Question

Sarah demonstrated a magic trick by rubbing a plain white paper with a handkerchief. It was observed that green letters appeared on the paper after rubbing. Which of the following materials might have been used by her in the magic trick?

• A. Sulphuric acid and phenolphthalein
• B. Vinegar and turmeric
• C. Soap and red cabbage juice
• D. Hydrochloric acid and methyl orange

Answer 1

The correct option is C Soap and red cabbage juice

Indicators are substances that help us to distinguish between acids and bases through colour change.
The following table depicts the colour change observed when these indicators are added in acidic or basic medium: $$\begin{array}{cccc}\text{Indicator}& \text{Colour of the Indicator}& \text{Acidic}& \text{Basic}\\ \text{Methyl orange}& \text{Orange}& \text{Pale pink}& \text{Pale yellow}\\ \text{Phenolphthalein}& \text{Colourless}& \text{Colourless}& \text{Pink}\\ \text{Turmeric}& \text{Yellow}& \text{Yellow}& \text{Red}\\ \text{Red cabbage}& \text{Purple}& \text{Red}& \text{Green}\end{array}$$From the above table it is clear that red cabbage juice turns green in the presence of a basic solution like soap. Also, we know that soap solution is white in colour. Hence we can conclude that a soap solution is used to write on the paper and the red cabbage juice is present in the handkerchief.