Time: 30 minutes

Difficulty level: 1

Grouping: single

Materials per Student:

2 cobalt glass plates Bunsen Burner Flint lighter

Ceramic plate 10 splints: 1-Li, 2-Na, 2-K, 1-Ba, 1-Ca, 1-Cu, 1-Sr, 1-Na/K 2 splints: unknown1, unknown 2

Materials - teacher use:

• 0.5 M solutions of nitrate salts
• wood splints of the cations listed

Preparation time: if the nitrate solutions are prepared, 30 to 45 minutes; if the nitrate solutions are not prepared, two hours

Preparation: Obtain ten 150 ml beakers and fill seven of them to a depth of approximately 2 cm with one of the seven nitrate solutions listed above. Label the beakers with a marker. In the eighth beaker, mix equal amounts of sodium and potassium nitrate solutions. In the ninth and tenth beakers, mix equal amounts of the nitrates you wish to use as unknowns. Choose unknowns that have distinct color differences, such as lithium and copper. Place the numher of wood splints needed in the nitrate solutions (you will need two to four treated splints for each student). Allow the splints to soak for two to four hours in the nitrate solution. Remove the splints and label the dry ends just prior to use. The splints should be damp in order to prevent them from burning.

Background: This variation of the traditional flame test avoids the problems of contamination, waste disposal, and use of concentrated acids.

Safety: Use caution when igniting the Bunsen burner. Wet the wood splints before disposing of them in the nonhazardous waste container.

Disposal: Collect the unused nitrate solutions for future use in this experiment.

Pitfalls: Students may have difficulty distinguishing the calcium and strontium color differences.

Typical results: Typical student results are shown in the model data table.

Time: 60 minutes

Difficulty level: 3

Grouping: pairs

Materials per Pair

crucible and cover Bunsen Burner triangle pipe and stem iron ring electronic or centigram balance

Ceramic plate crucible tongs ring stand 4g magnesium sulfate

Materials per class: 4 centigram (or 2 electronic) balances

Preparation time: If all the equipment is available, no preparation is required.

Background: This experiment is designed to replace a similar experiment using barium chloride. Barium chloride is highly toxic and creates a disposal problem. Magnesium sulfate is essentially nonhazardous and can be flushed down the drain. Review and demonstrate the proper technique for transferring a crucible and cover and for heating a crucible. The cover must be placed slightly ajar when heating the crucible. Keep the cover on the crucible when it is being cooled to avoid mass transfer. If the lab is split over two days, place the crucibles in a desiccator.
Heat the crucible gently during the first five minutes. A crackling sound indicates the heat is too strong. Be sure that the students adjust their burners to produce a blue flame.
Three heatings may be required to completely dehydrate the magnesium sulfate. Depending on the students' skill level, you may want to provide additional information for the analysis of the data.

Safety: Students should handle the crucible and cover only with crucible tongs. A frequent cause of burns is touching hot crucibles, iron rings, crucible covers, and pipe stems.
Review the procedure for evaluating the temperature of a crucible (Fig. T17, p.10 of student book). Crucibles and covers are expensive and break easily. Have students transport the crucible and cover on a ceramic plate.

Disposal: Flush the magnesium sulfate down the drain or place it in the nonhazardous waste container.

Pitfalls: Intense heating may result in rapid evolution of water vapor, causing the crucible cover to fall off and magnesium sulfate to be lost. Improper technique in handling the crucible and cover may result in breakage.

Typical results: Student values should be within 5 percent of the accepted value of 51.2 percent. Experimental error is comparable to experiments using barium chloride. A typical student outcome is shown in the model data and calculations tables.

Calculations:

• Step 1: 42.94g - 38.63g = 4.31g
• Step 2: 40.73 g - 38.63 g = 2.10 g
• Step 3: 4.31 g - 2.l0 g = 2.21g
• Step 4: 2.21 g/4.31 g x 100% = 51.3%
• Step 5: Ea = O-A
  = 51.3% - 51.1%
  = 0.2%
• Step 6: Er = Ea/A x 100%
  = 0.2%/51.1% x 100%
  = 0.4%

Time: Procedure: 30-40 minutes; Analysis (equations): 30 minutes

Difficulty level: 2

Grouping: single

Materials

96-well plate 6 prefilled, labeled pipets containing the following: 0.1 M solutions: silver nitrate, barium nitrate cobalt(II) nitrate, copper(II) nitrate, and lead(II) nitrate

8 prefilled, labeled pipets containing the following: 0.1 M solutions:  sodium iodide, sodium carbonate, sodium oxalate,potassium ferricyanide, sodium bicarbonate, sodium phosphate, sodium sulfate, and sodium silicate pipet rack

Preparation time: One to two hours will be required to prepare the prefilled pipets.

Preparation: Prepare the pipets by filling labeled weighing boats with the 14 solutions listed in the materials list. The instructor should fill the pipets. Six to eight pipets can be filled simultaneously. A set of pipets can be used for ten or more lab experiments. This procedure prevents solution contamination and reduces lab time.

Background: This is a colorful display of double replacement reactions that significantly reduces hazardous waste generation.

Safety: Students should wear chemical splash goggles, aprons, and gloves. The 0.1 M solutions of nitrates are weak oxidizers. The silver, barium, lead, and cobalt ions are toxic.

Disposal: Have students place the contents of the well plates in a plastic tote tray labeled "hazardous waste." At the end of each period pour the waste into a labeled waste container. The label should read: "hazardous waste: nitrates and reaction products of: Ag⁺, Ba⁺², Co⁺², Cu⁺³, Fe⁺³, Pb⁺², Na⁺, K⁺, NO₃^-, I^-, C0₃^-2, C₂0₄^-2, Fe(Cn)₆^-3, HCO₃^-, PO₄^-2, SiO₃^-, S0₄^-2."

Pitfalls: The greatest source of error is failure to place the reagents in the proper well.

Typical results: A typical data table is shown below.