Inorganic and Applied Chemistry

Download free books at BookBooN.com

Inorganic and Applied Chemistry

general an indicator may be represented as ”HIn”. Colour indicators exhibit one colour with the proton and

another colour without the proton. A well-known example is phenolphthalein which is opaque in its HIn

form while the colour changes to violet in it’s In- form. We will briefly look into how such a molecule may

function as indicator in order to achieve knowledge of what is going on during titration.

We look at a representative hypothetical color indicator HIn which is a weak acid with a Ka value of 1.0 · 10-

(^8) M. HIn is in equilibrium with:
HIn(aq)  H+(aq) + In-(aq)
The indicator is red in its HIn form while the colour is blue when on the In- form. Correspondingly, the
equilibrium reaction the following equilibrium fraction is achieved:
  
 
 
HIn
In
H
K
HIn
K H In a
a



Assume that a few drops of indicator is added t a solution where pH = 2.0. From above we get that the
relation between In- and HIn is:
 1000000
1
10

1. 0108
   (^)
    M
   M
   H
   K
   pH
   a
   Acids and bases
   Dedicated Analytical Solutions
   FOSS
   Slangerupgade 69
   3400 Hillerød
   Tel. +45 70103370
   http://www.foss.dk
   The Family owned FOSS group is
   the world leader as supplier of
   dedicated, high-tech analytical
   solutions which measure and
   control the quality and produc-
   tion of agricultural, food, phar-
   maceutical and chemical produ-
   cts. Main activities are initiated
   from Denmark, Sweden and USA
   with headquarters domiciled in
   Hillerød, DK. The products are
   marketed globally by 23 sales
   companies and an extensive net
   of distributors. In line with
   the corevalue to be ‘First’, the
   company intends to expand
   its market position.
   Employees at FOSS Analytical A/S are living proof of the company value - First - using
   new inventions to make dedicated solutions for our customers. With sharp minds and
   cross functional teamwork, we constantly strive to develop new unique products -
   Would you like to join our team?
   FOSS works diligently with innovation and development as basis for its growth. It is
   reflected in the fact that more than 200 of the 1200 employees in FOSS work with Re-
   search & Development in Scandinavia and USA. Engineers at FOSS work in production,
   development and marketing, within a wide range of different fields, i.e. Chemistry,
   Electronics, Mechanics, Software, Optics, Microbiology, Chemometrics.
   Sharp Minds - Bright Ideas!
   We offer
   A challenging job in an international and innovative company that is leading in its field. You will get the
   opportunity to work with the most advanced technology together with highly skilled colleagues.
   Read more about FOSS at http://www.foss.dk - or go directly to our student site http://www.foss.dk/sharpminds where
   you can learn more about your possibilities of working together with us on projects, your thesis etc.
   Please click the advert