11_LAB_113

Determining Enthalpy of Strong Acid and Base Reactions Introduction The purpose of this experiment is to determine the heat of acid base reactions in order to determine enthalpy for a reaction through measurements of the change in temperature and heat capacity of the solution. Chemical reactions always involve the exchange of energy and in this experiment, the focus will be on heat energy. It is quite difficult to measure this heat energy so the experimenter will be tasked with determining enthalpy by measuring heat change in different reactions (French, et al. 60). A calorimeter is an insulated device that measures heat changes in a chemical reaction while minimizing heat loss to the surroundings (French, et al. 60). In this experiment, a Styrofoam cup will be inserted into a beaker to provide insulation and stability (French, et al. 60). Once this has been set up, the procedure will be performed on cold and hot water to determine the heat lost to the calorimeter through the following relationship 1: q cal = –q hw – q cw (French, et al. 60). To determine the quantities of the variables within the equation, there are a few equations that will be noted. For calculating the individual terms in the previous equation, the relationship 2: q = ms Δ T will be applied to situations in which varying masses of a substance are unknown and the specific heat, s , has been determined (French, et al. 61). The equation 3: q = C Δ T will be applied to situations in which there is a fixed mass, m, such as a calorimeter and the heat capacity, C , will be determined through experimentation (French, et al. 61). According to French, et al. “formulas 1 and 3 will be inserted into equation 2 to derive the equation 4: C cal Δ T cal = –(m cw ) (s water )( Δ T cw ) – (m hw )(s water )( Δ T hw ) where

 ΔT cal = change in temperature of the calorimeter (equals Δ T cw because they both start and end at the same temperature)  m cw = mass of the cold water  s water = specific heat of water  ΔT cw = change in temperature of the cold water  m hw = mass of the hot water  ΔT hw = change in temperature of the hot water which can be further expanded to generate the relationship 5: C ca l (T f – T i, cw ) = –(m cw )(s water ) (T f – T i, cw ) – (m hw )(s water ) (T f – T i, hw ).” Since equation 4 and 5 are derived from the previous equations, they are useful in the experiment because of the role of equation 5 in determining the enthalpy for the reaction. “The result of this equation provides the experimental value for C cal which will be used in further equations to determine the heat of the entire reaction” (French, et al. 62). Calorimeters are not perfect in the way they function which results in heat being lost to the surroundings as discussed earlier. Due to this fact, heat that is gained and lost in a reaction will be absorbed by the solution or the calorimeter (French, et al. 62). However, it is possible to determine the heat of a reaction through calculation of the heat of the solution and calorimeter which was determined in equation 1 and 3. According to French, et al. “this can be used to form the equation 6: q rxn = -q soln – q cal which can be further expanded into equation 7 q rxn = –m soln sΔT – C cal ΔT where  m soln is the total mass of the combined solution  s is the specific heat of the water  ΔT is the change of temperature of the solution and the calorimeter during the reaction.”

 2.0 M hydrochloric acid solution (HCl)  2.0 M sodium hydroxide solution (NaOH)  2.0 M ammonium chloride solution (NH 4 Cl)  2.0 M ammonium hydroxide solution (NH 4 OH)  Aqueous Ammonia  ring stand  iron clamp  cardboard square  beakers, assorted sizes Procedure Procedure was adapted from French, et al. 1. Turn on the temperature probe, go to the main menu and select function to use the probe for temperature vs time. 2. Calibrate the temperature probe to room temperature. 3. Fill the graduated cylinder with 25ml of cold water and pour into the Styrofoam cup calorimeter. 4. Cover calorimeter with cardboard square and place the measurement probe into the cold water and record the initial temperature. 5. Fill the graduated cylinder with 25 ml of hot water. 6. Turn on the measurement probe to start recording data (display then start/stop) 7. Pour the hot water into the Styrofoam cup calorimeter and cover with cardboard square

8. Record final temperature and turn off the data collection once the curve has flatlined. 9. Save file as “010” 10. Repeat steps 1-8 with aqueous solutions making sure to always add 25ml of base to the 25 ml of acid. a. Reaction 1 is an aqueous solution of base: sodium hydroxide (NaOH) and hydrochloric acid (HCl). Save measurement file as “001.” b. Reaction 2 is an aqueous solution of ammonium chloride (NH 4 Cl) and sodium hydroxide (NaOH). Save measurement file as “002” c. Reaction 3 is an aqueous solution of hydrochloric acid (HCl) and ammonia (NH 3 ). Save measurement file as “003” Discussion The purpose of this experiment is to determine enthalpy of a reaction by measuring the change in heat of acid base reactions. The summary of the temperature results will be presented as followed: In the cold and hot water reaction, the initial and final temperature were 27.365° (±.0146) and 32.39° (±.888) respectively; in reaction 1, the initial and final temperature were 22.378° (±.06) and 33.796° (±.01); in reaction 2, the initial and final temperature were 23.002° (±.02) and 24.091° (±.007); in reaction 3, the initial and final temperature were 23.788° (±.012) and 30.697° (±.05). The density of water as well as each of the acids and bases is 1.00 g/ml and 1.03 g/ml respectively. Using the mass and temperature of the hot and cold water, as well as the change in temperature for the calorimeter, the energy was calculated for each of those entities. From there,

In “Determining Enthalpy of Strong Acid and Base Reactions,” I learned more about how to use a calorimeter to measure heat change between two substances and how to use this to determine the enthalpy for the overall solution. An example of where enthalpy is illustrated in real life is the situation with the fridge one might have at home. The temperature of your food is entirely dependent on the enthalpy of vaporization. Regarding the experiment, the only suggestion I have is finding a way to insulate the calorimeter more because I feel as if the current method allows for significant heat loss through the cardboard square on the top. Works Cited French, April, et al (Department of Chemistry, University of Kentucky). “Enthalpy of Reaction.” Macmillan Learning Curriculum Solutions: Plymouth, MI, 2020; p. 59-64. Web. Accessed September 21, 2021.