Which indicator in the table would be best for distinguishing between lemon juice (pH = 2.3) and potato juice (pH = 5.8)? | Indicator | Colour at different pH | |-------------------------|------------------------| | (A) Crystal violet | 0.2 - yellow | 1.8 - blue | | (B) Methyl orange | 3.2 - red | 4.4 - yellow | | (C) Bromothymol blue | 6.0 - yellow | 7.6 - blue | | (D) Phenolphthalein | 8.2 - colourless | 10.0 - pink | - HSC - SSCE Chemistry - Question 7 - 2016 - Paper 1

• Crystal violet: Changes from yellow at pH 0.2 to blue at pH 1.8. This does not provide a clear distinction as it does not cover pH 2.3 to 5.8.
• Methyl orange: Changes from red at pH 3.2 to yellow at pH 4.4. Since lemon juice is at pH 2.3 (below 3.2) and potato juice is at pH 5.8 (above 4.4), it will clearly indicate a difference.
• Bromothymol blue: Changes from yellow at pH 6.0 to blue at pH 7.6, which is not suitable as both juices lie below 6.0.
• Phenolphthalein: Changes from colourless at pH 8.2 to pink at pH 10.0, which is also not effective for distinguishing these juices.

The best indicator for distinguishing between lemon juice (pH 2.3) and potato juice (pH 5.8) is Methyl orange (B), as it clearly differentiates between an acidic solution (lemon juice) and a more neutral solution (potato juice) with distinct color changes.