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SALT ERROR OF INDICATORS DUE TO STANDARD ALKALINE BUFFERS THEMSELVES. II
J W McBain1, M E Laing, O E Clark
1Chemical Laboratories of Stanford University, California.
The Journal of General Physiology
|October 30, 2009
Summary
Color indicators show varying accuracy in alkaline solutions. Some indicators like alizarin yellow G are reliable, while others, such as phenolphthalein, exhibit significant errors due to salt error in alkaline buffers.
Area of Science:
- Analytical Chemistry
- Physical Chemistry
Background:
- Accurate pH determination is crucial in chemical analysis.
- Indicator color changes are commonly used for pH estimation.
- Alkaline buffers can introduce complexities in indicator-based pH measurements.
Purpose of the Study:
- To re-evaluate the accuracy of acid-base indicators in alkaline buffers.
- To identify indicators that are reliable for pH measurements in alkaline conditions.
- To investigate the source of discrepancies observed with certain indicators.
Main Methods:
- Electrometric determination of hydroxyl ion concentration.
- Comparison of indicator color changes in pure sodium hydroxide and alkaline buffers.
- Graphical recording of allowances for the neutralizing effect of dilute alkali.
Main Results:
- Electrometric measurements confirmed the purity of sodium hydroxide and theoretical hydroxyl ion concentrations.
- Alizarin yellow G, tropaeolin O, and thymol violet showed minimal error in alkaline buffers.
- Phenolphthalein, o-cresol phthalein, thymol blue, and phenol red exhibited significant discrepancies, attributed to salt error.
Conclusions:
- Alizarin yellow G, tropaeolin O, and thymol violet are suitable for pH measurements in alkaline buffers.
- Phenolphthalein, o-cresol phthalein, thymol blue, and phenol red are unreliable in alkaline buffers due to salt error.
- Salt error within the alkaline buffer itself is the primary cause of discrepancies for certain pH indicators.
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