When turmeric is added to lemon juice, it does not change its color and remains yellow. This is because lemon juice is an acidic substance, and turmeric acts as a natural pH indicator that stays yellow in acidic environments.
Turmeric as a Natural pH Indicator
Turmeric, derived from the Curcuma longa plant, contains a compound called curcumin, which is responsible for its vibrant yellow color and its ability to act as a natural pH indicator. A pH indicator is a chemical detector that reveals the pH level of a solution by changing color.
The pH scale ranges from 0 to 14, classifying substances as acidic, neutral, or basic (alkaline):
- Acidic solutions have a pH less than 7 (e.g., lemon juice, vinegar).
- Neutral solutions have a pH of exactly 7 (e.g., pure water).
- Basic (alkaline) solutions have a pH greater than 7 (e.g., baking soda solution, soap).
As stated in the provided reference, "Acidic medium have a range of pH about less than 7, and basic medium is found to have pH range higher than 7." The reference further clarifies that "When turmeric paper is dipped in acidic solution like vinegar or lemon juice then it doesn't change its colour and remains yellow in colour."
Color Changes of Turmeric with pH
Turmeric's color response to different pH levels is quite distinct:
| pH Range | Solution Type | Turmeric Color | Example |
|---|---|---|---|
| pH < 7 | Acidic | Yellow | Lemon juice, Vinegar |
| pH > 7 | Basic | Reddish-brown | Baking soda, Soap |
| Around pH 7 | Neutral | Yellow | Pure water (slight change possible with trace impurities) |
Practical Insights and Examples
Understanding turmeric's behavior with lemon juice (and other substances) has several practical applications:
- Homemade pH Indicator: Turmeric can be easily used at home to test the acidity or alkalinity of various household liquids.
- Example 1: If you add a pinch of turmeric powder to a glass of lemon juice, it will simply dissolve, keeping the solution a vibrant yellow.
- Example 2: In contrast, if you add turmeric to a solution of baking soda (which is basic), it will turn a distinct reddish-brown color, demonstrating a clear chemical reaction.
- Educational Demonstrations: It's a popular and safe substance for science experiments in schools to teach about pH and chemical indicators.
- Culinary Context: While primarily used for flavor and color, this property explains why turmeric dishes prepared with acidic ingredients (like lemon or vinegar) retain their bright yellow hue.
In summary, the interaction of turmeric with lemon juice is a simple chemical reaction demonstrating turmeric's role as a natural pH indicator, where its color remains unchanged due to the acidic nature of lemon juice.
