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Determination of K, ΔG˚, ΔH˚, and ΔS˚

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1 Determination of K, ΔG˚, ΔH˚, and ΔS˚
Borax Na2B4O7·10H2O (Sodium Tetraborate Decahydrate ) Determination of K, ΔG˚, ΔH˚, and ΔS˚

2 Quiz Question # 4 Look at following equation to write down your Ksp:


4 First things first… Safety: Turn in Lab Reports LAB! Put bags away
Goggles Lab Jacket Turn in Lab Reports LAB!

5 Borax Equilibrium

6 Let’s Simplify!!

7 Today’s Rxn

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 beaker Heat 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, observations Type in you and your partner’s data in class computers on opened excel spreadsheet Trial 1 Name [HCl] Temp Volume Borax Solution Used Volume HCl used (M) (°C) (mL) Jack and Jill 0.250 33 5.2 5.9

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 used mol borate ion [Borax] (M) Ksp lnKsp ΔG (kJ/mol) Temp (K) Ksp lnKsp ΔG (kJ/mol) 1/T

13 Data Tables (con’t) Table 5 – use ΔH and ΔS to solve for ΔG for each Temp Temp (K) ΔG (kJ/mol)

14 Graph: Make using Table 4 data

15 Calculations Find molarity of borax (mol/L) [Borax] Find Ksp
Find moles borate (use moles HCl) Find volume of solution (borate + HCl) Find Ksp Ksp = 4[Borax]

16 Calculations Determine dH (kJ/mol) and dS (J/mol K) from this graph.
note: dH = ΔH Use trendline from graph y = mx + b

17 Calculations con’t Calculate the values for dG for each sample using:
dG = -RT ln Ksp used for table 4 dG = dH - TdS with your solved values for dH and dS used for table 5

18 Discussion Analysis Consider the following:
Compare solving delta G between the two equations, which yielded better results? Consider the precision of the graphs

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