
Procedure: You will be given 8 vials of different kinds of white powder. Your task is to identify these
unknowns based on their different physical and chemical properties.
Tests:
1. Solubility in Water
Place a pea-sized amount of the unknown solid in a test tube and add 5 mL of water. Swirl the
test tube to mix the contents. If it dissolves completely, there will be no crystals or powder left
in the mixture. Record what happens to each household chemical in Table 2.
2. Tincture of Iodine
NOTE! Test the unknown household chemicals that were insoluble in water only. Place a peasized amount of each household chemical in a separate well in a spot plate. Add 2 drops of
tincture of iodine to the unknown. A deep blue color forms if the substance contains starch.
3. Phenolphthalein (PHTH)
NOTE! Test the unknown household chemicals that were soluble in water only. Place 10 drops
of each dissolved unknown into a separate well of the spot plate. Add a drop of
phenolphthalein (PHTH) to the dissolved unknown and a bright pink color will result if the
solution is alkaline (pH >7).
4. Acetic Acid 5%
Test all unknown household chemicals. Place a pea-sized amount of each household chemical
in a separate well in a spot plate. Add 2 drops of acetic acid to the unknown. The formation of
bubbles is a sign of the carbonate ion, which decomposes to gaseous carbon dioxide upon
treatment with an acid.
5. Sodium Hydroxide (0.3 M)
NOTE! Test the unknown household chemicals that were soluble in water only. Place 10 drops
of each dissolved unknown into separate wells of the spot plate. Place 5 drops of NaOH onto
the dissolved unknown. A solid precipitate will form when the reagent is added if the unknown
contains magnesium sulfate.
6. Crystal Shape
NOTE! Test the unknown household chemicals that were soluble in water only. Place a peasized amount of each household chemical on a watch glass. Use a clean spatula to separate the
individual crystals. Use a hand lens (or dissecting microscope) to observe the shape of the
crystals for each unknown chemical.
INVESTIGATIVE SCIENCE LAB: MYSTERY POWDERS
Data
Unknown
number
Test #1
Solubility
Test #2
Iodine
Name_____________________
Prd____Date_______________
Test #3
PHTH
Test #4
Acetic acid
Test #5
NaOH
Test #6
Crystal shape
#1
#2
#3
#4
#5
#6
#7
#8
Analysis and Conclusions
1. Identify your unknowns.
Unknown #1 ________________________
Unknown #5 ________________________
Unknown #2 ________________________
Unknown #6 ________________________
Unknown #3 ________________________
Unknown #7 ________________________
Unknown #4 ________________________
Unknown #8 ________________________
2. Which of the tests used in this experiment measure physical properties and which measure
chemical properties? Be sure to identify all 6 tests in your answer.
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
3. Create a qualitative analysis scheme to show how the chemicals can be systematically identified.
This should be a flow chart that someone could follow to determine the identity of these 8
chemicals. (HINT: Which test should be done first, second, etc.)
Use the back of this page to show your flow chart →