CHM 2046C Module 11 Chapter 17 Sample Exam

Part D: pH Scale Calculations 10 points

What is the pH and pOH of the following solutions:

 

(1) 0.000675 M HCl

 

pH = -Log [H+] = -Log [0.000675] = 3.17

 

pOH = 14.00 pH = 14.00 3.17 = 10.83

 

 

 

(2) 0.0025 M Ca(OH)2

 

The dissociation reaction: Ca(OH)2 Ca 2+ + 2 OH 1-

 

A 0.0025 M Ca(OH)2 solution produces a 2 x 0.0025 M hydroxide ion or 0.050 M hydroxide ion

 

pOH = -Log [OH-] = -Log [0.0050] = 2.30

 

pH = 14.00 pOH = 14.00 2.30 = 11.70

 

 

(3) The pH of a cup of coffee is 4.32, calculate the [H3O+1 ]:

 

[H+] = 10pH = 10-4.32 = 0.0000479 = 4.79 x 10-5

 

 

(4) A detergent solution has a pH of 11.45. What is the [OH 1- ]?

 

[H+] = 10pH = 10-11.45 = 3.55 x 10-12

 

pOH = 14.00 pH = 14.00 11.45 = 2.55

 

[OH-] = 10pOH = 10-2.55 = 0.00282 = 2.82 x 10-3