Learn the procedure for making a potassium chromate indicator solution.
The compound that changes color when exposed to acidic or basic solutions is called an indicator. Color indicators are commonly used to measure pH and are added to the reaction mixture to identify the titration endpoint/equivalence point.
Potassium chromate (K2CrO4) also known as tarpachite is an inorganic compound that is yellow orthorhombic or hexagonal crystal at room temperature. Potassium chromate comes in powder form and appears as a yellow compound that is soluble in water and it is insoluble in alcohol and ether.
K2CrO4 is used as an indicator in the detection of chloride by titration with standard silver nitrate (AgNO3) solution. The potassium chromate indicator method commonly known as Moore (Mohr) technique is a precipitation titration method. A change in color from yellow to reddish-brown indicates the endpoint.
How to prepare potassium chromate indicator for titration:
- Weigh accurately 05.00 gm of potassium chromate and pour it into a 100.00 ml volumetric flask containing 50.00 ml of distilled water and swirl until it completely dissolved.
- Once it is dissolved, dilute to 100.00 ml with distilled water.
- The concentration of the prepared solution is about 50 grams/liter.
Potassium chromate has pKa (Strongest Basic) values of -6.2; its suitable acidity range is pH 6.5 to 10.5, though when there are ammonium salts in solution, the solution acidity pH 6.5 to7.2 is suitable. It is the most commonly used indicator in the determination of chloride by titration with standard silver nitrate solution.
When Cl- or Br- ions coexist, the potassium chromate indicator method can only be used for direct titrations. The iodide ion and the thiocyanate ion cannot be determined with this method.
References:
- Wikipedia contributors. (2022, February 3). Methylene blue. In Wikipedia, The Free Encyclopedia. Available Here:
- Potassium Chromate indicator- riccachemical Available Here:
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