Question

4.A saturated solution of manganese(II) hydroxide (Mn(OH)₂) was prepared, and an acid-base titration carried out to determine its K_sp at 25^oC. The endpoint was reached when 50.00 mL of Mn(OH)₂ solution was titrated with 3.42 mL of 0.00100 M HCl solution.

(a)Write the balanced equation for the reaction between Mn(OH)₂ and HCl.

(b)Write the equilibrium equation for the dissolution of Mn(OH)₂ in water and then calculate the   K_sp for Mn(OH)₂.

(c)Calculate ΔG^o for dissolution.  

Answer 1

(a)Write the balanced equation for the reaction between Mn(OH)2 and HCl.

Mn(OH)2+ 2HCl --> H2O(l) + MnCl2(aq)

(b)Write the equilibrium equation for the dissolution of Mn(OH)2 in water and then calculate the  Ksp for Mn(OH)2.

Ksp = [Mn+2][OH-]^2

mol of HCl = MV = 0.001*3.42*10^-3 = 0.00000342

mol of base = 1/2mol of acid = 0.00000342/2 = 0.00000171 mol of base

[base] = mol/V = (0.00000171)/(50*10^-3) = 0.0000342 M

[Mn+2] = 0.0000342

[OH-] = 2*0.0000342

Ksp = (0.0000342)((2*0.0000342)^2)

Ksp = 1.600*10^-13

c)

dG = -RT*ln(K)

dG = -8.314*298*( 1.600*10^-13)

dG = 3.964*10^-10 J/mol