Which of the following statements about universal indicator is/are true ?
- 1. It is a mixture of several indicators.
- 2. It shows different colours at different concentrations of hydrogen ions in solution.
- 3. It helps to determine the strength of given acid and base in titration.
Select the correct answer using the code given below :
1 only
1 and 2 only
2 and 3 only
1, 2 and 3
Answer is Wrong!
Answer is Right!
This question was previously asked in
UPSC CDS-2 – 2021
Statement 2: The colour of a universal indicator changes gradually with the concentration of hydrogen ions (or hydronium ions) in the solution, covering the full pH scale (typically from pH 0-14). Different colours correspond to different pH values, which reflect different hydrogen ion concentrations. This statement is true.
Statement 3: While a universal indicator shows the pH throughout a titration, providing insight into how the pH changes with the addition of titrant (related to strength), it does not typically help determine the *strength* in the sense of quantitative concentration determination or finding a precise endpoint for volumetric analysis in titration. Specific indicators with sharp colour changes near the equivalence point are used for accurate titration. Universal indicator gives an approximate pH, which *can* give a general idea of strength (e.g., a strong acid causes a lower pH than a weak acid at the same concentration), but it’s not its primary use in quantitative titration analysis. Therefore, this statement is less accurate or potentially misleading in the context of standard titration procedures for determining strength (concentration). Considering the options, and the definite truth of statements 1 and 2, option B (1 and 2 only) is the most likely correct answer if statement 3 is considered not entirely true or imprecise for typical quantitative strength determination in titration.
– It provides a spectrum of colours corresponding to different pH levels.
– It is useful for estimating the pH of a solution but less so for precise titration endpoints.