Question

Enthalpy and Entropy Changes of Dissolving Borax

Plot your values of ln(K_sp) vs. 1/T and find the slope and y-intercept of the best fit line. Use the equation for the best fit line and the following equation

ln(K)=−ΔH∘RT+ΔS∘Rln(K)=−ΔH∘RT+ΔS∘R to calculate ΔH° and ΔS° for dissolving Borax

Please help me solve the incorrect ones, thank you!

Table 2. Calculations ~60°C trial ~50°C trial ~40°C trial ~30°C trial ~20°C trial Vol. of HCl used (mL) 15.00 13.00 6.000 10.00 2.00 Moles of HCI used (mol) 7.6e-3 6.5e-3 3.0-30 5.0e-3 1.00-3 Moles of borate present (mol) 3.75e-3 3.25e-3 1.5e-3 2.52-3 0.5e-3 [Borate] (M) 0.757 0.656 0.505 0.303 0.101 Ksp 1.7310 1.129 0.1110 0.515 0.004 In(Ksp) 0.549 0.1210 -2.198 -0.663 -5.521 1/T (K-1) 3.02e-3 3.11e-3 3.21e-3 3.32e-3 3.43e-3

Answer 1

A graph was plotted between lnKsp vs 1/T

lnKsp = -∆Ho/R (1/T) + ∆So/R

y= 12630 x + 39.099

slope = -12630

-∆Ho/R = -12630 ; ∆Ho/R = 12630 ; ∆Ho = R x 12630

∆Ho = R x 12630 = 8.314 J/mol K x 12630 K = 105005.82 J/mol

∆Ho = 105 kJ/mol

y-intercept = 39.099

∆So/R = 39.099 ; ∆So/R = 39.099 ; ∆So/R = 39.099

∆So = R x 39.099 = 8.314 x 39.099 = 325.07 J/mole

1. For exothermic reactions, ∆H <0, with increase in temperature, lnKsp decreased

     For endothermic reactions, ∆H >0 with increase in temperature, lnKsp increased.

A. Solubility will increase, because as T increases the -∆Ho/RT term becomes smaller, therefore K will get larger

2. D (All of the above)

To make sure no more sodium borate would dissolve in the solution, to ensure the dissolution process is at equilibrium, to make sure the solution is saturated with sodium and borate ions.