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

The yellow solution can be assessed for its usefulness as an acid–base indicator by examining the color changes it exhibits when in contact with various substances. An effective acid-base indicator should show distinct color changes for acidic and basic solutions.

1. Response to Acids and Bases: The solution turns red in the presence of 0.1 M hydrochloric acid, indicating that it functions as an acid-base indicator, presenting a clear color shift for an acidic environment.

2. Testing with Bases: In contrast, when tested with 0.1 M ammonia, the solution remains yellow. This suggests that the indicator is less effective in indicating basicity as it shows no color change.

3. Neutral Solutions: With pure water and lemon juice (which is slightly acidic), the yellow solution maintains its color in the case of pure water and changes to orange with lemon juice.

Overall, while the yellow solution demonstrates some functionality as an indicator (e.g., red for acid), it lacks a notable reaction to a basic situation (remains yellow). Thus, it can be considered useful, but its limitations in detecting bases must be noted.