Question

Which plot represents a spectrophotometric titration, where the titrant alone absorbs light in the visible region? 

• A. (A)
• B. (B)
• C. (C)
• D. (D)

Hint:

In spectrophotometric titrations, a sharp change in absorbance at the endpoint indicates a significant reaction between the titrant and analyte.

Answer 1

The Correct Option is A

Spectrophotometric titration where titrant alone absorbs:

Key conditions:

• Titrant absorbs light in the visible region
• Analyte (substance being titrated) does NOT absorb
• Product formed does NOT absorb

Expected behavior:

Before endpoint:

• Titrant is consumed by reaction with analyte
• No excess titrant present
• Absorbance remains low/constant (near zero)

At endpoint:

• All analyte has reacted
• Any additional titrant added remains in solution

After endpoint:

• Excess titrant accumulates in solution
• Absorbance increases linearly with added titrant volume
• Slope depends on titrant concentration and molar absorptivity

Analyzing the plots:

(A):

• Low constant absorbance before endpoint
• Sharp increase at endpoint
• Linear increase after endpoint
• Matches expected behavior 

(B):

• High initial absorbance
• Decrease at endpoint
• Suggests analyte absorbs (opposite scenario) 

(C):

• Increasing absorbance before endpoint
• Plateau after endpoint
• Suggests product absorbs (different scenario) 

(D):

• Triangular peak at endpoint
• Not consistent with titrant absorption behavior 

Answer: (A)