use alka seltzer to explore reaction rate experiment

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Experiment: test the effect of temperature on reaction time.

Can you make an Alka-Seltzer tablet dropped in water fizzle faster or more loudly by changing the water’s temperature?

Figure 1. In this experiment, we investigate how to make Alka-Seltzer tablets plunked in water fizzle faster and more furiously.

asadykov/iStock/Getty Images Plus

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• Google Classroom

By Science Buddies

July 12, 2023 at 6:30 am

Objective : To measure the effect of temperature on the rate of a chemical reaction

Areas of science : Chemistry, science with your smartphone

Difficulty : Easy intermediate

Time required : 2–5 days

Prerequisites : None

Material availability : Readily available

Cost : Very low (under $20)

Safety : Adult supervision may be needed when working with hot water solutions

Credits : Andrew Olson, PhD, Science Buddies; edited by Svenja Lohner, PhD, Science Buddies

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, as shown in the main image up top (Figure 1). And like a soda, the bubbles are carbon dioxide gas (CO 2 ). However, with Alka-Seltzer, the CO 2  is produced by a  chemical reaction  that occurs when the tablets dissolve in water.

Alka-Seltzer  is a medical drug that works as a pain reliever and an  antacid  (antacids help neutralize stomach acidity, such as heartburn). The pain reliever used is aspirin and the antacid used is  baking soda (sodium bicarbonate, NaHCO 3 ). To take the tablets, they should be fully dissolved in a glass of water. When sodium bicarbonate dissolves in water, it dissociates (splits apart) into sodium (Na + ) and bicarbonate (HCO 3 ) ions. (An  ion  is a  molecule  that has a charge, either positive or negative.) The bicarbonate reacts with hydrogen ions (H + ) from citric acid (another ingredient in the tablets) to form carbon dioxide gas and water. In other words, carbon dioxide gas is a  product  of this reaction. The reaction is described by Equation 1 below:

Equation 1. 3HCO 3 − + 3H + → 3H 2 O + 3CO 2

So how is  temperature  related to this  bicarbonate reaction ? 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, or  rate , of the bicarbonate reaction?

In this chemistry science project, you will find out for yourself by plopping Alka-Seltzer tablets into water at different temperatures and measuring how long it takes for the chemical reaction to go to completion. In addition, you can record the sound of the Alka-Seltzer fizzle using a smartphone equipped with a sensor app. Do you think it will fizz more loudly in hot or cold water?

Terms and Concepts

• Chemical reaction
• Alka-Seltzer
• Baking soda, or sodium bicarbonate
• Temperature
• Bicarbonate reaction
• Reaction rate
• What is the bicarbonate reaction? What are its products?
• Keeping in mind that an increase in temperature reflects an increase in the average molecular motion, how do you think increasing temperature will affect the reaction rate?
• What temperature change do you think would be required to increase, or decrease, the reaction time by a factor of two?
• What other factors besides temperature can affect how well a chemical reaction takes place?

Materials and Equipment

• Alka-Seltzer tablets (at least 12; if you plan to do additional variations to the project, you will want to get a larger box)
• A suitable thermometer is available from  Amazon.com
• A standard kitchen candy thermometer will also work fine
• Clear drinking glasses or jars; about 8 ounces, or 240 milliliters (two of the same size)
• Graduated cylinder, 100 mL. A 100 mL graduated cylinder is available from Amazon.com . Alternatively, measuring cups may be used.
• Masking tape
• Hot and cold tap water
• With option 2 in procedure: Stopwatch or a clock or watch with a second hand
• Optional: A helper
• Lab notebook
• With option 1 in procedure: Smartphone with a sensor app such as phyphox, available for free on  Google Play  for Android devices (version 4.0 or newer) or from the  App Store  for iOS devices (iOS 9.0 or newer).
• With option 1 in procedure: Small sealable (waterproof) plastic bag that fits your phone inside of it

Experimental Procedure

Note : In this science project, you will investigate how water temperature affects the dissolving time of an Alka-Seltzer tablet. You will use a smartphone equipped with a sensor app to record the fizzing sound of the Alka-Seltzer reaction in water and measure the time it takes for one Alka-Seltzer tablet to react completely in water. The app creates a graph that will not only give you information about the reaction time but will also allow you to assess how loud each reaction was based on the measured sound intensities. If you do not have a phone, you can observe the reaction and use a stopwatch to time how long it takes for each tablet to dissolve.

