luminol experiment lab report

Experimental Techniques

If your school has palm-top computers with scientific interfaces then this will make your job a lot easier. For my project I was able to create a basic light detector by using an LDR (light dependant resistor) connected through a support system to a palm-top which could be adjusted to take and automatically log measurements of light intensity over a set period and with set intervals. After calibrating the LDR with a light source of known intensity, I was able to set-up the equipment, press “go” and after thirty seconds I had more than 250 sets of data in a spreadsheet.

It should be noted that often, an increase in rate will compromise total light yielded (light sticks can glow for weeks in a freezer).

Without this equipment a more traditional (but less accurate) approach can be adopted by laying out a long thin piece of transparent tubing around a clamp stand with a funnel at the top through which to pour your reactants. An estimation of relative rate can be made by noting the time or point on the tube at which luminescence stops.

Tip : Always try to secure your glassware and spend a bit of extra time putting items necessary for the reaction in easily accessible places because you are likely to spend a lot of time fumbling around in the dark.

Variables to Explore

Concentration We’ll start with the obvious ones, this is GCSE stuff. The more concentrated your solution is, the more light it will produce (unless of course there is a significant amount of colour from your reactants – in this case there will be an awkward relationship as concentration increases because your solution will begin to absorb its own light). This is obviously due to the fact that there are more molecules reacting, producing more light. One thing you might want to explore is the Beer-Lambert Law. This should be in textbooks but will allow you to make a quantified analysis of increasing light production.

Temperature Temperature is another obvious one. Higher temperature means a higher rate. For “mickey mouse” points you could show that the reaction is less bright in an ice bath than in a warm water bath. Note that not all chemiluminescent reactions get faster with increasing temperature (do chemistry at university to find out about this one).

The rate of the reaction of luminol is a little more complicated than you will have come across in school but I will attempt to explain it using some interesting concepts. Talking about the Arrhenius rate law will no-doubt get you points so do this and you should be able to get a good mark. For an excellent mark, read on.

The Steady-State Approximation The luminol reaction could be seen as being made up of two steps; the attack by base and then the subsequent oxidation (the last step is so fast that it will have no effect on the overall rate). To explain the diagram, the first step is in equilibrium so will have a forward and reverse rate constant, k 1 and k -1 . The second step has rate constant, k 2 .

The overall rate law is going to be a combination of both these steps but because there is a lot more water around in an aqueous solution than there is oxygen, k -1 will be much larger than k 2 . (A) is going to be an awkward thing to measure, it will proceed to products very quickly and therefore be at low concentrations and very short lived.

The steady-state approximation allows us to deal with this problem by assuming that the concentration of (A) will be low and steady (or in other words d[(A)]/dt will be approximately zero).

Writing the rate law in terms of (A) (d[(A)]/dt) allows us to remove it by saying that this is zero.

The rate law is d[(A)]/dt = k 1 [luminol][NaOH] 2 – k -1 [(A)][H 2 O] 2 = 0

Which becomes (remembering that water has unit activity (ideal concentration)),

k 1 [luminol][NaOH] 2 = k -1 [(A)]

(White et al have shown that the reaction is strictly pseudo first order (reaction behaves as first order although may not necessarily be first order, this might occur when one rate constant is much smaller than another and becomes negligible in comparison) where k' = 2.5 x 10 -2 sec -1 )

I found chemiluminescence to only appear at pHs higher than 8-9 and found luminol to only dissolve easily at approximately 11.

Dyniewski et al have shown that three separate pKa values exist at pH = 1.5, 8, and 11.8 corresponding to each of the three hydrogen atoms able to dissociate.

Due to this, complete dissociation wil occur at around pH 11.8 making the luminol fully ionised and the most soluble in aqueous solvent. Below pH 8, the dissociation necessary for the reaction to proceed cannot occur and so there is no luminescence.

The pH chemistry of luminol chemiluminescence is very complicated and I failed to get any kind of conclusive data from my own experiments.

Addition / Concentration of Catalyst

Other Ideas

For a further investigation into luminol, try investigating electrochemiluminescence.

