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Alkalinity of water is measured by titration against a standard acid using

  • A.phenolphthalein and then methyl orange
  • B.Eriochrome Black T alone
  • C.starch and then iodine
  • D.potassium permanganate as a self-indicator

Answer: A

The phenolphthalein end point at about pH 8.3 accounts for hydroxide and half the carbonate, and the methyl orange end point near pH 4 completes the carbonate and the bicarbonate. Comparing the two readings identifies which species are present.

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