Qualitative Analysis of Household Compounds

Sue Magrames and Matt Spreadbury-Oak Forest High School

1-708-687-0500 ext. 3712

Goal: To use simple chemical and physical tests to correctly identify seven white solid compounds commonly found in the home. The solids will be chosen from the following list:

Compounds used as unknowns / Source
sodium chloride / table salt (uniodized))
sodium bicarbonate / baking soda
sodium hydroxide / drain opener (lye)
calcium carbonate / chalk
calcium sulfate / plaster of paris
starch / cornstarch
fructose / fruit sugar
sucrose / table sugar
magnesium sulfate / Epsom salts
Test reagents / Quantity provided
phenolphthalein extracted from laxative tablets / about 3 mL
iodine (tincture) / about 3 mL
vinegar / about 10 mL
distilled or deionized water / about 200 mL
CuSO4-NaOH-Na2CO3 (Clinitest urine sugar test tablets) / 1 tablet, broken
Na2CO3 (washing soda) / about 2 grams

Equipment provided

spot plate or well plate glass rod or toothpicks for stirring

wash bottle w/distilled water scoopula or spatula

conductivity tester (9v LED) dropper

STUDENTS MUST PROVIDE THEIR OWN SAFETY GLASSES!

General rules for this event:

1. Students will work as individuals.

2. Students must wear safety glasses and follow all standard safety practices. Taste-testing is

specifically prohibited.

3. Each student will receive about 3 grams of each unknown and the listed quantities of the

test reagents. These will not be refilled.

4. Each student may bring in one 4x6" note card with prepared notes/procedures. No other

notes or references are allowed. Calculators are neither needed nor permitted.

Score will be the number of unknowns correctly identified. Time will be used as a tie-breaker.

Background information

An article in the Journal of Chemical Education (Qualititative Analysis of Eleven Household Compounds, Solomon, JChEd 68:328, April 1991) provides the basis for this experiment (but a number of alterations have been made). Analytical tests include solubility in water, iodine test for starch, acid test for carbonate, precipitation reactions, copper(II) reduction of monosaccharides, phenolphthalein for base.

Significant changes from the cited procedure are:

1. Students will not have to prepare any reagents. All will be in ready-to-use form.

2. Students will use spot plates or well plates for testing.

3. Conductivity testers are used for the final test to distinguish salt from sugar.

4. The test for MgSO4 is changed from that in the above Journal article. Addition of

Na2CO3 produces insoluble MgCO3. This replaces formation of Mg(OH)2 by addition of

NaOH.

5. Students may modify the procedure if desired, but must follow usual safety practices

and use only the materials provided.

General procedure:

1. Test solid for solubility. Use several drops of water and a very small sample of solid.

2. Iodine test for starch: Add 1 drop of tincture of iodine to any insoluble sample in water.

Dark blue/black color indicates presence of starch.

4. Phenolphthalein test for NaOH: Add 1 drop phenolphalein to the sample solution. Bright

pink/red color is positive for NaOH. [Lighter pink color may be observed with NaHCO3.]

5. Sodium carbonate test for MgSO4: Add a few grains of Na2CO3 to the sample solution.

White precipitate is positive for magnesium sulfate. (This is a change from the JchEd

article--solutions of NaOH will not be provided.)

6. Vinegar test for NaHCO3 and CaCO3: Combine a few drops of vinegar with a small amount

of unknown. The evolution of CO2 indicates the presence of the carbonate or bicarbonate.

7. CuSO4 test for reducing sugar: Add about ¼ of a test tablet to the sample solution. A

red/yellow color indicates the reduction of Cu2+ by fructose.

8. Conductivity test for NaCl: Put a small amount of sample solution in a well and test. (NaCl

is an electrolyte.)

Analytical Scheme

NaCl, NaHCO3, CaSO4, NaOH, MgSO4, CaCO3, Cornstarch, Sucrose, Fructose

Water

Insoluble Soluble

CaSO4, Cornstarch, CaCO3 / NaCl, NaHCO3, NaOH, MgSO4, Sucrose, Fructose

Iodine Phenolphthalein

Brown Blue Colorless Pink

CaSO4, CaCO3 / Cornstarch / NaCl, MgSO4, Sucrose, Fructose / NaOH (dark) NaHCO3 (light)

Vinegar Na2CO3 Vinegar

Bubbles No change Bubbles None

CaCO3 / CaSO4 / NaHCO3 / NaOH

No reaction White ppt.

NaCl, Sucrose, Fructose / MgSO4

CuSO4 tabs

Red/yellow ppt. No reaction

Fructose / NaCl, Sucrose

Conductivity

Electrolyte Nonelectrolyte

NaCl / Sucrose

Qualitative Analysis

Name______

School______

Session______Time______

***SET NUMBER______

***OMISSION OF SET NUMBER RESULTS IN DISQUALIFICATION***

Match the numbered unknowns with the lettered compounds listed at right. Write the correct letter for each sample:

1. ______A. calcium carbonate

2. ______B. calcium sulfate

3. ______C. fructose

4. ______D. magnesium sulfate

5. ______E. sodium bicarbonate

6. ______F. sodium chloride

7. ______G. sodium hydroxide

H. starch

I. sucrose

Number correct______

Place______