4/09/2014

CLASS BLOG:

We were given two handouts: ACID/BASE PROPERTIES LAB

We were going over two example problems

- Video on this is going to be posted (5:00 pm or later) to help you prepare for the QUIZ TOMORROW!

Notes (just in case the video fails):

• LeChatelier's Principle
• Ksp
• Calculate [  ] at equilibrium
• Calculate Ksp (using solubility) 
• Calculate S (solubility) 
• have to be given Ksp
• Need number of ions and memorize algorithms
• Ksp - Common Ion Problems

• Solubility and Ksp Problems
• Ex 1: Which of the following has the lowest solubility?
• a.) AgC2H3O2  Ksp= = 1.9 x 10 ^-3
• b.) AgCl  Ksp = 1.8 x 10 ^ -10
• c.) BaCrO4  Ksp = 1.2 x 10^ -10 (Ksp smaller, so lowest solubility)

2 ions : AgC2H3O2 (s) -------> Ag+ (aq) + C2H3O2 - (aq)

....so on for the next two dissociations...

all have two ions! 

• Ex 2: Which of the following has the lowest solubility?
• a.) MgCO3  Ksp = 6.8 x 10 ^-6
• b.) PbCl2  Ksp = 1.7 x 10^-5
• c.) Al(OH)3  Ksp = 2.0 x 10^-31 (SMALLEST Ksp)

write out the dissociations.... 

1st (a.) one has two ions, so take the square root of Ksp.

2nd (b.) one has 3 ions! Take the cube root of that Ksp/4.

3rd (c.) one has 4 ions! Take fourth root of Ksp/27.

• Common Ion Problem
• What is the solubility of PbCl2 in 0.100M MgCl2? The Ksp of PbCl2 = 1.7 x 10^-5
• Dissociation equation: MgCl2 ----> Mg 2+ (aq) + 2Cl- (aq)
• MgCl2 = 0.100M. and Mg= 0.100M.  and Cl= 0.200M.
• PbCl2 <-----> Pb2+ (aq) + 2 Cl- (aq)
•              I         0                   0.2
•              C       +x                  +2x
•              E        (x)             (0.200+2x)
• Use ice for PbCl2
• 1.7x10^-5 = (x)(0.200+2x)^2 , Get rid of the small x; (2x)
• 1.7x10^-5 = (x)(0.200)^2  
• 1.7x10^-5 = 0.04x
• x = solubility = 4.25 x 10^-4

HOMEWORK: STUDY!

NEXT BLOGGER WILL BE: EJ REYNOLDS