What concentration of aqueous Ba(OH)2 yields a pH of 9.0? A) 1x10−5 M B) 2x10−5 M C) 5x10−6 M D) 1x10−9 M E) 5x10−10 M

option C) 5x10−6 M

Explanation:

Recall that pH + pOH = 14

9.0 + pOH = 14

pOH = 14 - 9.0

pOH = 5.0

Then, find the concentration of aqueous Ba(OH)2 that yields a pOH of 5.0

Ba(OH)2 = Ba2+ + 2OH-

Since pOH = - log(OH-)

5.0 = - 2 x log(OH-)

2 x (OH-) = Antilog (-5.0)

2 x (OH-) = 0.00001

(OH-) = 0.00001/2

(OH-) = 0.000005

Then, 0.000005 in standard form = 5x10−6 M

c. heat could easily travel through the molecules in the air and escape/enter the flask. removing the air slows down the heat transfer.