Rates of Reactions

Objectives

  • Explain how concentration, temperature, catalysts, and surface area affect the rate of a reaction.
  • Predict relative reaction rates based on variations in concentration, temperature, and surface area.
  • Draw conclusions based on experimental data.
  • Determine if a chemical reaction has occurred.
  • Perform and record laboratory measurements using common laboratory equipment.
  • Explain the importance of collecting accurate experimental data.

Related Textbook

Please read chapter 8 of your textbook before beginning this lab. The textbook provides terms, concepts, and other important background information to help you complete this assignment.

Introduction

Chemical reactions can occur at different speeds, or rates of reactions.  Several factors influence the rate of chemical reactions.  These factors include:

  • Concentration of the Reactants
  • Catalysts
  • Temperature
  • Surface Area

In the body, special proteins called enzymes catalyze reactions that would not normally occur at biological temperatures.  Catalysts lower the amount of energy, or activation energy, needed to start a chemical reaction.  Hormones secreted by various parts of the endocrine system help to regulate various bodily functions, including the rate of reactions in the cell.

A note on surface area: as something is broken into smaller pieces, the overall surface area of the item increases.  This is because more surface is exposed for chemicals to react with it.  This means that a whole tablet of Alka Seltzer® has less surface area than a tablet that is broken into smaller pieces.  A crushed tablet will have more surface area than a tablet that has been broken into pieces.

In this experiment, you will perform several different reactions and make predictions on how the concentration, temperature, and surface area influence the reaction rate.  Be sure to read the information covering reaction rates in your textbook after completing this laboratory experiment; you will be tested over that information on the lab final exam.

You will organize your data for this lab into a data table. Click below for a copy of the data table you will need for this lab. It will download to your computer. If you have trouble downloading it, check to ensure blockers are disabled.

The Rates of Reaction Data Table

Experimental Procedure

Chemicals and Supplies

Alka Seltzer® (6 tablets, make sure this is regular Alka Seltzer® and not cold and flu)

Sodium bicarbonate (baking soda), NaHCO3

Acetic Acid (vinegar), HC2H3O2

Digital Balance

9 glasses (drinking glasses are fine)

Paper cupcake liners (weigh boats)

Ice

Digital Thermometer

100mL graduated cylinder

Timer with a Second Hand

2 spoons

Spatula

Pan, Kettle, or microwave-safe container (for heating water)

DI water (distilled or deionized water available at your local grocery story)

PART A: Effect of Temperature on the Rate of Reaction

  1. Obtain 3 clean and dry glasses. Add 100mL of ice water (less than 5ºC) to one glass, 100mL of room temperature water to the second glass, and 100mL of hot water (more than 50ºC) to the third glass.  Record the temperature of each glass of water next to the type of water in the glass on the data table.
  2. Obtain 3 whole Alka Seltzer® Drop one tablet in each glass simultaneously.
  3. Observe the reactions and record what you see happen on the data table provided. Note which tablet completely dissolved first, second, and third.  Record this information on your data table under the column titled “Relative Reaction Rate.”

PART B: Effect of Surface Area on the Rate of Reaction

  1. Obtain 3 clean and dry glasses. Add 100mL of DI water to each glass.  Record the temperature of each amount of DI water on the data table.  The water in each glass should be within 1ºC of each other.  If the temperature of the 3 glasses varies more than 1ºC, allow them to sit for a while until they are all within 1ºC of each other.
  2. Obtain 3 Alka Seltzer® Carefully cut one of the tablets into quarters (4 equal-size pieces).  Using the 2 spoons, carefully crush one of the tablets into a powder, collecting the pieces in a paper cupcake liner.  Leave the third tablet in one piece.
  3. Add the whole tablet to one glass and record the time it takes for the tablet to fully react with the water. Record the time on the data sheet provided.
  4. Repeat step 3 using the broken and crushed tablets, placing each in a different glass.
  5. Record your observations on the data table. Note which tablet completely dissolved first, second, and third.  The tablet with the shortest reaction time has the fastest reaction rate.  Record this information on your data table under the column titled “Relative Reaction Rate.”

