8 Gibbs Free Energy (ΔG), Enthalpy (ΔH), and Entropy (ΔS) =m x + b
9 Changes in Procedure Each group does one temp (assigned). 2 trials. Add 2 scoops of borax and 75 mL of distilled water to a beakerHeat the solution (<50 °C) so that the solution is saturated. Heat slowly! No need to speed up the heating process.Once slightly above assigned temperature, take off hotplate.If all the solid has dissolved, add some more borax to beaker.Pour 5 mL of the solution into a graduated cylinder once the solution is at the desired temperature. Record volume to tenths place.Be sure to record temperature to the tenths place.
10 Procedure (continued) Add the 5 mL of solution to an Erlenmeyer with 50 mL distilled water, 5 drops bromocresol green, mix thoroughly, add a little distilled water to rinse the graduated cylinder into the Erlenmeyer (Quantitative Transfer)Titrate with HCl (clean/rinse buret and fill w/ ~20 mL HCl)REPEAT! The above steps for two more titrations.DO NOT try to prepare three samples at once, unless you can guarantee the temperature of the borax solution will not change dramatically!
11 Volume Borax Solution Used Turn in class:Pre-lab, filled in data tables, observationsType in you and your partner’s data in class computers on opened excel spreadsheetTrial 1Name[HCl]TempVolume Borax Solution UsedVolume HCl used(M)(°C)(mL)Jack and Jill0.250335.25.9
12 Formal Lab Report – due in two weeks Table 1, 2 – for each trial solve for:Table 4 – average the trials to find (for each temp):Temp (K)mol HCl usedmol borate ion[Borax] (M)KsplnKspΔG (kJ/mol)Temp (K)KsplnKspΔG (kJ/mol)1/T
13 Data Tables (con’t)Table 5 – use ΔH and ΔS to solve for ΔG for each TempTemp (K)ΔG (kJ/mol)