On shaking: it is BLUE!. . . . On standing it is COLORLESS! Here is why this happens…
WHY DOES THE COLOR CHANGE ??
What is in the solution?
- Sodium hydroxide – makes the solution basic
- Glucose acts as a reducing agent (loses electron)
- Methylene blue – acts as an indicator for the reaction
What is happening?
Glucose is a reducing agent and in basic solution will reduce methylene blue to a colourless form.
Shaking the solution admits oxygen which will re-oxidise the methylene blue back to the blue form.