Using the provided information in the following paper chromatogram. The calculated R_f value of A ..

Q: Why do we measure the distance from the base line and not the bottom of the paper?

The base line is where the mixture was initially applied. Measuring from the bottom of the paper would include the portion dipped in the solvent before the solvent reached the spots, which doesn't represent the actual migration of the compounds.

Q: Can the $R_f$ value ever be greater than 1?

No, the $R_f$ value can never exceed 1. The solvent front represents the maximum distance the mobile phase has travelled. A solute cannot travel faster or further than the solvent carrying it.

Q: What does it mean if a compound has an $R_f$ value of 0?

An $R_f$ value of 0 means the compound did not move from the base line at all. This indicates that the compound is completely insoluble in the mobile phase and has a very strong affinity for the stationary phase.

Q: For compound B, why is the distance 4 cm and not 2 cm?

The diagram shows a 2 cm distance from the base line to spot A, and another 2 cm distance from spot A to spot B. Since $R_f$ is always measured from the base line, the total distance for B is $2 \text{ cm} + 2 \text{ cm} = 4 \text{ cm}$.

Q: Why do different compounds have different $R_f$ values?

Different compounds have varying degrees of solubility in the mobile phase and varying affinities for the stationary phase. A compound that is more soluble in the solvent will travel further, resulting in a higher $R_f$ value.

Question

Using the provided information in the following paper chromatogram.
The calculated $R_f$ value of A ......... $	imes 10^{-1}$.

Sigma Percentile · Accepted Answer

The process of paper chromatography is like a race where different molecules run at different speeds. Some molecules love the paper (the stationary phase) and prefer to stay behind, while others love the solvent (the mobile phase) and rush ahead with it.

To quantify this race, chemists use a brilliant little metric called the **Retention Factor**, or simply, the **$R_f$ value**.

### The Master Equation

The $R_f$ value is a simple ratio. It compares how far a specific compound travelled to how far the solvent itself travelled.

$$R_f = \frac{	ext{Distance travelled by solute}}{	ext{Distance travelled by solvent front}}$$

The golden rule of chromatography is that **all distances must be measured from the base line**—the exact starting line where the mixture was initially spotted.

### Analyzing the Setup

Let's look at the chromatogram provided in the problem. We have a base line at the bottom and a solvent front at the top.

If we look at the left side of the diagram, the total distance from the base line to the solvent front is explicitly given:

$$	ext{Distance travelled by solvent} = 5 	ext{ cm}$$

Now, we need to find the distance for our compound of interest, Compound A. Looking at the right side of the diagram, the first spot (which corresponds to Compound A) is located exactly $2 	ext{ cm}$ above the base line.

$$	ext{Distance travelled by A} = 2 	ext{ cm}$$

### Final Calculation

Now, we simply plug these values into our master equation:

$$R_f = \frac{2}{5}$$

$$R_f = 0.4$$

The problem asks us to express this value in the specific format of $X 	imes 10^{-1}$. We can easily rewrite $0.4$ in scientific notation:

$$0.4 = 4 	imes 10^{-1}$$

Therefore, the integer value we are looking for is **$4$**.

### Beyond the Question: What about Compound B?

As a thought experiment, let's calculate the $R_f$ value for Compound B. The diagram shows a $2 	ext{ cm}$ gap between Spot A and Spot B. However, remember our golden rule: we must measure from the base line!

The total distance for Compound B from the base line is $2 	ext{ cm} + 2 	ext{ cm} = 4 	ext{ cm}$.

$$R_{f(B)} = \frac{4}{5} = 0.8$$

Notice that Compound B has a higher $R_f$ value ($0.8$) compared to Compound A ($0.4$). This physically means that Compound B has a higher affinity for the mobile phase (the solvent) and a lower affinity for the stationary phase (the paper) than Compound A. It's winning the race!

Animated Solution for Chemistry - Organic Chemistry: Using the provided information in the following paper chromatogram. The calculated $R_{f}$ value of A ......... $\times 1 0^{- 1}$ .

Enter Numerical Value:

Visualized Solution

$R_{f} Value in Chromatography$

$R_{f} Formula$

$Solvent Distance$

$Solute A Distance$

$Calculating R_{f}$

$Final Formatting$

$What about Compound B?$

The Sigma Insight: Nomenclature and Characterisation

The Master Equation

Analyzing the Setup

Final Calculation

Beyond the Question

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Animated Solution for Chemistry - Organic Chemistry: .math-text-wrapper .katex { font-size: 1.05em !important; } .math-text-wrapper .katex-display { margin: 1rem 0 !important; } Using the provided information in the following paper chromatogram. The calculated Rf​ value of A ......... ×10−1.