Chemiluminescence

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Chemiluminescence of Luminol

Introduction

In this experiment, luminol was mixed with hydrogen peroxide (an oxidising agent) resulting in chemiluminescence. The experimentis designed to see how the duration of luminescence is affected by varying temperatures. It has been made to be deliberately inaccurate, so another objective would be to see whether subjective observations can be improved by repetition and averaging.

Chemiluminescence is the production of light from a release of energy in a chemical reaction without the aid of heat. The light produced is due to electrons being given an excess of energy and this energy being released as the electrons revert to their ground state, a luminescent light being given off as a result.

An important use of this reaction is in forensic science where luminol and hydrogen peroxide are used to highlight samples of blood at a crime scene. The two chemicals react readily due to the iron present in haemoglobin, giving off a luminescent glow as a result.

Chemiluminescence occurs even in living organisms where it is termed bioluminescence. Using fireflies as an example, a reaction where luciferin combines with adenosine tri-phosphate (ATP) and reacts with the enzyme luciferase. The action of the enzyme acting on luciferase simulates something similar to luminol and a peroxide being catalysed by a transition metal catalyst, providing electrons with enough energy to reach a higher energy level which then gives off light as they relax back to their ground state.

- Reaction pathway of luminol

2H2O22H2O + O2(g) - Decomposition of Hydrogen Peroxide

In this experiment we used luminol and hydrogen peroxide solution. When the two react, a dianion is from the peroxide reacting with the luminol. As hydrogen peroxide reacts, oxygen is evolved which then reacts with the dianion to produce an unstable peroxide; the instability of the peroxide causes it to break down immediately and lose nitrogen, producing...
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