ACID BASE INDICATOR SMK NEGERI 13 BANDUNG

Acid – Base Indicators Weak organic acid or weak organic base which it’s ion colour differ from its molecule colour

Reactions  H-Ind  H + + Ind -  molecule Ion  Colour A Colour B  Ind-OH  Ind + + OH -  Molecule Ion  Colour X Colour Y

Acid Environmental : low pH, high concentration H +.  H-Ind  H + + Ind -  Constant Equilibrium of Indicator   [H + ] [Ind - ]  K ind =  [H-Ind]  If [H + ] high, hence the equilibrium shift up to the left ( dominant molecule H-Ind) so that dominant colour A.

Base environmental: high pH, concentration H + low  H-Ind H + + Ind -  Indicator equilibrium  [H + ] [Ind - ]  K =  [H-Ind]  If [H + ] is low, hence the equilibrium shift up to the right (dominant Ion Ind-) so that dominant colour B

How is the comparison of concentration of H-Ind and Ind-?  When H-Ind is dominant  H-Ind : Ind - > 1  When Ind - is dominant  H-Ind : Ind - < 1  In a moment will be happened by circumstance H-Ind : Ind - = 1: 1

When is H-Ind : Ind - = 1:1?  If constant equilibrium of indicator  [H + ] [Ind - ]  K ind =  [H-Ind]  Hence, H-Ind : Ind - = 1:1 when  K ind =[H + ],  or when the price of pH = pKind

What is appeared at that moment?  Mixture colour of A and B with comparison 1 : 1.  Example :  Red : Yellow = 1:1 = Orange  Blue : Yellow=1 :1 = green

What colour is appeared if H-Ind : Ind- NOT 1 : 1? Hind : Ind - > 1 Hind colour is dominant Hind : Ind - < 1 Ind - colour is dominant

____*_____*_____*_____ Hind Hind Hind Ind - Ind - Ind - >10 =1 <10 colour mixture colour colour A B

The Functions of Indicator.  Recognizing pH solution  Following the changed of pH at acid – base titration.  Detecting of equivalent point at acid – base titration.

Some indicators and range of pH.  Metil orange 3,1 – 4,4  Metil red 4,2 - 6,3  Phenol red 6,8 – 8,4  Phenolphthalein 8,3-10,0

The indicator range of pH  pH range, where about eyes of human being can see mixture colour.  pH range, where about indicator changed the colour.  A_______mixture___________B  pH X route pH pH Y

pK ind lay between pH X and pH Y pK ind = pH where H-Ind : Ind - = 1 : 1

Choosing of Indicator Objectives:  The equivalence point is detected better.  The titration discontinued at the equivalence point or near by possible with the equivalence point.  The end point near by possible with the equivalence point.

Criterion of Choosing Indicator  Value of pH titration solution at equivalence point.  Route of pH indicators.  The indicator selected which has route of pH near by possible with the price of pH of equivalence point.

Phenolphtalein Indicator Teknologi dan Rekayasa mages/lowres/phenolphtalein.jpg

Methyl Red Indicator Teknologi dan Rekayasa

Methyl Violet Teknologi dan Rekayasa

Thymol Blue Teknologi dan Rekayasa

Methyl Orange Teknologi dan Rekayasa

Bromcresol Purple Teknologi dan Rekayasa

Bromthymol Blue Teknologi dan Rekayasa

Phenol Red Teknologi dan Rekayasa

Chlorophenol Red Teknologi dan Rekayasa

Litmus Teknologi dan Rekayasa

Congo Red Teknologi dan Rekayasa

Thymol Blue Teknologi dan Rekayasa

Phenolphtalein Teknologi dan Rekayasa

Exercises 1.What is acid – base indicator? 2.What is the function of acid – base indicator? 3.Name the criteria of indicator choosing in acid base titration! 4.What are objectives of choosing the indicator at the titration. 5. Determining correct indicator for the titration of CH3COOH by NaOH !