Quick answer: The rate of reaction is how quickly reactants are used up or products form, measured as amount per unit time. This Chemistry 9-10 lab on rates of reaction gives the aim, the equipment, the safety points, a step-by-step method, sample results and 7 analysis questions; the answers are on a separate page and the lab sheet is a free printable PDF.
An effervescent tablet makes carbon dioxide when it meets water, so the fizzing is a clock for the reaction. You time the tablet at four temperatures, convert the times into rates and test whether the rate keeps doubling for every ten degrees. You also judge how reliable the stopwatch results are.
Level: Chemistry grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: HS-PS1-5
Aim
To investigate how the temperature of the water changes the time an effervescent tablet takes to stop fizzing, and so how it changes the rate of reaction.
Equipment
- Four identical effervescent tablets (citric acid with sodium hydrogencarbonate)
- Four 250 cm³ beakers and a measuring cylinder
- Thermometer, stopwatch, kettle, ice and cold tap water
- Heat-proof mat, paper towel and a marker pen
Safety
Wear safety goggles. Water at 60 °C can scald, so pour it carefully with an adult or teacher present. Do not eat or drink anything in the lab, and mop up spills at once.
Method
- Measure 200 cm³ of water into a beaker and adjust it with ice or hot water to 5 °C. Check with the thermometer.
- Drop in one tablet and start the stopwatch at once.
- Stop the stopwatch when the fizzing stops and record the time to the nearest second.
- Repeat with fresh water at 20 °C, 40 °C and 60 °C, using a new tablet each time.
Results
Sample results:
| Water temperature / °C | Time to stop fizzing / s |
|---|---|
| 5 | 190 |
| 20 | 80 |
| 40 | 25 |
| 60 | 9 |
Analysis questions
Question 1 Calculate the rates
Calculate the rate as 1 ÷ time for each temperature and express your answers in units of 10⁻³ s⁻¹ to three significant figures.Question 2 Graph and shape
Plot rate (y-axis) against temperature (x-axis) and describe the shape of the line.Question 3 Factor per ten degrees
Calculate the factor by which the rate increases between 20 °C and 40 °C. Find the average factor per 10 °C and compare it with the rule that the rate doubles.Question 4 Explain with collisions
Explain the trend using particles and activation energy.Question 5 Control variables
List three variables that must be kept the same and explain why.Question 6 Timing uncertainty
The stopwatch time is uncertain by ±1 s. Calculate the percentage uncertainty for the 9 s and 190 s results and state which is less reliable.Question 7 Improvements
State the conclusion and suggest two improvements to the method.
