How Fast Does an Alka-Seltzer® Tablet Make Gas?

Abstract

This is a straightforward, fun project to measure the rate of the chemical reaction that occurs when Alka-Seltzer® tablets are plopped into water. You'll track the volume of carbon dioxide gas produced at regular intervals after the reaction begins. How does changing the temperature of the water affect the production of gas?

Objective

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

Credits

Andrew Olson, Ph.D., Science Buddies

• Alka Seltzer® is a registered trademark of Bayer HealthCare LLC.

Last edit date: 2013-01-10

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:

The compounds on the left-hand side of the equation (bicarbonate ions and hydrogen ions) are called the reactants, and the compounds on the right-hand side of the reaction (water and carbon dioxide) are called the products.

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? In this project you can find out for yourself. You'll build a simple apparatus to collect the carbon dioxide gas produced by the chemical reaction. Then you'll plop Alka-Seltzer® tablets into water at different temperatures, and measure the volume of carbon dioxide gas collected at different time points.

Terms and Concepts

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

• Carbon dioxide gas (CO₂)
• Sodium bicarbonate (NaHCO₃)
• Citric acid (C₆H₈O₇)
• Reactants
• Products
• Ions
• Molecules
• Temperature
• Reaction rate

Bibliography

• Brown, W.P (2007). GCSE notes on the Rates of Chemical Reactions. Retrieved September 13, 2012 from http://www.docbrown.info/page03/3_31rates.htm
• Clark, J. (2002). Understanding Chemistry: Rates of Reaction Menu. Retrieved September 13,2012 from http://www.chemguide.co.uk/physical/basicratesmenu.html

Materials and Equipment

Supplies for this project are available in one convenient kit from the Science Buddies Store

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

• Safety goggles or safety glasses
• Alka-Seltzer® tablets (12)
• Thermometer; a good range would be -10°C to 110°C
• Means for capturing the gas and measuring the volume (choose one of the following two methods):
  • 60 mL syringe:
    • The Science Buddies Kit comes with this option. It is the easier of the two methods to set up.
  • 150mL or 200mL graduated cylinder and plastic dishpan or bucket of water:
• Plastic bottle with cap (1); must be wide-mouthed, clear, and hold 12 ounces or more
• Drill and drill bit (1) for drilling a hole in the bottle cap
  • The Science Buddies Kit comes with a pre-drilled bottle cap; no drilling is needed.
  • If you are not using the kit you will need a 7/32 in drill bit; this will be slightly smaller than the outer diameter of the aquarium tubing to assure an air-tight fit.
  • A center punch or hammer and sharp nail is recommended for getting the drill hole started.
• Aquarium tubing
  • Outer diameter: 5.6 mm (0.22 in)
  • Inner diameter: 4.7 mm (0.19 in)
  • 50 cm (about 2 feet) is good for use with syringe, 100 cm (about 3 feet) is good for use with graduated cylinder
  • Available at tropical fish stores, pet stores
• Measuring cup
• Permanent marker
• Hot and cold tap water
• Ice
• Stopwatch or clock with a second hand
• A helper
• Lab notebook

Order Product Supplies

Experimental Procedure

Note: In this experiment you will collect the carbon dioxide gas produced when a single Alka-Seltzer® tablet is placed in water. Choose either the syringe method or the graduated cylinder method for collecting the carbon dioxide gas. With the Science Buddies Kit you will use the syringe method

Experimental Setup Using Syringe

1. Drill a hole for the aquarium tubing in the center of the cap of the wide-mouth bottle.
   1. If you are using a Science Buddies Kit it comes with the bottle cap pre-drilled. Skip to step 2.
   2. Wear safety goggles for this step.
   3. The hole should be slightly smaller than the outer diameter of the aquarium tubing to assure an air-tight fit.
   4. Mark the location for the hole in the center of the bottle cap. Use a center punch or tap a nail with a hammer to make a small depression at the center location so the drill bit won't slip.
   5. Carefully drill the hole in the bottle cap. It is easiest to do this with the cap screwed in place on the empty bottle. Have your helper hold the bottle straight.
2. Squeeze one end of the tubing and press it into the hole. Push the tubing through to the other side of the cap (see illustration below). This should make an airtight seal.

   Aquarium tubing press-fit into drilled hole in bottle cap.

3. Press the other end of the tubing onto the end of the syringe. Tip: rotate the syringe so that the volume markings are easy to read when you set the syringe down.

   Aquarium tubing pressed on to end of syringe.

4. Here is a picture of the completed plastic bottle/syringe gas collection apparatus.

Experimental Setup Using Graduated Cylinder

1. Drill a hole for the aquarium tubing in the center of the cap of the wide-mouth bottle.
   1. Wear safety goggles for this step.
   2. The hole should be slightly smaller than the outer diameter of the aquarium tubing to assure an air-tight fit.
   3. Mark the location for the hole in the center of the bottle cap. Use a center punch or tap a nail with a hammer to make a small depression at the center location so the drill bit won't slip.
   4. Carefully drill the hole in the bottle cap. It is easiest to do this with the cap screwed in place on the empty bottle. Have your helper hold the bottle straight.
2. Squeeze one end of the tubing and press it into the hole. Push the tubing through to the other side of the cap (see illustration below). This should make an airtight seal.

   Aquarium tubing press-fit into drilled hole in bottle cap.