PART C: Effect of Concentration on Reaction Rate

  1. Obtain 3 clean and dry glasses.
    • To Glass #1, add 100mL of acetic acid. This glass will have the highest concentration (amount) of acetic acid.
    • To Glass #2, add 70mL of acetic acid and 30mL of DI water. Carefully swirl the glass to mix the water and acetic acid.  This glass will have the second-highest concentration of acetic acid.
    • To Glass #3, add no acetic acid and 100mL of DI water. This glass will have the lowest concentration of acetic acid.
  2. Record the temperature of the solutions in the three glasses. The solutions in each glass should be within 1ºC of each other.  If the temperature of the 3 glasses varies more than 1ºC, allow them to sit for a while until they are all within 1ºC of each other.
  3. Using the digital balance, obtain a 1g portion of sodium bicarbonate.

NOTE: To properly measure this amount of sodium bicarbonate, place a weigh boat on the digital balance and “TARE” the balance according to the directions provided with your balance.  This tells the balance to ignore the mass of the weigh boat and only measure the mass of the chemical.  Next, use a spatula to add 1g of sodium bicarbonate to the weigh boat.

Measuring slightly more or less than 1g of the chemical is okay.  Just be sure to write down exactly how much of the chemical you use.  Be sure to write down all of the numbers that appear on the balance, even if it’s a zero.  This is true of all of the experiments we will conduct in this course.

  1. Repeat step #3 twice more. When you are done, you should have three 1g portions of sodium bicarbonate.
  2. Add one portion of sodium bicarbonate to Glass #1 and record the time it takes for the reaction to stop. Record the time on the data table.
  3. Repeat step #5 for Glass #2 and Glass #3.
  4. Record your observations on the data table. Note which reaction finished first, second, and third.  The glass with the shortest reaction time has the fastest reaction rate.  Record this information on your data table under the column titled “Relative Reaction Rate.”

Waste Disposal

  • All solutions from this lab can be disposed of down the sink. Flush the sink with warm water after disposing of the chemicals.
  • Wash any other glassware used with soap and water once the experiment is complete.

Assignment

Once you have completed this experiment and recorded your data:

  • Submit your completed data table for this lab to the assignment folder on Brightspace. You will receive a zero for this assignment if the data table is incomplete and/or not submitted.
  • Complete the post-lab questions for this experiment (provided below) and submit them to the assignment folder on Brightspace. Your assignment can be neatly handwritten or typed using a program such as MSWord or Google Docs. If using a word processing program, please save your file as a .docx or .pdf file before submitting it to Brightspace.  Please number your answers to each question so I can clearly and easily follow your work. This assignment is worth 10 points.
  • There are no photos of the experiment required for this lab. You just need to complete and submit the data table and post-lab questions.

Rates of Reactions Post-Lab Questions

  1. Based on your observations, how does concentration affect reaction rates? Do your experimental findings agree with the information provided in your textbook?  If not, indicate what error(s) might have happened.  (2 points)
  2. Based on your observations, how does surface area affect reaction rates? Do your experimental findings agree with the information provided in your textbook? If not, indicate what error(s) might have happened.  (2 points)
  3. Based on your observations, how does temperature affect reaction rates? Do your experimental findings agree with the information provided in your textbook? If not, indicate what error(s) might have happened.  (2 points)
  4. Magnesium metal is placed in three test tubes containing hydrochloric acid. Test tube #1 contains 1M HCl, test tube #2 contains 0.1M HCl, and test tube #3 contains 6M HCl.  The bigger the number in front of the M, the more concentrated the solution.  Which test tube will have the slowest rate of reaction?  Why?  (1.5 points)
  5. A glow stick is added to a glass of ice-cold water, a glass of room-temperature water, and a glass of near-boiling water. Which stick will glow the brightest?  Why? (1.5 points)
  6. What is the purpose of enzymes in the body? How do they regulate rates of reaction?  (i.e., do they change the body’s temperature, affect chemical concentration, etc.). (1 point)

This page was created on July 6, 2023, and last updated on August 3, 2023.

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