Equilibrium prac with safranin & methylene blue

[vlclabbie]

Hi, my teacher wants to do this prac. I haven't got the recipe ..... can anyone help please?

Thanks!

Kel

[fibreweb]

The equilibrium reaction that I have uses methylene blue but not safranin.

Prepare a solution in one litre 25 gm NaOH, 15 gm glucose powder, 10 ml Methylene blue.

Almost immediatly after mixing the solution changes from deep blue to clear yellow.

Place in 250 ml conical flasks, add a rubber stopper and seal. The greater airspace above the solution the better the solution works.

Slight aggitiation of the flasks produces a blue tings, rapid shaking produces a bright blue colour. On standing the clolour reverts to a yellow/clear colour and the process can be repeated many times over several hours.

Safety: the stoppers are prone to pop out if the inside of the flask is whetted with sodium hydroxide before the stopper is added. They also tend to pop out when it is shaken.

The basic explanation is that it is caused by a complex which forms when Oxygen disolves in the solution and develops the blue colour. As the Oxygen is released, the blue colour is lost and the solution reverts to clear.
Someone may be able to tell us the actual reactions and products.

Wendy

[lada]

We do similar one called blue bottle.
Dissolve 12g of glucose in a L volumetric flask (volume not critical, I use about 900ml of water.)
Within 1 hr of classtime, dissolve 12g of NaOH in the glucose solution and add 1ml of methelene blue.
Stopper bottle and shake it. It will change from blue to clear on standing , back to blue with shaking.
Lada

[dime]

I do it in a 1.25 litre drink (plastic) bottle, so you can screw the cap on. No worries about a stopper coming out.

[Voice]

This is direct from a "demonstration" book. I am not this smart!
Methylene blue appears to act as a catalyst in the reaction of glucose with oxygen. Methylene blue is a redox indicator that is blue in its oxidised form and colourless in its reduced form. When the liquid is shaken dissolved oxygen oxidises the colourless methylene blue to the blue form. This is subsequently reduced slowly to the colourless form again by the alkaline form of glucose present in the solution. The coloured form of methylene blue is an intermediate in the reaction sequence.

The process may be repeated until either the oxygen in the flask or the glucose is consumed.

I have equations but unable to perfectly write them here.

I have used this demonstration for years. The kids love it.

Maree

[vlclabbie]

Thanks everyone - so helpful - as always!

The teacher may have it wrong about the safranine then......... does anyone use safranine as anything but an indicator during Gram stains?

Cheers Kel

[Rowyrow]

I found this , it uses other stains aswell as methylenen blue for this experiment. Lot's of different colour changes

[Labbie]

Thank you so much for that. Its great.

[vlclabbie]

Thanks Row! Awesome prac.