Portage Learning Chem 104 Lab Exam M3: Exam

Portage Learning Chem 104 Lab Exam


M3: Exam- Requires Respondus LockDown Browser

1. Show the calculation of the molar solubility (mol/L) of BaF2, Ksp of BaF2 = 1.0 x 10-6.

BaF2 (s) Ba+2 (aq) + 2 F-1 (aq)
(s) (s) (2s)
1.0 x 10-6 = [Ba+2] x [F-1]2
1.0 x 10-6 = [s] x [2s]2
1.0 x 10-6 = 4 s3
s = 6.30 x 10-3 mol/L
2. Show the calculation of the Ksp of AgCl if the solubility of AgCl is 0.0001921 g/100
ml.
MW of AgCl = 143.35
AgCl (s) Ag+ (aq) + Cl- (aq)
molar sol of AgCl = (0.0001921 g/100 ml) x (1000 ml / 1 L) x (1 mol / 143.35 g AgCl)
molar sol AgCl = 1.34 x 10-5 mol / L
This means that as 1.34 x 10-5 mol / L of AgCl dissolves, 1.34 x 10-5 mol / L of Ag+ and
1.34 x 10-5 mol / L of Cl- are formed since one mole of each ion forms from 1 mole of
AgCl


Ksp = [Ag+] x [Cl-] = (1.34 x 10-5) x (1.34 x 10-5) = 1.80 x 10-10


3. Show the calculations and predict if a precipitate of Ni(OH)2 will form if 1.0 x 10-4 M
Ni(NO3)2 is mixed with 1.0 x 10-5 M NaOH? The Ksp of Ni(OH)2 = 2.0 x 10-15.

Ni(OH)2 (s) Ni+2 (aq) + 2 OH-1 (aq


Ksp = [Ni+2] x [OH-1]2 = Ksp of Ni(OH)2 = 2.0 x 10-15
Qc = [Ni+2]initial x [OH-1]2initial = [1.0 x 10-4] x [1.0 x 10-5]2 = 1.0 x 10-14
Since Qc (1.0 x 10-14) > Ksp (2.0 x 10-15) the reaction should go in the REVERSE
direction (Precipitation) and Ni(OH)2 WILL precipitate.
4. State and explain which has greater entropy: CH3OH (l) at 65oC or CH3OH (g) at 65oC.
CH3OH (g) at 65oC has greater entropy since gas particles are in constant motion so
gases have greater entropy than liquids.