In this lab, students carry out an acid base reaction to calculate the heat of neutralization.
AP Chemistry Curriculum Framework
- Big Idea 3: Changes in matter involve the rearrangement and/or reorganization of atoms and/or the transfer of electrons.
- 3.4 The student is able to relate quantities (measured mass of substances, volumes of solutions, or volumes and pressures of gases) to identify stoichiometric relationships for a reaction, including situations involving limiting reactants and situations in which the reaction has not gone to completion.
- Big Idea 5: The laws of thermodynamics describe the essential role of energy and explain and predict the direction of changes in matter.
- 5.5 The student is able to use conservation of energy to relate the magnitudes of the energy changes when two nonreacting substances are mixed or brought into contact with one another.
- 5.6 The student is able to use calculations or estimations to relate energy changes associated with heating/cooling a substance to the heat capacity, relate energy changes associated with a phase transition to the enthalpy of fusion/ vaporization, relate energy changes associated with a chemical reaction to the enthalpy of the reaction, and relate energy changes to P∆V work.
- 5.7 The student is able to design and/or interpret the results of an experiment in which calorimetry is used to determine the change in enthalpy of a chemical process (heating/cooling, phase transition, or chemical reaction) at constant pressure.
By the end of this lesson, students should be able to
- Understand the heat of neutralization.
- Understand how exothermic reactions work.
This lesson supports students’ understanding of
- Heat of neutralization
- Acids and bases
Teacher Preparation: 1 hour
Lesson: 1 class period
- Foam cup
- Foam cup with hole
- 50-mL graduated cylinder
- 1.0-M HCl
- 1.0-M NaOH
- Beaker (optional)
- 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.
- 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.
For the Student
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.
- Define the word neutralization.
- Write the balanced molecular equation, complete ionic equation, and net ionic equation of the reaction between sodium hydroxide solution and hydrochloric acid solution.
Complete Ionic Equation
Net Ionic Equation
- A chemical reaction involves _ bonds and bonds. This change is always accompanied by an exchange in _.
- An exothermic process occurs when energy is to the surroundings while an endothermic process occurs when energy is from the surroundings.
- The reaction is highly (endothermic/exothermic) and produces molten iron and a flame that will burn under water.
- The dissolution of calcium chloride _______ (absorbs/releases) heat to the surroundings while the dissolution of ammonium nitrate (absorbs/ releases) heat from the surroundings.
- Hot packs use (endothermic/exothermic) reactions while cold packs use ____________ (endothermic/exothermic).
- The energy released when solid sodium hydroxide is dissolved in water would best be described as the heat of ___________ (reaction, neutralization, solution).
- Obtain two foam cups; one with a hole and one without a hole.
- 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.
- 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.
- If both solutions are the same temperature, then proceed. If the temperatures do not agree, wait 5 minutes and retake temperatures.
- 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.
- Record the highest temperature by the resulting solution.
Temperature of NaOH solution
Temperature of HCl solution
Highest Temperature of solution formed by mixing NaOH and HCl
Molarity of HCl solution
Volume of HCl solution
Temperature change of solution mixture
Total mass of solutions assuming density of 1.0 g/mL
Specific heat of solution assuming the same
specific heat as water
4.184 J/g °C
Heat released by neutralization reaction
Moles of HCl used
Heat of neutralization per mole of HCl Joules
Heat of neutralization per mole of HCl kilojoules
Two assumptions were made in this lab. What are they?