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Chemical Reactions

Investigation 1 – PreLab

 

 

 

 

 

 

 

Back to Investigation 1

ZERO-IN

Italicized font represents information to be shared orally or physically completed with the students at this time.

The non-italicized font represents additional information included to support the teacher’s understanding of the content being introduced within the CELL.

ASK WHY

Remind students 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. 

BRANCH OUT

Remind students that chemical engineers design and develop chemically based products such as rubber, plastic, soaps, and gasoline. They also test these products to make sure they are safe for consumers and the environment.

GET FOCUSED

Inform students that the Investigation is designed to help them to answer the following Focus Question:

  • In a chemical reaction, what is the relationship between the amount of reactants and the amount of products? As the amounts of the reactants increase, the amounts of the products produced also increase.

Note: This question is located in students’ SDRs at the beginning and end of the Investigation.

Note: This is a succinct response to the Focus Question and is placed here for your reference at this time. A fully developed response to the Focus Question can be found on the PostLab page.

GO DEEPER

As a class, read the Background(s) in the Investigation. Have students read the information aloud or silently to themselves. When students have finished, discuss the following concepts as a class:

  • Chemical reactions usually have two or more chemicals called reactants that are different from one another.
  • The reactants interact during the chemical reaction to form one or more products.
  • Products are substances that are different from the reactants and from each other.
  • All chemical reactions can be written as equations that are like sentences.
  • The reactant and product formulas are like words in a sentence.
  •  In an equation, the reactants and products are separated by an arrow, which represents the word “yield.”
  • Sometimes chemical reactions produce heat.
  • A calorimeter is a device that prevents the heat of a reaction from being lost to the surroundings.

Note: These concepts are integrated into the Background(s) and are used to deepen students’ comprehension of the big ideas.

 

LEARN THE LabLearner LINGO

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.

  • chemical reaction
  • reactant
  • product
  • formula
  • chemical equation
  • yield
  • calorimeter

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

Note: Additional words may be bolded within the Background(s). These words are not Key Terms and are strictly emphasized for exposure at this time.

SET FOR SUCCESS

  • Inform students that the following chemical equation is a chemical “sentence” that uses chemical “words” to describe what occurs during the reaction. To aid students’ understanding, write the equation on the board.

NH4OH+HCl

  • Discuss the concept that in a chemical reaction, chemical bonds between atoms are broken and reformed converting reactant chemical compounds into product chemical compounds.
  • Explain that in breaking and reforming chemical bonds, energy in the form of heat can be released or consumed in a chemical reaction. Use the following examples to illustrate this concept.
    • When “ice melt” or calcium chloride (CaCl2) is spread on icy roads in the winter, the ice melts due to the release of heat. The solid calcium chloride (CaCl2) gradually dissolves releasing heat energy as bonds are formed between the calcium (Ca+2), the chloride (Cl-1) and the water molecules.
    • Chemical cold packs contain solid ammonium nitrate (NH4NO3) and water in separate bags. When the inner bag of water is broken by squeezing, the solid and the water come in contact. The formation of bonds between the ammonium (NH4 +1), nitrate (NO3 -1) and the water molecules requires that heat is absorbed by the reaction. The cold pack feels cold to the touch because heat leaves our hand and is absorbed by the reaction.
  • Assess students’ prior knowledge and their understanding of the Background by asking them to predict the answers to the following questions.
    • What happens to the reacting chemicals in a chemical reaction?
    • What is produced in a chemical reaction?
    • How do you know that a chemical reaction has occurred?

Note: Students should write their predictions in the Prediction section of their SDRs.

  • Explain to students that they will use a calorimeter to investigate whether or not heat is a relevant variable in chemical reactions.

Note: Students will be asked to record and use data about heat to estimate the amount of the chemical products that are produced.

  • Play the video below. Stop to ask students questions or answer students’ questions when necessary. Remind students to follow along with their SDRs and make any notes that they think might be helpful.
  • After the video, direct students to divide into their lab groups to discuss their strategy for the lab. For example, they may assign certain group members to perform specific functions during the lab.

Note: The purpose of the video is to allow students to anticipate the laboratory experience they will soon encounter. Students 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. 

HOMEWORK

Tell students that they should review the Investigation in preparation for the Lab.