A chloroform solution of pure organic compound was spotted at a distance 0.80cm from the...
A chloroform solution of pure organic compound was spotted at a distance 0.80cm from the base of a 20cm long chromatoplate. If the compound has the \(r_f\)-value of 0.505 and moves half way up the 20cm long plate, which is the distance of the solvent front from the top of the plate upon elution?
- A) 0.80cm
- B) 1.0cm
- C) 1.2cm
- D) 1.4cm
Correct Answer: B) 1.0cm
Explanation
An important concept in chromatography is the \(r_f\)-value, which stands for the retention factor. The \(r_f\)-value is a ratio that compares the distance traveled by a compound to the distance traveled by the solvent front. It is calculated using the following formula:
\(r_f = \frac{distance \, traveled \, by \, the \, compound}{distance \, traveled \, by \, the \, solvent \, front}\)In this question, you are given the \(r_f\)-value of the compound (0.505) and the distance the compound traveled (10 cm, as it moved halfway up the 20 cm long plate). You are asked to find the distance of the solvent front from the top of the plate upon elution.
First, let's find the distance traveled by the solvent front. We can rearrange the formula for the \(r_f\)-value to solve for the distance traveled by the solvent front:
\(distance \, traveled \, by \, the \, solvent \, front = \frac{distance \, traveled \, by \, the \, compound}{r_f}\)Substitute the given values:
\(distance \, traveled \, by \, the \, solvent \, front = \frac{10 \, cm}{0.505} \approx 19.8 \, cm\)Now, to find the distance of the solvent front from the top of the plate, subtract the distance traveled by the solvent front (19.8 cm) from the total length of the plate (20 cm):
\(distance \, of \, the \, solvent \, front \, from \, the \, top \, of \, the \, plate = 20 \, cm - 19.8 \, cm = 1.0 \, cm\)Therefore, the correct answer isOption B: 1.0 cm.