Turning 'red wine' into 'water'

Read our standard health & safety guidance

Lesson organisation

A simple demonstration with good visual impact and ideal for an Open Day aimed at all age groups.

An A-level group 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.

Apparatus and chemicals

For each demonstration:

Wine or fruit juice bottle (750 cm³ or larger)
Wine glasses (or similar), 5 (see note 1)
Beakers or conical flasks (250 cm³),
Beaker or conical flask (1 dm³)
Measuring cylinders (10 cm³)

Potassium manganate(VII) (potassium permanganate) (Oxidising, Harmful), 0.4 g
Barium chloride-2-water (Toxic), 24 g
Sodium thiosulfate-5-water (Low hazard), 25 g
Sodium carbonate (anhydrous) (Irritant), 22 g
Dilute sulfuric acid, 2 mol dm^-3 (Corrosive at this concentration), 100 cm³
Deionised or distilled water, 1.5 dm³

Technical notes

Potassium manganate(VII) (Oxidising, harmful) Refer to CLEAPSS Hazcard 81
Barium chloride-2-water (Toxic) Refer to CLEAPSS Hazcard 10A
Sodium thiosulfate-5-water (Low hazard) Refer to CLEAPSS Hazcard 95C
Sodium carbonate (anhydrous) (Irritant) REfer to CLEAPSS Hazcard 95A
Dilute sulfuric acid (Corrosive at concentration used), 100 cm³. Refer to CLEAPSS Hazcard 98A and Recipe card 69

1 Other types of glass, or even beakers, could be used instead of wine glasses, but the 'wine' into 'water" effect is obviously diminished.

2 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.

Procedure

Before the demonstration

i Make up the following four solutions:

A 24 g of barium chloride in 100 cm³ of deionised water (this is about 1 mol dm^-3).
B 25 g of sodium thiosulfate in 100 cm³ of deionised water (this is about 1 mol dm^-3).
C 21 g of sodium carbonate in 100 cm³ of deionised water (this is about 2 mol dm^-3).
D 0.4 g of potassium manganate(VII) dissolved in 100 cm³ of 2 mol dm^-3 sulfuric acid, and then made up to 1 dm³ with deionised water. This gives a solution of about 0.0025 mol dm^-3 which can then be transferred to the wine bottle.

ii Line up the five glasses on the bench. Out of sight of the audience (beforehand):

1 Leave the first empty.
2 Place about 1 cm³ of the sodium thiosulfate solution into the second.
3 Place about 1 cm³ of the sodium thiosulfate solution and 3 cm³ of the barium chloride solution into the third.
4 Place 3 cm³ of the barium chloride solution into the fourth.
5 Place 1 cm³ of the sodium thiosulfate solution and 3 cm³ of the sodium carbonate solution into the fifth.

None of these volumes or concentrations needs to be too precise. These relatively small volumes of liquid will almost certainly not be spotted by the audience.

The demonstration

a 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.

b The following changes will be seen:
Glass 1: 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 milk shake’.
Glass 5: The ‘red wine’ has turned into ‘fizzy lemonade’.

Teaching notes

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:

Glass 2
The purple manganate(VII) ions are reduced to colourless Mn²⁺ ions - 'water' or 'white wine'.

2MnO₄^–(aq) + 16H⁺(aq) + 10S₂O₃^2–(aq) → 2Mn²⁺(aq) + 5S₄O₆^2-(aq) + 8H₂O(l)

Glass 3
The purple manganate(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 manganate(VII) solution, hence the illusion of 'milk'.

Ba²⁺(aq) + SO₄^2-(aq) → BaSO₄(s)

Glass 4
The precipitate of barium sulfate forms as above, but the purple colour of the potassium manganate(VII) remains - 'raspberry milk shake'.

Glass 5
The purple manganate(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'
CO₃^2–(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’.

Health & Safety checked, August 2008