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Chem 122L - Determination of the Thermodynamic Parameters of the Solvation of Borax

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Chem 122L - Determination of the Thermodynamic Parameters of the Solvation of Borax Powered By Docstoc
					                                                                                             Colton Lake
                                                                                           Chem 122-08
                                                                                           April 10, 2010
                Determination of the Thermodynamic Parameters of the Solvation of Borax

  I.    Abstract
        In the Determination of the Thermodynamic Parameters of the Solvation of Borax lab, we are
        able to calculate the thermodynamic parameters of borax by titrating two solutions of Borate
        solutions against HCl. From our titrations, we are able to calculate the Borax concentrations as
        well as     ,    ,      and Ksp for both solutions.

  II.   Introduction

In the Determination of the Thermodynamic Parameters of the Solvation of Borax lab, we are
attempting to study Gibb’s Free Energy Change, Standard Enthalpy Change, and Standard Entropy
change. We also are studying the effect that temperature has in each of the previous areas. To do this,
we had to create two borate solutions with the same concentrations, and place one in a cold
environment and allow the other solution to remain at room temperature. We then prepare and
standard HCl solution in order to titrate and determine the concentration of Borate in each solution.
Dissolution of Borax in water is as follows:

 III.   Procedure
        Preparation of Sat’d Sodium Borate Solutions
             Add 22g of Borax and 400mL of distilled water to two separate 500mL Erlenmyer Flasks.
               Add stir bar to each.
             Allow one to stir for thirty minutes at room temperature
             Allow on the stir for thirty minutes in an ice water bath.
             After the thirty minutes are up, allow for the excess Borax to settle. Take temperature
               of each and record.

        Preparation and Standardization of the HCl Solution

                In fume hood, add 3.5 mL of Concentrated HCl to 400mL of distilled water in 500mL
                 Erlenmyer Flask.
                Weigh out three 0.15g portions of Anhydrous Primary Std. Grade Sodium Carbonate.
                Add 50mL of water and dissolve the solid
                Add Bromocresol Green.
                Titrate to endpoint (yellow green indicator color).
                Repeat for each solution
                Calculate HCl concentration.

        Determination of the Borate Concentration

                Record the temeperature of the Borax solution.
                Pipet a 10mL aliquot into a 125mL Ernlenmyer flask. Add 20mL of distilled water and a
                 few drops of Bromthymol Blue indicator.
                                                                                         Colton Lake
                                                                                       Chem 122-08
                                                                                       April 10, 2010
          Titrate aliquot to yellow green endpoint.
          Repeat titration on two additional aliquots.
          Repeat this procedure for other Borax solution.
IV.   Data
      Preparation of Sat’d Sodium Borate Solutions
      Amount of Water Used 400mL
       Amount of Borax Used 21.999g


      Preparation and Standardization of the HCl Solution

      Trial   Weight of         (g)   HCl used at Endpoint (mL)     Concentration of HCl (M)
       1             .1526                      30.20                       .0953
       2             .1534                      29.98                       .0966
       3             .1513                      30.12                       .0951


      Determination of the Borate Concentration

              Warm Solution (24.5 )    Cold Solution (1.1 )
      Trial    Volume Titrated (mL)    Volume Titrated (mL)
       1             30.23                    14.21
       2             30.45                    14.13
       3             30.11                    14.36

V.    Data Analysis
         1. Molar mass of Borate: 381.37g

  Trial Concentration of Borate Warm Solution (M)        Concentration of Borate Cold Solution (M)
    1                       .1513                                          .0710
    2                       .1522                                          .0706
    3                       .1505                                          .0718
  Average                     .1513                                        .0711
                     2
          2. Ksp=[Na] [Borate]
             [Na]=2[Borate]
          3. ∆Go=-RTln(Ksp)
          4. ∆Ho=-(ln(    )    )/((1/T2)-(1/T1))
          5. ∆So=-(∆Go-∆Ho)/T
             Solution         Ksp                  ∆Go              ∆Ho               ∆So
                              .01385               10584.90 J/mol   65584.01 J        184.87 J/K
             Warm Solution
                              .00144               14910.89 J/mol   65584.01 J        184.87 J/K
             Cold Solution
                                                                                       Colton Lake
                                                                                     Chem 122-08
                                                                                     April 10, 2010
VI.   Post Lab
          1. This reaction is endothermic and enthapically unfavorable. This is the same as the
              assumptions that were made in the pre lab
          2. The reaction is entropically favorable. This is the same as the assumptions that were
              made in the pre lab.
          3. The Boron atoms are the pink atoms. The geometry around the boron atoms is trigonal
              planar.
          4. This means that the reaction is spontaneous and exothermic since it is a combustion
              process.
          5. The Standard State is the stable and pure form of a substance at a standard
              temperature and pressure. ∆G has a contribution from the tendancy toward
              randomness in a reaction where as ∆Go is the standard Gibb’s Free Energy change.

				
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