Qualitative Analysis of Household Products
(or Kitchen Qual)
Introduction
Chemists often find themselves faced with the question: "What the heck is it?"
Sometimes “it” is a reaction that has gone astray and looks vaguely like tar. Other times “it”
could be a mystery - a white powder left at the scene of a crime: sugar, talc or any variety of
illegal drugs. The criminal justice system has increasingly relied on the chemical identification
techniques. Often identification is a very long and tedious process of proving what the substance
is NOT. Clues from the area where the substance was found typically help to narrow the list.
Today you will be the investigating chemist in a perplexing mystery. You were cleaning your
basement shelves and found three unmarked bottles containing white powders. Since the
powders can't possibly be anything illegal, you look
around the shelves to see what the bottles might
Possible Unknowns
Source
Chemical
contain. You find a bucket of white chalk pieces, a
Washing
Soda
Sodium
Carbonate
- Na2CO3
box of table sugar, cornstarch, Epsom salts, Plaster of
Drain Opener
Sodium hydroxide - NaOH
Paris from an old art project, laundry detergent, drain
Plaster of Paris Calcium sulfate - CaSO4
opener, and a box of Estee fruit sugar. Since these
White chalk
Calcium carbonate - CaC03
substances are all white powders you consider some
Cornstarch
Cornstarch
Fruit sugar
Fructose - C6H1206
simple physical and chemical tests that will reveal
Table
sugar
Sucrose - C12H22011
their identity by process of elimination. Technically
Epsom salts
Magnesium Sulfate - MgSO4
speaking, you've designed a qualitative analysis
scheme. (Qualitative analysis is only concerned with
what the substance is. Quantitative analysis is concerned with determining how much of each
substance is present.) The scheme acts as a separation flow chart (see below) answering “If it
reacts like …, then it must be X” statements. Conveniently, even the reagents you use are fairly
common household products: water, vinegar, Tincture of iodine, laxative tablets, and copper test
tablets. Using these simple chemical tests, you will determine the identity of several unknown
powders.
First, you make use of the substances’ solubility in water. Most of the chemicals will
dissolve readily in water but calcium sulfate, calcium carbonate, and cornstarch are insoluble.
These three compounds can be distinguished from one another with chemical tests using iodine
and vinegar. Cornstarch will form a complex with iodine resulting in a dark blue color while
calcium sulfate and calcium carbonate are unreactive. The cornstarch, a polymer of sugar
molecules, wraps itself around I2 molecules like a constrictor wraps its prey.
Cornstarch + I2  Starch-I2 Complex (dark blue)
The other two white powders, calcium sulfate and calcium carbonate, can then be tested
with vinegar. The vinegar (~ 5% acetic acid, CH3COOH (a source of H+)) will react with the
carbonate ions to initially form carbonic acid (an acid-base neutralization reaction). The carbonic
acid is unstable and eventually decomposes to water and carbon dioxide (bubbles!).
CO32- + 2 H+  H2CO, (carbonic acid)
H2CO3  H2O + CO2 (g) (bubbles)
The next task is to differentiate the powders that are soluble in water: sodium hydroxide,
sodium carbonate, sucrose, fructose, and magnesium sulfate. We can use an acid-base indicator
(a substance that changes color depending on the pH) to determine if the unknown solutions are
acidic, neutral or basic. Common household indicators could be plants (beet juice or red
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cabbage) or laxatives! We will be using phenolphthalein, a compound once found in certain
laxative tablets. Phenolphthalein turns from colorless to pink in basic solutions. Only two of the
soluble unknowns (sodium hydroxide and sodium carbonate) form basic solutions (alkaline)
when mixed with water.
Of the last three (sucrose, fructose, and magnesium sulfate) only the magnesium sulfate
forms a white solid with drain opener (sodium hydroxide). The precipitate is the main ingredient
in Milk of Magnesia, magnesium hydroxide.
MgSO4 (aq) + 2 NaOH (aq)  Na2SO4 (aq) + Mg(OH)2 (s)
This is considered a "double replacement" reaction since all of the ions "switch partners."
Finally, copper reduction test tablets will be used to distinguish fructose from sucrose.
The tablets are used for water analysis and are available in most variety stores. Fructose has the
ability to reduce copper (II) to copper metal forming a red/brown precipitate:
Cu2+ (aq) + 2 electrons  Cu° (s).
