A natural indicator was made by heating yellow flowers with water - HSC - SSCE Chemistry - Question 23 - 2004 - Paper 1

The yellow solution serves as an acid-base indicator due to its ability to change color in response to different pH levels. The results indicate a clear change when tested with different substances:

1. Acidic Substance: 0.1 M hydrochloric acid turned the solution red, indicating that the yellow solution can effectively signal acidic conditions.

2. Neutral Substance: Pure water and oven cleaner both retained the yellow color, suggesting that the solution does not change under neutral conditions, which can be a limitation of its use as a universal indicator.

3. Basic Substance: 0.1 M ammonia resulted in a yellow color, indicating that the solution may also be useful in identifying certain bases, although it does not show a dramatic color change as seen with acids.

4. Other Compound: Lemon juice turned the solution orange, implying that the indicator can detect moderate acidity effectively.

In conclusion, while the yellow solution is useful as an indicator for certain ranges of pH, its limitations include lack of a distinct change across all pH levels, particularly in neutral and mildly basic solutions.