Plop, Plop, Fizz Fast: The Effect of Temperature on Reaction Time

Related Links

• Science Fair Project Guide

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• Chemistry Safety Guide
• Visualizing Molecules in Three Dimensions

Project Summary

Difficulty	4
Time required	Short (several days)
Prerequisites	None
Material Availability	Readily available
Cost	Very Low (under $20)
Safety	Adult supervision recommended when working with hot water solutions

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Sponsor

Sponsored by a generous grant from the Camille and Henry Dreyfus Foundation

Objective

The goal of this project is to measure the effect of temperature on the rate of a chemical reaction.

Introduction

You may have seen a television commercial for Alka-Seltzer tablets, or heard one of their advertising slogans: "Plop, plop, fizz, fizz, oh what a relief it is!®" When you drop the tablets in water, they make a lot of bubbles, like an extra-fizzy soda. And like a soda, the bubbles are carbon dioxide gas (CO₂). However, with Alka-Seltzer®, the CO₂ is produced by a chemical reaction that occurs when the tablets dissolve in water.

The main ingredients of Alka-Seltzer tablets are aspirin, citric acid, and sodium bicarbonate (NaHCO₃). When sodium bicarbonate dissolves in water, it dissociates (splits apart) into sodium (Na⁺) and bicarbonate (HCO₃⁻) ions. The bicarbonate reacts with hydrogen ions (H⁺) from the citric acid to form carbon dioxide and water. The reaction is described by the following chemical equation:

So how does temperature come into this? In order for the reaction shown above to occur, the bicarbonate ions have to come into contact with the hydrogen ions. Molecules in a solution are in constant motion, and are constantly colliding with one another. The hydrogen and bicarbonate ions must collide at the right angle and with enough energy for the reaction to occur. The temperature of a solution is a measure of the average motion (kinetic energy) of the molecules in the solution. The higher the temperature, the faster the molecules are moving. What effect do you think temperature will have on the speed of the bicarbonate reaction? You can find out for yourself by plopping Alka-Seltzer® tablets into water at different temperatures, and timing how long it takes for the chemical reaction to go to completion.

Terms, Concepts and Questions to Start Background Research

To do this project, you should do research that enables you to understand the following terms and concepts:

• Molecules
• Temperature
• Reactants
• Products
• Reaction rate

Questions

• Keeping in mind that an increase in temperature reflects an increase in the average molecular motion, how will increased temperature affect the reaction rate?
• What temperature change is required to increase the reaction time by a factor of 2?
• What temperature change is required to decrease the reaction time by a factor of 2?

Bibliography

• Bayer HealthCare, 2005. "Temperature and Rate of Reaction," Bayer HealthCare, LLC [accessed May 8, 2007] http://www.alka-seltzer.com/as/experiment/student_experiment1.htm.
• Swanson, G.C., date unknown. "Chemistry Experiments for the Home: Bubble Rate," Science Department, Daytona Beach Community College [accessed May 8, 2007] http://faculty.dbcc.edu/swansoj/Bubble_Rate.htm.

Materials and Equipment

To do this experiment you will need the following materials and equipment:

• At least 12 Alka-Seltzer® tablets (if you plan to do additional variations to the project, you'll want to get a larger box)
• Thermometer (good range would be -10°C to 110°C
  • E.g. catalog # WW6332000 from Science Kit & Boreal Lab or catalog #15V1460 from Wards Natural Science
  • Standard kitchen candy thermometer will also work fine
• Clear 12 ounce (355 mL) drinking glass (or larger)
  • note: Use Pyrex glass when working with water heated on the stove or in the microwave)
• Measuring cup
• Masking tape
• Something to stir with (a teaspoon or a chopstick, for example)
• Hot and cold tap water
• Ice
• Stop watch (you can also use a clock or watch with a second hand)
• A helper
• Lab notebook
• Pencil

