Several reactions will be studied during this experiment. (1) HCl (aq) + NaOH (aq) --> NaCl (aq) + H 2 O (l) Δ H =?

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1 Calorimetry Calorimetry is the study of heat involved in a chemical reaction. A coffee-cup calorimeter is often used to measure the reaction enthalpy ΔH and the heat q involved in a chemical reaction. Several assumptions are made in a coffee-cup calorimetry experiment. It is assumed that the coffee-cup is a perfect insulator, the density of the final solution is that of water, 1.00 g/ml, and the specific heat of the solution is that of water J/g o C. [See the sample calculations for more information regarding the calculations of ΔH and q. Prior to lab read the sections of our textbook that discuss calorimetry, enthalpy, specific heat, and Hess Law.] Several reactions will be studied during this experiment. (1) HCl (aq) + NaOH (aq) --> NaCl (aq) + H 2 O (l) Δ H =? Strong acid + Strong base neutralized (2) HCl (aq) + NH 3(aq) --> NH 4 Cl (aq) Δ H =? Strong acid + weak base (3) NH 4 Cl (aq) + NaOH (aq) --> NaCl (aq) + H 2 O (l) + NH 3(aq) Δ H =? Weak acid + strong base (4) NH 4 Cl (s) --> NH 4 + (aq) + Cl - (aq) Δ H =? The reaction enthalpy for the dissolving of solid NH 4 Cl in H 2 O will also be measured to determine if this reaction is endothermic or exothermic. (5) The specific heat capacity of a metal cylinder can also be determined by heating a metal cylinder to a high temperature and then submerging it in a beaker of room temperature water. The heat lost by the metal cylinder will be gained by the water. q metal + q water = zero q metal = - q water Upon completion of this experiment, students will be able to 1. Use a thermometer to measure solution temperatures 2. Calculate the enthalpy of a reaction from experimental data 3. Calculate the specific heat of a metal 4. Determine whether a reaction is endothermic or exothermic

2 This experiment contains several parts. Each part has instructions and a worksheet to enter collected data and make calculations. Each part will be done in duplicate. Your instructor will decide which sections of this experiment will be done. The five parts to the experiment are: 1. Determination of reaction enthalpy for NaOH-HCl. 2. Determination of reaction enthalpy for HCl- NH Determination of reaction enthalpy for NH 4 Cl NaOH. 4. Determination of reaction enthalpy for dissolving NH 4 Cl. 5. Determination of specific heat of a metal cylinder Download the Data Spreadsheet Chemicals: Aqueous solutions of 2.00 M HCl, NaOH, NH 3, NH 4 Cl Solid NH 4 Cl (or ammonium nitrate may be substituted) Metal cylinder Lab Equipment: 2 Thermometers 2 Styrofoam cups with a plastic lid Tape for labels ml graduated cylinders ml graduated cylinders ml beakers Hot Plate Sample Calculation: A student was studying the reaction of sodium hydroxide with formic acid CHO 2 H in a coffee-cup calorimeter ml of 1.00 M NaOH was mixed with 50.0 ml of 1.00 M CHO 2 H. Prior to mixing the initial temperature of the two solutions was the same, 25.3 o C. After mixing the solution reached a maximum temperature of 31.8 o C. The chemical reaction is shown below. NaOH (aq) + CHO 2 H (aq) NaCHO2 (aq) + H2O (l) Calculate a. heat of the surroundings, q surr, b. heat of the system, q sys,

3 c. the reaction enthalpy, H rxn. Assume the density of the final solution is that of water, 1.00 g/ml, the specific heat of the solution is that of water J/g o C, and that the coffee-cup is a perfect insulator. a. Heat of surroundings = Heat of solvent water q (surr) = q (water) q (H2O) = (mass solution) x (specific heat water) x (T final -T initial ) mass solution = (total solution volume) x ( density solution) total solution volume = ( ) ml = ml density solution = 1.00 g/ml (approx. that of water) mass solution = ml x 1.00 g/ml = 100. g specific heat of water =specific heat of solution = J/(g o C) q (H2O) = 100.g x [4.184 J/(g o C)] x (31.8 o C o C) = 2,700 J q (surr) = +2,700 J = +2.7 kj (2 sig figs from temp change) b. Heat of system = - Heat of surroundings q (sys) = - q (surr) q (sys) = - 2,700 J = kj c. Enthalpy of reaction = Heat of system / moles of limiting reagent Δ H (rxn) = q (sys) / (mole limiting reagent)* *moles of limiting reagent = Molarity x Volume (L). Since both reagents have equal concentrations, equal volumes, and a 1:1 mole ratio in the balanced reaction, the reagents are stoichiometrically equal and either may be used as the limiting reagent. moles CHO 2 H = 1.00 M x 50.0 ml x (1 L/1000mL) =.0500 mol moles NaOH = 1.00 M x 50.0 ml x (1 L/1000mL) =.0500 mol Δ H (rxn) = kj / mol = - 55 kj/mol

