Its not that hard.
Half of the inch part is 1/2 inch which is also 4/8.
half of the 3/4 part is 3/8 you get by multiplying the denominator by 2.
Put it all back together and you get the 4/8 part and the 3/8 part so in total its 7/8 of an inch.
The Rf value represents the difference between the migration of the developing solvent and the compound being evaluated in Thin-Layer Chromatography (TLC). The Rf value serves as a simple measurement of the relative binding of the compound of interest under the experimental conditions.
RF value (in chromatography) The distance travelled by a given component divided by the distance travelled by the solvent front. For a given system at a known temperature, it is a characteristic of the component and can be used to identify components.
Beside above, how do you calculate the RF value What does this tell you? You divide the distance of your compounds by the distance of your solvent, and youve got the Rf ratio. The farther a compound travelled, the larger its Rf value. Logically, you can conclude that if a compound A travels farther than compound B in a polar solvent, then it is more polar than solvent B.
Keeping this in view, how is an RF value useful?
Rf value stands for the retardation factor value. It tells us how far the unknown pigment traveled in relation to the distance the solvent traveled. The Rf value is useful for scientists because it allows scientists to identify the pigment by comparing its Rf value to that of a known standard.
What is the relationship between structure and RF value?
It is a measure of how strongly the substituents are attached (adsorp) to the stationary phase. The stronger the adsorption, the lower is the Rf value. By the way, Rf can be calculated by dividing the distance covered by the substituent with distance covered by the mobile phase.