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Synthesis of Luminol

Instructor prep, student protocol.

• Synthesis of 3-Nitrophthalhydrazide
• Synthesis of 3-Aminopthalhydrazide
• Chemiluminescence of Fluorescence

Source: Lara Al Hariri and Ahmed Basabrain at the University of Massachusetts Amherst, MA, USA

In this lab, you'll synthesize 3-aminophthalhydrazide, which is also called luminol, in a 2-step process. The first step is a condensation reaction between 3-nitrophthalic acid and hydrazine.

During this step, the carboxylic acid groups are substituted with NH groups to produce 3-nitrophthalhydrazide and two water molecules. You must work in a fume hood throughout this lab because the reactions produce toxic vapors and gases.

• Before you get started, put on a lab coat, splash-proof safety glasses, and nitrile gloves. Note: Hydrazine is highly toxic and flammable, so avoid touching it and keep anything containing hydrazine closed or covered when you transport it between fume hoods.
• Now measure 10 mL of deionized water and pour it into a 25-mL Erlenmeyer flask. Clamp the flask on a hot plate and place a thermometer in it.
• Then, start heating the water. You'll want the temperature of the water to be 80 °C, so set the hot plate setting to slightly higher.
• While it heats, set up a Bunsen burner under a clamp fixed on a lab stand.
• Obtain a 25-mL test tube and adjust the clamp so that it will hold the test tube about 5 – 7 cm above the flame. Then, remove the test tube and place it in a 400-mL beaker.
• Once the water reaches 80 °C, adjust the heat setting to keep the temperature stable.
• Then, weigh 0.6 g of 3-nitrophthalic acid in a tared weighing boat. Pour the 3-nitrophthalic acid into your test tube. Then, bring the test tube and a test tube stopper to the solvent hood.
• Use the provided volumetric pipette to carefully measure 0.9 mL of the 10% v/v hydrazine solution and transfer it to the test tube. Remember to cap the bottle of hydrazine solution and stopper your test tube before you return to your hood.
• Clamp the test tube over the Bunsen burner and remove the stopper. Then, pour ~2 mL of triethylene glycol into a graduated cylinder and set it out of the way in your hood.
• Now, add 2 or 3 boiling chips to the test tube. Place a high-temperature thermometer in the test tube and ignite the Bunsen burner. Heat the mixture with a medium flame until the 3-nitrophthalic acid dissolves.
• Then, add the triethylene glycol and increase the heat of the flame. Note: Once the water from the hydrazine solution has boiled off, the temperature will continue increasing.
• When the reaction mixture reaches 210 °C, turn down the heat and keep the mixture between 210 °C and 220 °C for 3 – 4 min.
• Then, extinguish the flame and wait for the mixture to cool to 100 °C.
• Turn off the hotplate, remove the thermometer, and unclamp the flask. Use tongs to hold the flask and measure 8 mL of hot water with the graduated cylinder. Pour this hot water into the test tube and remove the thermometer.
• Obtain a piece of plastic paraffin film and cover the mouth of the test tube. Then, use tongs to transfer the test tube to the holding beaker.
• At a lab sink, hold the test tube under running tap water to cool it, being careful not to let water into it.
• Then, dry the outside of the tube and bring it back to your hood. Clamp the tube upright and remove the paraffin film. Let the yellow 3-nitrophthalhydrazide precipitate in the tube for 15 min.
• While you wait, add ~10 mL of deionized water to a 25-mL Erlenmeyer flask. Prepare an ice bath in a 250-mL beaker and start chilling the water in it.
• Then, set up for vacuum filtration using a 250-mL filter flask, a Büchner funnel, and a piece of circular filter paper.
• Once the product has precipitated for at least 15 min, obtain a Pasteur pipette and wet the filter paper with a few drops of cold water.
• Then, turn on the vacuum and pour the contents of the test tube into the Büchner funnel. Rinse the remaining solid into the funnel with 1 – 2 mL of cold water.
• Remove the boiling chips with tweezers and rinse them with a few drops of cold water to finish collecting the product.
• Turn off the vacuum pump once no more liquid is dripping into the flask from the funnel.

