pH indicator

Universal indicators and pH calculation

1. Ph definition : The definition of pH is the negative logarithm of the  hydrogen ion (H+) activity  in a given solution.  • The range of the  p h scale  is from 0 to 14. 7-Jan-17 ALINA SHERIN 1

2. Acidity or alkalinity of a solution So why are the hydrogen (H+) ions of interest?  The hydrogen ions (H+) are what determines if a solution is acidic, alkaline or neutral. If we can  measure the hydrogen ion content  of a solution, we can determine the acidity or alkalinity of that solution. 7-Jan-17 ALINA SHERIN 2

3. Water molecules are in continuous motion. When two water molecules collide, a hydrogen and hydroxide ion are created. This process in which water itself dissociates (splits) into hydrogen and hydroxide ions is called auto dissociation or self ionization . 7-Jan-17 ALINA SHERIN 3

4. p H , pOH and pKw 7-Jan-17 ALINA SHERIN 4

5. pH INDICATOR pH indicators are substances, usually a weak acid or base, that changes color depending on the pH of the solution it is mixed with. 7-Jan-17 ALINA SHERIN 5

6. Universal Indicator 7-Jan-17 ALINA SHERIN 6

7. Example of common indicators of pH LITMUS 7-Jan-17 7 ALINA SHERIN

8. Phenolphthalein Color in Acid: Colorless  Color in Base: Pinkish violet color  Approximate pH range for color change: 8.3 -10.0 7-Jan-17 8 ALINA SHERIN

9. Methyl Orange: Color in Acid: Red Color in Base: Yellow  Approximate pH range for color change: 3.1-4.4 7-Jan-17 9 ALINA SHERIN