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International Journal of Interdisciplinary Research

Table 1 pK a values of indicator washcloths at different temperatures

From: Indicator washcloth for detecting alkaline washing solutions to prevent dermatitis patients and babies from skin irritation

Type of indicator washcloth pK a at 4 °C pK a at 20 °C pK a at 40 °C
IW1 (Strongly coloured) 7.32 7.31 7.24
IW2 (washed 80 times) 7.28 7.42 7.12
IW4 (Weakly coloured) 7.58 7.63 7.57
  1. The sensitive range of indicator washcloth covers 1.5 units above and below the pK a value, with corresponding colour changes from green to orange and to red at increasing pH