Lab

Summary

In this lab, students carry out an acid base reaction to calculate the heat of neutralization.

Grade Level

High school

Objectives

By the end of this lesson, students should be able to

• Understand the heat of neutralization.
• Understand how exothermic reactions work.

Chemistry Topics

This lesson supports students’ understanding of

• Heat of neutralization
• Acids and bases

Time

Teacher Preparation: 1 hour

Lesson: 1 class period

Materials

• Foam cup
• Foam cup with hole
• 50-mL graduated cylinder
• Thermometer
• 1.0-M HCl
• 1.0-M NaOH
• Beaker (optional)

Safety

• Always wear safety goggles when working with chemicals.
• When working with acids, if any solution gets on students’ skin, they should immediately alert you and thoroughly flush their skin with water.
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.

Teacher Notes

• Students can be given a target temperature change to create in a set amount of water. They should select the appropriate salt (based on positive or negative temperature change) and use proportional math to calculate the amount of salt needed.
• This is an activity that I designed with a colleague over the past school year. We have several other target labs that we do through the year. Neither of us has seen a lab like this previously, and together we have nearly 20 years of experience. 

Downloads

•  Teacher Guide.doc
•  Teacher Guide.pdf
•  Student Activity.doc
•  Student Activity.pdf

Submitted by
William Kane
Lockport Township High School
Lockport, Illinois

Thanks to
Flinn Scientific

For the Student

Lesson

Background

A chemical reaction involves breaking bonds and forming new bonds. This change is always accompanied by an exchange in energy. If energy is released to the surroundings then the reaction is exothermic and the products have less energy than the reactants. If energy is absorbed from the surroundings then the reaction is endothermic and the products have more energy than the reactants.

Energy exchanges when a substance dissociates and dissolves in water. For example, when sodium hydroxide pellets are added to water, the temperature of the water can become so hot that the solution steams. Hot packs and cold packs used by athletes contain compounds that release or absorb heat when dissolved in water. The heat associated with a process like this is called the heat of solution.

Hot Pack CaCl₂+ H₂O ⇾ Ca²⁺ + 2Cl^-+ H₂O + Heat

Cold Pack NH₄NO₃ + H₂O+ Heat ⇾ NH₄⁺+ NO₃^-+ H₂O

In this lab, aqueous sodium hydroxide and aqueous hydrochloric acid will neutralize each other and heat will be released. This heat is called the heat of neutralization or the heat of reaction.

Prelab Questions

1. Define the word neutralization.
2. Write the balanced molecular equation, complete ionic equation, and net ionic equation of the reaction between sodium hydroxide solution and hydrochloric acid solution.

• Molecular Equation
• Complete Ionic Equation
• Net Ionic Equation

3. A chemical reaction involves                 _ bonds and                      bonds. This change is always accompanied by an exchange in                                         _.
4. An exothermic process occurs when energy is           to the surroundings while an endothermic process occurs when energy is             from the surroundings.
5. The                          reaction is highly                 (endothermic/exothermic) and produces molten iron and a flame that will burn under water.
6. The dissolution of calcium chloride         _______ (absorbs/releases) heat to the surroundings while the dissolution of ammonium nitrate                  (absorbs/ releases) heat from the surroundings.
7. Hot packs use                           (endothermic/exothermic) reactions while cold packs use   ____________ (endothermic/exothermic).
8. The energy released when solid sodium hydroxide is dissolved in water would best be described as the heat of ___________ (reaction, neutralization, solution).

Procedure

1. Obtain two foam cups; one with a hole and one without a hole.
2. Obtain a clean dry 50-mL graduated cylinder. Obtain exactly 30.0 mL of a 1.0-M NaOH solution. Insert a thermometer into the graduated cylinder and record the temperature to the nearest tenth degree.
3. Obtain a second clean dry 50-mL graduated cylinder. Obtain exactly 30.0 mL of a 1.0-M HCl solution. Rinse and dry the thermometer used earlier, then take the temperature of HCl to the nearest tenth degree.
4. If both solutions are the same temperature, then proceed. If the temperatures do not agree, wait 5 minutes and retake temperatures.
5. Transfer the NaOH into the foam cup. Then pour the HCl into the foam cup. Quickly, place the cup with the hole on top of the solution. Insert the thermometer through the hole and gently stir. Stabilize the cup by having one person stir, while another holds the cup or place the cup in a beaker.
6. Record the highest temperature by the resulting solution.

Data

Calculations

Conclusion

Two assumptions were made in this lab. What are they?

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