1. ACID-BASE INDICATORS An acid-base indicator is a weak acid or a weak base. Examples of indictors used in acid base reactions -Litmus -Phenolphthalein -Methyl orange thymol blue, tropeolin OO, methyl yellow, methyl orange, bromphenol blue, bromcresol green, methyl red, bromthymol blue, phenol red, neutral red, phenolphthalein, thymolphthalein, alizarin yellow, tropeolin O, nitramine, and trinitrobenzoic acid.

2. The pH range of indictors indctorspK i nd pH litmus6.55-8 methylorange3.73.1-4.4 phenophthaline9.38.3-10.0 Indictors dose not change colour sharply at one particular pH, they change over a narrow range of pH

4. Litmus Indicators as weak acids Litmus Litmus is a weak acid. It has a seriously complicated molecule which we will simplify to HLit. The "H" is the proton which can be given away to something else. The "Lit" is the rest of the weak acid molecule. The un-ionised litmus is red The ionised litmus is blue

5. What happened when Adding hydrogen ions

6. Adding hydroxide ion

7. If the concentrations of HLit and Lit - are equal: At some point during the movement of the position of equilibrium, the concentrations of the two colours will become equal. The colour you see will be a mixture of the two. red blue brown

8. Phenolphthalein is a chemical compound with the formula C20H14O4 (often written as "HIn" or "phph"). Often used in titrations, it turns colorless in acidic solutions and pink in basic solutionschemical compoundformulaCHOtitrationsacidicbasic Collarless acidic

9. Pk ind value indictor Pk ind litmus6.5 methylorange3.7 phenolphthaline9.3

10. The importance of pK ind Think of what happened through the color change.at this point the concentration of the acid and its ion are equal pH=pk ind This means that the end point for the indictor depends entiry on what pK ind value is

12. Methyl orange What is methyl orange? How is it made? Methyl orange is an intensely colored compound used in dyeing and printing textiles. It is also known as C.I. Acid Orange 52, C.I. 13025, helianthine B, Orange III, Gold orange, and Tropaeolin D. Chemists use methyl orange as an indicator in the titration of weak bases with strong acids. It changes from red (at pH 3.1) to orange-yellow (at pH 4.4): pH-related color changes result from changes in the way electrons are confined in a molecule when hydrogen ions are attached or detached. Methyl orange in acidic solution. Methyl orange in acidic solution.Methyl orange in basic solution.

13. Titration curves for strong base with strong acid indctorspK i nd pH methylorange3.73.1-4.4 phenophthaline9.38.3-10.0 Both of ph.ph and M.O. are useful

14. Titration curves for strong acid v weak base This time we are going to use hydrochloric acid as the strong acid and ammonia solution as the weak base. indctorspK i nd pH methylorange3.73.1-4.4 phenophthaline9.38.3-10.0 MO is useful and ph.ph is useless

15. Titration of weak base with strong acid indictorpK ind pH Methyl orange Phenolphaline 3.7 9.3 3.1-4.4 8.3-10.0 M.O is useful phph is useless

16. Choosing indictor for titration Titration of weak base with strong acid indictorpK ind pH Methyl orange Phenolphaline 3.7 9.3 3.1-4.4 8.3-10.0 Both phph and M.O are useful

17. Titration curves for weak base v strong acid Ph.ph is useful M.O is useless indctorspK i nd pH methylorange3.73.1-4.4 phenophthaline9.38.3-10.0

18. Titration curves for weak base with week acid Both phph and MO are useless indctorspK i nd pH methylorange3.73.1-4.4 phenophthaline9.38.3-10.0

19. Titration of sodium carbonate with HCl Phph useful for detect first endpoint MO is useful for detect the second end point

20. A summary of the important curves The way you normally carry out a titration involves adding the acid to the alkali. Here are reduced versions of the graphs described above so that you can see them all together