Which chemical is used as the reagent to measure residual chlorine in water samples?

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Multiple Choice

Which chemical is used as the reagent to measure residual chlorine in water samples?

The reagent used to measure residual chlorine is DPD, which stands for N,N-diethyl-p-phenylenediamine. When chlorine is present, DPD is oxidized and turns a pink color; the intensity of that pink is proportional to the chlorine concentration, so you can compare to a color chart or read it with a photometer to determine residual chlorine levels. The other options are pH indicators and are used to show acidity or basicity, not to quantify chlorine residual, so they don’t provide a reliable measure of chlorine.

The reagent used to measure residual chlorine is DPD, which stands for N,N-diethyl-p-phenylenediamine. When chlorine is present, DPD is oxidized and turns a pink color; the intensity of that pink is proportional to the chlorine concentration, so you can compare to a color chart or read it with a photometer to determine residual chlorine levels. The other options are pH indicators and are used to show acidity or basicity, not to quantify chlorine residual, so they don’t provide a reliable measure of chlorine.

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