Which one of the following is commonly used as an indicator to measure the exact pH?

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RRB ALP CBT I 17 Aug 2018 Shift 3 Official Paper
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  1. Eosin
  2. Litmus
  3. Universal indicator
  4. Phenolphthalein

Answer (Detailed Solution Below)

Option 3 : Universal indicator
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Detailed Solution

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The correct answer is Universal indicator.

Key Points

  • Acids are compounds that, when dissolved in water, form free hydrogen ions (H+ ions).
  • When bases are dissolved in water, they form hydroxyl ions (OH-).
  • Hydrogen ions are abundant in acidic solutions and limited in basic solutions.
  • The pH scale is used to determine the acidity or basicity of an acid or base.
  • The pH scale goes from 0 to 14 on the scale.
  • pH indicators are made up of several chemical compounds known as universal indicators.

Additional Information

  • Eosin:
    • Eosin is the maximum appropriate stain to mix with an alum hematoxylin to illustrate the overall histological structure of a tissue.
  • Litmus:
    • Litmus paper is filter paper that has been treated with soluble natural dyes provided by lichens.
    • Litmus paper is a piece of paper that produces results that can be used as a pH indicator.
  • Phenolphthalein:
    • Phenolphthalein is an organic compound that is used medicinally as a bleach.
    • It has the chemical formula C20H14O4. It is written as “phph” or HIn. It is used in acid-base titration as an indicator.

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