Now it is time to design your own experiment to test how particle size (or surface area) affects reaction rate. Answer the next seven questions about your experiment that tests the effect of particle size on reaction rate.
1) What you would do (what would be your procedure)? List the steps. Make sure your list includes the things you will keep constant. You should write the procedure with enough detail so that I could do the experiment by reading what you wrote.
Hint: You are welcome to use the alka seltzer tablet and water reaction again to design this experiment that tests the effect of particle size on reaction rate. You are not required to use the alka seltzer experiment, you could design a different experiment but it must test particle size affect on reaction rate.
Procedure:
1. Gather materials: Alka seltzer tablets, water, two beakers, stopwatch, scale
2. Cut one Alka seltzer tablet in half using a clean and dry knife. Leave the other tablet as a whole.
3. Fill both beakers with 100mL of water at room temperature.
4. Drop one whole Alka seltzer tablet into one beaker and start the stopwatch immediately. Record the time it takes for the tablet to completely dissolve.
5. Repeat step 4 for the half tablet in the second beaker.
6. Measure the weight of the remaining undissolved Alka seltzer tablet in both beakers using the scale.
7. Keep the following constant throughout the experiment:
- Water temperature
- Room temperature
- Amount of water (100mL)
- Type of Alka seltzer tablet
- Concentration of Alka seltzer
- Amount of time from dropping the tablet to recording data
2) What is the independent variable?
The independent variable is the particle size of the Alka seltzer tablet (whole or half).
3) What is the dependent variable?
The dependent variable is the time it takes for the Alka seltzer tablet to completely dissolve.
4) What constants will you keep the same for all trials?
The constants that will be kept the same for all trials are the water temperature, room temperature, amount of water, type of Alka seltzer tablet, concentration of Alka seltzer, and amount of time from dropping the tablet to recording data.
5) How many trials will you run for each particle size?
Two trials will be run for each particle size.
6) How will you analyze your data?
The time it takes for the Alka seltzer tablet to completely dissolve in each trial will be recorded and averaged for each particle size. The weight of the undissolved Alka seltzer tablets will also be recorded and compared between the two particle sizes.
7) What conclusion(s) do you expect to find from your experiment?
I expect to find that the Alka seltzer tablet with the smaller particle size will dissolve faster than the tablet with the larger particle size. This is because a smaller particle size will have a larger surface area available for the water to react with, increasing the rate of the reaction.
To design an experiment to test the effect of particle size on reaction rate, let's consider the reaction between an Alka-Seltzer tablet and water as an example. The procedure for this experiment is as follows:
Materials needed:
- Alka-Seltzer tablets
- Water
- Stopwatch or timer
- Graduated cylinder
- Beakers or cups
- Scale
- Stirring rod
Procedure:
1) Begin by setting up a workspace with all the necessary materials.
2) Fill two beakers or cups with the same amount of water. Make sure the amount of water is consistent for each trial.
3) Weigh several Alka-Seltzer tablets and record their weight. Label each tablet so you can identify the particle size later.
4) Crush one Alka-Seltzer tablet into a fine powder using a mortar and pestle. Alternatively, you can use a pill crusher or break the tablet manually using a flat surface and a rolling pin.
5) Drop the crushed tablet into one of the beakers containing water. Start the stopwatch or timer immediately.
6) Observe and record the time it takes for the reaction to complete, indicated by the cessation of bubbling and the tablet fully dissolving.
7) Repeat steps 4-6 using different-sized particles. For example, you can repeat step 4 using a whole tablet, another tablet crushed with less force, and another tablet cut into small pieces.
8) Each time, drop the specified particle size into the second beaker containing water, starting the timer immediately. Observe and record the time taken for the reaction to complete.
9) Repeat each particle size trial at least three times to ensure reliable data and calculate an average reaction time.
10) Remember to keep the amount of water, temperature, and concentration of water consistent in each trial to maintain a fair test.
11) Compile all your data and analyze it to determine the effect of particle size on reaction rate.
Note: The particle size can be varied according to your experimental design, and it is essential to maintain all other factors constant, except for the independent variable being tested - particle size.