Upon the addition of sodium hydroxide, turmeric in a sugar solution will turn red. This distinct color change occurs because the addition of sodium hydroxide renders the solution basic.
Understanding Turmeric as a Natural pH Indicator
Turmeric, derived from the Curcuma longa plant, is widely recognized for its vibrant yellow color, which comes from the compound curcumin. Curcumin acts as a natural pH indicator, meaning its color changes depending on the acidity or alkalinity (pH level) of the solution it is in.
- In Acidic Solutions: Turmeric typically retains its yellow color.
- In Neutral Solutions: Turmeric remains yellow, showing no significant color change from its natural state. A plain sugar solution is generally considered neutral.
- In Basic (Alkaline) Solutions: Turmeric undergoes a noticeable transformation, changing from yellow to a reddish-brown or red color.
The Specific Reaction: Turmeric in Sugar Solution with Sodium Hydroxide
The provided reference explicitly details the color change under specific conditions:
The turmeric in the sugar solution will turn red upon addition of sodium hydroxide as the solution will turn basic.
This phenomenon is due to the following steps:
- Initial State: A sugar solution, by itself, is neutral. If turmeric were simply added to it without any other reagents, it would likely remain yellow.
- Addition of Sodium Hydroxide: Sodium hydroxide (NaOH) is a strong base. When added to the neutral sugar solution, it significantly increases the concentration of hydroxide ions (OH-), thereby raising the solution's pH and making it alkaline (basic).
- Color Change: As the solution becomes basic, the curcumin molecules in the turmeric undergo a structural change that results in the absorption and reflection of light differently, causing the solution to appear red.
For context on turmeric's general indicator properties, the reference also notes:
Whereas the turmeric in the hydrochloric solution will undergo no change as the solution will become neutral upon addition of the base and turmeric is yellow in acidic as well as neutral solution.
This further illustrates that turmeric maintains its yellow hue in both acidic and neutral environments, reinforcing that a basic condition is necessary for the red color change.
Practical Insights into Turmeric's Indicator Properties
Understanding turmeric's behavior as a pH indicator extends beyond theoretical knowledge, offering several practical applications:
- DIY pH Testing: Turmeric can be easily used at home to create a simple pH indicator paper or solution to test various substances, such as household cleaners, soaps, or even the acidity of soil for gardening.
- Educational Chemistry Experiments: Its clear and dramatic color change makes it an excellent, safe, and natural material for science demonstrations in educational settings to teach fundamental concepts of acids, bases, and pH.
- Cooking Observations: Although not used for precise pH measurement, chefs and home cooks might occasionally notice subtle color shifts in dishes containing turmeric when combined with ingredients that are particularly acidic (like lemon juice) or alkaline (like baking soda).
Summary Table: Turmeric as a pH Indicator
To further clarify turmeric's color responses based on pH, the following table summarizes its typical behavior:
| Solution Type | pH Range | Turmeric Color | Example of Use |
|---|---|---|---|
| Acidic | Less than 7 | Yellow (retains natural color) | Testing lemon juice or vinegar |
| Neutral | Around 7 | Yellow (retains natural color) | Testing pure water or plain sugar solution |
| Basic | Greater than 7 | Red (specifically with NaOH in sugar solution) | Testing baking soda solution or soap |
Key Takeaway
The exact answer to the question, based on the provided reference, is that turmeric in a sugar solution will turn red when sodium hydroxide is added, as this renders the solution basic. Without the addition of a basic substance, turmeric would typically remain yellow in a neutral sugar solution.
