Chemistry Lab II Exam 1 Study Guide - Chemistry Lab II Exam...

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Chemistry Lab II - Exam 1 Study GuideExperiment 1: Solubility of BoraxThere are two processes that occur when a salt is dissolved in water:The salt crystal must first be separated into ions:oThis process is endothermicsince it requires energy to break a bond (+ΔH). oThis process also has a positive change in entropysince it results in the formationof more particles (+ΔS).Each ion is then hydratedby the surrounding water molecules:oThis process is exothermicsince it involves the formation of new bonds (-ΔH).oThe process also has a negative change in entropysince it results in fewer particles, as water molecules are organized around the ions (-ΔS).The enthalpy of dissolution(entire reaction) is the sum of the enthalpiesof both processes. This can be endothermic (+) or exothermic (-) depending on the magnitudes of the processes. The change in entropyof the reaction is the sum of the changes in entropyof the two processes. This can be positive (+) or negative (-) depending on the magnitudes for the processes.Ksp = [Na+]2 [B4O5(OH)42-], in order to substitute the tetraborate anion for the sodium cation, one must look at the stoichiometry of the equation. 1[Na+]= 2[B4O5(OH)42-], so Ksp = 4[B4O5(OH)42-]3Looking at the titration reaction, it takes 2 acid molecules to neutralize one tetraborate anion.
ΔG° = -RTlnKsp = ΔH° - TΔSlope = m = -ΔH/R, so ΔH=(slope)(-R)

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