• Do your background research and make sure that you are familiar with the terms and concepts in the Background.
• In your lab notebook, make a data table like Table 1. You will record your results in this data table.
• Add 200 mL (a little less than 1 cup) of water to the drinking glass, or fill it up to about 1 inch below the rim.
• Use a piece of masking tape on the outside of the glass to mark the water level, placing the tape with its top edge even with the water level in the glass, as shown in Figure 2.
• Note:  You do not want to fill the glass completely full because the bicarbonate reaction produces bubbles that could splash out.
• 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. Be careful when handling the hot water.
• For ice water, fill the glass about half full with ice cubes, then add cold tap water to a bit above the level of the masking tape. Stir for a minute or two so that the temperature equilibrates. Once temperature has equilibrated, remove the ice cubes from the water’s surface using a spoon or other utensil immediately before adding the Alka-Seltzer tablet. (Pour out any extra water so that the water is up to the level of the masking tape.)

• Open the sensor app on your phone and select the sound sensor (audio amplitude in phyphox). Remember, that when you are using the phyphox app you will have to calibrate the audio amplitude sensor (sound sensor) before you do any measurements. Do this calibration before you start your investigation, so you get correct sound intensity readings. To calibrate your sound sensor in phyphox, follow the instructions in the sound sensor calibration video . You will have to re-calibrate the audio amplitude sensor (re-set the decibel offset) every time you start a new recording! Once you have calibrated the sensor, make sure you know where the microphone is located on your phone and do a quick test to see if your sound measurement is working. For example, you could record yourself clapping or singing to check if the sensor behaves as expected.
• Once you have confirmed that the sensor works and you are familiar with the app, you can start with the experiment. You should do this experiment in a quiet environment. The background reading of your sound meter when there is no noise in the room should be in the range between 20–40 decibels (dB).
• Measure the temperature of the water (in Celsius [C]) in the first glass that you prepared, and record it in the data table in your lab notebook. Remove the thermometer from the glass before continuing with the next step.
• Put your phone in the waterproof plastic bag and make sure it is sealed well. You don’t want it to get wet!

• Take one whole Alka-Seltzer tablet out of its package and hold it above the glass filled with water. In the phyphox app, start a new recording for your first experiment by pressing the play button.
• Once the recording starts, drop the tablet into the water.  Note : You have to be very quiet during the experiment. Any sound that you make will be recorded and could affect your data. Try to be as quiet as possible while you are recording your data!
• You will immediately see and hear bubbles of CO 2  streaming out from the tablet.
• The tablet will gradually disintegrate. Observe the graph recorded by the app, and how the sound sensor is responding to the fizzling while all of the solid white material from the tablet disappears.

• Your data should look something like the graph in Figure 4. Your graph should show an increased sound intensity for as long as the Alka-Seltzer reaction took place. The sound level of the reaction might be louder in the beginning and decrease as the tablet gets smaller. In the graph, every bubble that pops in the solution is represented by a spike.
• Measure the time between the beginning of your reaction (when you dropped the tablet and the sound intensity started to increase) and the end of the reaction (when the sound intensity reached background levels again or does not change significantly anymore). In phyphox, you can use the “pick data” function to select the respective data points and view their time and decibel values. For example, the reaction in Figure 4 started a little after 3 seconds and ended at about 66 seconds.
• Calculate the time difference between these two points. The result is the reaction time for your first trial. Record the reaction time (in seconds [s]) in the data table in your lab notebook.
• 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. You should only use whole tablets.
• After filling the glass to the level of the masking tape, measure the temperature of the water (in Celsius [C]), and record it in the data table in your lab notebook.
• Remove the thermometer from the glass before continuing with the next step.
• 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.
• You will immediately see bubbles of CO 2  streaming out from the tablet.
• The tablet will gradually disintegrate. Watch for all of the solid white material from the tablet to disappear.
• When the solid material has completely disappeared, and the bubbles have stopped forming, say “Stop!” to have your helper stop the stopwatch.
• Record the reaction time (in seconds [s]) in the data table in your lab notebook.
• Repeating an experiment helps ensure that your results are accurate and reproducible.
• When you are done, you should have done a total of three trials for each of the three temperatures.
• Calculate the average reaction time for each of the three water temperatures. Record your results in the data table in your lab notebook.
• Make a graph of the average reaction time, in seconds (on the Y-axis), vs. water temperature, in degrees Celsius (on the X-axis).
• Hint:  If you are having trouble explaining your results, try re-reading the Introduction in the Background.
• If you chose to use a sensor app to record your data, look at the graphs for each water temperature again. Write down the maximum sound intensity that you observed during the Alka-Seltzer reaction (not including the initial or end peaks) for each trial. You can get the number in the phyphox app by using the “pick data” tool to select the timepoint at which the sound intensity is highest. In the example shown in Figure 4, this would be around 35 seconds with a sound intensity of about 50 decibels. Calculate the average for each of the three water temperatures and record your results in the data table in your lab notebook.
• Make a graph of the average maximum sound intensity, in decibels (on the Y-axis), vs. water temperature, in degree Celsius (on the X-axis).
• Which reaction was the loudest? Did you expect these results?

