Fun with luminol

Luminol is a chemical frequently used to produce blue light by chemiluminescence.

One classic demonstration uses luminol in a reaction carried out as it spirals down a length of tubing such as the one shown here:

Chemiluminescence, courtesy of Nigel Evans, Bloxham School.

Chemiluminescence, courtesy of Nigel Evans, Bloxham School.

Another demonstration uses luminol in a spray to detect fake ‘blood spatter’ such as is often seen in TV forensic science dramas. In our school chemistry club we used a recipe published by Anne Marie Helmenstine on About.com This recipe requires two solutions which are mixed together in equal proportions shortly before use. Solution 1 – Luminol stock solution (2 g luminol + 15 g potassium hydroxide + 250 mL water). Solution 2 – 3% hydrogen peroxide in water (our local pharmacy supplied a 6% hydrogen peroxide solution which needed to be diluted by half with water). However, because this mixture uses a fairly concentrated solution of potassium hydroxide, which is corrosive, it must be used in a fume cupboard. Under such conditions we were unable to see much of a glow when sprayed onto test paper ‘painted’ with an iron (III) chloride solution.

We had much more fun by pouring the luminol mixture into a Petri dish in a darkened room. We then added 0.1M iron (III) chloride and 0.1M copper (II) sulfate using dropping pipettes. In this way more students were able to investigate this exciting reaction for themselves:

Luminol reaction in a Petri dish

Luminol reaction in a Petri dish

In another similar experiment we tried electrolysing the reaction mixture using graphite electrodes and 9v from a power pack:

Electrolysing the luminol reaction

Electrolysing the luminol reaction

You too might have some fun if you try this. Happy Halloween from our Chemistry Club.

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