Indicators, acid-base neutral salt error

Errors in Measurements with Indicators.—Three chief sources of error in connection with pll determinations by means of indicators may be mentioned. In the first place, if the test solution is not buffered, eg., solutions of very weak acids or Imsos or of neutral salts of strong acids and bases, the addition of the indicator may produce an appreciable change of pH this source of error may be minimized by employing small amounts of indicator which have been previously adjusted, as a result of preliminary experiments, to have approximately the same pH as the test solution. Such indicator solutions are said to be isohydric vith the test solution. 

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