JEE Mains · Chemistry · STD 11 - 6.2. Equilibrium - II (icon Equilibrium)
The titration curve of weak acid vs. strong base with phenolphthalein as indictor) is shown below. The \(K _{\text {phenolphthalein }}=4 \times 10^{-10}\). Given: \(\log 2=0.3\) The number of following statements which is/are correct about phenolphthalein is \(.....\). \(A\). It can be used as an indicator for the titration of weak acid with weak base. \(B\). It begins to change colour at \(pH =8.4\) \(C\). It is a weak organic base \(D\). It is colourless in acidic medium
- A \(1\)
- B \(2\)
- C \(3\)
- D \(4\)
Answer & Solution
Correct Answer
(B) \(2\)
Step-by-step Solution
Detailed explanation
\((B)\) \(pk _{ In }=-\log \left(4 \times 10^{-10}\right)=9.4\) Indicator range \(\Rightarrow pk _{\text {In }} \pm 1\) i.e. \(8.4\) to \(10.4\) \((D)\) In acidic medium, phenolphthalein is in unionized form and is colourless.
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