Popping good chemistry: investigate chemical reactions and irreversible changes

In this investigation, learners explore changing materials, irreversible changes and gases around us, using a simple chemical reaction. Use in a lesson, science club or as a Science Week activity. Choose from a version for primary aged learners (9–11 years) or one for lower secondary learners (11–14 years).

Equipment

• Safety glasses
• Empty vitamin C tube
• 2 x vitamin C tablets per group (more to allow for repeats)
• Water
• Measuring cylinder or jug
• Timer or stopwatch
• Spillage tray and paper towels

Resources

You can buy tubes of vitamin C tablets relatively cheaply from large supermarkets, pharmacies and pound shops. The tubes can be washed, dried and used a few times. 

Safety and hazards

Read our standard health and safety guidance and carry out a risk assessment before running any live practical.

Discuss hazards and control measures with learners. The lid pops off suddenly and it is important to ensure that all learners wear eye protection. Remind learners not to look directly down at the tubes once the reaction has started and not to point them directly at anyone. If a lid does not pop off within the expected time, learners should let you know and you can carefully remove the lid.

Remind learners never to eat or drink anything during a science experiment. The solution is an irritant if in contact with eyes – tell learners to wash their hands after the practical.

Method

Full step-by-step instructions for the lesson are given in the primary teacher notes. In the secondary version learners can plan their own investigation, choosing an independent variable to investigate.

1. Remember to follow the safety instructions.
2. Fill the empty tube with water, then pour it into a measuring cylinder. Write down the volume and calculate half. This is the volume of water you will use for each repeat.
3. Measure the volume of water from step 2 and pour it into the tablet tube. Place the tablet tube in a test tube rack.
4. Put one tablet in the tube and put the lid on firmly. Work with a partner to make sure you start the timer as soon as the lid is on.
5. Stop the timer when the lid pops off.
6. Record the time taken.
7. Change your independent variable at least twice (making sure you still have a fair test) and repeat steps 3–6.

Learning objectives

For primary learners

Understanding

• I can describe an irreversible change.
• I know that an irreversible change produces new materials.
• I understand that some solids dissolve.

Enquiry skills

• I can make and test predictions.
• I can make observations, take measurements and record my results.
• I understand what ‘variables’ are.
• I can suggest how to improve my investigation.

For secondary learners

Understanding

• Describe chemical reactions as the rearrangement of atoms.
• Represent chemical reactions using formulas and equations.

Skills

• Make predictions, observations and measurements.
• Identify variables and how to make an experiment fair.
• Identify patterns and make conclusions from results.
• Evaluate the reliability of methods and suggest improvements.

Background science

This investigation shows how carbon dioxide gas, produced here from the chemical reaction between sodium hydrogencarbonate (commonly known as bicarbonate of soda) and citric acid, causes the pressure inside a sealed tube to increase, making the lid pop off.

Both sodium hydrogencarbonate and citric acid are solids in the tablet and are not free to react to form carbon dioxide until the tablet is dissolved in water. Once dissolved, it is the gas produced in the reaction that creates the bubbles of carbon dioxide that learners can observe.

This is a neutralisation reaction and can be described by the following word and chemical equations:

sodium hydrogencarbonate + citric acid à sodium citrate + water + carbon dioxide

3NaHCO₃ + C₆H₈O₇ → Na₃C₆H₅O₇ + 3H₂O + 3CO₂

Vitamin C is needed to make collagen for healthy skin, hair and bones. It also helps us to absorb iron and aids in wound healing. There are claims that it boosts our immune system. Our bodies can’t make vitamin C, so we must get it from the food we eat. Citrus fruits, like oranges, red peppers and broccoli are examples of foods high in vitamin C.

People who aren’t eating a balanced diet may take vitamin pills or tablets to make sure they get enough vitamins. A fizzy tablet can be a good way to take extra vitamins because after the reaction, vitamin C is dissolved in the water and can be absorbed by the body more quickly.