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MgO Calorimetry

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  • Week 1: Calibrating Calorimeter 


     Beakers with clear liquids: HCl and NaOH. The NaOH is covered.
    HCl(aq) and NaOH(aq) are provided for you, with the concentrations labeled. Be sure to record these concentrations. 
    Keep the NaOH(aq) covered with a watch glass to avoid carbon dioxide gas from dissolving and changing the concentration. Note that CO(g) dissolves as carbonic acid.  

    Top: Ball and stick representation of Hydrochloric acid molecule.  
    Bottom: Molecular structure of Sodium Hydroxide molecule.

     Pouring HCl into the Coffee Cup  

    Pour the required amount of HCl (aq) into a styrofoam cup labeled HCl. This will hold the HCl (aq) at constant temperature. The NaOH can be transferred into the Calorimeter cup (not shown). While these solutions come to a steady temperature, you can set-up your MicroLab. 


    IMAGE: University of Liver Pool chemistry structure pages
     Basic MicroLab Time/Temp set-up.

    Setting up the MicroLab can be done just like was done for the 1 - Intro to Calorimetry experiment, with one exception: set the data collection interval in the bottom left corner to 2.0 seconds instead of the default 0.5 seconds. This is accomplished by double-clicking the text "Repeat every 0.5 seconds" in the lower-left corner. 
     Take temperature of HCl

    Once you are ready, place the HCl cup in place and measure the temperature for at least 20-30 seconds (10-15 data points). 
    Simply raise the thermister and replace the HCl (aq) with the calorimeter containing NaOH (aq). 
    Adding Stir Bar  

    When initially taking the temperature of the NaOH(aq), do not add the stir bar
     Set-up of Calorimeter  

    This is the set-up of the calorimeter with the lid in place. The thermister should have a black mark on it indicating where to place it. 
     Black mark on thermister showing depth.

    Do not lower the thermister below this point or you could puncture the styrofoam cup bottom. Record the temperature of the NaOH (aq) for at least 20-30 seconds (10-15 data points). Again, DO NOT PRESS STOP ON THE MICROLAB.
     Lid of Calorimeter lifted along the thermister.  
    To add the HCl (aq) and the stir bar to the NaOH (aq), raise the lid of the calorimeter without moving the thermister. The stir bar should be stirring vigorously enough to create a small vortex on the surface of the liquid, but not so vigorously that you see bubbles. 

    NaOH (aq) + HCl (aq→ H2O (l) + NaCl (aq)
    Continue taking data for an additional 5 minutes (an additional 300 seconds, or 150 data points). Record the time at which you dumped the HCl (aq) into the NaOH (aq). 
    Adding HCl to NaOH Microlab File  

    The data collected will have some jumps when you removed the thermister from the HCl (aq). You should see flat lines before the initial dip, after the dip, and then a slowly descending line after the reaction occurs. 

    Week 2: MgO Calorimetry

    In this week, you will be reacting a solid with a liquid. It is important that the total volume of solution in the coffee-cup calorimeter is consistent with last week's calibration and that you are using the same calorimeter with lid you used last week. The total volume of 1M HCl (aq) used for all trials this week will be 75 mL from the pump dispenser (3x25mL pumps). This can be dispensed straight into a clean, dry calorimeter. 

    There are two parts to the experiment: Reacting Mg (s) with HCl (aq) and reacting with MgO (s) with HCl (aq). Although the procedure shown here is specific to the second part of the experiment (part 3 in lab manual), the first part is almost exactly the same (part 2 in lab manual).
     Weight full vial of MgO

    The mass of the solid reagent used will determined indirectly by weighing a vial both before you add the reagent and then again after adding. 
    First weigh the full vial and record the mass. The mass shown here is 9.1408 g MgO (s).

    IMAGE: C. B. Walker and M. Marezio, Acta Met., 1959, 7, 769.


    The MicroLab should be set up identical to last week's setup. Then, begin recording data on the MicroLab and ensure you have 20-30 seconds (10-15 data points) of steady temperatures recorded for the HCl (aq) solution. Make sure that the stir bar is spinning at a rapid enough speed to create a slight vortex at the surface of the solution without generating any bubbles. 

    Record the time that you dump the vial of reagent into the calorimeter. It is not very important that you get all of the reagent into the calorimeter. Any residue left in the vial will be accounted for by weighing the vial afterward. Ensure that the powder is poured directly into the center of the calorimeter solution surface to avoid sticking to the edges and make sure that the powder does not clump up in the solution. 

    MgO (s)+2 HCl (aq)  MgCl2 (aq)+H2O (l)

    charge-dipole interactions, ion-dipole interactions

     Post-weigh empty vial.

    To determine how much reagent was added to the solution, weigh the vial again. The mass shown below is 8.5442 g. 
    Continue to take temperature data using the MicroLab until an additional 10 minutes (600 seconds or 300 data points) to establish a smooth cooling line, as shown below for both Mg(s) (silver metal) and then for MgO(s) (white powder).
    MicroLab data for MgO(s) + HCl(aq). The Mg(s) + HCl(aq) data will appear similar, but with a different maximum temperature.