Keerthi wrote a secret message to her grandmother on her birthday using orange juice. Can you assist her grandmother in revealing the message? Which indicator would you use to make it visible?
To reveal the secret message written with orange juice, turmeric solution or turmeric paper can be used. Orange juice is acidic in nature.
When turmeric solution is sprayed on the paper, the areas with orange juice writing will not show any colour change (as turmeric does not change colour in acidic solutions), while the surrounding paper treated with a basic solution beforehand would appear red.
Alternatively, if the paper was pre-treated with a basic solution like soap solution and dried, spraying turmeric would turn the background red while the orange juice areas remain yellow, making the message visible.
Explanation
The chapter explains that turmeric paper turns red in basic solutions but remains unchanged in acidic and neutral solutions. Orange juice is acidic. For a secret message to appear, the paper can be pre-treated with a basic solution. When turmeric is applied, the basic background turns red while the acidic writing remains yellow, creating contrast. This principle is demonstrated in the chapter's opening scenario where words appear on white paper when sprayed with a solution.
Solution Steps
Use turmeric solution or turmeric paper as the indicator to reveal the message
Orange juice is acidic in nature
Turmeric does not change colour in acidic solutions but turns red in basic solutions
Pre-treat the paper with a basic solution (like soap solution) and let it dry
Write the message with orange juice on the pre-treated paper
Spray turmeric solution - the background turns red while the message areas remain yellow, creating contrast