In the second step of the luminol synthesis, you'll reduce the nitro group of 3-nitrophthalhydrazide using sodium dithionite in a basic solution of NaOH. This will produce 3-aminophthalhydrazide dianion.

After the reduction, you'll add acetic acid to protonate the dianion, forming luminol. Sodium dithionite is highly reactive and degrades quickly, so you'll use a slight excess of it. After the reduction, you'll protonate the luminol dianion to decrease its solubility in water. Lastly, you'll precipitate and collect luminol as a yellow solid.

• Place a clean 25-mL test tube in a beaker and use a clean spatula to transfer your 3-nitrophthalhydrazide to the test tube.
• Set the Büchner funnel aside and clamp the test tube over the Bunsen burner. Leave the filter flask in place for later.
• Now, use a 10-mL graduated cylinder to obtain 3 mL of approximately 3 M NaOH. Pour the sodium hydroxide solution into the test tube and stir the mixture with a glass rod until the 3-nitrophthalhydrazide dissolves.
• Now, weigh 2 g of sodium dithionite in a tared weighing boat and add it to the test tube. Obtain 3 mL of deionized water and pour it into the tube.
• Stir the mixture well to dissolve as much of the solid as you can. Then, add a few clean boiling chips to the test tube and ignite the Bunsen burner.
• Heat the mixture to boiling over a medium flame and then let it boil for 5 min.
• While you wait, measure 1.5 mL of glacial acetic acid and bring it to your hood.
• Once the reaction mixture has boiled for 5 min, shut off the Bunsen burner and add the acetic acid to the tube. Let the mixture cool to room temperature, which usually takes 10 –15 minutes. Meanwhile, prepare an ice bath in a 600-mL beaker.
• Once the mixture has cooled, place it in the ice bath and wait 15 min for the luminol to precipitate.
• Reassemble the vacuum filtration setup using a clean Büchner funnel and a new piece of filter paper, and start cooling another 10 mL of deionized water in an ice bath.
• Once the luminol has been in the ice bath for at least 15 min, wet the filter paper with cold water. Then, collect the solid luminol by vacuum filtration.
• Retrieve the boiling chips and rinse the luminol with more cold water. Once liquid stops dripping from the funnel, turn off the vacuum and transfer the luminol to a 50-mL beaker.
• Now, prepare the combined filtrate for disposal. First, label a 250-mL beaker ‘hydrazine and dithionite waste’. Transfer the filtrate to the beaker and rinse the flask with deionized water to remove residual hydrazine and dithionite.
• Next, dilute the filtrate with 10 mL of deionized water. Then, measure 10 mL of 1 M sodium carbonate and add it to the combined filtrates.
• Bring a 50-mL graduated cylinder to the waste hood. Measure 40 mL of 10% sodium hypochlorite and pour it into the filtrate mixture. Place the beaker on the hot plate, add a stir bar, and secure a thermometer in the beaker.
• Heat the mixture to 50 °C while stirring. The mixture must stay at 50 °C for 1 h to oxidize leftover hydrazine and dithionite, so make sure that the temperature is stable and set a timer for 1 h before starting the last part of the lab.

For the last part of the lab, you'll mix some of the luminol you made with dimethyl sulfoxide over solid potassium hydroxide. The hydroxyl ions deprotonate the two amine groups. Then, ambient oxygen oxidizes the luminol dianion to 3-aminophthalate, or 3-APA, in an excited state. This unstable complex will quickly relax to the ground state, releasing energy as visible light. Since the excited 3-APA was the product of a chemical reaction, the emitted light is called chemiluminescence.

Once you have seen the chemiluminescence from the oxidation reaction, you'll add fluorescein, a fluorescent molecule, to the mixture. Some excited 3-APA will transfer energy directly to fluorescein rather than emitting light, giving you a solution with two different light-emitting compounds.

