Congo red paper
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Description
A acid-base indicating paper. Congo red paper is made by impregnating filter paper with a 0.1% aqueous solution of Congo red dye. Congo red is red above pH 5 and blue below pH 3. It is only sensitive to strong acids (mineral acids) and not weak acids (organic acids).
Synonyms and Related Terms
Congo blue paper; Riegel's paper; Herzberg's paper