Inorganic and Applied Chemistry

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Inorganic and Applied Chemistry





  

^

(^952)
2 14 2

1. 010


2. 010


3. 0 10
   A
   OH HA
   M
   M
   M
   K HA
   K
   K A
   a
   w
   b
   Once again we look at the initial and end concentrations:
   [A2-] 0 = 3.3 · 10-2 M
   [HA-] 0 = 0 M
   [OH-] 0 0 M (the autoprotolysis of water is neglected)
   And the end concentrations are thereby:
   [A2-] = (3.3 · 10-2 – x) M
   [HA-] = x M
   [OH-] x M
   Hereby we arrive at the following equation:
   x M
   x
   K M x x
   b
   4
   2
   (^55). 7 10


4. 310


5. 010
   (
   The concentration of OH- ions is 5.7 · 10-4 M which is why the concentration of H 3 O+ ions is found as:
     M
   M
   HO OH K HO M
   w
   11
   4
   14 2
   (^335). 710 1.^710


6. (^010)
    
   (
   why pH becomes:
   pH log 1. 710
   11  10. 8
   After the second point of equivalence the solution only contains a solution of the weak base A2- as well as
   the strong base OH- ions from the added NaOH in excess. In such a case we will as earlier neglect the
   contribution from A2- to pH and thereafter calculate pH as if there were only the strong base OH- present
   in the solution.
   5.6.2 Colour indicators for acid/base titration
   Apart from using a pH meter to determine the pH value in a given solution a colour indicator is often added
   to a given solution that is to be titrated. Such a colour indicator changes colour when the point of equivalence
   is reached. A typical colour indicator is a complex molecule, often being actually a weak acid itself. In
   Acids and bases