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Grades 9 and 10 Intermediate About 20 min Version 1 Awaiting review Premium

Reaction rate: the fizzy tablet race

A fizzy (effervescent) tablet contains an acid and baking soda. When it touches water they react and make carbon dioxide gas: that is the fizzing. The rate of a reaction is how fast it happens. In this experiment you will change one thing at a time, the water temperature or the size of the pieces, and time how long the tablet takes to react completely.

What you will learn

  • Describe what is meant by the rate of a reaction.
  • Explain how temperature affects reaction rate.
  • Explain how surface area (crushing a solid) affects reaction rate.
  • Plan a fair test by changing only one variable at a time.

Before you start

  • Know that bubbles of gas are evidence of a chemical reaction. Try Signs of a chemical reaction first.

Materials

  • Water at different temperatures (100 mL per beaker)
  • 4 fizzy (effervescent) tablets, one of them crushed

Equipment

  • 4 beakers (200 mL)
  • Thermometer
  • Stopwatch

Procedure

  1. Each beaker holds 100 mL of water. A is cold (10 °C), B is at room temperature (25 °C), C is warm (50 °C) and D is at room temperature (25 °C).
  2. Add one whole tablet to Beakers A, B and C.
  3. Add one crushed tablet to Beaker D.
  4. Use the timer buttons to let time pass, and watch each tablet.
  5. Record how long each reaction takes to finish.

How this simulation is simplified

  • Reaction times are typical values for one effervescent tablet in 100 mL of water. Real times depend on the brand of tablet.
  • The water stays at the same temperature while the tablet reacts.
  • The crushed tablet reacts as one powder; real crushed pieces vary in size.