What safety equipment is required before preparing luminol synthesis solutions?

Before starting, put on a lab coat, splash-proof safety glasses, and nitrile gloves. Both the hydrazine and NaOH solutions must be prepared and handled in a fume hood because the chemicals are hazardous. Hydrazine is flammable, toxic, and explosive, while NaOH is highly corrosive and can cause skin damage.

How do you prepare a 10% hydrazine solution by volume?

Measure 8.4 mL of deionized water into a 30-mL beaker. Add 1.6 mL of hydrazine hydrate to reach a total volume of 10 mL. Stir the mixture with a glass rod until well mixed, then transfer to a labeled 20-mL glass bottle and store in a flammables cabinet.

What are the steps for preparing a 2.8 to 3 M sodium hydroxide solution?

Measure 2.2 to 2.4 g of solid NaOH and add it to a 50-mL beaker. Pour 20 mL of deionized water into the beaker and stir on a stir plate until the NaOH completely dissolves. Transfer the solution to a labeled 20-mL glass bottle, cap it, and store in the appropriate cabinet.

What waste management setup is needed before starting the luminol synthesis experiment?

Reserve a separate dark room for the experiment. Prepare a container for fluorescein waste and ensure a glass waste container is available. Set out a 10% sodium hypochlorite solution and a 1 M sodium carbonate solution in the waste hood, along with a wash bottle filled with deionized water.

Which chemicals and equipment should be placed in the central fume hood?

Place triethylene glycol, the hydrazine solution, the NaOH solution, glacial acetic acid, and dimethyl sulfoxide in the central hood. Also set out a 1-mL graduated pipette and a pipette controller designated specifically for hydrazine in the same hood to prevent cross-contamination.

What glassware and equipment should be set up at each student lab station?

Each pair of students needs graduated cylinders, Erlenmeyer flasks, beakers of various sizes, test tubes, Büchner funnels, a stirring hotplate, Bunsen burner, lab stands with clamps, thermometers, spatulas, boiling chips, stirring rods, and filter adapters. Additional items include flask tongs, tweezers, pipette bulbs, and laboratory tape for labeling.

What materials should be brought to the balance area before the experiment begins?

Bring containers of 3-nitrophthalic acid, anhydrous sodium dithionite, solid potassium hydroxide, and fluorescein to the balance area. Ensure sufficient laboratory wipes, spatulas, and weighing boats are available for all students to accurately measure and handle these solid reagents during preparation.

Synthesis of Luminol

Concepts Instructor Prep Student Protocol

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Ordinarily, when reactants change to products, the difference in their energy is known as the enthalpy of the reaction, which can be either exothermic, where heat is released, or endothermic, where heat is absorbed.

In a chemiluminescent reaction, the reactants form an intermediate, which is in an electronically excited state. This intermediate is unstable. As it relaxes down to the ground state, the electrons in the intermediate releases energy in the emission of visible light rather than in the form of heat.

This phenomenon is similar to fluorescence. Recall that the electrons in a molecule occupy the ground state. When they absorb energy, such as when exposed to a certain wavelength of light, they become excited and transition to a higher, excited energy level. As the excited state relaxes back down to the ground state, the excess energy is emitted in the form of visible light.

However, it is important to distinguish between the two. The difference is how the electrons of the molecules are excited. In chemiluminescence, energy generated from a chemical reaction excites the electrons…whereas in fluorescence, the electrons are excited by direct absorption of light energy or other electromagnetic radiation. As the electrons relax down to ground state, both types of luminescence release the energy as emitted light.

Let’s take a look at an example of each. When you shine UV light on a bottle of tonic water, the electrons in quinine absorb the energy and are excited to a higher energy level. When the electrons relax, they release energy in the form of blue light.

Now, consider a glow stick, which has an outer tube containing diphenyl oxalate and a dye, and an inner tube containing hydrogen peroxide. When you bend the glow stick, the inner tube breaks, allowing the reactants to mix. The hydrogen peroxide oxidizes the diphenyl oxalate to form phenol and cyclic peroxide. The cyclic peroxide decomposes to carbon dioxide, releasing energy that excites the dye to a higher energy level. As the dye relaxes to the ground state, a photon of light is released. Here, the process is chemiluminescence because the energy provided to excite the dye comes from a chemical reaction.

In this lab, you will synthesize 3-aminophthalhydrazide, also known as luminol, by performing a series of reactions. You will then react the luminol with dimethyl sulfoxide over solid potassium hydroxide to observe its chemiluminescence.

At the end of this lab, students should know...

$$\rightleftharpoonup{xx}$$ $$\longleftharp{xx}$$, $$\longrightharp{xx}$$,

What is the lowest energy state that an electron can occupy?

The lowest energy state that an electron can occupy is the ground state.

How is an electron elevated to a higher energy level?

An electron is elevated to a higher energy level when it absorbs energy equal to the difference between the higher energy level and the lower energy level. This correlates to specific energy intervals as electrons cannot exi...

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