4 Download the Data Spreadsheets Part 1: Determination of reaction enthalpy for NaOH-HCl HCl (aq) + NaOH (aq) --> NaCl (aq) + H 2 O (l) Δ H =? You are to perform two trials for this reaction. All solutions can be washed down the drain with plenty of water. Rinse and dry the calorimeter and graduated cylinders before beginning a new reaction. 1. Obtain exactly 50.0 ml of each reagent (NaOH & HCl) in separate, clean and dry graduated cylinders. Label with tape each graduated cylinder as NaOH or HCl. Record these values on your data sheet as volume of acid/base in cylinder before pouring into cup. 2. Measure the temperature of each solution using the same thermometer to +/- 0.5 o C. Remember to rinse and dry the thermometer between measurements. If the two solutions are not at the same temperature (+/- 1 o C), calculate and record the average of the two solution temperatures as T initial. 3. This step must be done quickly! With the help of your lab partner, add the two reagent solutions to your calorimeter, place the lid on the cup (with the thermometer inserted into the hole in the lid) and begin monitoring the temperature of the reaction solution while slowly swirling the cup. When the maximum temperature has been observed, record it as T final. 4. Using a 10.0 ml graduated cylinder, measure the volume of each reagent solution that remains in the larger graduated cylinders. Record these values as volume of acid/base in cylinder after pouring. Calculate and record the volume of acid/base reacted. 5. All solutions can be washed down the drain with plenty of water. 6. Repeat steps 1-4 for the second trial of this reaction. 7. Calculate q (water), q (surr), q (sys), H (rxn) and average H (rxn) Part 2: Determination of reaction enthalpy for NH3-HCl HCl (aq) + NH 3(aq) --> NH 4 Cl (aq) Δ H =? You are to perform two trials for this reaction. All solutions can be washed down the drain with plenty of water. Rinse and dry the calorimeter and graduated cylinders before beginning a new reaction.

5 1. Obtain exactly 50.0 ml of each reagent (NH 3 & HCl) in separate, clean and dry graduated cylinders. Label with tape each graduated cylinder as NH 3 or HCl. Record these values on your data sheet as volume of acid/base in cylinder before pouring into cup. 2. Measure the temperature of each solution using the same thermometer to +/- 0.5 o C. Remember to rinse and dry the thermometer between measurements. If the two solutions are not at the same temperature (+/- 1 o C), calculate and record the average of the two solution temperatures as T initial. 3. This step must be done quickly! With the help of your lab partner, add the two reagent solutions to your calorimeter, place the lid on the cup (with the thermometer inserted into the hole in the lid) and begin monitoring the temperature of the reaction solution while slowly swirling the cup. When the maximum temperature has been observed, record it as T final. 4. Using a 10.0 ml graduated cylinder, measure the volume of each reagent solution that remains in the larger graduated cylinders. Record these values as volume of acid/base in cylinder after pouring. Calculate and record the volume of acid/base reacted. 5. All solutions can be washed down the drain with plenty of water. 6. Repeat steps 1-4 for the second trial of this reaction. 7. Calculate q (water), q (surr), q (sys), H (rxn) and average H (rxn) Part 3: Determination of reaction enthalpy for NaOH-NH4Cl. NH 4 Cl (aq) + NaOH (aq) --> NaCl (aq) + H 2 O (l) + NH 3(aq) Δ H =? You are to perform two trials for this reaction. All solutions can be washed down the drain with plenty of water. Rinse and dry the calorimeter and graduated cylinders before beginning a new reaction. 1. Obtain exactly 50.0 ml of each reagent (NaOH & NH 4 Cl) in separate, clean and dry graduated cylinders. Label with tape each graduated cylinder as NaOH or NH 4 Cl. Record these values on your data sheet as volume in cylinder before pouring into cup. 2. Measure the temperature of each solution using the same thermometer to +/- 0.5 o C. Remember to rinse and dry the thermometer between measurements. If the two solutions are not at the same temperature (+/- 1 o C), calculate and record the average of the two solution temperatures as T initial. 3. This step must be done quickly! With the help of your lab partner, add the two reagent solutions to your calorimeter, place the lid on the cup (with the thermometer inserted into the hole in the lid) and begin monitoring the temperature of the reaction solution while slowly swirling the cup. When the maximum temperature has been observed, record it as T final.

