![]() The process can be repeated for over 20 cycles.The more shaking, the longer the blue colour will take to fade.The colour will change to blue and will fade back to colourless over about 30 seconds.Holding the stopper securely in place, shake the flask vigorously so that air dissolves in the solution.Stopper the flask and label it IRRITANT (due to the potassium hydroxide present). The resulting blue solution will turn colourless after about one minute.Add 5 cm 3 of the methylene blue solution.Add 300 cm 3 of water and 10 g of glucose and swirl until the solids are dissolved.Weigh 8 g of potassium hydroxide into the 1 dm 3 conical flask.Make a solution of 0.05 g of methylene blue in 50 cm 3 of ethanol (0.1%).Less than 20 minutes beforehand, preferably. Ethanol (IDA – Industrial Denatured Alcohol), C 2H 5OH(l), (HIGHLY FLAMMABLE, HARMFUL) – see CLEAPSS Hazcard HC040a.Methylene blue (HARMFUL) – see CLEAPSS Hazcard HC032.Glucose (dextrose), C 6H 12O 6(s) – see CLEAPSS Hazcard HC040c.Potassium hydroxide, KOH(s), (CORROSIVE, IRRITANT) – see CLEAPSS Hazcard HC091b.Wear goggles when preparing the solution. Read our standard health and safety guidance.Access to a nitrogen cylinder (optional).Ethanol (IDA – Industrial Denatured Alcohol) (HIGHLY FLAMMABLE, HARMFUL), 50 cm 3.Potassium hydroxide (CORROSIVE, IRRITANT), 8 g.Eye protection: goggles should be worn when preparing the solution.The demonstration lasts about 3–5 minutes, but about 15–20 minutes is needed for the preparation beforehand. The reactions involved are not part of a normal chemical curriculum, but this experiment has a good visual impact and would be one way of stimulating interest in chemistry, perhaps via an open day. When the dissolved oxygen has been consumed, the methylene blue is slowly reduced back to its colourless form by the remaining glucose, and the cycle can be repeated many times by further shaking. Shaking the solution raises the concentration of oxygen in the mixture and this oxidises the methylene blue back to its blue form. RSC Yusuf Hamied Inspirational Science ProgrammeĪn alkaline solution of glucose acts as a reducing agent and reduces added methylene blue from a blue to a colourless form.Introductory maths for higher education.The physics of restoration and conservation.
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