• Now, measure about 0.2 g of the luminol you made and place it in a 15-mL Erlenmeyer flask. It's OK if the solid is still damp.
• Obtain 5 – 7 pellets of potassium hydroxide and pour them into the flask. Then, bring the flask, a stopper, and a 10-mL graduated cylinder to the solvent hood.
• Measure 2 mL of DMSO, add it to the flask, and stopper it. Put the graduated cylinder in your fume hood and bring the flask to a dark room.
• Shake the stoppered flask vigorously until you see chemiluminescence and then put the flask down. The light fades quickly because both the oxidation and relaxation are fast processes.
• Shake the flask and let the light fade 6 – 10 more times without opening the flask. The light will be progressively dimmer as the oxygen in the flask is consumed. Note: To make it brighter, leave the flask open in your fume hood for a minute to replenish the oxygen.
• Close the flask, return to the dark room, and shake the flask again to see the effect.
• Now, measure 0.2 g of fluorescein dye and add it to your flask. Stopper the flask and return to the dark room. Shake the flask vigorously until the mixture is glowing brightly and then set it down to observe the difference in color from luminol alone.
• When you're finished, check on the filtrate. Once it has been at 50 °C for at least 1 h, turn off the hotplate and wait for the beaker to cool to room temperature.
• Then, add about 10 mL of tap water to the filtrate and flush it down the drain.
• Dispose of the remaining chemical and glass waste in the appropriate containers, clean your glassware and tools, and put away your lab equipment.

Under your oxidation reaction conditions, excited 3-APA emits blue-green light in a broad range around 500 nm when it relaxes, and fluorescein is excited by absorbing light at 480 – 490 nm and 515 – 525 nm.

When you add fluorescein to the luminol oxidation reaction mixture, excited 3-APA can transfer energy that fluorescein would absorb as light directly to a nearby fluorescein molecule in a special interaction called nonradiative energy transfer. The resulting excited fluorescein emits yellow-green light when it relaxes.

Excited 3-APA is highly unstable, so if no fluorescein is close enough for nonradiative energy transfer, it will relax by emitting light as usual. Thus, a spectrum of your final glowing mixture would show contributions from both blue-green and yellow-green light.

How to Make Luminol Glow: Glowing Reaction Activity

Luminol is a chemical that produces a beautiful blue fluorescence when oxidized by hydrogen peroxide. In addition to providing one of the best-known examples of chemiluminescence, it is also a valuable crime scene investigation tool whose blue glow reveals the presence of blood.

For teachers, demonstrating the luminol reaction can add to discussions of oxidation-reduction reactions, conservation of energy, and electron energy levels. The following demonstration is ideal for middle and high school students.

• 1 g Luminol
• 20 mL Sodium Hydroxide Solution (1 M)
• 10 mL Hydrogen Peroxide (3%)
• 0.2 g Potassium Ferricyanide
• 4-ft Piece of Rubber Tubing
• Support Ring

Preparation

You will need a separate beaker for each of the 2 stock solutions you’ll prepare. Prepare the solutions immediately before use. Don lab coat or apron, goggles, and gloves before preparing solutions.  Caution:   Hydrogen peroxide is a strong oxidizer. Avoid skin contact. Sodium hydroxide and its solutions are caustic and can irritate skin. Avoid skin contact.

• To prepare stock solution A, fill a beaker with 100 mL of water. Add 0.18 g of luminol and 3.0 mL of sodium hydroxide solution (1 M).
• To prepare stock solution B, fill another beaker with 100 mL of water. Add 1 mL of hydrogen peroxide (3%) and 0.03 g of potassium ferricyanide.

To set up the apparatus, follow the steps in the figures below.

• Dim the lights.
• Simultaneously pour an equal amount of solution A and solution B into the funnel.
• As the 2 solutions mix, a blue light is emitted that is relatively bright and should last for several minutes.

Reactions that produce light without heat are called  chemiluminescent reactions . Perhaps the most familiar chemiluminescent reactions are those that occur in living organisms and are referred to as  bioluminescence . A classic example of this is the light produced by fireflies.

The reaction in this demonstration is an oxidation-reduction reaction in which a photon of light is released from an excited molecule. In the reaction, luminol is oxidized and its electrons elevated to an excited state. When the electrons return to the ground state, visible light is emitted.

