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Chemical Reactions

Investigation 3 – PreLab









Remember that everything in the environment, whether naturally occurring or man-made, is composed of chemicals, and research of chemicals has led to the discovery and development of new and improved paints, medicines, cosmetics, electronic components, and thousands of other products.


Pharmacists distribute prescription drugs to people. To do this safely, they must understand the chemical composition of these drugs so that they can create special versions of medications for patients who may have allergies to certain substances, give the right dosage, and give patients advice on the possible side effects.


This Investigation is designed to help you to answer the following Focus Question:

  • In a chemical reaction, what is the relationship between the amount of reactants and the amount of products? 

Note: This question is located in your SDR at the beginning and end of the Investigation.


As a class, read the Background(s) in the Investigation. When finished, discuss the following concepts as a class:

  • In a chemical reaction, the reactants interact to form the products.
  • The consumption of the reactants takes place at the same rate as the production of products.
  • To measure the rate of a reaction, scientists measure the disappearance of one of the reactants or the production of one of the products. 
  • A catalyst affects the rate of a reaction.
  • A catalyst is neither a reactant nor a product since it is not consumed or produced in a chemical reaction.



The following list includes Key Terms that are introduced in the Investigation Background(s). They should be used, as appropriate, by teachers and students during everyday classroom discourse.

  • rate
  • wavelength
  • nanometer
  • spectrophotometer
  • absorbance
  • catalyst

Note: Definitions to these terms can be found on the Introduction page to the CELL.


  • The following chemical equation describes the reaction that you will analyze in this Investigation.

CHEM reaction

  • Acetone and iodine are the two reactants while monoiodoacetone and hydrogen iodide are the two products of the chemical reaction.
  • The HCl is a catalyst for the reaction and is neither a reactant nor a product. It does not participate in the reaction directly but serves to speed up the reaction. Since the same amount of HCl is added to the reaction in each Trial, its effect on the rate of the reaction in each Trial will be the same.
  • Predict the answers to the following questions.
    • Do chemical reactions always produce products at the same rate? 
    • What factors affect how fast a chemical reaction takes place?
    • If you change the amount of a reactant, what happens to the time it takes to complete a chemical reaction?

Note: You will be able to answers these questions after they have completed the Investigation.

  • Play the video below. Remember to follow along with your SDR and make any notes that you think might be helpful in the lab.
  • After the video, divide into your lab groups to discuss strategy for the lab. For example, you may assign certain group members to perform specific functions during the lab.

Note: The purpose of the video is to allow you to anticipate the laboratory experience you will soon encounter. You should leave this PreLab session with a firm idea of what to expect and how to perform in the lab.

Note: Homework is posted below the video.


You should review the Investigation in preparation for the Lab. You might also want to review the operation of the spectrophotometer in the Procedural Toolbox or here.