[angeloposteraro]

Hello all,

I have recently done the "blue bottle reaction" whereby D-glucose oxidizes methylene blue in an alkaline environment to form a colorless species. The solution is shaken and oxygen from the atmosphere reduces the methylene blue into the colored species, and then the glucose acts again to form the colorless species and so on...

now, for about 5-10 cycles this happened as expected, but now the reaction forms a mauve/purple colour as opposed to the blue that methylene usually resembles.

I used NaOH, Methylene Blue, and Crown brand Glucose corn syrup.

I'm curious as to what would cause the methylene blue to now be purple, perhaps the solution is too alkaline ?

[opti384]

Usually, the color of methylene blue depends on the amount of oxygen. If oxgen is saturated inside the bottle, the color will be mauve/purple instead of blue.