Fun with Dry Ice

Required Training	Required PPE
UC Lab Safety Fundamentals Online Cryogen Safety at UC Davis	Lab coat, safety glasses/goggles, nitrile gloves, cryogen gloves
Performers Required: 1
Equipment	Chemicals
Bubble Machine (Jug with hose)	Dry Ice
Tongs	Universal Indicator(Methyl orange, methyl red, bromothymol blue, phenolphthalein)
Cup or breaker (approx. 250 mL)	Glycerine
Transparent TPX 500 mL graduated cylinder (500 mL)

Procedure:

Fog in a Bubble

1.) Fill the jug approx. ¼ full with warm water then place a few pieces of dry ice inside using tongs or cryo gloves. Cover the opening with a lid, leaving approx. ⅛ open (this controls the flow of the fog). You should be able to see the fog coming from the nozzle, if not adjust lid or add more dry ice.

2.) Fill a cup or beaker with enough bubble solution to submerge the nozzle of the hose.

Bubble solution (1 L): 70 mL glycerine, 150 mL Dawn Dish Soap, 780 mL DI Water

3.) Submerge the nozzle for a few seconds then remove from solution, allowing carbon dioxide and water vapor to form a bubble. The bubble will naturally fall when enough force is supplied by the weight of the gaseous mixture. When the hose is not in use, point it away from individuals.

4.) Using cotton gloves, gently play with the bubbles. Nitrile gloves and most surfaces will pop the bubble.

Dry Ice as An Acid

1.) Fill the TPX graduate cylinder with 5 mL of universal indicator. Pour in water until the 450 mL mark.

Universal Indicator (1 L): 0.05 g methyl orange, 0.15 g methyl red, 0.30 bromothymol blue, 0.35 g phenolphthalein, bring to volume with 2 parts ethanol: 1 part water

2.) Place a small piece of dry ice inside the cylinder using tongs or cryo gloves. Observe over time as the solution goes from green to orange to red.

Clean-up: Wipe any surface that may have come into contact with the bubble solution or the bubbles themselves. The solution contains glycerine which is very sticky. Pour the contents of the graduated cylinder into a beaker and adjust the pH to - to allow for drain disposal.

Hazards: Dry ice sublimes at -78.5 °C (194.5 K), and prolonged contact with skin will cause frostbite. Never place dry ice in a closed container, as the build-up of pressure may cause the container to burst, which could injure anyone nearby.Gaseous CO2 is safe on the skin, but caution should be taken to avoid direct contact with dry ice. For the bubble machine, DO NOT use hot or boiling water as this can cause the jar to melt or crack.

Principle: Dry ice goes through sublimation, where it is converted directly from a solid into a gas. This process skips over liquid, hence why it’s called dry ice, there is no liquid leftover if you leave it out unlike with water ice. Placing it in water generates gaseous CO2 and water vapor. The soap and glycerin serve to trap the CO2 and water vapor. This bubble will not float unlike normal bubbles. This is because CO2 and water are heavier than the surrounding air, hence it sinks. CO2 reacts with water to form carbonic acid ( H2CO3) a weak acid which is found in carbonate beverages. Universal indicators are made up of a solution of several different indicators, allowing for smooth color changes over a wide range of pH values to indicate both acidity or alkalinity of solution. The mixture of indicators it what allows the transition from green (neutral) to organe () to red ().

Notes: The color of the soap is not reflected in the bubble, which can be very interested for audiences to see! The temperature of the water dictates the rate of fog formation. The longer the demo, the more the dry ice cools down the water, reducing the amount of fog created.

Indicator	Low pH colour	Transition pH range	High pH colour
Thymol blue (first transition)	Red	1.2 – 2.8	Yellow
Methyl orange	Red	3.2 – 4.4	Yellow
Methyl red	Yellow	4.8 – 6.0	Red
Bromothymol blue	Yellow	6.0 – 7.6	Blue
Thymol blue (second transition)	Yellow	8.0 – 9.6	Blue
Phenolphthalein	Colourless	8.3 – 10.0	Fuchsia