Lab Report 21 - Thermodynamics of Borax Dissolution REBECCA FORLOINE LAB PARTNER DANA MARCH 3 2015 Having read the Georgia Institute of Technology

# Lab Report 21 - Thermodynamics of Borax Dissolution REBECCA...

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Thermodynamics of Borax Dissolution REBECCA FORLOINE LAB PARTNER: DANA MARCH 3, 2015 Having read the Georgia Institute of Technology Academic Honor code, I understand and accept my responsibility as a member of the Georgia Tech Community to uphold the Academic Honor Code at all times. In addition, I understand my options for reporting honor violations as detailed in the code.
Data and Results A. Data Tables and Plots a. Table 1. Data for Standardization Trials Mass Na 2 CO 3 (g) Volume HCl (ml) [HCl] (mol/L) 0.205 42.5 0.0910 0.272 63.0 0.0810 0.220 51.2 0.0840 Mean [HCl]: 0.0853 St. Deviation [HCl]: 0.00513 b. Table 2. Titration of Saturated Borate Solutions with HCl Temperate (K) Volume HCl, Endpoint (ml) [borate] (mol/L) 298 14.0 0.000595 310 19.2 0.000816 286 9.3 0.000395 c. Table 3. Equilibrium Constants and Temperatures Temperature (K) K sp 1/ T (1/K) ln K sp 298 8.43E-10 0.0034 -20.9 310 2.17E-09 0.0032 -20.0 286 2.47E-10 0.0035 -22.1 d. Plot 1. Natural Log of K sp versus 1/T
3.15E-033.20E-033.25E-033.30E-033.35E-033.40E-033.45E-033.50E-033.55E-03 -22.5 -22.0 -21.5 -21.0 -20.5 -20.0 -19.5 -19.0 -18.5 f(x) = - 6871.43x + 2.15 R² = 0.93 1/Temperature (1/K) ln Ksp B. Sample Calculations a. Exact molarity of HCl solution from trial 1 i. 0.205 g N a 2 C O 3 × 1 mol 105.99 g × 1 0.0425 L × 2 = 0.091 M HCl b. Molarity of borate anion from results of titration (same trial) i. 0.0853 M HCl × 1 2 = .04265 mol Borate × 1 0.0140 L = 0.000595 M Borate c. Calculations of Ksp (same trial) i. 2 × 0.000595 ¿ 2 = 8.43 10 10 0.000595 mol× ¿ d. Calculation of ΔH o i. lnKsp = Δ Ho R ( 1 T ) + Δ So R ii. The slope of the graph above is equal to –ΔH o /R iii. Δ H o =− 1 ( 8.314 ) ( 6871.4 ) = 57128 J / mol e. Calculations of ΔS o i. The y-intercept of plot 1 is equal to ΔS o /R ii. Δ S o = ( 8.314 ) ( 2.1471 ) = 17.851 J / K f. Calculations of ΔG o i. ΔG =− RTlnKsp
ii. 8. ΔG =( 298 K ) ¿ 314J/molK)(-20.9) = 51.8kJ/mol iii. ¿ iv. ΔG = Δ H T ΔS v. ΔG = 51. 8kJ/mol Discussion A. Objectives The general objectives for this experiment were to measure three chemically important thermodynamic parameters for the dissolution of borax in water. More specifically it was important to quantify borate ion