Instrumental Methods Of Analysis

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)