Introduction
Ethanol is a common chemical compound used in various industries, including pharmaceuticals, perfumes, and fuel. However, the purity of ethanol is crucial in determining its quality and safety for use. One of the widely used methods to test the purity of ethanol is the Potassium Dichromate Test. In this article, we will discuss the principle, procedure, and interpretation of the Potassium Dichromate Test for ethanol.
Principle
The Potassium Dichromate Test is based on the oxidation of ethanol by Potassium Dichromate (K2Cr2O7) in the presence of concentrated sulfuric acid (H2SO4). The reaction produces a green-colored compound called Chromium (III) sulfate (Cr2(SO4)3). The intensity of the green color indicates the purity of ethanol. The more intense the green color, the purer the ethanol.
Procedure
To perform the Potassium Dichromate Test, you will need the following materials:
- Potassium Dichromate (K2Cr2O7)
- Concentrated Sulfuric Acid (H2SO4)
- Ethanol sample
- Distilled water
- Test tubes and test tube holder
- Measuring cylinder and pipette
- Heat source (Bunsen burner or hot plate)
- Beaker and stirring rod
Now, follow these steps:
- Measure 5ml of ethanol sample using a measuring cylinder and transfer it to a test tube.
- Add 1ml of concentrated sulfuric acid to the test tube using a pipette. Be careful while adding sulfuric acid, as it is highly corrosive and can cause severe burns.
- Add a small crystal of Potassium Dichromate to the test tube.
- Heat the test tube gently over a Bunsen burner or hot plate until the solution turns green. Do not overheat the solution to avoid the formation of a black precipitate.
- Allow the solution to cool; then add distilled water dropwise while stirring with a stirring rod until the solution turns yellow.
- Compare the color of the solution with a standard color chart to determine the purity of ethanol.
Interpretation
The intensity of the green color of the solution obtained after heating indicates the purity of ethanol. A deep green color indicates pure ethanol, while a light green or yellow color indicates impurities in ethanol. The color of the solution after dilution with distilled water should be yellow. If the solution turns black after heating, it indicates the presence of organic impurities in ethanol.
Tips
- Use only laboratory-grade reagents and equipment to perform the Potassium Dichromate Test.
- Be careful while handling concentrated sulfuric acid, as it can cause severe burns.
- Do not overheat the solution, as it can lead to the formation of a black precipitate.
- Use a standardized color chart to compare the color of the solution.
- Perform the test in a well-ventilated area to avoid exposure to toxic fumes.
Conclusion
The Potassium Dichromate Test is a simple and effective method to determine the purity of ethanol. It is widely used in various industries to ensure the quality and safety of ethanol products. By following the procedure and tips mentioned in this article, you can perform the Potassium Dichromate Test with ease and accuracy.