Answer to Question #336712 in General Chemistry for Josie

Question

How do I calculate the Ksp, Delta G, and Delta S from my data table? The experiment aims to find the solubility curve of potassium nitrate dissolving in water. For example, when 2 grams of KNO3 dissolve in 5 ml of H20, crystals reappeared at 25° celsius.

Answer 1

KNO₃ (s) ⇌ K⁺ (aq) + NO^3- (aq) 

 Calculate the concentration of KNO₃ 

2.0 g × (1 𝑚𝑜𝑙 / 101.1 𝑔) × (1/1 𝐿) = 0.02 mol/L 

Calculate the K_sp 

K_sp = [K⁺][NO^3-] 

[K⁺] - molar concentration of K⁺ (mol/L), [NO^3-] - molar concentration of NO^3- (mol/L) 

K_sp = 0.02*0.02 = 0.0004

Determine the ΔG based on the Ksp 

ΔG = -RTlnK_sp    

 R = 8.314 J/L*mol, T - temperature in Kelvin 

ΔG = -(8.314 J/K*mol)(25°C + 273 K)(ln0.0004) = 19374.61 J/mol 

ΔG = ΔH – TΔS 

The ΔH and ΔS based on data at different temperatures

a plot of lnKsp versus 1/T yields a straight line with a slope of –ΔH/R and a y-intercept of ΔS/R. So the ΔH and ΔS can be calculated based on the linear equation obtained from the linear fitting of the graph.