In a solution phenolphthalein is colourless but methyl orange is yellow. What type of solution could it be?
Answer and explanation
Correct answer: Neutral or slightly basic
Indicator colours must be interpreted together with their transition ranges. Phenolphthalein is colourless in acidic, neutral and mildly basic solutions, becoming pink only in a more strongly basic range. Methyl orange is yellow when the solution is not sufficiently acidic, including neutral and basic conditions. Hence the observations are consistent with a neutral or slightly basic solution, so A is the best answer. A strong base would generally turn phenolphthalein pink.
Frequently asked questions
What is the correct answer to this question?
Neutral or slightly basic
Why is this the correct answer?
Indicator colours must be interpreted together with their transition ranges. Phenolphthalein is colourless in acidic, neutral and mildly basic solutions, becoming pink only in a more strongly basic range. Methyl orange is yellow when the solution is not sufficiently acidic, including neutral and basic conditions. Hence the observations are consistent with a neutral or slightly basic solution, so A is the best answer. A strong base would generally turn phenolphthalein pink.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Chemical Substances – Nature and Behaviour. Topic: Acids, Bases, and Salts.
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