Indicator , colour changes

The indicator colour change is affected by the hydrogen ion concentration of the solution, and no account of this has been taken in the above expression for the formation constant. Thus solochrome black, which may be written as H2In , exhibits the following acid-base behaviour ... 

To determine the cadmium content, add 20-25 mL of the 1,10-phenanthroline solution and titrate the liberated EDTA with the 0.05M lead nitrate solution until the colour change from yellow to red-violet occurs — a little practice is required to discern the end point precisely. Introduce further 2-5 mL portions of the 1,10-phenanthroline solution and note whether the indicator colour changes if so, continue the titration with the lead nitrate solution. The consumption of lead nitrate solution corresponds to the cadmium content. 

The ability of purified PemB to demethylate pectin was confirmed using different techniques. Addition of PemB to a pectin solution (98% methylated) caused an acidification of the reaction medium tested by NaOH titration and by pH indicator colour change. Analysis of the reaction end products by gas chromotography indicated that methanol was formed. These results showed that PemB is able to demethylate pectin, liberating acidic groups and methanol. 

Using the criteria for indicator colour change applied in developing equation (5.2), the potential range over which the indicator changes can be computed from an analogous equation... 

S.No. Name of Indicator Colour-change observed Acidic... 

Indicator Colour change at endpoint Approximate range... 

Replace the beaker with the Erlenmeyer flask that you prepared earlier. Place a sheet of white paper under the Erlenmeyer to help you see the indicator colour change that will occur near the endpoint. 

The indicator colour change may be easily obscured where coloured solutions must be titrated, where the solution is turbid or where a coloured precipitate is the product of the titration reaction. 

Using the criteria for indicator colour change applied in developing equation... 

Alkalimetric titration Powdered tablets equivalent to 50 - 200 mg of glafenine are placed in 150 mL conical flask. 25 mL of 0.1N HCi are added and shaken for 2 - 3 minutes. The bromocresol green indicator is added to the mixture (2 - 3 drops) and titration is carried out with 0.1 N NaOH. The indicator colour changes from yellow to bluish green at the end point. This method could be adopted for different dosage forms determination. Each mL of 0.1 N HCI volumetric solution is equivalent to 37.28 mg of glafenine (10). 

Used as a 0.1 or 1 % soln. in cone. H2SO4 for photometric detn. of V 559 nm, e 42700) redox indicator (colour change colourless blue). Cryst. powder. Sol. alkalis, cone, acids. 

Used as acid-base indicator (colour change rose yellow). Cryst. 

Used as 0.1% MeOH soln. as an acid-base indicator (colour change pink -> yellow). Cryst. Sol. MeOH si. sol. H2O. p i 6.15 (H2O). 

Redox indicator (colour change colourless - blue). Used as a 0.2% soln. in glac. AcOH. Cryst. (ligroin). Sol. acids, AcOH, C H insol. H2O. Mp 103°. 

Used as redox indicator (colour change colourless... 

Used as acid-base indicator (colour change red - yellow pH range 3.8-5.8). Orange cryst. (H2O). Sol. EtOH, Mc2CO mod. sol. H2O. 

Acid-base indicator (colour change red - blue) redox indicator. Used as 0.02% aq. soln. of Na salt. Dark green cryst. powder. Sol. H2O, EtOH, MejCO. pK 5.7. E° -b 0.668 V (30°). 

Used as 0.1% aq. soln. as a redox indicator (colour change pink - yellow). Dark blue cryst. powder. Sol. H2O. E° +1.13 V (IMH2SO4). 

Isol. from logwood under alkaline oxidn. conds. Used as 0.03% soln. in aq. MeOH for photometric detn. of B (2, 505 nm, e 23000), Hf (2, 520 nm, e 58000), Ga, Sn. Acid-base indicator (colour change yellow - red purple) biological stain. Brownish-red needles (EtOH). Mp 250° dec. 

Redox indicator acid-base indicator (colour change brownish-red blue). Used as a 0.02% aq. soln. Red cryst. Sol. H2O. pA j 8.7. E° +0.544 V. 

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