Experimental Procedure

1. Do your background research and make sure that you are familiar with the terms, concepts, and questions, above.
2. In this experiment, you will be measuring the time it takes for one Alka-Seltzer® tablet to react completely in water. You will investigate how the reaction time changes with water temperature.
3. You'll use the same glass for repeated trials, so it is convenient to mark the desired water level.
   1. Use the measuring cup to add 8 ounces (236 mL) of water to the glass. (If you're using metric volume units, rounding up to 250 mL is fine.)
   2. Use a piece of masking tape on the outside of the glass to mark the water level. Place the tape with its top edge even with the water level in the glass.
   3. Now you can use the masking tape to fill the glass to the right level for each trial.
4. For observing the reaction, you will use the same volume of water at three different starting temperatures: hot tap water, cold tap water, and ice water.
   1. For the hot and cold tap water, run the water until the temperature stabilizes. Fill the glass with water to the level of the masking tape.
   2. For ice water, fill the glass about half full with ice cubes, then add cold tap water to the level of the masking tape. Stir for a minute or two so that the temperature equilibrates.
5. Here is how to measure the reaction time:
   1. Fill the glass with water to the level of the masking tape.
   2. Measure the temperature of the water, and record it in your lab notebook.
   3. Remove the thermometer. (It's not a good idea to use the thermometer as a stirring rod. It might break.)
   4. Have your helper get ready with the stop watch, while you get ready with an Alka-Seltzer® tablet. Have your helper count one–two–three. On three, the helper starts the stop watch and you drop the tablet into the water.
   5. You'll immediately see bubbles of CO₂ streaming out from the tablet.
   6. Stir the water gently and steadily. Use the same stirring method and speed for all of your experimental trials. The tablet will gradually disintegrate. Watch for all of the solid white material from the tablet to disappear.
   7. When the solid material has completely disappeared, and the bubbles have stopped forming, say "Stop!" to have your helper stop the stopwatch.
   8. Record the reaction time in your lab notebook.
   9. Tip: be careful when opening the packets and handling the Alka-Seltzer® tablets. The tablets are thin and brittle, so they break easily. If some of the tablets are whole, and some are broken into many pieces, the separate trials will not be a fair test.
6. For each of the three temperatures, you should repeat the experiment four times, for a total of 12 trials. You can organize your data in a table like the one below.

   Condition	Temperature (°C)	Reaction Time (s)				Average Reaction Time (s)
   		Trial #1	Trial #2	Trial #3	Trial #4
   Hot Tap Water
   Cold Tap Water
   Ice Water

7. Calculate the average reaction time for each of the three water temperatures.
8. Make a graph of the average reaction time, in seconds, (y-axis) vs. water temperature, in degrees Celsius (x-axis).
9. How does reaction time change with temperature?

Variations

• More advanced students should also calculate the standard deviation of the reaction times for each temperature.
  • Use the standard deviation to add error bars to your graph.
  • For example, say that the average reaction time for one temperature was 45 seconds, and the standard deviation was 5.2 seconds (these are made-up numbers). You would graph the symbol for the data point at 45 seconds, and then draw short vertical bars above and below the symbol. Each vertical bar would have a length equivalent to 5.2 seconds.
  • Error bars give your audience a measure of the variance in your data.
• Adult supervision required. Is reaction rate predictable over a larger temperature range? Water remains liquid above 0°C and below 100°C. Repeat the experiment at one or more additional high temperatures to find out. Use Pyrex glass for containing heated water, and use appropriate care (e.g. wear hot mitts and safety goggles) when handling hot water.
• Surface area of reactants, see:
• In this experiment you observed the reaction mixture and watched as the tablets dissappeared and formed gas bubbles. For more advanced versions of this experiment, you can build a simple apparatus so that you can measure the volume of the gas produced over time. Because you will be able to collect data at multiple time points, you get information about how the reaction rate changes over time. For more advanced versions of measuring the reaction rate, see the Science Buddies projects:
  • How Fast Does an Alka-Seltzer® Tablet Make Gas?, and
  • Can You Change the Rate of a Chemical Reaction by Changing the Particle Size of the Reactants?.

• For more science project ideas in this area of science, see Chemistry Project Ideas

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Credits

Andrew Olson, Ph.D., Science Buddies

Sources

• Bayer HealthCare, 2005. "Temperature and Rate of Reaction," Bayer HealthCare, LLC [accessed May 8, 2007] http://www.alka-seltzer.com/as/experiment/student_experiment1.htm.
• Swanson, G.C., date unknown. "Chemistry Experiments for the Home: Bubble Rate," Science Department, Daytona Beach Community College [accessed May 8, 2007] http://faculty.dbcc.edu/swansoj/Bubble_Rate.htm.