3. You will be collecting carbon dioxide from the Alka-Seltzer® chemical reaction by displacing water trapped in an inverted graduated cylinder. Here's how to set it up:
   1. Fill your plastic dishpan (or bucket) about one-third full with water.
   2. Fill the graduated cylinder with water.
      1. If your dishpan is deep enough, fill the graduated cylinder by tipping it on its side inside the dishpan. Allow any bubbles to escape by tilting the cylinder up slightly, while keeping it under water. Keeping the opening of the cylinder under water, turn it upside down and attach it to the side of the dishpan with masking tape (or have your helper hold it in place).
      2. If your dishpan is not deep enough, fill the graduated cylinder completely using the faucet and cover the top tightly with plastic wrap. Quickly invert the cylinder and place the opening in the dishpan, beneath the surface of the water. Remove the plastic wrap. Attach the cylinder to the side of the tub with packing tape (or have your helper hold it in place).
   3. The graduated cylinder should now be upside down, full of water and with its opening under the surface of the water in the dishpan. Place the free end of the tubing from the plastic bottle inside the graduated cylinder. Your apparatus is now ready to trap carbon dioxide from the Alka-Seltzer® chemical reaction (see illustration below).

      Schematic diagram of inverted graduated cylinder gas collection apparatus.

   4. You can test your gas collection apparatus by blowing gently into the tube. The bubbles you create should be captured inside the cylinder. (You'll need to re-fill the cylinder before starting your experiment.)

Running the Experiment

1. In this experiment, you will be measuring the reaction rate for the production of carbon dioxide gas from a single Alka-Seltzer® tablet.
   1. You will measure the volume of gas produced at 10-second time intervals after the reaction begins.
   2. You will investigate how the reaction rate changes with water temperature.
2. You'll use the same plastic bottle for repeated trials, so it is convenient to mark the desired water level.
   1. The actual volume of water used is not critical, as long as it is at least 240 ml (8 oz.).
   2. The smaller the air space in the bottle, the sooner you will be able to start collecting carbon dioxide gas.
   3. You do want to use the same amount of water for each trial. Use a permanent marker to mark the water level on the outside of the bottle. Place the tape with its top edge even with the water level in the bottle.
3. For measuring the reaction rate, you will use the same volume of water at three different starting temperatures: hot tap water, cold tap water, and ice water.
   • For the hot and cold tap water, run the water until the temperature stabilizes. Fill the bottle with water to the level of the masking tape.
   • For ice water, fill the bottle about half full with ice cubes and then add cold tap water to the level of the masking tape. Stir for a minute or two so that the temperature equilibrates.
4. Here is how to measure the reaction rate:
   1. Fill the glass bottle 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.
   4. Have your helper get ready with the stop watch, while you get ready with an Alka-Seltzer® tablet. Hold the tablet in one hand and the bottle cap ((with tubing attached) in the other hand.
   5. Have your helper count one–two–three. On three, the helper starts timing and you drop the tablet into the water.
   6. Quickly cap the bottle tightly. You'll immediately see bubbles of CO₂ streaming out from the tablet.
   7. Using the hand that you don't use for writing, swirl the bottle gently, keeping the bottom of the bottle flat on the table top.
   8. Every ten seconds, your helper should call out "Time!" You should immediately read the carbon dioxide volume (in the syringe or graduated cylinder) and write it down in your lab notebook. Prepare a table like the one below to keep your data organized.

      Water temp. (°C)	Trial #	Volume of CO2 after reaction begins (times in seconds)
      		10	20	30	40	50	60	70	80	90	100	110	120

   9. Continue recording the volume of gas at ten-second intervals until the volume is no longer changing. At this point, the reaction is complete.
   10. 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.
5. For each of the three temperatures, you should repeat the experiment four times, for a total of 12 trials.

Analyzing Your Data

1. For each water temperature, calculate the average volume of gas at each time point for the four trials (see the table below)

   Water temp. (°C)	Trial #	Volume of CO2 after reaction begins (times in seconds)
   		10	20	30	40	50	60	70	80	90	100	110	120
   17°C	1
   17°C	2
   17°C	3
   17°C	4
   Average	—

2. Make a graph of the volume of CO₂, in mL, (y-axis) vs. time after the reaction begins, in seconds (x-axis).
   1. You can include the data from all three temperatures on one graph.
   2. Use a different symbol and color for each temperature.
   3. Remember to include a legend that identifies the temperature associated with each symbol.
3. More advanced students should also calculate the standard deviation of the reaction times for each temperature.
   1. Use the standard deviation to add error bars to your graph.
   2. For example, say that the average volume for 17°C water 30 seconds after the reaction began was 45 mL, and the standard deviation was 5.2 mL (these are made-up numbers). You would graph the symbol for the data point at 45 mL, and then draw short vertical bars above and below the symbol. Each vertical bar would have a length equivalent to 5.2 mL.
   3. Error bars give your audience a measure of the variance in your data.
4. How does reaction rate change with temperature?

Variations

• For more basic experiments on reaction rates using Alka-Seltzer® tablets, see the Science Buddies projects
  • Plop, Plop, Fizz Fast: The Effect of Temperature on Reaction Time, and
  • Big Pieces or Small Pieces: Which React Faster?
• We suggested above that you choose one apparatus (syringe or graduated cylinder) for collecting the carbon dioxide gas produced in this reaction. If you're looking for a more ambitious project, you could compare the results you obtain using both methods. Which method has the least variability? Which method gives the most accurate results? Which method is easiest to use?
• Advanced. What is the temperature of the solution when the reaction is complete? For an explanation of the temperature change, see Helmenstine, 2007.

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