6 4. Using a 10.0 ml graduated cylinder, measure the volume of each reagent solution that remains in the larger graduated cylinders. Record this value as volume of acid/base in cylinder after pouring. Calculate and record the volume that reacted. 5. All solutions can be washed down the drain with plenty of water. 6. Repeat steps 1-4 for the second trial of this reaction. 7. Calculate q (water), q (surr), q (sys), H (rxn) and average H (rxn) Part 4: Determination of reaction enthalpy for dissolving NH 4 Cl NH 4 Cl (s) --> NH 4 + (aq) + Cl - (aq) Δ H =? 1. Weigh out 10.0 grams of solid NH 4 Cl. Record the mass to the nearest g. 2. In a clean, dry graduated cylinder, obtain exactly 50.0 ml of R.O. water. Record this value on your data sheet as volume of H 2 O in cylinder before pouring into cup. 3. Measure the temperature of R.O. H 2 O using the same thermometer to +/- 0.5 o C. Remember to rinse/dry the thermometer between measurements. Record this temperatures as T initial. 4. Add the 50.0 ml of H 2 O to the calorimeter. 5. This step must be done quickly! With the help of your lab partner, add the solid NH 4 Cl to your calorimeter, place the lid on the cup (with the thermometer inserted into the hole in the lid) and begin monitoring the temperature of the reaction solution while slowly swirling the cup. When the minimum temperature has been observed, record it as T final. 6. Using a 10.0 ml graduated cylinder, measure the volume of H 2 O remaining in the graduated cylinder. Record this value as volume of H 2 O in cylinder after pouring. Calculate and record the volume of water added to the cup. 7. Repeat steps 1-6 for the second trial of this reaction. 8. Calculate q (water), q (surr), q (sys), H (rxn) and average H (rxn) 9. Wash all glassware before returning it to your drawer. Rinse the styrofoam cup and lid. Do NOT throw them away. Return them to the bin. Part 5: Determination of the specific heat capacity of a metal cylinder CAUTION: The hot plate, beaker, and steam are very hot! Use caution and tongs. 1. Record the mass of a metal cylinder to +/ grams. 2. Obtain ml of HOT water from the sink. Place the hot water in a 100 ml beaker on a hot plate. Set the heat setting to Setting # 6 or C. Cover with a watch glass. 3. After the water boils, use tongs to remove the watch glass and carefully submerge the metal cylinder in the boiling H 2 O. Caution: steam is very hot!

7 4. Heat for at least 15 minutes in the boiling H 2 O. Measure the temperature of the boiling water bath to +/- 0.5 o C. Record this as the INITIAL temperature of the heated metal cylinder. 5. While the metal cylinder is heating, use a clean graduated cylinder to measure 50.0mL of room temperature H 2 O. Put this water in another 100 ml beaker. Measure and record the temperature to+/- 0.5 o C. This is the INITIAL temperature of the room temperature H 2 O. 6. Assume 1 ml H 2 O = 1 gram H 2 O. Calculate and record the mass of the room temperature water. Remember: Density of H 2 O = 1 gram per 1 ml. 7. With tongs, remove the metal cylinder from the boiling water and submerge it in the room temperature H 2 O. Gently stir the water with the thermometer to transfer the heat from the hot metal cylinder to the water. Record the HIGHEST temperature that this H 2 O reaches as the FINAL temperature of the metal cylinder and the FINAL temp. of the H 2 O. When taking the temperature reading, the thermometer should not be touching the bottom of the beaker nor the metal cylinder. 8. Repeat this experiment again. Record your data as Trial Dry the metal cylinder and return it. Leave the hot plate in the hood to cool. 10. Calculate Delta T, q (water), q (metal), Follow-up questions: Athletes often use hot/cold packs for muscle and joint sprains and to reduce swelling from injuries. The hot/cold packs have 2 separate chambers for chemicals and water. When the seal between the chambers is broken and the hot/cold pack is shaken vigorously, the chemicals begin to mix and the chemical reaction begins. Depending on the reaction, heat will either be given off or absorbed. You are working for a company that produces hot packs and cold packs for sports injuries. In lab today you collected data for the reaction enthalpy Δ H of several reactions. a) Based on your experimental Δ H values, which reactions could be used in a hot pack? b) Which reactions could be used in a cold pack? c) Using the internet, find out what reaction is often used in a hot pack? d) Using the internet, find out what reaction is often used in a cold pack?