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• 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 water heated on the stove or in the microwave, and use appropriate care (e.g., wear hot mitts and safety goggles) when handling hot water. A standard candy thermometer should be able to measure the temperatures in this higher range.
• You could turn the bicarbonate reaction into a home-made lava lamp. To do this, you will want to use a tall jar or empty clear plastic 1-liter or 2-liter bottle, fill it with 2 to 5 centimeters (cm) of water, add 5 drops of food coloring, and then fill it at least three-quarters full with vegetable oil. You could repeat the science project using your homemade lava lamp at a cold and a hot temperature. To do this, you will need to figure out a way to make the prepared bottle hot or cold. (For example, to make it hot you could let it sit in a large bowl of hot water, and to make it cold you could store it in a refrigerator or freezer.) You will also want to use one-quarter of an Alka-Seltzer tablet at a time (instead of a whole tablet). How does the bicarbonate reaction look and function in the home-made lava lamp?

This activity is brought to you in partnership with  Science Buddies . Find  the original activity  on the Science Buddies website.

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The Alka Seltzer Reaction

Introduction & motivation.

Chemical reactions are one of the primary focuses for Chemical Engineers. From synthesizing polymers to treating water to creating fertilizers, chemical reactions are important in nearly every aspect of daily life. One job of Chemical Engineers is to classify, understand, and control these reactions to speed them up or slow them down.

Chemical reactions occur when bonds within molecules are broken or formed. There are several things that signify that a chemical reaction took place. These include a change in color, the production of a gas or solid, and of course a change in chemical composition. The starting chemicals before a reaction are called the reactants , and the chemicals that are produced are called the products . The reaction in this activity involves using sodium bicarbonate and citric acid to produce water and carbon dioxide.

Reaction : HCO 3 – (aq) + H + (aq) → H 2 O (l) + CO 2 (g)

The tablets contain sodium bicarbonate (NaHCO 3 ) and citric acid. When the tablet is dissolved in water, bicarbonate (HCO 3 – ) and hydrogen ions (H + ) are formed. Once in solution, the two chemicals can then react according to the reaction listed above. For the reaction to occur, the HCO 3 – and H + must collide at the right angle with the right amount of energy. The chances of this happening are better when the tablet is crushed into more pieces since the molecules have more opportunities to collide and when the temperature is higher, since the molecules are moving faster.

In this activity, students will experiment with the reaction between Alka Seltzer tablets and water in different conditions. By changing temperature and the surface area available for reaction, students will begin to see what factors chemical engineers can control to get the desired result.

This activity introduces the reaction used for the Alka Seltzer Rockets activity, so it is typically performed before building rockets to understand the nature of the reaction before using it.

Chemical Safety:

• Sodium Bicarbonate
• Alka Seltzer tablets
• Large beakers
• Food coloring
• Stopwatches
• Metal spoons
• Thermometers

Before the experiment, ask students to hypothesize what will make the reaction go the fastest and what makes them think that. This can be anything, but try to seek answers with specific regard to the variables being changed in this activity.

The Effect of Temperature on Rate of Reaction

• Partially fill a large beaker with ice cubes. Fill the beaker with water up to the 250 mL mark with cold water and stir the ice water until the temperature equilibrates.
• Measure the temperature of the water and record it in the table.
• Add a tablet and record the time it takes for the tablet to react.
• Repeat 1-2 with room temperature water, then with hot water heated to 70 degrees C using a hot plate.

The Effect of Surface Area on Rate of Reaction

• A whole tablet
• A tablet broken into quarters
• A tablet ground into powder: Place the tablet it a piece of weighing paper (wax or parchment paper work as well) and break it either with your hands or crush it using the back of a metal spoon.
• Add 250 mL of water to a large beaker.
• Measure and record the temperature of the water and make sure it is consistent between trials.
• One student should be ready with a stopwatch and another student should be ready with the whole tablet. The student with the stopwatch should count to three and on three start the stopwatch. At the same time, the other student should drop the tablet into the water.
• Gently stir the water at a consistent speed and pattern.
• As soon as the last of the tablet disappears, yell “Stop!,” stop the stopwatch, and record the time in the table.
• Repeat Steps 2-6 with the quartered tablet and the crushed tablet.

At the end, collect and present all class data on the board. Highlight discrepancies and the general trend.

