Which of the following is not an acid-base indicator?

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RRB Group D Previous Year Paper (Held on: 26 Aug 2022 Shift 2)
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  1. Methyl Orange
  2. Starch Paper
  3. Litmus
  4. Phenolphthalein

Answer (Detailed Solution Below)

Option 2 : Starch Paper
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Detailed Solution

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The correct answer is Starch Paper

Key Points

  • Starch Paper is not an acid-base indicator.
  • Acid-base indicators are substances that change color in response to changes in pH, helping to determine the acidity or alkalinity of a solution.
  • Methyl Orange, Litmus, and Phenolphthalein are common acid-base indicators used in various chemical analyses.
  • Starch Paper is typically used to detect the presence of iodine, not for measuring pH levels.

Additional Information

  • Methyl Orange changes color from red to yellow over a pH range of 3.1 to 4.4.
  • Litmus turns red in acidic conditions and blue in alkaline conditions, with a pH range of about 4.5 to 8.3.
  • Phenolphthalein is colorless in acidic to neutral solutions and turns pink in basic solutions, with a pH range of 8.2 to 10.
  • These indicators are essential tools in titrations and other laboratory experiments to determine the pH of different solutions.
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