These products are simple, completely impregnated indicator papers which do not have a colour chart and hence do not allow exact pH determinations. Instead they indicate alkalinity or acidity of the water sample.
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Congo PaperColour change: red → blue (pH 5.0 → pH 3.0)
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Litmus Paper BlueColour change: blue → red (pH 8.0 → pH 5.0)
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Litmus Paper RedColour change: red → blue (pH 5.0 → pH 8.0)
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Phenolphthalein PaperColour change: white → pink-red (pH 8.3 → pH 10.0)
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