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Difficulty: MediumPure and Impure Substances and Criteria of Purity

A chemist carried out paper chromatography to analyze a food coloring sample XX. The solvent front traveled 15.0 cm15.0\text{ cm} from the baseline, while the sample produced a single spot that traveled 6.0 cm6.0\text{ cm}. What is the RfR_f value of sample XX, and what does the single spot indicate regarding its purity?

  1. Rf=0.40R_f = 0.40, indicating that the sample is pureAnswer
  2. B
    Rf=2.50R_f = 2.50, indicating that the sample is pure
  3. C
    Rf=0.40R_f = 0.40, indicating that the sample is a mixture
  4. D
    Rf=2.50R_f = 2.50, indicating that the sample is a mixture

Answer

Rf=0.40R_f = 0.40, indicating that the sample is pure
The retention factor RfR_f is calculated using the formula Rf=distance traveled by spotdistance traveled by solvent front=6.0 cm15.0 cm=0.40R_f = \frac{\text{distance traveled by spot}}{\text{distance traveled by solvent front}} = \frac{6.0\text{ cm}}{15.0\text{ cm}} = 0.40. In paper chromatography, a pure substance produces only one single spot, demonstrating that no additional component fractions are present in the sample.

Step-by-Step Solution

1
Calculate the Retention Factor (RfR_f)
Rf=Distance traveled by solute spotDistance traveled by solvent front=6.0 cm15.0 cm=0.40R_f = \frac{\text{Distance traveled by solute spot}}{\text{Distance traveled by solvent front}} = \frac{6.0\text{ cm}}{15.0\text{ cm}} = 0.40
The RfR_f value is defined as the ratio of the distance moved by the substance spot to the distance moved by the solvent front from the baseline.
2
Interpret the chromatogram for purity criteria
Single spot confirms a pure substance
A pure chemical compound produces a single characteristic spot in paper chromatography under specific solvent conditions, whereas a mixture separates into two or more spots.

Key Concept

Criteria of Purity: RfR_f Value and Chromatography
Estimated Time:1m 0s
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Topics

Pure and Impure Substances and Criteria of Purity