By:- Atit s gaonkar XII A

Chemistry

Investigatory

PROJECT

INDEX• Theory• Reaction

• How To PrepareApparatusProcedurePrecautions

• Explanation.• Application .

REDOX REACTION

Blue bottle experiment

Theory

• A colorless solution partially fills a flask, is shaken, and the solution becomes blue. Upon standing, the solution returns to colorless. • Further shaking regenerates the blue

color. Repeating the shaking/standing procedure allows multiple observations. Other indicators produce different color changes.

• The color change results from the reversible oxidation-reduction reaction of the methylene blue indicator. In alkaline solutions, glucose is oxidized to D-gluconic acid or alpha-D-gluconolactone.• The Reaction is as follows ( next

slide ).

Reaction

HOCH2 (CHOH) 4 CHO + 3OH-

HOCH2 (CHOH) 4 CO2 + 2H2O + 2e-

O2 + MB(Colourless) MBox

(Blue)(Fast)

MBox(Blue) + CH

MB(Colourless) + X.

Where CH is the carbohydrate (in this case, dextrose), MB is the reduced (colourless) form of methylene blue, MBox is the oxidized (blue) form, and X- represents the oxidation products from glucose (gluconic acid – different carbohydrates form different acids like arabinoic, formic, oxalic and erythronic acids).

HOW TO

PREPARE

BLUE BOTTLE

Apparatus

• Water• Sodium hydroxide• Glucose• Methylene blue• 1 litre container (bottle or glass

jar will do). • 2 teaspoons

• Sodium hydroxide is the active ingredient in Caustic Soda which can be found in the laundry section of your supermarket. It is usually used to unblock drains.

• Glucose can be bought from your chemist. It comes in both powder and tablet form. The powder works the best for this activity. If you buy the tablets, crush them with a mortar and pestle or the back of spoon

• Methylene blue is traditional medication for freshwater aquarium fish.

Procedure Pour 500ml of water into a 1 litre

container.

Add a heaped teaspoon (approximately 8 grams) of sodium hydroxide and dissolve by swirling.

Add two level teaspoons (approximately 10 grams) of glucose and dissolve by swirling.

Add 3-4 drops of methylene blue. Swirl the mixture and stop. The liquid should appear blue.

Let the solution sit for a while and it should become clear. 

Give the flask a few quick shakes so that air dissolves in the solution. If you are using a lid check that it is on properly and take special care not to spill any liquid.

The colour will change to blue.

This will fade back to a colourless liquid again over a short period of time.

The more shaking, the longer the blue colour will take to fade.

The process can be repeated for over 20 cycles, you may have to allow more air in if you are using a container with a lid. After some hours, the solution will turn yellow and the colour changes will fail to occur.

Precautions Sodium hydroxide is a powerful

base (the opposite to an acid). Avoid contact with hands and clothes and wash thoroughly in case of contact.

BEFORE AFTER

EXPLANATION

TRANSFORMATION

• Redox reactions involve the transfer of electrons from one substance to another.• Reduction describes the uptake

of an electron by a molecule or atom. Oxidation describes the loss of an electron by a molecule or atom. These two terms go together, because in a chemical reaction, one cannot occur without the other; electrons lost by one compound must be gained by another.

• The bottle contains sodium hydroxide, glucose, water and an indicator called methylene blue. Glucose is a reducing agent that will reduce methylene blue to a colourless form. Shaking the solution provides oxygen which will re-oxidise the methylene blue back to the blue form.

• You should also notice that once the mixture has gone colourless, a blue zone remains close to the surface. This is due to oxygen dissolving into the mixture from the air space within the flask.

• In first stage of the blue bottle experiment, the methylene blue dye acts an oxidizing agent and the glucose acts as a reducing agent. The methylene blue oxidizes the glucose to gluconic acid and the glucose reduces the methylene blue to its colorless form. The result is a bottle of colorless solution.

• When the bottle is shaken, the surface are of the liquid temporarily increases, causing more oxygen to dissolve in the ethanol. The additional oxygen acts as an oxidizing agent and changes methylene blue to its blue, oxidized form. The result is a dramatic color change from colorless to blue.

• When the shaking is stopped, the oxygen levels in solution begin to drop. With less oxygen present, the methylene blue once again is reduced to its colorless form by the glucose, and observers will see the color fade and disappear. The color change can be repeated many times simply by shaking the bottle to induce the blue color and then allowing it to sit still in order to make it disappear.

APPLICATIONsOf the

principle of,Blue bottle experiment

• Energy is stored and released through redox reactions. Photosynthesis involves the reduction of carbon dioxide into sugars and the oxidation of water into molecular oxygen. The reverse reaction, respiration, oxidises sugars to produce carbon dioxide and water.

• Oxidation is part of daily life and can be useful and annoying for people. Useful oxidizing agents are bleaches and antiseptics. Not so useful is the oxidising action of oxygen in the air that can corrode metals. This is known as rust when the metal is iron or tarnish when the metal is copper. When exposed to oxygen most metals will oxidize, although in some cases like aluminium, the oxidised layer then prevents further oxidation.

THANK YOU

That’s All From My Presentation

ATIT S. GAONKAR

BY:-

XII AKENDRIYA

VIDYALAYA KARWAR