The Question is from neet-chemistry chemical-equilibrium , and it was created by the author A.RAMA NAGESWARARAO

Question

Which indicator works in the pH range $8 - 9\;.8$?

A.RAMA NAGESWARARAO · Accepted Answer

## CORE INFORMATION
✓ **Answer**: A
## CONCEPT FRAMEWORK
 **Primary Concept**: Acid-base indicators and their pH ranges
 **Related Topics**: Titration, pH scale, weak acids and bases
 **Prerequisites**: Understanding of pH and its relation to acidity and basicity.
## SOLUTION PATHWAY
**Given Information**:
  The pH range is $8 - 9.8$
  We need to identify the indicator that changes color within this range.
**Method & Steps**:
 1. Identify the pH range of each indicator.
  Reasoning: Different indicators change color at different pH ranges due to their different $pK_a$ values (the negative logarithm of the acid dissociation constant).
  Formula/Rule:  There is no single formula, but knowledge of the typical pH ranges of common indicators is required.
 2. Compare the given pH range with the known pH ranges of the indicators.
  Working:  
  Phenolphthalein:  Changes color in the pH range of approximately 8.2 - 10.0
  Methyl orange: Changes color in the pH range of approximately 3.1 - 4.4
  Methyl red: Changes color in the pH range of approximately 4.4 - 6.2
  Litmus: Changes color in the approximate pH range of 4.5 - 8.3
 3. Select the indicator whose pH range overlaps with the given range.
  Result: Phenolphthalein's pH range ($8.2 - 10.0$) fully encompasses the given range ($8 - 9.8$).
  Verification: Check the pH range of phenolphthalein in a reliable chemistry resource. 
 ## OPTION ANALYSIS
A ✓: Phenolphthalein changes color in the pH range of approximately 8.2 - 10.0, which includes the given range of 8 - 9.8.
B :x: Methyl orange changes color in the acidic pH range (3.1 - 4.4), far below the given range.
C :x: Methyl red changes color in the slightly acidic to neutral pH range (4.4 - 6.2), far below the given range.
D :x: Litmus paper changes color around pH 7, but its range isn't precise enough and doesn't fully cover 8-9.8.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing the pH ranges of different indicators:  Memorizing the approximate ranges of common indicators is crucial.
  2.Not considering the entire range: The indicator's range must fully or largely overlap with the specified range.
 **Quick Tips**:
  1.Create a table summarizing the pH ranges of common indicators for quick reference.
  2.Remember that phenolphthalein is commonly used in titrations involving strong bases and weak acids, which often have equivalence points in the slightly basic range.

A.RAMA NAGESWARARAO · Answer

The correct Option is "Phenolphthalein"

A.RAMA NAGESWARARAO · Answer

Methyl orange

A.RAMA NAGESWARARAO · Answer

Methyl red

A.RAMA NAGESWARARAO · Answer

Litmus

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