SIX SOLUTIONS
Introduction:
You will receive six chemicals to study: aqueous silver nitrate; aqueous sodium chloride; aqueous
sodium carbonate; aqueous nitric acid; aqueous sodium bromide; and water. After studying the
reactions of known samples, you will have an opportunity to analyze an unknown.
Safety:
Wear eye protection at all times. Concentrated nitric acid is corrosive to flesh and causes severe
burns. Solutions of nitric acid stain flesh and damage clothing. Solutions of silver nitrate are toxic
and stain flesh and clothing. Avoid contact with silver nitrate and nitric acid. Wash immediately
with water if contact occurs. Do not ingest chemicals
Procedure:
Chemicals will be mixed systematically, two at a time, to discover the behavior of each combination.
The chemicals may be mixed either in a 96-well plate or as puddles on an acetate sheet.
To remove a sample from a pipet storage device, hold the tip of the pulled pipet inside the top of a
well or above an acetate sheet, making sure not to contaminate the pipet by touching the tip to the
well, sheet, or drops of other chemicals. Squeeze very gently. Individual drops will emerge.
Use a toothpick to mix different chemicals.
96-well plates are labeled. Rows are designated with letters. Columns are designated with numbers.
Each well's coordinates are embossed on the bottom of the plate; it is difficult to read. When using
acetate sheets, it is best to make a labeled grid on a piece of white paper, then paper clip the acetate
sheet to the paper and place the drops inside the appropriate boxes, just as you would with the
labeled wells.
Compound
AgNO 3
NaCl
Na2 CO 3
HNO 3
NaBr
H2O
NaBr
HNO 3
Na2 CO 3
NaCl
Since order of addition doesn't matter in this experiment, and adding a chemical to itself rarely gives
any useful information, a smaller number of combinations may be used, as shown in the diagram.
If you are using a 96-well plate, fill it with tap water, invert, and "flick" at the sink to clean. Use a
cotton swab to scrub residue from the walls and bottoms of the wells. If, instead, you are using
acetate sheets, simply rinse off the sheet under running water and wipe with a paper towel.
Your task comes in two parts. In the first part you must combine all of the solutions two-at-a-time to
discover which give detectable reactions. You must decide how to organize the experiment, which
observations are important, and how to record your data.
The second part of the experiment is to work on unknowns. First you must create the unknowns.
Study the unknowns. Mix the chemicals two-at-a-time making careful observations. Based upon
these observations and the knowledge you have from your earlier studies of the knowns, decide the
relationship between the number that was arbitrarily assigned and the identity of the chemical. Write
down an assignment for each unknown. When you are confident that you have correctly identified
all of the chemicals, remove the electrician's tape and check your answers. Repeat the experiment if
you have made any errors.
Questions:
1.Write a chemical equation for each combination that reacts.
2. List the identity of each unknown.
3. Explain your reasoning behind the identifications in number 2.
Description:
The students will receive six chemicals to study: aqueous silver nitrate; aqueous sodium chloride;
aqueous sodium carbonate; aqueous nitric acid; aqueous sodium bromide; and water.
After studying the reactions of known samples, students will have an opportunity to analyze an
unknown.
Lab Hints:
Acetate sheets may be used in place of 96-well plates. Laminates in which a paper sheet of a matrix
with some light and dark areas has been laminated serves the purpose well. The long term suitability
of the laminates is not proven at this time.
Materials (per student):
Chemicals stored in pipet-storage devices
0.2 M silver nitrate (6.5 g AgNO3 / 200 mL solution)
0.2 M sodium chloride (2.3 g NaCl/ 200 mL solution)
0.2 M sodium carbonate (4.2 g Na2CO3 / 200 mL solution)
0.2 M nitric acid (2.5 mL concentrate HNO3 / 200 mL solution)
0.2 M sodium bromide (4.0 g NaBr / 200 mL solution)
distilled water
96-well plate or acetate sheet
5 toothpicks
2 cotton swabs
12" black vinyl electrician's tape
6" masking tape