I need major help with these... Please show work and answer thank you!

Question

Question #1

The pH of a saliva sample was measured as 6.7 Convert the pH into the molarity of H₃O⁺ ions. 

Answer in units of mol/L. 

 

Question #2

A solution of HClO is mixed and found to have a pH of 4.34 Find what the initial concentration of HClO was for the solution. K_a=3.00 x 10^-8

Answer in units of mol/L

 

 

 

Answer 1

1) To find the concentration of H3O+ ions use the following equation:

 

pH = -log[H3O+]

 

2) First write down the equilibrium for the dissociation of HClO. This is

 

HClO  <=> H+ + ClO-

 

Then set up the ICE table to determine the initial concentration of HClO. 

 

     HClO     <=>     H+    +    ClO-

I:    ?                     0             0

C;  -x                    +x           +x

E:                          x             x

 

Then find the concentration of H+ by using the following formula

 

pH = -log[H+]

 

Notice from the ICE table that x = [H+] = [ClO-]. This allows you to find the equilibrium concentration of HClO from the equilibrium expression.

 

Ka = [H+][ClO-]/[HClO] = 3.00x10^-8 = (x)(x)/([HClO]0-x)

 

Since you know the concentration of H+ and ClO- you can then use the above expression to find the initial concentration of HClO

 

 

Answer 2

I am not really a chemistry buff; however, I found a reference that may help you. 

 

http://forums.studentdoctor.net/threads/how-do-i-find-the-concentration-of-h-when-im-given-ph.1143306/

 

Or this video on YouTube 

 

https://youtu.be/yE4M2Uuh-h4