Question

1. define ( r_f ) value.

1. a student performs this experiment and records the following data from the completed chromatogram:

• the solvent has moved 7.30 cm.
• component a produces a blue spot that has moved 5.80 cm.
• component b produces a pink spot that has moved 2.45 cm.
• component c produces a tan spot that has moved 4.10 cm.

calculate the ( r_f ) values for each component.

1. the unknown mixture spotted on the chromatogram described above produces 2 spots: one blue with an ( r_f ) value of 0.788 and one tan with an ( r_f ) value of 0.568. which components were present in the unknown mixture?

1. calculate the distance in cm moved by each components of the unknown mixture. account for any difference between these values and those observed for the known components.

Explanation:

Step1: Define $R_f$ value

The $R_f$ (retention factor) value in chromatography is the ratio of the distance a component travels to the distance the solvent (mobile phase) travels, expressed as:
$$R_f = \frac{\text{Distance moved by component}}{\text{Distance moved by solvent}}$$

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Step1: Calculate $R_f$ for Component A

Divide component A's distance by solvent distance.
$$R_f(A) = \frac{5.80\ \text{cm}}{7.30\ \text{cm}} \approx 0.795$$

Step2: Calculate $R_f$ for Component B

Divide component B's distance by solvent distance.
$$R_f(B) = \frac{2.45\ \text{cm}}{7.30\ \text{cm}} \approx 0.336$$

Step3: Calculate $R_f$ for Component C

Divide component C's distance by solvent distance.
$$R_f(C) = \frac{4.10\ \text{cm}}{7.30\ \text{cm}} \approx 0.562$$

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Step1: Match unknown $R_f$ values

Compare unknown $R_f$ values to calculated known values. The blue unknown ($R_f=0.788$) matches Component A ($R_f\approx0.795$, minor experimental error), and the tan unknown ($R_f=0.568$) matches Component C ($R_f\approx0.562$, minor experimental error).

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Step1: Calculate blue component distance

Rearrange $R_f$ formula: $\text{Distance} = R_f \times \text{Solvent distance}$
$$\text{Distance (blue)} = 0.788 \times 7.30\ \text{cm} \approx 5.75\ \text{cm}$$

Step2: Calculate tan component distance

Use rearranged $R_f$ formula for the tan spot.
$$\text{Distance (tan)} = 0.568 \times 7.30\ \text{cm} \approx 4.15\ \text{cm}$$

Step3: Explain distance differences

Small differences stem from experimental variation (e.g., uneven solvent flow, spotting technique, measurement error), which is normal in chromatography.

Answer:

1. The $R_f$ (retention factor) value is the ratio of the distance a solute component travels to the distance the solvent front travels in a chromatography experiment, used to identify components.

2.

• $R_f$ of Component A: $\approx 0.795$
• $R_f$ of Component B: $\approx 0.336$
• $R_f$ of Component C: $\approx 0.562$

1. Component A (blue spot) and Component C (tan spot) are present in the unknown mixture.

4.

• Distance moved by blue component: $\approx 5.75$ cm
• Distance moved by tan component: $\approx 4.15$ cm

The small differences between these values and the known components are due to normal experimental variability, such as minor inconsistencies in solvent flow, sample spotting, or measurement precision.