Q.32 A dye was allowed to undergo migration on a chromatographic paper using a
solvent. The dye, and the solvent-front migrated 5 and 20 𝑐𝑚 , respectively, from
the point of origin. The retention factor (rounded off to two places of decimals) for
the dye is _____.
The retention factor (Rf) for the dye is calculated as the ratio of the distance migrated by the dye to the distance migrated by the solvent front. Here, Rf = 5 cm / 20 cm = 0.25, rounded to two decimal places as specified.
Rf Formula
The retention factor in paper chromatography uses the formula Rf = Distance traveled by solute (dye) / Distance traveled by solvent front. This dimensionless value ranges from 0 (no movement, strong affinity for stationary phase like paper) to 1 (moves with solvent, weak stationary phase interaction).
In this case:
- Dye distance = 5 cm
- Solvent front distance = 20 cm
- Rf = 5/20 = 0.25
Step-by-Step Calculation
- Measure distances from the origin (baseline where dye is spotted).
- Divide dye migration by solvent front migration.
- Round to two decimals per question requirement.
No units needed as it’s a ratio; values >1 impossible since dye cannot exceed solvent movement.
Example verification: Similar problems (e.g., dye 5 cm, solvent 10 cm) yield Rf=0.50, confirming the method.
Common Errors
- Rf ≠ 0.50 (ignores 20 cm solvent distance)
- Rf=25 (units mistake, forgetting to divide)
- Rf=0.3 (rounding error)
Question has no options listed, but 0.25 fits exactly. Factors like temperature or solvent purity affect Rf but not this direct calculation.
Introduction to Retention Factor in Paper Chromatography
Retention factor (Rf) in paper chromatography measures solute movement relative to solvent, vital for separating mixtures in biochemistry and CSIR NET Life Sciences. For a dye migrating 5 cm while solvent front reaches 20 cm, calculate Rf precisely for identification. This technique uses paper as stationary phase, solvent as mobile phase.
Retention Factor Formula and Meaning
Rf = (distance by dye / distance by solvent front), always 0-1 range. Low Rf means strong paper binding; high Rf means solvent affinity. In this query: 5/20 = 0.25, rounded to two decimals.
Step-by-Step Rf Calculation Example
- Spot dye at origin on chromatographic paper.
- Run solvent; mark dye spot (5 cm) and front (20 cm).
- Compute Rf = 5/20 = 0.25.
CSIR NET-style problems match this exact calculation format.
Factors Affecting Retention Factor Value
- Solvent polarity
- Temperature
- Paper quality
Pure substances yield consistent Rf values; mixtures show multiple spots on chromatogram.
Applications in Life Sciences
Identifies pigments, amino acids in biotechnology research. CSIR NET tests via problems like dye 5 cm solvent 20 cm expecting Rf 0.25 answer.
