MY PBL PROJECT

Materials

Procedures

• 1. Place five Petri dishes in a row in front of your class.

  2. Add about 5–7 g of sodium chloride to one Petri dish. Repeat this step, adding 5–7 g each of the other four metal chlorides to separate Petri dishes.

  3. Use a Beral pipet to add 7–10 mL of methyl alcohol into each Petri dish.

  4. Place the cap on the methyl alcohol bottle and remove the bottle from the demonstration area!

  5. Turn off the lights, light the alcohol/salt mixture in each dish, and observe the flame test colors.

  6. Extinguish the flames with the Petri dish covers or with 600-mL beakers.

Scientific Principle

• Emission spectra-The frequencies of light that an atom can emit are dependent on states the electrons can be in. A spectrum is formed that contains only a few colors at specific wavelengths, including the colors seen in the original flame.

• The visible region of the spectrum is that which is visible to the human eye (400–700 nm)

• Line spectrum- due to electrons in different excited states returning to lower energy ground states. Since each element has a specific group of electrons and energy levels, the wavelengths given off by the falling electrons can be used to identify an element.

• • Copper(II) chloride, CuCl₂, 5 g

  • Lithium chloride, LiCl, 5 g

  • Methyl alcohol, CH₃OH, 30 mL

  • Potassium chloride, KCl, 5 g

  • Sodium chloride, NaCl, 5 g

  • Petri dishes, borosilicate glass, Pyrex®, 5

  • Strontium chloride, SrCl₂ + 6H₂O, 5 g

  • Beaker, 600-mL

  • Butane or Piezo safety lighter

  • Safety shield (optional)

Safety Precautions

• • Use only borosilicate glass, Petri dishes. Do not use watch glasses—the methyl alcohol can easily spill out and spread the fire. Inspect the Petri dish and do not use if the Petri dish has any cracks or chips.

  • Never add additional methyl alcohol to the Petri dish after starting or performing the demonstration. Once the first Petri dish containing methyl alcohol has been lit, never add more methyl alcohol to any of the Petri dishes since you now have an ignition source. Methyl alcohol vapors can travel very quickly, ignite, and quickly flash back to the methyl alcohol bottle.

  • Perform the demonstration in a well-ventilated area. If the laboratory is not well-ventilated and the methyl alcohol sits in the Petri dish for a few minutes, methyl alcohol vapors can accumulate and lead to a small flash fire. It is best to add the methyl alcohol, cap the methyl alcohol container, remove the methyl alcohol container from the area, and then light the Petri dishes.

  • Do not immediately repeat the experiment. Never add additional methyl alcohol to a Petri dish until it has completely cooled to room temperature. The heat from the Petri dish or salts can ignite the methyl alcohol.