This set of “homemade” reactions is very similar to techniques used in analytical
laboratories. The methods are very reliable and effective while the cost of the reagents is
minimal.
Experimental Procedures
You will be drawing conclusions based only on your observations. Observe Carefully!
First test the Known Samples to identify what a positive or negative result will look like. Then
conduct the same tests with your unknowns. Be careful of contamination of the samples - always
use a clean spatula when switching powders and rinse the testubes well.
A. Solubility Test
1. Obtain a test tube and put a microspatula TIP (about 1/8th teaspoon) worth of the solid
unknown in the test tube.
2. Fill the test tube about ½ full with water. Cap the test tube with a stopper and shake.
3. If the powder does not dissolve (indicated by a cloudy solution), it is insoluble - go to step B.
If the powder dissolves or begins to dissolve it is soluble -go to step D.
B. Iodine Test (Done with the insoluble powder test tube from the solubility test.)
1. Add 2-3 drops of Tincture of Iodine to the test tube from the solubility test.
2. Observe the color. (Blue = Cornstarch, Brown = CaCO3 or CaSO4)
C. Vinegar Test (Done with NEW test tube and samples.)
1. Place a spatula tip of the insoluble powder into a clean test tube.
2. Add about 2 - 3 mL of vinegar.
3. If bubbles form the solid is CaCO3. If bubbles do NOT form the solid is CaSO4.
D. Phenolphthalein Test (Done with the resulting solution from A. Solubility Test)
1. Add 3 - 5 drops of phenolphthalein to the test tubes.
2. Observe the color.
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3. A dark pink color indicates a basic solution and the powder is either NaOH or Na2CO3 - go to
step E. A colorless solution indicates a slightly acidic solution and the powder may be
Sucrose, MgSO4,or Fructose - go to step F.
E. Vinegar Test #2 (Done with NEW test tube and samples.)
1. Place a spatula tip of powder into a clean test tube.
2. Add about 2-3 mL of vinegar.
3. If bubbles form the solid is Na2CO3. If bubbles do NOT form the solid is NaOH.
F. Sodium Hydroxide Test (Done with NEW test tube and samples.)
1. Place a spatula tip of powder into a clean test tube.
2. Add about 2 - 3 mL of water.
3. Add a few drops of 0.3 M NaOH and observe.
4. If a white precipitate (cloudy solution) forms the solid is MgSO4. If the solution remains
clear, the solid is either Sucrose or Fructose - go to step G.
Copper Sulfate Test (Done with NEW test tube and samples. Increase sample size to ~1/4 tsp)
1. Add about 2-3 mL of copper sulfate solution.
2. Add approximately 10 drops of 0.3 M NaOH.
3. Warm the test tube in a hot water bath and observe. Be patient - this reaction could take
several minutes. It is helpful to run a sample of fructose at the same time as your unknown.
4. If the solid is fructose a green color will initially be observed followed by the formation of a
red precipitate. If the solid is sucrose, the solution will remain light blue.
Sample Data Table (Indicate results of tests here.)
Unk #
Solubility
Iodine
Vinegar
1
Acid/Base
Indicator
NaOH
Vinegar
2
Copper
Reduction
Product
Identity
• Adapted from: Journal of Chemical Education, Volume 68' Number 4, April 1991, pp. 328-324.
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Household Product Qualitative Analysis Scheme
Sucrose, Fructose, CaCO3, NaOH,
MgSO4, CaSO4, Na2CO3, Cornstarch
Insoluble
Soluble
Water
CaCO3, CaSO4, Cornstarch
Blue
Sucrose, Fructose, NaOH, MgSO4, Na2CO3
Brown
Pink
Iodine
Cornstarch
Phenolphthalein
Colorless
CaCO3, CaSO4
NaOH, Na2CO3
Bubbles
Sucrose, Fructose,
MgSO4
No Bubbles
Vinegar
CaCO3
CaSO4
Bubbles
No Bubbles
Vinegar
Na2CO3
NaOH
Sodium
Hydroxide
NaOH
MgSO4
Sucrose, Fructose
Red precipitate
Copper
Sulfate
Fructose
Sucrose
4
White
precipitate