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Chemistry LibreTexts

Instant Coca-Cola

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Required Training

Required PPE

UC Lab Safety Fundamentals

Lab coat, safety glasses/goggles, nitrile gloves

Performers Required: 1

Equipment

Chemicals

Empty 581 mL (20-oz) Coca-Cola bottle or 50 mL sealable container

Soluble starch

Three graduated 25-mL beakers or vials, labelled Solution 1, Solution 2, and Solution 3.

Potassium iodate (KIO3)

Sodium sulfite (Na2SO3)

Sulfuric acid (H2SO4), 18M

Procedure:

1.) Preparation of solutions:

Solution 1: add 0.4 g soluble starch to 200 mL boiling water. Let cool to room temperature before use.

Solution 2: add 3 mL H2SO4 to 200 mL water, then add 10 g KIO3 and stir until dissolved.

Solution 3: add 4.2 g Na2SO3 to 200 mL water and stir until dissolved.

2.) Place ~500 mL of water inside a clean, empty Coca-Cola bottle. This comes to just above the top of the label.

3.) Add 20 mL of Solution 1 (starch), then recap the bottle and shake well for several seconds. Performance tip - shaking the bottle by rotating the wrist rather than shaking up and down vertically provides a more evenly distributed solution that performs better..

4.) Add 15 mL of Solution 2 (KIO3/H2SO4), then recap the bottle and shake well again.

5.) Add 25 mL of Solution 3 (Na2SO3), then quickly recap the bottle and shake very well for ~3-5 seconds to thoroughly mix the contents. It will take ~18 seconds from the moment Solution 3 is added for the solution to abruptly (almost instantaneously) turn a dark blue/black color. With practice it is possible to add Solution 3, re-cap the bottle, and shake to mix in the first 8 seconds; you can then lead the audience in counting up, once per second, such that the transition happens exactly at 10.

Table Demo Procedure:

  1. Place 20 mL of water inside a clean, empty 50 mL sealable container.
  2. Add 1 mL of Solution 1 (starch), then recap the container and shake well for several seconds.
  3. Add 0.5 mL of Solution 2 (KIO3/H2SO4), then recap the container and shake well again.
  4. Add 1 mL of Solution 3 (Na2SO3), then quickly recap the container and shake very well for ~3-5 seconds to thoroughly mix the contents. It will take ~8 seconds from the moment Solution 3 is added for the solution to abruptly (almost instantaneously) turn a dark blue/black color.

Clean-up: Wash the bottle/container out with water. All waste can be rinsed down the drain.

Hazards: KIO3 is an oxidizer and should be kept away from flammable materials and reducing agents. H2SO4 is strongly oxidizing and corrosive, and will cause immediate chemical burns on contact.

Principle: Bisulfite anions (HSO3-) from Na2SO3 reduce KIO3 to form iodide anions (I-), which further react with KIO3 to form iodine (I2). In solution I2 reacts with I- to form triiodide anions (I3-). I3- is immediately reduced back to I- by any remaining HSO3-. Once the supply of HSO3- is exhausted, I3- persists in solution and reacts with starch molecules to form a dark blue starch-iodine complex. Excess I3- is a brown color in solution, and together this produces the dark blue/black/brown color of coca-cola. As the concentration of I3- rises extremely quickly, the color change is almost instantaneous. The volume of Solution 3 (Na2SO3) added to the reaction will change the time required for the color change – larger volumes will increase the delay, and smaller volumes will decrease it.

Notes: It has not yet been conclusively determined if starch-I3- or starch-I5- is responsible for the blue-black color. In general, the reaction occurs faster if more of solution 2 is added. Sodium bisulfate or sodium carbonate can remove any staining that occurs in the reusable plastic bottle. Several different problems can be encountered with this demo, each relating to a different starting solution:

1. The solution gradually transitions to a medium brown color, rather than an abrupt change, indicating a problem with the starch solution. Make sure the mixture is brought to a boil in order to dissolve a sufficient amount of starch. Over time bacteria will eat the starch and decompose the solution; if this occurs, remake Solution 1.

2. The solution takes a very long time (> 25-30 seconds) before the abrupt color change occurs, indicating a problem with the KIO3 solution. Over a long period of time the KIO3 can crystallize out of the solution; if this occurs, remake Solution 2.

3. The solution changes to a dark blue/black color much too quickly (< 5 seconds), indicating a problem with the Na2SO3 solution. Na2SO3 is slowly oxidized by air to Na2SO4, losing its reducing ability; if this occurs, remake Solution 3.


Instant Coca-Cola is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.

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