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Can You Change the Rate of a Chemical Reaction by Changing the Particle Size of the Reactants?

Difficulty
Time Required Short (2-5 days)
Prerequisites None
Material Availability Readily available
Cost Very Low (under $20)
Safety Adult supervision required for use of power drill (one hole required when building the simple experimental apparatus)

Abstract

The ingredients in Alka-Seltzer® tablets undergo a chemical reaction that produces carbon dioxide gas as soon as the tablets hit water. Do you think you can cause the tablets to produce gas faster by breaking them into smaller pieces before dropping them in water? Find out for yourself with this project.

Objective

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

Credits

Andrew Olson, Ph.D., Science Buddies

Cite This Page

MLA Style

Science Buddies Staff. "Can You Change the Rate of a Chemical Reaction by Changing the Particle Size of the Reactants?" Science Buddies. Science Buddies, 2 Sep. 2014. Web. 21 Sep. 2014 <http://www.sciencebuddies.org/science-fair-projects/project_ideas/Chem_p030.shtml>

APA Style

Science Buddies Staff. (2014, September 2). Can You Change the Rate of a Chemical Reaction by Changing the Particle Size of the Reactants?. Retrieved September 21, 2014 from http://www.sciencebuddies.org/science-fair-projects/project_ideas/Chem_p030.shtml

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Last edit date: 2014-09-02

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:

acid hydrolysis of bicarbonate

So how does particle size come into this? In order for the reaction shown above to take place, the ingredients in the tablet first have to dissolve. The tablet has a large surface area, so this step should be pretty fast, right? What effect do you think particle size will have on the speed of the bicarbonate reaction? You can find out for yourself by plopping prepared Alka-Seltzer® tablets (whole tablets, halved tablets, quartered tablets, and powdered tablets) into water at the same temperature, and measuring the volume of carbon dioxide gas collected at regular intervals after the reaction starts.

Terms and Concepts

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

  • Molecules
  • Temperature
  • Reactants
  • Products
  • Reaction rate
  • Sodium bicarbonate (NaHCO3)
  • Citric acid (C6H8O7)

Questions

  • Do you think changing the particle size will have a measurable effect on the chemical reaction rate?
  • Will smaller particles speed up or slow down the reaction?

Bibliography

Materials and Equipment

These items can be purchased from Carolina Biological Supply Company, a Science Buddies Approved Supplier:

  • Aquarium, or air line, tubing (50 cm, or 2 ft, long for use with the syringe, or 100 cm for use with the graduated cylinder). It should have an inside diameter of 4.7 mm, or 0.19 inches, and an outer diameter of 5.6 mm, or 0.22 inches. Alternatively this tubing may be available at tropical fish stores and pet stores.
  • Safety goggles or safety glasses
  • 60 mL syringe. Alternatively, you could use a 150 mL or 200 mL graduated cylinder and a plastic dishpan or bucket of water. Choose one of these methods for capturing the gas and measuring the volume.
  • Thermometer. A good range would be -10°C to 110°C. Alternatively, a standard kitchen candy thermometer will also work fine.
You will also need to gather these items:
  • Alka-Seltzer® tablets (at least 12). Tip: If you plan to do additional variations to the project, you will want to get a larger box.
  • Sheet of blank paper
  • Hammer
  • Piece of scrap wood
  • Clear, wide-mouth plastic bottle with cap (12 ounces or larger, e.g., a small Gatorade® bottle)
  • Drill
  • 5.56 mm (7/32 in) drill bit (should be slightly smaller than the outer diameter of aquarium tubing to assure an air-tight fit)
  • Center punch (or hammer and sharp nail)
  • Measuring cup
  • Masking tape
  • Hot and cold tap water
  • Ice
  • Clock or watch with a second hand
  • A helper
  • Lab notebook

Disclaimer: Science Buddies occasionally provides information (such as part numbers, supplier names, and supplier weblinks) to assist our users in locating specialty items for individual projects. The information is provided solely as a convenience to our users. We do our best to make sure that part numbers and descriptions are accurate when first listed. However, since part numbers do change as items are obsoleted or improved, please send us an email if you run across any parts that are no longer available. We also do our best to make sure that any listed supplier provides prompt, courteous service. Science Buddies does participate in affiliate programs with Amazon.comsciencebuddies, Carolina Biological, and AquaPhoenix Education. Proceeds from the affiliate programs help support Science Buddies, a 501( c ) 3 public charity. If you have any comments (positive or negative) related to purchases you've made for science fair projects from recommendations on our site, please let us know. Write to us at scibuddy@sciencebuddies.org.

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Experimental Procedure

Note: In this experiment you will collect the carbon dioxide gas produced when the contents of a single Alka-Seltzer® tablet are placed in water. Choose either the syringe method or the graduated cylinder method for collecting the carbon dioxide gas.

Experimental Setup Using Syringe

  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). This should make an airtight seal.

    aquarium tubing press-fit into drilled hole in bottle cap

    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

    Aquarium tubing pressed on to end of syringe.

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

    plastic bottle/syringe gas collection apparatus

    Experimental Setup Using Graduated Cylinder

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). This should make an airtight seal.

    aquarium tubing press-fit into drilled hole in bottle cap

    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).

      schematic diagram of inverted graduated cylinder gas collection apparatus

      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 as you vary the particle size of the reactants.
  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 piece of masking tape on the outside of the bottle to mark the water level. 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 the same starting temperature. You will use four different particle sizes for the Alka-Seltzer® tablets:
    1. A whole tablet
    2. A tablet broken in half
    3. A tablet broken in quarters
    4. A tablet ground into powder. To do this, fold a single tablet to be ground inside a clean piece of paper. Place the folded paper on a piece of scrap wood, and use the hammer to firmly pound the tablet about ten times. Stop immediately if the paper shows signs of tearing: you don't want to lose any of the powder. You can also use the back of a metal spoon or ice cream scoop to carefully crush your tablet into a powder once it is wrapped in paper if you do not want to use a hammer and piece of wood. Crushing the tablet this way may take a little more time.
  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 (or tablet pieces) 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 to keep your data organized.

      Particle Size
      (whole/halves/quarters/powder)
      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. Remember that you need to have three whole tablets for this experiment.
  5. For each of the four particle sizes, you should repeat the experiment three times, for a total of 12 trials.

Analyzing Your Data

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

    Particle Size
    (whole/halves/quarters/powder)
    Trial # Volume of CO2 after reaction begins (times in seconds)
    10 20 30 40 50 60 70 80 90 100 110 120
    whole tablet 1                        
    whole tablet 2                        
    whole tablet 3                        
    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 four particle sizes on one graph.
    2. Use a different symbol and color for each particle size.
    3. Remember to include a legend that identifies the particle size associated with each symbol.
  3. More advanced students should also calculate the standard deviation of the reaction times for each particle size.
    1. Use the standard deviation to add error bars to your graph.
    2. For example, say that the average volume for two half-tablets 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 particle size?

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Variations

  • For more basic experiments on reaction rates using Alka-Seltzer® tablets, see the Science Buddies projects
  • 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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