In Part 2 of Lab #12 you will also determine G° for the solid dissolving in wate

Question

In Part 2 of Lab #12 you will also determine G° for the solid dissolving in water. Suppose you use the same solid as in Question #3 (that is, the molar mass is 95.8 g/mol) and obtain the following data:

Mass of solid 2.968 g

Volume of solution 5.37 mL

Volume of water 2.86 mL

Temperature of solution 25.4 °C

Part 1: Determine the concentration of the solid. 5.77 M You are correct.

Part 2: Determine G° if we assume K = [solid] in the saturated solution. -4.35 kJ/mol You are correct.

Part 3: Determine the value of the equilibrium constant, K, if we take into account the volume of water added to the saturated solution. 10.8 You are correct.

Part 4: Determine G° if we take into account the volume of water added to the saturated solution: ? kJ/mol

PLEASE EXPLAIN IN DETAIL HOW TO FIND THE ANSWER TO PART 4.

Explanation / Answer

Part 4:
mass of solid = 2.968 g
Molar mass of solid = 95.8 g/mol
Number of moles of solid = mass/molar mass = 2.968/95.8 = 0.031 mol

Total volume = 5.37 mL + 2.86 mL = 8.23 mL = 0.00823 L

[solid] = number of moles/volume = 0.031/0.00823 = 3.77 M

K = 3.77
T = 25.4 oC = (25.4 + 273) K = 298.4 K

G° = -R*T*ln K
         = 8.314 * 298.4 * ln 3.77
         = 3292 J/mol
         = 3.29 KJ/mol

Answer: 3.29 KJ/mol

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