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

Looking at the indicators in the table:

• Crystal violet: Changes from yellow at pH 0.2 to blue at pH 1.8, not suitable as it won't distinguish between 2.3 and 5.8.
• Methyl orange: Changes from red at pH 3.2 to yellow at pH 4.4; suitable since the pH 2.3 will show red and pH 5.8 will show yellow.
• Bromothymol blue: Changes from yellow at pH 6.0 to blue at pH 7.6, unsuitable as both juices fall outside this range.
• Phenolphthalein: Remains colourless at pH 8.2 and turns pink at pH 10.0; therefore unsuitable for the given pH levels.

Based on this evaluation, methyl orange is the best choice.

Thus, the best indicator for distinguishing between lemon juice and potato juice is (B) Methyl orange.