The ups and downs of chemistry

Design and make a device (with final dimensions NOT exceeding 15 cm × 15 cm × 15 cm) which will sink in water, and then after a reasonable length of time, rise to the surface.

This session could take around two hours and 30 minutes, or can be used for homework over a number of weeks.

Equipment

Apparatus

• A selection of junk materials
• Plastic beakers, 100 cm³
• Stop clocks
• Masses, 10g 
• Rubber bands
• Rubber tubing (1 metre)
• Sticky tape or masking tape
• String
• Identical teaspoons (plastic can be used)
• Ruler, 30 cm 
• Plastic buckets for ‘test runs’

Chemicals

For students who have studied neutralisation reactions:

• Hydrochloric acid, 0.5 mol dm-3 
• Marble chips
• Tartaric acid

Selection of chemicals:

• Salt
• Sugar
• ‘Alka Seltzer’ tablets
• Andrews’ liver salts, or a mixture of solid sodium hydrogencarbonate/citric acid (1 teaspoon of sodium hydrogencarbonate to 3 teaspoons of citric acid).
• Access to water. 

Health, safety and technical notes

• Read our standard health and safety guidance here. 
• Wear eye and/or clothing protection if desired.
• This is an open-ended problem-solving activity, so the guidance given here is necessarily incomplete.
• Citric acid is an eye irritant, wear eye protection, see CLEAPSS Hazcard HC036c

Possible approaches

Generating a gas which causes a container to become buoyant; weighting a container with soluble material and allowing water to dissolve it so that the container then rises to the surface. (The sinking or floating/rising aspects could be investigated separately.) 

Possible extensions

Increasing the complexity of the behaviour required in terms of time limits and depth limits. Extend to actual lifting of a submerged object.