How to Determine the Assay of Hydrochloric Acid


Hydrochloric acid is a saturated solution of hydrogen chloride gas dissolved in water and is highly corrosive. Hydrochloric acid is between 36.5 to 38 percent hydrogen chloride. Concentrated solutions ranging from 33 to 40 percent hydrogen chloride are also available. Determination of assay of hydrochloric acid is done by titrating it against standardized sodium hydroxide using methyl red as test solution. Each mililiter of 1 Normal sodium hydroxide is equivalent to 36.46 mg of HCl.

Things You'll Need

  • Electronic balance
  • Glass-stoppered flask
  • Hydrochloric acid
  • Methyl red
  • Sodium hydroxide
  • Measure 20 ml of water in a 250-ml glass-stoppered flask and tare this, set the scale to zero, on an electronic balance.

  • Add 3ml of hydrochloric acid and note the weight of the added hydrochloric acid.

  • Dilute the solution by again adding 25 ml of water and add few drops of methyl red test solution.

  • Titrate this against 1 Normal standard sodium hydroxide solution and note the end point when the color changes from orange to yellow with a single drop.

  • Ensure accuracy of the value by repeating the titration by following the same procedure.

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