Use acidified potassium permanganate – or ‘red wine’ – to make ‘water’, ‘milk’ and ‘lemonade’ in this engaging demonstration
In this experiment, students observe as a solution of acidified potassium permanganate(VII) (‘red wine’) is poured into a set of glasses containing small amounts of different colourless solutions, made up from barium chloride, sodium thiosulfate, sodium carbonate and sulfuric acid. Barely visible from a distance, these colourless solutions react with the potassium permanganate(VII) to create the illusion of red wine turning into milk, raspberry milkshake and fizzy lemonade.
This simple demonstration is ideal for an open day aimed at all age groups, while in class advanced students could be asked to write equations for the reactions involved.
The demonstration lasts about 5 minutes, but about 20–30 minutes are needed for the preparation beforehand.
- Eye protection
- Wine or fruit juice bottle, 750 cm3 or larger
- Wine glasses (or similar), x5 (see note 8 below)
- Beakers or conical flasks, 250 cm3
- Beaker or conical flask, 1 dm3
- Measuring cylinders, 10 cm3
- Potassium permanganate(VII) (OXIDISING, HARMFUL), 0.4 g
- Barium chloride dihydrate (TOXIC), 24 g
- Sodium thiosulfate-5-water, 25 g
- Sodium carbonate (anhydrous) (IRRITANT), 22 g
- Dilute sulfuric acid, 2 M (CORROSIVE), 100 cm3
- Deionised or distilled water, 1.5 dm3
Health, safety and technical notes
- Read our standard health and safety guidance.
- Wear eye protection throughout (the solutions are TOXIC).
- Potassium permanganate(VII), KMnO4(s), (OXIDISING, HARMFUL) – see CLEAPSS Hazcard HC081.
- Barium chloride dihydrate, BaCl2.2H2O(s), (TOXIC) – see CLEAPSS Hazcard HC010a.
- Sodium thiosulfate-5-water, Na2S2O3.5H2O(s) – see CLEAPSS Hazcard HC095a.
- Sodium carbonate (anhydrous), Na2CO3(s), (IRRITANT) – see CLEAPSS Hazcard HC095a.
- Dilute sulfuric acid, H2SO4(aq), (CORROSIVE at concentration used), 100 cm3 – see CLEAPSS Hazcard HC098a and CLEAPSS Recipe Book.
- Other types of glass, or even beakers, could be used instead of wine glasses, but the ‘wine’ into ’water” effect is obviously diminished.
- Do not leave the solutions in the glasses or bottle after the demonstration in case they are mistaken for real drinks! Dispose of the contents IMMEDIATELY after the demonstration.
Before the demonstration
- Make up the following four solutions:
- 24 g of barium chloride dihydrate in 100 cm3 of deionised water (this is about 1 M, TOXIC).
- 25 g of sodium thiosulfate in 100 cm3 of deionised water (this is about 1 M).
- 21 g of sodium carbonate in 100 cm3 of deionised water (this is about 2 M, IRRITANT).
- 0.4 g of potassium permanganate(VII) dissolved in 100 cm3 of 2 M sulfuric acid, and then made up to 1 dm3 with deionised water. This gives a solution of about 0.0025 M which can then be transferred to the wine bottle.
- Line up the five glasses on the bench. None of the volumes or concentrations needs to be too precise – the relatively small volumes of liquid will almost certainly not be spotted by the audience. Out of sight of the audience (beforehand):
- Leave the first empty.
- Place about 1 cm3 of the sodium thiosulfate solution into the second.
- Place about 1 cm3 of the sodium thiosulfate solution and 3 cm3 of the barium chloride solution into the third.
- Place 3 cm3 of the barium chloride solution into the fourth.
- Place 1 cm3 of the sodium thiosulfate solution and 3 cm3 of the sodium carbonate solution into the fifth.
- With a suitable patter, pour a glassful of the permanganate solution from the wine bottle into each glass. Do not exceed 200 cm3 for any glass to ensure that the reactants already in the glasses remain in excess.
- The following changes will be seen:
- Glass 1: there is no change.
- Glass 2: the ‘red wine’ has turned to ‘water’ or ‘white wine’.
- Glass 3: the ‘red wine’ has turned to ‘milk’.
- Glass 4: the ‘red wine’ has turned to ‘raspberry milkshake’.
- Glass 5: the ‘red wine’ has turned into ‘fizzy lemonade’.
It is best to remove the ‘drinks’ fairly quickly as glasses 2 and 5 may gradually go cloudy due to the formation of colloidal sulfur from excess thiosulfate and acid and the white precipitates in glasses 3 and 4 will settle out, spoiling the illusion.
The reactions taking place are summarised below.
The purple permanganate(VII) ions are reduced to colourless Mn2+ ions – ‘water’ or ‘white wine’.
2MnO4–(aq) + 16H+(aq) + 10S2O32–(aq) → 2Mn2+(aq) + 5S4O62–(aq) + 8H2O(l)
The purple permanganate(VII) ions are reduced as above and the barium ions form insoluble barium sulfate with the sulfate ions present in the acid used to make up the potassium permanganate(VII) solution, hence the illusion of ‘milk’.
Ba2+(aq) + SO42–(aq) → BaSO4(s)
The precipitate of barium sulfate forms as above, but the purple colour of the potassium permanganate(VII) remains – ‘raspberry milk shake’.
The purple permanganate(VII) ions are reduced, as above, and the carbonate ions react with the hydrogen ions present in the acidified solution to form carbon dioxide – ‘fizzy lemonade’
CO32–(aq) + 2H+(aq) → H2O(l) + CO2(g)
Other ‘drinks’ could be devised based on this or other systems. For example, manipulating the amount of thiosulfate in glass 5 so that the permanganate ends up in slight excess, gives ‘pink champagne’.