Final answer:
The pH range of indicator paper is based on the pKa ± 1 of the indicator used. Universal pH papers contain a mixture of indicators to cover a broad pH range, and the observed color is compared to a chart to estimate the solution's pH.
Step-by-step explanation:
The pH range of an indicator paper color indicator is determined by the pKa of the indicator used. The color change interval, or the pH interval, for an acid-base indicator is typically around the pKa value ± 1. This means that an indicator will start to change color when the pH of the solution is within one pH unit above or below its pKa. For example, if an indicator has a pKa of 7, it will change color over the approximate pH range of 6 to 8.
pH papers contain a mixture of indicators, allowing them to exhibit different colors over a range of pH values. For instance, universal indicator papers can provide a broad measurement of pH by displaying a variety of colors corresponding to different pH levels. The exact color observed can then be compared to a standard chart to estimate the pH of the solution.