• Which combination of factors made the reaction go the fastest? The slowest? (Higher surface area and temperature make the reaction go faster. Since the reaction occurs on the surface of the tablet pieces, more access to it will make the reaction go faster because there are more molecules to make bumping together more likely. Higher temperature gives more energy to the molecules, meaning they are more likely to have enough energy for the reaction to continue. The opposite is true for the slowest rate – low surface area and temperature.)
• Why would we want reactions to happen faster or slower? (e.g. we want rusting reactions to be slower to protect metal products, but we want redox reactions that recharge our phone batteries to be fast.)
• Is there a limit to how fast we can make the reaction? Would we want to place a limit if there is not a physical one? (Reactions have maximum rates for a few reasons, like the amount of surface area available to react, if the mixture makes it difficult for molecules to move, etc. If the rate were increased too high, it becomes a safety concern! Sometimes reactions get too fast, too hot, and can’t be slowed down. This is a dangerous runaway reaction , the last thing a chemical engineer wants!)
• Why did any discrepancies come up in the data? What ways could we make our process better to limit those from affecting the class data as a whole? (Discrepancies come up from human error with measuring time, not having precise sizes of tablets, imprecise temperature control across trials, and how hard it is to see a reaction is finished! Let students get creative with suggesting improvements, but a few could include using a grid and knives to chop up tablets or putting the ground tablets through a sieve, using a robot to stir and observe the reaction, and putting the beakers in water baths.)
• We know Alka Seltzer is a medicine to make us feel better. Why might it be designed to fizz? (Fizzing helps the aspirin in the tablet quickly absorb into the bloodstream, making the medicine fast-acting. It might also make it more appetizing to drink!)

Additional Resources

• How Does Alka Seltzer Work?
• VIDEO: Why Does Alka Seltzer Fizz?
• ← Alka Seltzer Rockets
• Separations Activity →

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LAB in Observations , Chemical Change , Reaction Rate , Scientific Method , Experimental Design . Last updated October 14, 2019.

In this lab, students will explore factors that effect reaction rate and develop a general statement that describes how the factors (temperature, particle size, and concentration) effect the rate based on experimental data. This is an inquiry-based activity.

Grade Level

High or middle school

By the end of this lesson, students should be able to

• Devise a method to measure reaction rate
• Design a controlled experiment
• Describe how temperature, particle size and concentration affect the rate of a reaction.

Chemistry Topics

This lesson supports students’ understanding of

• Reaction rates

Teacher Preparation : 20 minutes

Lesson : 1 class period

• 6 Alka-Seltzer tablets
• Beakers (5)
• Graduated cylinder
• Mortar and pestle or zipper plastic bags
• Thermometer
• Baking soda
• Other materials as requested by student
• Always wear safety goggles when handling chemicals in the lab.
• Students should wash their hands thoroughly before leaving the lab.

Teacher Notes

• This lab was developed with inquiry in mind. For more information about inquiry-based activities and how to plan them, watch the archived webinar “ Cookbook to Inquiry .”
• It is up to the students to determine how to measure the reaction rate.

For the Student

The two main ingredients in Alka-Seltzer are citric acid and sodium bicarbonate, an acid and base. When these substances react, one of the products is carbon dioxide gas.

Using Alka-Seltzer antacid tablets, design experiments to study how temperature, particle size, and concentration affect the rate of reaction.

• All procedures must be approved by your teacher.
• Be specific about your procedures.
• Only vary one variable.
• Make sure all containers are clean and dry before starting the experiment.

Before you begin:

Place one Alka-Seltzer tablet in a container. Add 20 mL of water. Observe the reaction.

Observations

PART I: Temperature’s effects on reaction rate Write a procedure to test the effect of temperature on rate using the Alka-Seltzer and water reaction you just carried out. Your teacher must approve your procedure before you can carry out the experiment.

Procedure _______ (teacher’s initials)

Was your prediction correct?

Write a statement that describes the effect of temperature on reaction rate.

PART II: Particle size’s effect on reaction rate Write a procedure to test the effect of particle size on rate using the Alka-Seltzer and water reaction you just carried out. Your teacher must approve your procedure before you can carry out the experiment.

Write a statement that describes the effect of particle size on reaction rate.

PART III: Concentrations effects on reaction rate Baking soda is sodium bicarbonate. Vinegar is acetic acid in water. These chemicals react to produce carbon dioxide gas, the same product released by the Alka-Seltzer tablet in water. Place a small amount of baking soda two containers. Pour 10 mL of water in one container and 10 mL of vinegar in another container. Make observations.

Design an experiment to see how the concentration of vinegar effects the reaction rate.

Write a statement that describes the effect of concentration on reaction rate.

To clean up: Pour solutions down the sink. Clean and dry all containers.