**Investigating the Heat Associated with the
Reaction of Sodium Hydroxide and Hydrochloric Acid**

IIIA. Qualitative Investigation of the reaction of sodium hydroxide and hydrochloric acid

http://www.chem.iastate.edu/ChemEdGroup/GREENBOWE/sections/projectfolder/flashfiles/thermochem/calorimetry.html

Activity 3.1: Predictions. Do not use the computer simulation during this part of the activity.

For each task, please provide an answer and an explanation.

If we mix 300 mL of 1.0 M HCl and 300 mL of 1.0 M NaOH in a calorimeter what will happen to the temperature? Initially, the solutions have the same temperature. Prediction: increase, decrease, or stay the same Explain.

If we double the volume of each solution, keeping the concentration of each solution at 1.0 M, and mix the solutions what will happen to the temperature? Initially, the solutions have the same temperature.

The change in temperature will _____________ compared to the change in temperature in the first activity.

Explain.

Have a staff member check your predictions, explanations and reasoning. _________

Activity 3.2 . Now, use the computer simulation to duplicate activity 3.1

Activity 3.3. Work in pairs, but coordinate your work so you can share your data with another pair of students. Design an experiment that will answer a question you have about the temperature changes associated with the reaction of an acid and a base. Use the computer simulation to perform these experiments. In each experiment, state what the independent and dependent variables are. What will you keep constant throughout your experiment and what will you vary. Be sure to record the data from the simulation. You might find it helpful to make a graph to show relationships.

IIIB. Investigation of the reaction of sodium hydroxide and hydrochloric acid (laboratory activity)

Work in pairs. Write a question that you and your partner can answer by designing a series of experiments that measure the temperature changes that occur when sodium hydroxide reacts with hydrochloric acid. By doing these experiments you will calculate the enthalpy of neutralization, Hneutralization,. Compare your experimental value with a value that is reported in the literature (your textbook or a handbook of physical constants).

You will have available to you a maximum of 200 mL of 3 M NaOH and 200 mL of 3 M HCl(aq) solutions to work with. If your class runs out of NaOH and HCl solutions the stock room will not refill the empty bottles. Plan your work so that your data will add something to the class data.. You will need to make 1.0 M, 2.0 M, etc. solutions of HCl by diluting some of the 3 M solution of HCl. You will need to do the same for the NaOH solutions. Set-up a ring-stand and clamp to suspend a thermometer into a calorimeter so the thermometer does not touch the bottom or sides of the calorimeter.

Suggested Activity 3.6 In this activity, the total volume of solution will be kept constant and the volume and Molarity of NaOH will be kept constant. You will add increasing number of moles of HCl to the NaOH solution in the calorimeter. Assume that density of the solutions are close to 1.0 g/mL. Make a data table and record the moles of HCl mixed, temperature change of the solution, total mass of the solution, q of the solution in Joules, and q of the solution in kJ. (q = mcT) Assume that the resultant solution has a specific heat of 4.18 J/g°C. The mass is the total mass of solution. For example:

Calorimetry experiment # : mix 50 mL ?M HCl with 50 mL 1.0 M NaOH

mol HCl temp. change (°C) total mass(g) q, heat soln (J) q, heat soln (kJ)

0.0125 1.67 100 700.75 0.7

0.025

0.0375

0.05

0.0625

0.075

0.1

What relationship can be displayed when a graph of T vs. moles of acid present is constructed? Is there a limiting reagent present? If so, identify it. What relationship can be displayed when a graph of q (heat of solution in kJ) vs. moles of HCl present is constructed?

Suggested Activity 3.7. In this activity, you will keep the volume and molarity of NaOH constant while mixing in increasing amounts of HCl. The mass of the solution will vary. For example, mix 100 mL of 1.00 M NaOH with 10 mL of 1.00 M HCl and record the change in temperature of the solution. Next mix, 100 mL of 1.0 M NaOH and 20 mL of 1.0 M HCl, etc. Assume that density of the solutions are close to 1.0 g/mL. Make a data table and record the moles of HCl mixed, temperature change of the solution, total mass of the solution, q of the solution in Joules, and q of the solution in kJ. For example:

Calorimetry experiment # : Mix x mL 1.0M HCl + 100 mL of 1.0M NaOH

mol HCl q soln (kJ) q soln (J) total mass (g) temp. change (°C)

0.02 1.12 1,120 120 2.23

0.04

0.06

0.08

0.1

0.2

0.3

What relationship can be displayed when a graph of T vs. moles of HCl present is constructed? Is there a limiting reagent present? If so, identify it. What relationship can be displayed when a graph of q (heat of solution in kJ) vs. moles of HCl present is constructed?

What gains heat? What loses heat? Calculate the heat of reaction (q = mcT)? Assume that the resultant solution has a specific heat of 4.18 J/g°C. The mass is the total mass of the solution. Calculate the enthalpy of neutralization, Hneutralization,. Compare your experimental value with a value that is reported in the literature (your textbook or a handbook of physical constants).

Part IIIC. Reaction of Sodium Hydroxide and Hydrochloric Acid (Details and Understanding)

Write an equation that describes the reaction that happened. Assume that your calorimeter is a perfect insulator - no heat escapes or enters the interior of the calorimeter. Identify the system and the surrounding. Draw a diagram.

How does the Law of Conservation of Energy apply to your experiment? During the reaction, heat is transferred. What gives up heat? What takes in heat? Write an algebraic equation that expresses this relationship.

Calculate the heat that was gained or lost by the solution, qsoln.. Calculate the heat of reaction, qrxn. You may use the formula q = mcT. Assume that the specific heat of the solution is 4.18 joules/gram °C. IN this calculation "m:" is the total mass of the solution = the mass of the water plus the mass of your magnesium sulfate sample. Pay particular attention to the sign (positive or negative) of your value of qsoln and qrxn . In your experiment, what did you measure? What did you calculate? In order to determine qrxn, you needed to make an inference. What specifically do you infer? Identify the qrxn process as exothermic, endothermic, or neither.

Your classmates have data for other sample sizes for the reaction of sodium hydroxide with hydrochloric acid. Record at least five other data sets in you lab notebook. Do any of the experiments need to be repeated? Should they?

What pattern is shown by the data? It might be helpful to graph the data. In your experiment, what is the dependent variable what are the independent variables? What factors or variables do you control or keep constant? What variable do you manipulate? Give an algebraic equation that expresses this pattern. Write a question that your graph can help answer.

Do you need to reconsider and modify your experiment? Would it help to keep the total mass of the solution constant? Would it help to look at the relationship of the number of moles of base or acid, mass of solution, and T? Is there a limiting reagent present? Do you need to do an additional experiment?

Calculate the change in enthalpy of the reaction, Hrxn. This is called the change in enthalpy of neutralization, Hneutralization,. Compare your experimental value of Hneutralization with a value that is reported in the literature (your textbook or a handbook of physical constants). Calculate a percent error.