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Lab 8

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Lab 8 Powered By Docstoc
					                                                                               Noah Stewart-Maddox

                                                                                         Chem 122

                                                                                           4/9/12

Determination of the Thermodynamic Parameters
              for the Solvation of Borax

Abstract: In this lab, we will discover the thermodynamic parameters of Borax through titration.
We will use a HCl mixture to titrate our Borax solution at two different temperatures which will
allow us to calculate the Borax concentration along with ∆G°, ∆H°, ∆S°, and Ksp at both
temperatures.

Introduction: In this lab, we will study the effects of temperature on various thermodynamic
parameters. We will use two borax solutions, one at room temperature and the other in an ice
water bath to have a large difference, which will allow us to calculate the values much
differently. We created a HCl solution to titrate using the equation
                              This will give us the about of borate concentrated.

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 0.15g of NaCO3
            Add to 50mL water
            Add Bromocresol Green and titrate

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 Bromthymol Blue indicator
           Titrate and record
           Repeat titration on twice more
           Repeat this procedure for other Borax solution

Data Analysis:

Preparation and Standardization of the HCl Solution

        Trial         Start(mL)                 End(mL)                        ∆V(mL)
         1               2.0                      23.0                          21.0
         2               1.0                      21.5                          20.5
         3               3.0                      25.8                          20.2
                                                       Average:                20.6mL vdfvdfvdfvvff

.15g/20.6= .0014mol Na2CO3 * 2 = .0028mol HCl / .0206L = .137M HCl

Determination of Borate concentration

                 Warm Solution (21.0 )    Cold Solution (3 )
        Trial     Volume Titrated (mL)   Volume Titrated (mL)
         1               20.2                    15.5
         2               21.1                    14.0
         3               20.8                    13.0
Data Analysis:

   1.




    Trial   Concentration Warm Borate Solution (M)              Concentration of Cold Borate (M)
      1                       .138                                           .106
      2                       .144                                           .096
      3                       .143                                           .089
   Average                    .142                                           .097
              2
   2. Ksp=[Na] [Borate] [Na]=2*[Borate] Ksp=4*[Borate]3
   3.

   4. ∆Ho

   5. ∆So=
   6.                          Ksp             ∆Go (kJ/mol)     ∆Ho (kJ)         ∆So (kJ/K)
              Solution
                               .011            110.23           360.23           0.85
              Warm Solution
                               .004            126.7            “”               0.85
              Cold Solution
Conclusion: This lab was an interesting application of thermodynamic laws to calculate an
unknown entropy. We used previously learned techniques relating to titration to easily obtain
this. The main error would come from measurements and improper mixtures.

Post-Lab Questions:

1. This reaction is endothermic and enthapically unfavorable. This agrees with the pre-lab
2. The reaction is entropically favorable. This does agree with 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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