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Experiment_619_Heat of Solution_1_1_3

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    305600
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    Student Name 

     

    Laboratory Date: 

    Date Report Submitted: 

    ___________________________ 

     

    Student ID 

     

    Experiment Number and Title 

    Experiment 619Heat of Solution  

     

     

     

    Experiment 619:  Heat of Solution 

     

    Section 1:  Purpose and Summary 

     

    • Determine the heat of solution of two ionic compounds: ammonium chloride and calcium chloride. 

    • Determine which dissolution process is endothermic and which one is exothermic. 

     

    Physical processes, like dissolution, involve heat changes. Some release heat, while others absorb heat. In this experiment, students will determine the amount of heat involved when ammonium chloride (or calcium chloride) is dissolved in water.  The calculation is based on the calorimetry equation:  

    Heat given off or absorbed = (mass)(specific heat)(change in temperature) 

    q = m × c ×  ΔT 

     

    The heat of solution (ΔHsoln) is the energy involved in dissolving a specific amount of solute in a given solvent. A process that gives off heat is called exothermic (-ΔHsoln), and a process that absorbs heat is called endothermic (+ΔHsoln). Based on observations and calculations, students will classify which dissolution process is endothermic and which is exothermic.   

    ΔH = q / n where n = mole of limiting reagent 

     

    Section 2:  Safety Precautions and Waste Disposal 

     

    Safety Precautions: 

     

    Use of eye protection is recommended for all experimental procedures.  

      

    Waste Disposal: 

     

    The reaction mixtures used in this experiment may be safely disposed of in the sink, followed by copious amount of running water. 

     

    Section 3: Procedure 

     

    Part 1:  Dissolution of ammonium chloride 

     

    1.  Obtain two Styrofoam cups. Construct a simple calorimeter by nesting one cup inside the other. Weigh the cups. Record exact mass. 

    1. Mass of cups: 

     

    ______________ grams 

    1.  Measure 100 mL laboratory water using a graduated cylinder, and transfer into the Styrofoam cup. Weigh again. Record exact mass. 

    1. Mass of water + cups: 

     

    ______________ grams 

    1.  Cover cup with a lid with two holes – one for inserting a thermometer and the other for a stirring rod. Record the temperature of the water to ±0.1oC. This is the initial temperature (Ti). 

    1. Initial temperature, Ti (oC): 

    1.  Using the tare function, weigh about 20 grams of solid ammonium chloride (NH4Cl) on a weighing paper/boat. Record the exact mass. 

    1. Mass of NH4Cl: 

     

    ______________ grams 

    1.  Transfer the ammonium chloride into the Styrofoam cup. Put the lid back, quickly insert the thermometer and stirring rod, and stir the mixture vigorously. Be careful not to hit the thermometer while stirring. Immediately record the temperature of the mixture to ±0.1oC. Continue stirring. Record the temperature of the water at 30 second intervals for 10 minutes until the temperature becomes constant. Use the table below for recording data. The minimum temperature reached is the final temperature (Tf). (Note: One partner should be holding the cup and stirring, while the other is taking the time-temperature readings.)  

    1. Final temperature, Tf (oC): 

    1.  Discard the mixture by dumping it into the sink. Rinse the Styrofoam cup thoroughly and wipe dry.  

     

     

     

    Time (s) 

    Temperature (oC) 

    Time (s) 

    Temperature (oC) 

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

    Part 2:  Dissolution of calcium chloride 

     

    1.  Obtain two Styrofoam cups. Construct a simple calorimeter by nesting one cup inside the other. Weigh the cups. Record exact mass. 

    1. Mass of cups: 

     

    ______________ grams 

    1.  Measure 100 mL laboratory water using a graduated cylinder, and transfer into the Styrofoam cup. Weigh again. Record exact mass. 

    1. Mass of water + cups: 

     

    ______________ grams 

    1.  Cover cup with a lid with two holes – one for inserting a thermometer and the other for a stirring rod. Record the temperature of the water to ±0.1oC. This is the initial temperature (Ti). 

    1. Initial temperature, Ti (oC): 

    1. Using the tare function, weigh about 20 grams of solid calcium chloride dihydrate (CaCl2×2H2O) on a weighing paper/boat. Record the exact mass. 

    1. Mass of CaCl2×2H2O: 

     

    ______________ grams 

    1.  Transfer the calcium chloride into the Styrofoam cup. Put the lid back, quickly insert the thermometer and stirring rod, and stir the mixture vigorously. Be careful not to hit the thermometer while stirring. Immediately record the temperature of the mixture to ±0.1oC. Continue stirring. Record the temperature of the water at 30 second intervals for 10 minutes until the temperature becomes constant. Use the table below for recording data. The maximum temperature reached is the final temperature (Tf). (Note: One partner should be holding the cup and stirring, while the other is taking the time-temperature readings.)  

    1. Final temperature, Tf (oC): 

    1.  Discard the mixture by dumping it into the sink. Rinse the Styrofoam cup thoroughly and wipe dry.  

     

     

     

    Time (s) 

    Temperature (oC) 

    Time (s) 

    Temperature (oC) 

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

    Section 4: Calculations 

     

    SHOW YOUR WORK on the space provided below. 

     

    Part 1: Calculating the heat involved in the dissolution of ammonium chloride 

     

    1.  Calculate the mass of the solution [(b) + (d) – (a)], in grams. 

    Mass of the solution (g): 

     

     

    1.  Calculate the change in temperature of the solution, ΔT = Tf - Ti,  [(e) – (c)] 

    ΔT (oC): 

     

     

    1.  Assuming that the specific heat of the solution is 4.18 J/g-oC, calculate the amount of heat involved in dissolving ammonium chloride. Is this heat lost or heat gained? 

    Amount of heat involved, (J):  

    1.  Calculate the number of moles of ammonium chloride used. 

    Moles of NH4Cl: 

     

     

    1.  Calculate the ‘heat of solution’ of NH4Cl (ΔHsoln) in kJ/mol. Make sure to include the appropriate sign (+ or -).  

    (ΔHsoln) in kJ/mol: 

     

     

     

    Part 2: Calculating the heat involved in the dissolution of calcium chloride 

     

    1.  Calculate the mass of the solution [(b) + (d) – (a)], in grams. 

    Mass of the solution (g): 

     

     

    1.  Calculate the change in temperature of the solution, ΔT = Tf - Ti,  [(e) – (c)] 

    ΔT (oC): 

     

     

    1.  Assuming that the specific heat of the solution is 4.18 J/g-oC, calculate the amount of heat involved in dissolving calcium chloride. Is this heat lost or heat gained

     

    Amount of heat involved, (J):  

    1.  Calculate the number of moles of calcium chloride used. 

    Moles of CaCl2

     

     

    1.  Calculate the ‘heat of solution’ of CaCl2 (ΔHsoln) in kJ/mol. Make sure to include the appropriate sign (+ or -). 

    (ΔHsoln) in kJ/mol: 

     

     

     

     

    Post Lab Questions: 

     

    1. Which dissolution process is exothermic, and which is endothermic? Explain.  

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

    1. Compare your calculated ΔHsoln values with your classmates. How will you explain the difference in your values? Discuss some possible sources of deviation. 

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     


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