Factors affecting Indicators Range_1573353290.pptx

Factors affecting Indicators Range

1. Factors affecting Indicators Transition Range Effect of concentration-

2. Increasing the concentration of An indicator Affect the transition range as follows The equilibrium expression for dissociation of colourless acid form of ph.ph In] [H] / Hin = Ka In constant (minimum value) … .[H] = ka/[In] x Hin

3. Effect of Temperature The ionization constant of the acidic indicators rise with temperature up to a certain maximum then fail as temp. rise Due to the dielectric constant D of water which makes it harder to separate the ions

4. Effect of Solvents The addition of a miscible solvent to water ( such ….?) decreases the dielectric constant and the ionization of the indicators decreases So the change of the color occur at higher pH in the presence of solvent than in pure water

5. Effect of diverse ions The effect may due to Changes in the absorption spectrum of one or both forms Electrostatic attraction which may shift the equilibrium between the acidic and the basic forms of the indicators Removal of the hydrogen ions by their interaction with the salt, thus changing the pH

6. Effect of large molecules and colloids Often active site in the large molecule will react with and indicators and alter the pH

7. Mixed indicators These indicators are used when it is necessary to locate the pH of an end point within close limits Suitable mixture of two indicators bromocresol and methyl red The acidic and basic colors of the mixture are orange and green respectively

8. Screened indicators Increase the sharpness of the colours chang at the end point Consists of an indicators and an inert dye Whose colour does not chang with pH Methyl orange with xylene - cyanol

9. Turbidity indicators Salts of mixed organic acids or bases of higher molecular weight Useful in the titration of weak acids or bases

10. Fluorescence An organic substances which fluoresce under the influence of ultraviolet light