QUALITATIVE AND QUANTITATIVE ANALYSIS 



53 



A list of the color change and pH range of some of the more 

 common indicators is given below. 



The indicators for measuring the hydrogen-ion concentration 

 are prepared as follows: 0.1 gram of the dry powder is ground in 

 a mortar with varying amounts of N/20 NaOH and diluted to 

 25 cubic centimeters with water. 



N/20 NaOH 

 Used, Cubic 

 0.1 Gram of Indicator Centimeters 



Phenol red 5.7 



Brom phenol blue 3.0 



Cresol red 5.3 



Brom cresol purple 3.7 



Thymol blue 4.3 



Brom thymol blue 3.2 



Methyl red 7.4 



For colorimetric tests, dilute the stock solution of 25 cubic 

 centimeters with distilled water to 250 cubic centimeters or a 

 concentration of 0.04 per cent of the indicator. Take 5 drops of 

 this dilute solution to 10 cubic centimeters of the liquid to be 

 tested. 



Color Change and pH Range of Certain Indicators 



Common name 



Color change Range pH 



Thymol blue (acid) . . . . 



Brom phenol blue 



Brom cresol green 



Methyl red 



Brom cresol purple 



Chlor phenol red 



Brom thymol blue .... 



Phenol red 



Cresol red 



Thymol blue (alkaline) 



Phenolphthalein 



Methyl orange 



Litmus 



Cochineal 



Alizarin red 



Congo red 



Red-yellow 



Yellow-blue 



Yellow-green 



Red-yellow 



Yellow-purple 



Yellow-red 



Yellow-blue 



Yellow-red 



Yellow-red 



Yellow-blue 



Colorless-red 



Orange red-yellow 



Red-blue 



Yellow-lilac 



Yellow-pink 



Blue-red 



1.2 to 



3.0 to 



Oto 



.4 to 



.2 to 



.2 to 



6.0 to 



6.8to 



7.2 to 



8.0 to 



8.3 to 



3.1 to 

 4.5 to 

 4.8 to 

 5.0 to 

 3.0 to 



2.8 

 4.6 

 5.6 

 6.0 

 6.8 

 6.8 

 7.6 

 8.4 

 8.8 

 9.6 

 10.0 

 4.4 

 8.3 

 6.2 

 6.8 

 5.0 



