Presence of Hydrogen Peroxide

To determine the presence of hydrogen peroxide (H₂O₂) in milk, you can use a potassium iodide (KI) test or a paraphenylenediamine test. Hydrogen peroxide is sometimes added as a preservative to prevent spoilage.

Method 1: Potassium Iodide (KI) Test

Materials Required:

• Milk sample
  
  

• Potassium iodide (KI) solution (freshly prepared)
  
  

• Dilute hydrochloric acid (HCl)
  
  

• Test tube
  
  

Procedure:

1. Take 5 mL of milk in a test tube.
   
   

2. Add 1 mL of freshly prepared potassium iodide solution.
   
   

3. Add a few drops of dilute hydrochloric acid (HCl).
   
   

4. Observe any color change.
   
   

Observation & Interpretation:

• If hydrogen peroxide is present, the solution will turn yellow or brown due to the liberation of iodine.
  
  

• If absent, no significant color change occurs.
  
  

Method 2: Paraphenylenediamine Test

Materials Required:

• Milk sample
  
  

• 1% Paraphenylenediamine solution
  
  

• Test tube
  
  

Procedure:

1. Take 5 mL of milk in a test tube.
   
   

2. Add 2–3 drops of paraphenylenediamine solution.
   
   

3. Observe the color change.
   
   

Observation & Interpretation:

• If hydrogen peroxide is present, the solution will turn blue.
  
  

• If absent, no color change will be observed.
  
  

Why is This Test Important?

• Hydrogen peroxide is sometimes added to milk as an illegal preservative.
  
  

• Prolonged consumption can be harmful, leading to digestive issues.