CHM 1025C     Module Eight-Chapter 15.8-15.9   Name:__Answers___

 

Part L:   pH Scale Calculations (Section 15.8-15.9)                            10 points

What is the pH and pOH of the following solutions:

 

pOH = 14.00 – pH         Kw = 1.00 x 10-14  =  [H3O1+][OH1-]        [H3O1+] is the same as [H1+]

 

 

 (1)        0.0100 M HCl

 

pH = -Log [H+] = -Log [0.0100] = 2.00

 

pOH = 14.00 – pH  =  14.00 – 2.00  = 12.00

 

 

(2)   0.0055 M Mg(OH)2        

 

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

 

A 0.0055 M   Mg(OH)2  solution   produces a 2 x 0.0055 M hydroxide ion or 0.0110 M hydroxide ion

 

pOH = -Log [OH-] = -Log [0.0110] = 1.96

 

pOH = 14.00 – pH  =  14.00 – 1.96  = 12.04

 

 

(3)  The pH of vinegar is 2.85, calculate the [H3O1+]:

 

[H+] = 10–pH  =  10-2.85   =  0.00141 M

 

 

 

(4) Easy Off Oven Cleaner has a pH of 11.70. What is the [H3O1+] and [OH 1- ]?

 

[H+] = 10–pH  =  10-11.70   =  1.995 x 10-12 M 

 

pOH = 14.00 – pH  =  14.00 – 11.70  = 2.30

 

[OH-] = 10–pOH  =  10-2.30   =  0.00501 M