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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