Light’s wavelength determines its color. Light at a wavelength of 680 nm is red; at 500 nm, green; and at 425 nm, blue. The energy of one quantum (one photon, one particle) of light is inversely proportional to its wavelength. Thus: E = hc/l

where  E  is the energy of one quantum of light of wavelength (l),  h  is Planck’s constant and  c  is the speed of light.

In the reaction, hydrogen peroxide oxidizes luminol to produce aminophthalic acid, nitrogen gas, water, and light.

Whether from fireflies or luminol, visible light is produced by the release of light energy from energized atoms. Our chemistry kits below include material along with complete instructions and background information for this interactive activity.

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Hello, I followed the experiment exactly and was not able to get any light. What could be some issues? Is there a difference between regnant grade vs lab grade ?

Thank you for reaching out! After consulting with the product team specific to the Carolina Chemonstrations Luminol Light Up Kit, their suggestions were to check your hydrogen peroxide. The hydrogen peroxide should be 3% and check expiration dates since it can degrade. Additionally the hydroxide solution cannot be old, too weak or too strong—the 1M solution should be made up fresh. Hopefully this helps!

How bright is it suppose to glow? I tried it out in a dark room and it wasn’t really visible.

Hi! Make sure to check your hydrogen peroxide. The hydrogen peroxide should be 3% and check expiration dates since it can degrade. Additionally the hydroxide solution cannot be old, too weak or too strong—the 1M solution should be made up fresh. Hopefully this helps!

Hello, I was wondering on how you are supposed to dispose of the chemicals after use.

Hi! Please follow your state’s guidelines for chemical disposal, or also the instructions listed on the chemical’s mSDS sheet. You can find all of Carolina’s mSDS sheets at the link below: https://www.carolina.com/teacher-resources/msds-material-safety-data-sheets/10857.co?intid=srchredir_msds

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Question: Synthesis of Luminol lab report NOTE: mechanism is not needed in this case DATA: 3-nitrophthalic acid used: 200 mg 8% aqueous hydrazine used: 0.4mL 3-nitrophthalhydrazide obtained: 130 mg sodium hydrosultafe dihydrate: 0.6 g luminol obtained: 70 mg NOTES: compute yield for nitrophthalhydrazide in the first step! (assume nitrophthalic acid is limiting

Synthesis of Luminol lab report

NOTE: mechanism is not needed in this case

3-nitrophthalic acid used: 200 mg

8% aqueous hydrazine used: 0.4mL

3-nitrophthalhydrazide obtained: 130 mg

sodium hydrosultafe dihydrate: 0.6 g

luminol obtained: 70 mg

compute yield for nitrophthalhydrazide in the first step! (assume nitrophthalic acid is limiting reagent)

compute yield for luminol in the second step! (using nitrophthalhydrazide as limiting reagent)

compute yield for the overall reaction! What conclusion can you draw about multi step reactions and yields?

the lab report need to have

ABSTRACT - Short summary of the experiment as a whole. It has to include 1-2 sentences of background theory, 1-2 sentences about what you did in the experiment, 1-2 sentences about the most important results and 1 sentence of conclusion.

OBSERVATION AND DATA (RESULTS) - Tabulate and organize the data obtained. This includes making graphs of the data and computations IF NEEDED!

REACTION MECHANISM - Proper arrow pushing formalism. Draw non bonding electron pairs, formal charges, and curved arrows which follow the electron flow.

DISCUSSION - 5-6 sentences. EXPLAIN the observations and data using the theory of the experiment. WHY did you get the data? Does the data obtained agree with the expectations? If not, why is it different? What are possible sources of error? A good rule of thumb is to have 1 sentence of explanation for each observation or data value you have. The individual assignments will have helpful questions showing you what to cover in your discussion.

This AI-generated tip is based on Chegg's full solution. Sign up to see more!

Calculate the number of moles of 3-nitrophthalic acid used by using its molar mass and the available mass of 200 mg.

Luminol synthesis is carried out by dehydration of 3-nitrophtha …

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