3. a. Using the data given, calculate each significant figures. of the thermodyn

Question

3. a. Using the data given, calculate each significant figures. of the thermodynamic quantities for Pbs dissolving in water at 25°C (use 298.15 K). Calculate and report each to 3 Thermodynamic Quantity AH t in kJ/mole So in J/mole PbS -98.32 91.34 24 1.7 10.5 Pb 33.05 14.64 AH 12967 aso =-009548 Go . 158.14 kJ/mole reaction kJ/mole reaction kJ/mole reaction b. From the AG value, calculate the Ksp for a saturated solution of Pbs. Ksp = 197e-28 X c. Confirm the solubility rules by calculating the molar solubility for Pbs and then decide, is this salt soluble, slightly soluble or insoluble in water. Please note that in the case of very soluble salts, the Ksp will often be so large that the molar solubility becomes an "unrealistically large" number. This happens because in these cases, the mole fraction of dissolved ions becomes so large, that ignoring solvent (water) becomes an invalid assumption that can introduce great error. Calculate the molar solubility as you normally would. If you get a huge value, this (while not completely accurate) will confirm that it is a soluble salt. Molar solubility = 0 This means that PbS is insolube in water

Explanation / Answer

Part1:

I strongly believe in significant figures, please use 5 significant figure as early as used for this also, although they are asked us to calculate and report each to 3 significant figures. If you used 5 sig fig then you must use 5 sig fig in all answers according to software programming.

Answer: 1.9733e-28

You did correct method, for instance

Go = RTlnKeq ; Go = 158.14 kJ/mol = 158140 J/mol

Keq = e-(Go/RT) = e-(158140 J / (8.3145 J/mol.K x 298.15K) = e-63.792670513 = 1.9733e-28

The standard value of Ksp for PbS = 1 x 10-28 (OR) 1e-28

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Part2:

Ksp = [Pb2+] [S2¯] = [X] x [X] = 1.9733e-28

X2 = 1.9733e-28, both sides square root results

x = (1.9733e-28) = 1.4047e-14

Molar solubility = 1.4047e-14

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