THE CHEMICAL TRAFFIC LIGHT EXPERIMENT: ~ Quimica

THE CHEMICAL TRAFFIC LIGHT EXPERIMENT:

- Suhail Ansari,

Batch (2k17), Chemical Engg.,

BIT Sindri, Dhanbad.

Here’s the magic of chemicals!!

Here’s the beauty of chemistry!!

The chemical traffic light experiment is such a pleasant and eye-catching experiment to do.

It is a color-changing Redox reaction in which the color changes gradually from yellow to red, then red to green and further back to its yellow color, simply by shaking.

MATERIALS REQUIRED:

1.GLUCOSE

2.SODIUM HYDROXIDE DRAIN CLEANER (NaOH)

3.WATER SOLUBLE BLUE DYE CALLED INDIGO CARMINE

4.DISTILLED WATER

5.A CYLINDRICAL BEAKER AND A CONICAL FLASK

PROCEDURE:

1.Take 150ml of distilled water in a beaker followed by 3g of Glucose.

2.Add 5g NaOH drain cleaner in the beaker and stirred well until it all dissolved.

3.Take 100ml of distilled water in conical flask and add small amount of approximately 20mg Indigo Carmine in it which forms a BLUE color solution.

(If you add too much Indigo Carmine, then make sure to dilute it with more distilled water accordingly.)

4.Add sugar solution that you made, to Indigo Carmine solution. The BLUE color immediately changes to GREEN.

5.After about 2 mins, it eventually transitioned to YELLOW color.

6.Give the flask a gentle shake and watch the solution turn from YELLOW to RED.

7.Further, more vigorously shake will turn the solution from RED to GREEN.

8.Let the solution stand still, the solution reverts back to YELLOW and the same process can be repeated.

EXPLANATION:

The Indigo Carmine which is in its Blue form which dominates when the pH of the solution is less than about 11.4. Distilled water has a pH of around 7. The moment basic sugar solution was added to Indigo Carmine solution, the pH was increased causing a basic nature with a pH above 11.4. At this pH, a lot of Indigo Carmine starts to get deprotonated which caused its structure to change. This new form of it resembles a from BLUE to YELLOW color.

Indigo Carmine is sensitive to Oxidation & Reduction. Under normal condition, the Indigo Carmine is in its oxidised form because its always in contact with the oxygen present in the air and Glucose being as Reducing sugar in presence of strong base like NaOH, reacts to form a Glucoside Anion which wants to donate a pair of electrons. These electrons were picked up by the Indigo Carmine which first reduces it to a RED color then to a GREEN one. It’s not happening because of shaking, it’s due to the air present inside the flask.

While, after a time, some of the oxygen dissolved into the solution & it re-oxidises the Indigo Carmine all its way back to BLUE form & then if we stand the flask still, it further shows YELLOW color and this repetition continuously goes on up to a certain limit. The solution “dies’’ after 5 or 6 cycles. To revive it, further add extra 1mg of Indigo Carmine. It is basically a Cycle between Fully Oxidised form to Fully Reduced form.