Fizzy drinks’ froth

This experiment should take between one and two hours. 

Equipment

Materials per group

• Cans of fizzy drink
• Anti-bumping granules
• Sand or other particulate material

Equipment per group 

• −5 to +100°C thermometer
• Access to water baths and a refrigerator
• Safety glasses

Health, safety and technical notes 

• Read our standard health and safety guidance here. 
• Wear eye protection. 
• This is an open-ended problem-solving activity, so the guidance given here is necessarily incomplete.

Commentary 

This phenomenon is widely known and occurs with any substance that is under pressure. There are a number of variables to control and monitor: temperature, degree of shaking, size of can etc, and it is possible to build up a set of conditions that are known to maximise the degree of frothing and to minimise it. 

The explanation for this phenomenon is based on nucleation. It is difficult to determine this from experimentation. When the pressurised can is shaken, small vapour bubbles of gas enter the drink and these act as a ‘nucleus’ for dissolved gas. 

When the can is opened, the pressure drops and the bubbles expand rapidly, shooting to the surface, causing the drink to froth out of the can.

The critical step for students is to sprinkle sand (or similar particulate material) into the fizzy drink - bubbles immediately form around these small particles and hence give a clue to the formation of bubbles when the can is shaken.

Students may be interested to link this phenomenon with (a) the principle of crystallisation and (b) how antibumping granules work (or glass coasters in milk saucepans).

Notes

This resource is part of a collection of problem-solving activities, designed to engage learners in small group work. Find out how to use these resources, and obtain a list of suggested ‘junk items’ here.